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Cognitive dietary restraint is associated with eating behaviors, lifestyle practices, personality characteristics and menstrual irregularity in college women
Appetite 40 (2003) 185–192 www.elsevier.com/locate/appet
Research Report
Cognitive dietary restraint is associated with eating behaviors, lifestyle practices, personality characteristics and menstrual irregularity in college women Judy A. McLean, Susan I. Barr* Human Nutrition, University of British Columbia, 2205 East Mall, Vancouver, B.C., Canada V6T 1Z4 Received 8 August 2001; revised 5 June 2002; accepted 12 July 2002
Abstract This study characterized associations of restraint with selected physical, lifestyle, personality and menstrual cycle characteristics in female university students. The survey instrument, distributed to 1350 women, included standardized questionnaires (Three-Factor Eating Questionnaire, Perceived Stress Scale and Rosenberg’s Self-esteem Scale), and assessed weight and dieting history, exercise, lifestyle characteristics, menstrual cycle characteristics and whether participants were following vegetarian diets. Among the 596 respondents included in the analysis (44%), women with high ðn ¼ 145Þ; medium ðn ¼ 262Þ or low ðn ¼ 189Þ restraint had similar ages, heights and weights. Despite this, compared to women with low scores, those with high scores exercised more (4.6 ^ 5.3 vs. 3.2 ^ 3.5 h/wk), were more likely to be vegetarian (14.5 vs. 3.7%), have a history of eating disorders (13.7 vs. 1.2%), be currently trying to lose weight (80.3 vs. 15.3%), report irregular menstrual cycles (34.7 vs. 17.0%), and have scores reflecting lower self-esteem and higher perceived stress. Menstrual irregularity was an independent predictor of restraint score, and restraint score was the only variable to differentiate women with regular and irregular menstrual cycles. We conclude that women with high restraint may use a combination of behavioral strategies for weight control, and differ from women with low restraint scores in personality characteristics and weight history. Some of these behaviors or characteristics may influence menstrual function. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Restrained eating; Vegetarianism; Menstrual disturbances
Introduction Many women consciously try to limit their food intake to achieve or maintain a desired body weight. This is referred to as dietary restraint or cognitive dietary restraint, a type of eating behavior governed by cognitive processes rather than by physiological mechanisms such as hunger and satiety (Gorman & Allison, 1995). Although several scales to assess dietary restraint exist, the Restraint Factor scale of the Three-Factor Eating Questionnaire (TFEQ; Stunkard & Messick, 1985) is considered to be robust and have good psychometric properties (Gorman & Allison, 1995). Typically, women with high scores for restraint are very aware of the amount and type of food they consume although reports vary as to whether their energy intakes are actually lower * Corresponding author. E-mail address: [email protected] (S.I. Barr).
than those of women with low restraint scores (Barr, Prior, & Vigna, 1994b; McLean, Barr, & Prior, 2001a; Schweiger et al., 1992; Smith et al., 1998; Tuschl, Laessle, Platte, & Pirke, 1990a). Previous studies have found women with high restraint scores to be generally similar to those with low restraint scores in terms of age, height, weight and Body Mass Index (BMI) (Barr, Janelle, & Prior, 1994a; Barr et al., 1994b; Laessle, Tuschl, Kotthaus, & Pirke, 1989a; Pirke et al., 1990; Schweiger, Tuschl, Laessle, Broocks, & Pirke, 1989; Van Loan & Keim, 2000). Where a difference has been found has been in menstrual cycle, and particularly ovulatory, characteristics. Several studies have reported that women with high restraint scores were more likely to experience disturbances of ovulation including a higher proportion of anovulatory cycles and short luteal phase or cycle lengths (Barr et al., 1994a,b; Lebenstedt, Platte, & Pirke, 1999; Schweiger et al., 1992).
0195-6663/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0195-6663(02)00125-3
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Women with varying scores for dietary restraint have previously been characterized according to several physical and lifestyle variables which may increase physical or psychological stress and consequently impact on the menstrual cycle (Barr et al., 1994a,b; Laessle et al., 1989; Schweiger et al., 1992; Tuschl, Platte, Laessle, Stichler, & Pirke, 1990b). Unfortunately, many of these studies had small numbers of subjects or used exclusion criteria, which may have limited the findings to a select group. Accordingly, the purpose of this study was to characterize a large, unselected group of university women with regard to dietary restraint, and to assess whether differences existed among women categorized as having low, medium or high restraint in terms of eating behaviors, lifestyle habits, selected personality characteristics and menstrual regularity.
Subjects and methods Participants Female students aged 18 and above at the University of British Columbia were recruited during classes in biochemistry, human nutrition, psychology, family science, nursing and human kinetics. All women students in the selected classes received a questionnaire that they were requested to complete at home and return to class during the following week. There were no exclusion criteria, nor were any incentives provided for participation. The study protocol was approved by the University’s Clinical Screening Committee for Research and Other Studies Involving Human Subjects, and the data were gathered during 1997. Questionnaire The questionnaire included previously validated, standardized scales designed to assess eating behaviors, perceived stress, and self-esteem. It also sought data on physical and lifestyle characteristics, such as age, height, weight, dieting history, menstrual cycle history, exercise, special diets (e.g. vegetarian), and use of vitamin or mineral supplements. Eating behaviors The 51-item TFEQ (Stunkard & Messick, 1985) was used to assess perceptions of three dimensions of human eating behavior: (1) cognitive restraint of eating, (2) disinhibition and (3) hunger. To make the TFEQ suitable for individuals who don’t consume meat, the first item was altered from, “When I smell a sizzling steak or see a juicy piece of meat, I find it very difficult to keep from eating, even if I have just finished a meal”, to “When I smell my favorite food, I find it very difficult to keep from eating, even if I have just finished a meal”. Responses to items on the TFEQ were scored according to the instructions
provided by Stunkard and Messick (1985) and summed to obtain scores for restraint, disinhibition and hunger. Physical and lifestyle characteristics Participants reported their present height and weight as well as their highest and lowest adult weights. They were also asked, “At what weight do you feel your best?” which was subsequently referred to as their ‘best’ weight. From these values, BMI, highest BMI, lowest BMI, and best BMI were calculated in kg/m2. Participants were asked whether they were currently trying to lose weight, had ever tried to lose weight, or had ever been diagnosed with or treated for an eating disorder. Weight fluctuation was determined by the number of times that . 5 lbs was lost in the past two years. Participants were asked whether they were currently having menstrual cycles and if so, whether their cycles were irregular or regular. They were also asked the average length of their cycle and whether they were presently, or had in the past six months, used oral contraceptives. Lifestyle information included questions regarding alcohol and coffee or tea consumption, cigarette usage, vitamin, mineral and medication use as well as hours of weekly exercise. Participants identified whether they were following lacto-ovo vegetarian, vegan or other special diets. Perceived stress and self-esteem The Perceived Stress Scale (PSS) (Cohen, Kamarck, & Mermelstein, 1983) measures the extent to which situations in one’s life are appraised as stressful. It consists of 14 statements asking about the respondents’ feelings and thoughts during the last month. Items were scored and totaled according to instructions provided by the authors, with higher scores reflecting higher perceived stress. Rosenberg’s Self-esteem Scale (RSS) is a widely used measure of self-esteem (Rosenberg, 1965). Items were scored according to Rosenberg’s original instructions. Higher scores indicate lower self-esteem. Statistical analysis Participants with complete responses to the TFEQ restraint scale were included in the analysis, and were grouped according to their restraint scale scores, based on quartiles established in a previous study of this population (unpublished). Those with scores of 0 –5 on the TFEQ restraint scale (the first quartile) were grouped as ‘low restraint’; scores 6 –12 (the second and third quartiles) as ‘medium restraint’ and scores 13 –21 (the fourth quartile) as ‘high restraint’. Group comparisons among the low, medium and high restraint groups were made by ANOVA. When significant F ratios were present, Duncan’s multiple range test was used to determine which means were significantly different. For comparisons of population proportions, chisquare ðx2 Þ was used. Stepwise multiple regression analysis was used to determine which characteristics independently
J.A. McLean, S.I. Barr / Appetite 40 (2003) 185–192
predicted dietary restraint scores, and discriminant analysis was used to examine variables that differentiated women with regular and irregular menstrual cycles. The statistical analysis was achieved through computer programs available in the Statistical Package for the Social Sciences, Personal Computer version 10.0 (SPSS Inc., 1999, Chicago, IL). Cases with missing values for variables other than the TFEQ restraint scale were excluded from analysis on a case-wise basis. The level of significance was set at P , 0:05 and comparisons were two-tailed.
Results Of 1350 questionnaires distributed, 761 (56%) were returned. A printing error resulted in the loss of 95 responses, and of the remaining 666, 596 (44% of distributed questionnaires) had complete responses to the TFEQ restraint scale. Just under 32% ðn ¼ 189Þ of women had low scores for restraint, 44% ðn ¼ 262Þ had medium restraint scores, and 24% ðn ¼ 145Þ had high restraint scores. Participants grouped according to restraint scores Descriptive and lifestyle characteristics Physical and lifestyle characteristics of women grouped according to their TFEQ restraint scale scores are presented in Table 1. Age, height, weight, BMI (kg/m2) and best BMI (calculated from weight given as ‘best weight’) were similar among the three groups. Highest BMI was higher in women grouped as having high or medium scores for restraint when
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compared to women in the low restraint group. Lowest BMI differed only between women with low and medium scores for restraint with the former group having lower values. Compared to women with low and medium scores for restraint, women with high restraint scores reported more hours of weekly exercise. Alcoholic beverage use did not differ among groups nor did the prevalence of vitamin or mineral supplementation. Women with high restraint scores tended to be more likely to smoke and to use more caffeinated beverages although the group differences were not significant ðP , 0:10Þ: The likelihood of following a lacto-ovo or vegan diet, however, increased significantly as the level of dietary restraint increased. With regard to vegetarianism, additional analyses were done to compare the 47 women who identified themselves as being vegetarian (i.e. excluding meat, fish and poultry) to the non-vegetarian women ðn ¼ 549Þ: Vegetarians were found to weigh more than non-vegetarians (60.4 ^ 12.5 vs. 57.1 ^ 9.5 kg, t ¼ 2:17; P ¼ 0:03), exercise more (5.5 ^ 6.2 vs. 3.5 ^ 3.6 h/wk, t ¼ 3:4; P , 0:001) and were more likely to smoke cigarettes (17.0 vs. 5.8%, x2 ¼ 9:5; P ¼ 0:002). A higher percentage of the vegetarian participants had a history of eating disorders (17.1 vs. 3.1%, x2 ¼ 17:9; P , 0:001). They also had higher restraint scores (11.4 ^ 5.6 vs. 8.4 ^ 5.2, t ¼ 3:8; P , 0:001) and self-esteem scores (indicating lower self-esteem) (2.0 ^ 1.9 vs. 1.4 ^ 1.5, t ¼ 2:2; P , 0:05). Weight fluctuation and dieting history Weight fluctuation and dieting history of participants grouped according to restraint scores are presented in
Table 1 Physical and lifestyle characteristics (mean ^ SD) of women with low, medium and high scores for dietary restraint Characteristic
All subjects ðn ¼ 596Þ
Restraint Low ðn ¼ 189Þ
Age (yr) Height (cm) Weight (kg) BMI (kg/m2) Highest BMI (kg/m2)d Lowest BMI (kg/m2)g Best BMI (kg/m2)h Exercise (h/wk) Caffeinated beverages (cups/d) Alcoholic beverages (drinks/wk) Cigarette smokers Vegetarian Using vitamin/mineral supplements a b c d e,f g h i
21.5 ^ 3.9 164.7 ^ 7.2 57.4 ^ 9.8 21.1 ^ 3.0 22.6 ^ 3.8 19.8 ^ 2.5 20.0 ^ 2.0 3.6 ^ 3.9 1.1 ^ 1.1 1.1 ^ 1.8 6.4% 7.9% 35.8%
21.2 ^ 3.3 164.7 ^ 7.4 56.4 ^ 10.9 20.8 ^ 3.8 21.9 ^ 4.1e 19.4 ^ 2.8e 20.0 ^ 2.3 3.2 ^ 3.5e 0.9 ^ 1.0 1.3 ^ 2.1 5.9% 3.7% 35.8%
a
Medium ðn ¼ 262Þ 21.6 ^ 3.4 164.5 ^ 6.6 57.8 ^ 9.2 21.3 ^ 2.6 22.7 ^ 3.3f 20.0 ^ 2.4f 20.2 ^ 1.9 3.4 ^ 3.1e 1.0 ^ 1.1 1.0 ^ 1.6 4.6% 7.3% 35.5%
b
High ðn ¼ 145Þ
F ratio (or x2 )
P
1.118 0.113 1.351 1.515 6.356 3.806 2.475 5.867 2.657 1.413 x2 ¼ 5:3 x2 ¼ 13:4 x2 ¼ 0:03
0.328 0.893 0.260 0.221 0.002 0.023 0.085 0.003 0.071 0.244 0.071 0.001 0.986
c
21.7 ^ 5.2 164.9 ^ 8.0 57.8 ^ 9.0 21.2 ^ 2.5 23.3 ^ 4.0f 19.8 ^ 2.2e,f 19.8 ^ 1.9 4.6 ^ 5.3f 1.2 ^ 1.2 1.2 ^ 2.0 10.4% 14.5%i 36.4%
Score 0–5 on the TFEQ restraint scale (Stunkard & Messick, 1985). Score 6–12 on TFEQ restraint scale. Score 13–21 on TFEQ restraint scale. Calculated from weight given as ‘highest adult weight’. Means differ significantly between values in rows not sharing a common superscript (by one-way ANOVA and Duncan’s multiple range test). Calculated from weight given as ‘lowest adult weight’. Calculated from weight given as ‘best adult weight’. Percentages differ significantly among groups (chi-square).
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Table 2 Weight fluctuation and dieting history of women with low, medium, and high scores for dietary restraint Characteristic
Presently trying to lose weight Ever tried to lose weight History of eating disorders Weight fluctuatione,f a b c d e f g,h
All subjects ðn ¼ 596Þ
44% 74.5% 6.4% 1.5 ^ 2.0
Restraint Low ðn ¼ 189Þa
Medium ðn ¼ 262Þb
High ðn ¼ 145Þc
15.3% 49.7% 1.2% 1.1 ^ 1.4g
45.0% 80.3% 1.4% 1.5 ^ 1.5g
80.3% 96.5% 13.7% 2.1 ^ 3.0h
x2 or F
P
x2 ¼ 139:0 x2 ¼ 101:9 x2 ¼ 35:7 F ¼ 8:57
0.000 0.000 0.000 0.000
Score 0–5 on the TFEQ restraint scale (Stunkard & Messick, 1985). Score 6–12 on TFEQ restraint scale. Score 13–21 on TFEQ restraint scale. Percentages differ significantly among groups (chi-square). Number of times .5 lbs lost during the past two years. Mean ^ SD. Means differ significantly between values in rows not sharing a common superscript (by one-way ANOVA and Duncan’s multiple range test).
Table 2. In response to the question, “Are you presently trying to lose weight?” a significant difference was found among restraint groups with over 80% of women with high scores for restraint responding “yes”. A difference was also found in response to the question, “Have you ever tried to lose weight?” Over 90% of women in the high restraint group reported having tried to lose weight at some point. History of an eating disorder was also markedly higher in women in the high restraint group compared to those in the low or medium restraint groups. Of all women who provided this history, 77% were in the high restraint group. Finally, weight fluctuation (the number of times more than 5 lbs was lost) was higher in the previous 2 years in women with high scores compared to those with low or medium scores for restraint. Menstrual cycle characteristics Three hundred and ninety-four women reported that they were having menstrual cycles and were not using oral contraceptives. For these women, the proportions reporting irregular cycles were compared by restraint group (Fig. 1). The prevalence of self-reported menstrual cycle irregularity in women with high restraint (34.7%) was double that of women with low and medium scores (17.1 and 17.0%,
Fig. 1. Prevalence of self-reported menstrual cycle irregularity among women grouped according to scores on the TFEQ restraint scale (Stunkard & Messick, 1985). Scores in the low, medium and high restraint groups were 0– 5, 6–12, and 13 and above, respectively. Percentages differed significantly among groups (x2 ¼ 13:4; P ¼ 0:001).
respectively). This difference persisted when the analysis was repeated after excluding women who reported a history of an eating disorder: the prevalence of menstrual irregularity among women with high, medium and low restraint was 32.5%, 14.6 and 16.1%, respectively (x2 ¼ 12:0; P ¼ 0:003). No differences among restraint groups were detected in self-reported cycle length. In separate analyses, the women who reported irregular menstrual cycles were compared to those reporting regular cycles. It is notable that those reporting irregular cycles ðn ¼ 84Þ were comparable to those with regular cycles ðn ¼ 310Þ in terms of BMI (20.7 ^ 3.1 vs. 21.1 ^ 3.2 kg/m2) and hours of weekly exercise (3.1 ^ 3.1 vs. 3.3 ^ 3.5 hr/wk). However, they were more likely to smoke cigarettes (8.3 vs. 3.2%, x2 ¼ 4:1; P ¼ 0:042) and tended to be more likely to follow vegetarian diets (13.1 vs. 7.4%, P ¼ 0:10). Scores on the TFEQ restraint subscale were significantly higher in women reporting irregular cycles than in those reporting regular cycles (10.3 ^ 6.0 vs. 8.2 ^ 5.1, P ¼ 0:001), but the two groups did not differ in terms of scores on the TFEQ hunger and disinhibition subscales. Perceived stress scores did not differ between groups, while self-esteem scores were higher (1.9 ^ 1.8 vs. 1.5 ^ 1.5, P , 0:05), indicating lower self-esteem. Discriminant analysis revealed that restraint score was the only variable that significantly differentiated between women reporting regular and irregular menstrual cycles (Wilks’ Lambda Exact F ¼ 13:8; P , 0:001). Sixty percent of cases were correctly classified as regularly or irregularly menstruating. Eating behavior, perceived stress and self-esteem Participants’ scores on the TFEQ subscales, the PSS and RSS are presented in Table 3. There were no group differences on the TFEQ hunger subscale. All other scales differed among groups, and scores were highest in the high restraint group, reflecting higher perceived disinhibition, perceived stress, and lower self-esteem.
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Table 3 TFEQa subscale, PSSb, and RSSc scores (mean ^ SD) for women with low, medium and high scores for dietary restraint Characteristic
All subjects ðn ¼ 596Þ
Restraint d
TFEQ restraint TFEQ disinhibition TFEQ hunger Perceived stress Self-esteem
8.6 ^ 5.3 6.2 ^ 3.7 6.4 ^ 3.1 26.2 ^ 7.6 1.5 ^ 1.6
e
F
P
1865.1 34.7 2.10 13.1 18.7
0.000 0.000 0.124 0.000 0.000
f
Low ðn ¼ 189Þ
Medium ðn ¼ 262Þ
High ðn ¼ 145Þ
2.7 ^ 1.6g 4.8 ^ 3.3g 6.1 ^ 3.0 25.0 ^ 7.2g 1.1 ^ 1.5g
8.8 ^ 2.0h 6.3 ^ 3.6h 6.5 ^ 3.0 25.5 ^ 7.4g 1.4 ^ 1.5h
16.1 ^ 2.3i 8.1 ^ 3.8i 6.8 ^ 3.4 28.9 ^ 7.9h 2.2 ^ 1.8i
a
TFEQ ¼ Three-Factor Eating Questionnaire (Stunkard & Messick, 1985). PSS ¼ Perceived Stress Scale (Cohen et al., 1983). c RSS ¼ Rosenberg Self-Esteem Scale (Rosenberg, 1965). Lower scores reflect higher self-esteem. d Score 0–5 on TFEQ restraint scale. e Score 6–12 on TFEQ restraint scale. f Score 13–21 on TFEQ restraint scale. g,h,i Means differ significantly between values in rows not sharing a common superscript (by one-way ANOVA and Duncan’s multiple range test). b
Regression analysis Stepwise linear regression was conducted to determine which variables were independently associated with the dietary restraint score (Table 4). The final model included presently and previously trying to lose weight, history of an eating disorder, BMI, highest BMI, self-esteem score, menstrual regularity, and exercise. Variables that did not enter the equation included the number of times . 5 lbs had been lost in the past 2 years, vegetarianism, smoking, best BMI, lowest BMI, perceived stress, disinhibition and hunger.
Discussion This study of female university students revealed associations between dietary restraint and several variables related to efforts to control body weight. We also detected associations between restraint and menstrual irregularity, with potential long-term health implications. Before discussing these results, possible limitations of the study should be addressed. One limitation was the composition of the particular sample, which included
students recruited from biochemistry, human nutrition, psychology, family science, nursing and human kinetics classes. Compared to students in other disciplines, these students may have had a higher level of interest in health issues. This possibility, and the modest response rate, must be borne in mind when considering to whom the results might be generalized. A second limitation relates to the use of self-report data, and that some variables were assessed with single questions (e.g. smoking, vegetarianism, menstrual regularity) rather than validated scales. This is of greatest concern for menstrual regularity, as the associations between cognitive dietary restraint and irregular menstrual cycles were a major finding of the study. Limited data from a subset of participants suggest that the question used to assess menstrual regularity was reasonably reliable and valid. Women in the present study who reported regular menstrual cycles (among other criteria) were recruited to participate in an additional study. During the course of that study (McLean et al., 2001a), they completed the questionnaire again and kept menstrual cycle records for up to 3 months. Cycles were again reported to be ‘regular’, and only one woman was excluded because her recorded cycles did not meet the criterion for normal length (intervals of 21– 35
Table 4 Stepwise multiple regression of variables associated with dietary restraint score Variable entered at each step
B ^ SE
Standardized beta
t ðpÞ
Model R2
Constant Presently trying to lose weighta Previously tried to lose weighta Diagnosed or treated for eating disordera Menstrual regularityb BMI (kg/m2) Highest BMI (kg/m2) Rosenberg self-esteem scorec Exercise (h/wk)
21.77 ^ 2.61 4.41 ^ 0.55 3.03 ^ 0.65 4.37 ^ 1.43 21.55 ^ 0.60 20.65 ^ 0.16 0.42 ^ 0.14 0.42 ^ 0.15 0.17 ^ 0.07
–
20.68 (0.497) 8.03 (,0.001) 4.66 (,0.001) 3.06 (0.002) 22.59 (0.010) 24.06 (,0.001) 3.02 (0.003) 2.79 (0.006) 2.44 (0.015)
0.295 0.354 0.392 0.411 0.426 0.444 0.455 0.466
a b c
1 ¼ no, 2 ¼ yes. 1 ¼ irregular, 2 ¼ regular. Higher scores reflect lower self-esteem.
0.398 0.238 0.135 20.113 20.354 0.269 0.124 0.107
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days). Although this does not demonstrate reliability and validity of the question for those reporting ‘irregular’ cycles, it should be recognized that misclassification of menstrual regularity would likely attenuate the observed associations, rather than inflate them. Finally, rigid and flexible control dimensions of dietary restraint have recently been identified (Westenhoefer, Stunkard, & Pudel, 1999), and some data suggest that rigid control, but not flexible control, may be associated with eating disorder symptomatology (Stewart, Williamson, & White, 2002). This assessment tool was not available when our data were obtained, so we cannot determine whether the associations we observed were associated primarily with flexible or rigid control dimensions of restraint. In this study, irregular menstrual cycles were reported by a greater percentage of women with high restraint scores than with low or medium restraint scores; menstrual irregularity was independently associated with restraint score; and restraint score was the only variable that differentiated women with regular and irregular cycles. Although our results are self-reported, they concur with the findings of several studies in which menstrual cycle characteristics were directly monitored (Barr et al., 1994a, b; Lebenstedt et al., 1999; Schweiger et al., 1992). In these previous studies conducted with women who self-reported ‘regular’ cycles, an association was found between cognitive dietary restraint and subclinical ovulatory disturbances such as anovulation and short luteal phase cycles, which can occur within cycles of normal length. The present study differs from previous studies of restraint and the menstrual cycle in that instead of assessing subclinical disturbances that wouldn’t be evident to women, clinical disturbances (i.e. menstrual irregularity) were assessed. Establishing that dietary restraint has an independent association with menstrual irregularity requires consideration of potential confounding by other variables that may influence the cycle. These are discussed below, and include relative weight, exercise, vegetarianism, history of an eating disorder, and personality characteristics such as perceived stress and self-esteem. As has been observed by others (Tuschl et al., 1990b; Van Loan & Keim, 2000), women in this study with high scores for restraint had similar relative weights to those with low restraint scores. Although menstrual irregularity has been associated with unusually low body weight and with obesity (Clark et al., 1995; Rogers & Mitchell, 1952), BMI did not differ among women with low, moderate or high restraint scores in the present study, nor did BMI differ between those reporting regular and irregular cycles. Thus, relative weight did not confound the associations between restraint and menstrual irregularity. Several studies have suggested that the prevalence of menstrual disturbances is higher among women athletes than among sedentary women (Warren, 1992), and women with high restraint scores in the present study did report more hours of exercise. However, prospective studies in
which exercise was increased gradually do not support a causal role for exercise in menstrual dysfunction (Rogol et al., 1992), and short-term studies have demonstrated that normal release of luteinizing hormone (required for normal cycles) is maintained even when exercise is increased dramatically, provided that energy availability remains adequate (Loucks, Verdun, & Heath, 1998). In our study, hours of weekly exercise did not differ between women with regular and irregular cycles, suggesting that exercise did not confound the association between restraint and the menstrual cycle. Women with high restraint, however, may use exercise as an additional weight management strategy. Women commonly report weight management as a motivation for exercise (Biddle & Fox, 1998), and in a recent study, exercise was the most frequently reported weight loss practice among women (Neumark-Sztainer, Sherwood, French, & Jeffery, 1999). Women with high restraint scores were more likely to identify themselves as vegetarian, and associations between vegetarianism and menstrual irregularity have been reported in the literature (Barr, 1999). These studies, however, had a number of potential biases, including failure to control for oral contraceptive use and the possibility of a recruitment bias (vegetarians with menstrual disturbances might be more likely than those with normal cycles to volunteer for a study on this topic). A study that controlled these potential biases demonstrated that healthy vegetarian women do not have a higher prevalence of subclinical menstrual disturbances (Barr et al., 1994a). Thus, vegetarianism per se is unlikely to have confounded the association between restraint score and menstrual irregularity. Although our study was not designed to characterize vegetarian and non-vegetarian women, we did detect a number of differences between these two groups that are relevant to the suggestion that women with high restraint scores use a variety of strategies to control weight. In addition to higher restraint scores, vegetarian women had lower self-esteem, were heavier, exercised more, were more likely to smoke, and had a greater history of weight fluctuation and eating disorders, all of which support an association between vegetarianism and concern about body weight. However, vegetarianism did not enter the regression equation for restraint score, suggesting that the difference in restraint score between vegetarians and non-vegetarians was explained by associations with other variables that also differed between these groups. Our findings regarding vegetarian women are in contrast to much of the literature, which often reports that vegetarians are leaner and less likely to smoke cigarettes (Dwyer, 1988; Dwyer, Mayer, Dowd, & Mayer, 1974; Freeland-Graves, Greninger, Graves, & Young, 1986), and to common beliefs. These differences may be explained by the fact that many studies of vegetarians have used large groups such as Seventh Day Adventists who also practice other health promoting behaviors (Hunt, Murphy, & Henderson, 1988; Key, Thorogood, Appleby, & Burr,
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1996) or have had exclusion criteria which would have excluded many of our subjects (Barr et al., 1994a). This study did not intentionally recruit vegetarian women, which suggests that those included may be more representative of young vegetarian women than study volunteers described in other studies. Our finding that women with high restraint scores were more likely to be vegetarian likely reflects another socially acceptable way to control calorie and fat intake. As Gilbody suggested, vegetarianism may legitimize food avoidance (Gilbody, Kirk, & Hill, 1999). All characteristics assessed in relation to weight fluctuation and dieting history, including being diagnosed with or treated for an eating disorder, differed among women with low, medium and high scores for restraint. Many of these variables also entered the regression equation for restraint score. As dietary restraint reflects the cognitive attempt to control or limit food intake, the relationship between restraint group and dieting is not surprising, and has been reported by others (Barr et al., 1994a; Laessle et al., 1989; Schweiger et al., 1992; Tuschl et al., 1990b). The difference in prevalence of an eating disorder diagnosis between women with high scores and those with medium or low scores for restraint is also not unexpected as there were no exclusion criteria for participation. Women with eating disorders would most likely score high on any instrument assessing restrictive attitudes towards food intake. Importantly, the association between restraint and menstrual irregularity did not result from including these women, as the association persisted when they were excluded from analysis. Women with high restraint scores scored higher on the PSS. It could be hypothesized that those who perceive events in their lives as more stressful experience more negative feelings with regard to their weight and attempt to limit food intake to reduce their sense of dissatisfaction. Alternately, higher restraint may lead to a general feeling of stress, which is subsequently extrapolated into other situations. Although stress is known to be associated with menstrual cycle disturbances (Harlow & Matanoski, 1991), PSS scores were not independently associated with restraint scores, nor did PSS differ between women with regular and irregular cycles. Accordingly, perceived stress does not appear to explain the relationship between restraint and menstrual irregularity. Finally, women with high restraint scores had lower selfesteem, and self-esteem was independently associated with restraint score. While our data are cross-sectional, it has been hypothesized that low self-esteem predates the onset of eating disorders and is a necessary prerequisite for their development (Silverstone, 1992). Empirical evidence to support this has been obtained (Button, Sonuga-Barke, Davies, & Thompson, 1996). Accordingly, low self-esteem may increase women’s sensitivity to current cultural pressures to be thin, and therefore, susceptibility to dietary restraint. Although women reporting irregular menstrual
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cycles did have lower self-esteem, self-esteem scores did not differentiate women with regular and irregular cycles. The association between high levels of dietary restraint and menstrual irregularity has potential health implications for women. In addition to the obvious impact on fertility, bone health may be affected. High levels of dietary restraint may act as a subtle but frequently experienced stressor, activating the hypothalamic –pituitary– adrenal axis and leading to increased secretion of the stress hormone, cortisol. Recent studies (Anderson, Shapiro, Lundgren, Spataro, & Frye, 2002; Mclean et al., 2001a) have confirmed that cortisol secretion is increased in women with high scores for dietary restraint. Corticotropin releasing hormone may interfere with menstrual function by inhibiting gonadotropin secretion (Barbarino et al., 1989); menstrual dysfunction, whether marked or subtle, affects circulating sex steroids and is known to lead to bone loss (Prior, Vigna, Schechter, & Burgess, 1990; Rigotti, Neer, Skates, Herzog, & Nussbaum, 1991). In addition to affecting menstrual function, cortisol has the potential to adversely affect calcium homeostasis and inhibit bone formation through a number of mechanisms (Reid, 1997). Elevated cortisol, even within the normal range, is associated with lower values for bone mineral density (Dennison et al., 1999; Greendale, Unger, Rowe, & Seeman, 1999; Raff et al., 1999). Finally, we recently observed that restraint scores were an independent negative predictor of lumbar spine bone mineral density in young women (McLean et al., 2001b). In conclusion, our results support the concept that high levels of dietary restraint are not innocuous. Although restraint scores were the only variable that differentiated women with regular and irregular menstrual cycles, our data cannot exclude the possibility that associated behaviors and characteristics may act synergistically or additively in affecting menstrual cycle function.
References Anderson, D. A., Shapiro, J. R., Lundgren, J. D., Spataro, L. E., & Frye, C. A. (2002). Self-reported dietary restraint is associated with elevated levels of salivary cortisol. Appetite, 38, 13 – 17. doi:10.1006/ appe.2001.0459 Barbarino, A., De Marinis, L., Folli, G., Tofani, A., Della Casa, S., D’Amico, C., Mancini, A., Corsello, S. M., Sambo, P., & Barini, A. (1989). Corticotropin-releasing hormone inhition of gonadotropin secretion during the menstrual cycle. Metabolism, 38, 504 –506. Barr, S. I. (1999). Vegetarianism and menstrual cycle disturbances: is there an association? American Journal of Clinical Nutrition, 70, 549S–554S. Barr, S. I., Janelle, K., & Prior, J. C. (1994a). Vegetarian vs. nonvegetarian diets, dietary restraint, and subclinical ovulatory disturbances: prospective 6-mo study. American Journal of Clinical Nutrition, 60, 887– 894. Barr, S. I., Prior, J. C., & Vigna, Y. M. (1994b). Restrained eating and ovulatory disturbances: possible implications for bone health. American Journal of Clinical Nutrition, 59, 92–97.
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Biddle, S. J. H., & Fox, K. R. (1998). Motivation for physical activity and weight management. International Journal of Obesity, 22, S39–S47. Button, E. J., Sonuga-Barke, E. J., Davies, J., & Thompson, M. A. (1996). A prospective study of self-esteem in adolescent schoolgirls: questionnaire findings. British Journal of Clinical Psychology, 35, 193–203. Clark, A. M., Ledger, W., Galletly, C., Tomlinson, L., Blaney, F., Wang, X., & Norman, R. J. (1995). Weight loss results in significant improvements in pregnancy and ovulation rates in anolvulatory obese women. Human Reproduction, 10, 2705–2712. Cohen, S., Kamarck, T., & Mermelstein, R. (1983). A global measure of perceived stress. Journal of Health and Social Behavior, 24, 385–396. Dennison, E., Hindmarsh, P., Fall, C., Kellingray, S., Barker, D., Phillips, D., & Cooper, C. (1999). Profiles of endogenous circulating cortisol and bone mineral density in healthy elderly men. Journal of Clinical Endocrinology & Metabolism, 84, 3058–3063. Dwyer, J. T. (1988). Health aspects of vegetarian diets. American Journal of Clinical Nutrition, 48, 712– 738. Dwyer, J. T., Mayer, L. D. V. H., Dowd, K., & Mayer, J. (1974). The new vegetarians: the natural high? Journal of the American Dietetic Association, 65, 529 –536. Freeland-Graves, J. H., Greninger, S. A., Graves, G. R., & Young, R. K. (1986). Health practices, attitudes, and beliefs of vegetarians and nonvegetarians. Journal of the American Dietetic Association, 86, 913– 918. Gilbody, S. M., Kirk, S. F. L., & Hill, A. J. (1999). Vegetarianism in young women: another means of weight control? International Journal of Eating Disorders, 26, 87 – 90. doi: 10.1002/(SICI)1098108X(199907)26:1 , 87:AID-EAT11 . 3.0.CO;2-M. Gorman, B. S., & Allison, D. B. (1995). Measures of restrained eating. In D. B. Allison (Ed.), Handbook of assessment methods for eating behaviors and weight-related problems (pp. 149 –184). Thousand Oaks, CA: Sage. Greendale, G. A., Unger, J. B., Rowe, J. W., & Seeman, T. E. (1999). The relation between cortisol excretion and fractures in healthy older people: results from the MacArthur studies-Mac. Journal of the American Geriatrics Society, 47, 799 –803. Harlow, S. D., & Matanowski, G. M. (1991). The association between weight, physical activity, and stress and variation in the length of the menstrual cycle. American Journal of Epidemiology, 133, 38–49. Hunt, I. F., Murphy, N. J., & Henderson, C. (1988). Food and nutrient intake of Seventh-day Adventist women. American Journal of Clinical Nutrition, 48, 850– 851. Key, T. J., Thorogood, M., Appleby, P. N., & Burr, M. L. (1996). Dietary habits and mortality in 11,000 vegetarians and health conscious people: results of a 17-year follow up. British Medical Journal, 313, 775–779. Laessle, R. G., Tuschl, R. J., Kotthaus, B. C., & Pirke, K. M. (1989). Behavioural and biological correlates of dietary restraint in normal life. Appetite, 12, 83–94. Lebenstedt, M., Platte, P., & Pirke, K. M. (1999). Reduced resting metabolic rate in athletes with menstrual disorders. Medicine and Science in Sports and Exercise, 31, 1250–1256. Loucks, A. B., Verdun, M., & Heath, E. M. (1998). Low energy availability, not stress of exercise, alters LH pulsatility in exercising women. Journal of Applied Physiology, 84, 37 –46. McLean, J. A., Barr, S. I., & Prior, J. C. (2001a). Cognitive dietary restraint is associated with higher urinary cortisol excretion in healthy premenopausal women. American Journal of Clinical Nutrition, 73, 7–12. McLean, J. A., Barr, S. I., & Prior, J. C. (2001b). Dietary restraint, exercise and bone density in young women: are they related? Medicine and Science in Sports and Exercise, 33, 1292–1296. Neumark-Sztainer, D., Sherwood, N. E., French, S. A., & Jeffery, R. W. (1999). Weight control behaviors among adult men and women: cause for concern? Obesity Research, 7, 179–188.
Pirke, K. M., Tuschl, R. J., Spyra, B., Laessle, R. G., Schweiger, U., Broocks, A., Sambauer, S., & Zitzelsberger, G. (1990). Endocrine findings in restrained eaters. Physiology and Behavior, 47, 903–906. Prior, J. C., Vigna, Y. M., Schechter, M. T., & Burgess, A. E. (1990). Spinal bone loss and ovulatory disturbances. New England Journal of Medicine, 323, 1221–1227. Raff, H., Raff, J. L., Duthie, E. H., Wilson, C. R., Sasse, E. A., Rudman, I., & Mattson, D. (1999). Elevated salivary cortisol in the evening in healthy elderly men and women: correlation with bone mineral density. Journals of Gerontology Series A: Biological Sciences & Medical Sciences, 54, M479–M483. Reid, I. R. (1997). Glucocorticoid osteoporosis: mechanisms and management. European Journal of Endocrinology, 137, 209 –217. Rigotti, N. A., Neer, R. M., Skates, S. J., Herzog, D. B., & Nussbaum, S. R. (1991). The clinical course of osteoporosis in anorexia nervosa. A longitudinal study of cortical bone mass. Journal of the American Medical Association, 265, 1133–1138. Rogers, J., & Mitchell, G. W. (1952). The relationship of obesity to menstrual disturbances. New England Journal of Medicine, 247, 53 –55. Rogol, A. D., Weltman, A., Weltman, J. Y., Seip, R. L., Snead, D. B., Levine, S., Haskvitz, E. M., Thompson, D. L., Schurrer, R., & Dowling, E. (1992). Durability of the reproductive axis in eumenorrheic women during 1 yr of endurance training. Journal of Applied Physiology, 72, 1571–1580. Rosenberg, M. (1965). Conceiving the adolescent self-image. Princeton, NJ: Princeton University Press. Schweiger, U., Tuschl, R. J., Laessle, R. G., Broocks, A., & Pirke, K. M. (1989). Influences of nutrition, exercise and neurotransmitters. In K. M. Pirke, W. Wuttke, & U. Schweiger (Eds.), The menstrual cycle and its disorders (pp. 142 –149). New York: Springer. Schweiger, U., Tuschl, R. J., Platte, P., Broocks, A., Laessle, R. G., & Pirke, K. M. (1992). Everyday eating behavior and menstrual function in young women. Fertility and Sterility, 57, 771 –775. Silverstone, H. (1992). Chronic low self-esteem the cause of eating disorders? Medical Hypothesis, 39, 311– 315. Smith, C. F., Geiselman, P. J., Williamson, D. A., Champagne, C. M., Bray, G. A., & Ryan, D. H. (1998). Association of dietary restraint with eating behaviour, body mass, and hunger. Eating & Weight Disorders: EWD, 3, 7–15. Stewart, T. M., Williamson, D. A., & White, M. A. (2002). Rigid vs. flexible dieting: association with eating disorder symptoms in nonobese women. Appetite, 38, 39–44. doi:10.1006/appe.2001.0445. Stunkard, A. J., & Messick, S. (1985). The three-factor eating questionnaire to measure dietary restraint, disinhibition and hunger. Journal of Psychosomatic Research, 29, 71 –83. Tuschl, R. J., Laessle, R. G., Platte, P., & Pirke, K. M. (1990a). Differences in food-choice frequencies between restrained and unrestrained eaters. Appetite, 14, 9–13. Tuschl, R. J., Platte, P., Laessle, R. G., Stichler, W., & Pirke, K. M. (1990b). Energy expenditure and everyday eating behavior in healthy young women. American Journal of Clinical Nutrition, 52, 81–86. Van Loan, M. D., & Keim, N. L. (2000). Influence of cognitive eating restraint on total-body measurements of bone mineral density and bone mineral content in premenopausal women aged 18 –45 y: a crosssectional study. American Journal of Clinical Nutrition, 72, 837 –843. Warren, M. P. (1992). Eating, body weight, and menstrual function. In K. D. Brownell, J. Rodin, & J. H. Wilmore (Eds.), Eating, body weight and performance in athletes. Disorders of modern society (pp. 222 –234). Philadelphia: Lea & Febiger. Westenhoefer, J., Stunkard, A. J., & Pudel, V. (1999). Validation of the flexible and rigid control dimensions of dietary restraint. International Journal of Eating Disorders, 26, 53– 64.
Research Report
Cognitive dietary restraint is associated with eating behaviors, lifestyle practices, personality characteristics and menstrual irregularity in college women Judy A. McLean, Susan I. Barr* Human Nutrition, University of British Columbia, 2205 East Mall, Vancouver, B.C., Canada V6T 1Z4 Received 8 August 2001; revised 5 June 2002; accepted 12 July 2002
Abstract This study characterized associations of restraint with selected physical, lifestyle, personality and menstrual cycle characteristics in female university students. The survey instrument, distributed to 1350 women, included standardized questionnaires (Three-Factor Eating Questionnaire, Perceived Stress Scale and Rosenberg’s Self-esteem Scale), and assessed weight and dieting history, exercise, lifestyle characteristics, menstrual cycle characteristics and whether participants were following vegetarian diets. Among the 596 respondents included in the analysis (44%), women with high ðn ¼ 145Þ; medium ðn ¼ 262Þ or low ðn ¼ 189Þ restraint had similar ages, heights and weights. Despite this, compared to women with low scores, those with high scores exercised more (4.6 ^ 5.3 vs. 3.2 ^ 3.5 h/wk), were more likely to be vegetarian (14.5 vs. 3.7%), have a history of eating disorders (13.7 vs. 1.2%), be currently trying to lose weight (80.3 vs. 15.3%), report irregular menstrual cycles (34.7 vs. 17.0%), and have scores reflecting lower self-esteem and higher perceived stress. Menstrual irregularity was an independent predictor of restraint score, and restraint score was the only variable to differentiate women with regular and irregular menstrual cycles. We conclude that women with high restraint may use a combination of behavioral strategies for weight control, and differ from women with low restraint scores in personality characteristics and weight history. Some of these behaviors or characteristics may influence menstrual function. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Restrained eating; Vegetarianism; Menstrual disturbances
Introduction Many women consciously try to limit their food intake to achieve or maintain a desired body weight. This is referred to as dietary restraint or cognitive dietary restraint, a type of eating behavior governed by cognitive processes rather than by physiological mechanisms such as hunger and satiety (Gorman & Allison, 1995). Although several scales to assess dietary restraint exist, the Restraint Factor scale of the Three-Factor Eating Questionnaire (TFEQ; Stunkard & Messick, 1985) is considered to be robust and have good psychometric properties (Gorman & Allison, 1995). Typically, women with high scores for restraint are very aware of the amount and type of food they consume although reports vary as to whether their energy intakes are actually lower * Corresponding author. E-mail address: [email protected] (S.I. Barr).
than those of women with low restraint scores (Barr, Prior, & Vigna, 1994b; McLean, Barr, & Prior, 2001a; Schweiger et al., 1992; Smith et al., 1998; Tuschl, Laessle, Platte, & Pirke, 1990a). Previous studies have found women with high restraint scores to be generally similar to those with low restraint scores in terms of age, height, weight and Body Mass Index (BMI) (Barr, Janelle, & Prior, 1994a; Barr et al., 1994b; Laessle, Tuschl, Kotthaus, & Pirke, 1989a; Pirke et al., 1990; Schweiger, Tuschl, Laessle, Broocks, & Pirke, 1989; Van Loan & Keim, 2000). Where a difference has been found has been in menstrual cycle, and particularly ovulatory, characteristics. Several studies have reported that women with high restraint scores were more likely to experience disturbances of ovulation including a higher proportion of anovulatory cycles and short luteal phase or cycle lengths (Barr et al., 1994a,b; Lebenstedt, Platte, & Pirke, 1999; Schweiger et al., 1992).
0195-6663/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0195-6663(02)00125-3
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Women with varying scores for dietary restraint have previously been characterized according to several physical and lifestyle variables which may increase physical or psychological stress and consequently impact on the menstrual cycle (Barr et al., 1994a,b; Laessle et al., 1989; Schweiger et al., 1992; Tuschl, Platte, Laessle, Stichler, & Pirke, 1990b). Unfortunately, many of these studies had small numbers of subjects or used exclusion criteria, which may have limited the findings to a select group. Accordingly, the purpose of this study was to characterize a large, unselected group of university women with regard to dietary restraint, and to assess whether differences existed among women categorized as having low, medium or high restraint in terms of eating behaviors, lifestyle habits, selected personality characteristics and menstrual regularity.
Subjects and methods Participants Female students aged 18 and above at the University of British Columbia were recruited during classes in biochemistry, human nutrition, psychology, family science, nursing and human kinetics. All women students in the selected classes received a questionnaire that they were requested to complete at home and return to class during the following week. There were no exclusion criteria, nor were any incentives provided for participation. The study protocol was approved by the University’s Clinical Screening Committee for Research and Other Studies Involving Human Subjects, and the data were gathered during 1997. Questionnaire The questionnaire included previously validated, standardized scales designed to assess eating behaviors, perceived stress, and self-esteem. It also sought data on physical and lifestyle characteristics, such as age, height, weight, dieting history, menstrual cycle history, exercise, special diets (e.g. vegetarian), and use of vitamin or mineral supplements. Eating behaviors The 51-item TFEQ (Stunkard & Messick, 1985) was used to assess perceptions of three dimensions of human eating behavior: (1) cognitive restraint of eating, (2) disinhibition and (3) hunger. To make the TFEQ suitable for individuals who don’t consume meat, the first item was altered from, “When I smell a sizzling steak or see a juicy piece of meat, I find it very difficult to keep from eating, even if I have just finished a meal”, to “When I smell my favorite food, I find it very difficult to keep from eating, even if I have just finished a meal”. Responses to items on the TFEQ were scored according to the instructions
provided by Stunkard and Messick (1985) and summed to obtain scores for restraint, disinhibition and hunger. Physical and lifestyle characteristics Participants reported their present height and weight as well as their highest and lowest adult weights. They were also asked, “At what weight do you feel your best?” which was subsequently referred to as their ‘best’ weight. From these values, BMI, highest BMI, lowest BMI, and best BMI were calculated in kg/m2. Participants were asked whether they were currently trying to lose weight, had ever tried to lose weight, or had ever been diagnosed with or treated for an eating disorder. Weight fluctuation was determined by the number of times that . 5 lbs was lost in the past two years. Participants were asked whether they were currently having menstrual cycles and if so, whether their cycles were irregular or regular. They were also asked the average length of their cycle and whether they were presently, or had in the past six months, used oral contraceptives. Lifestyle information included questions regarding alcohol and coffee or tea consumption, cigarette usage, vitamin, mineral and medication use as well as hours of weekly exercise. Participants identified whether they were following lacto-ovo vegetarian, vegan or other special diets. Perceived stress and self-esteem The Perceived Stress Scale (PSS) (Cohen, Kamarck, & Mermelstein, 1983) measures the extent to which situations in one’s life are appraised as stressful. It consists of 14 statements asking about the respondents’ feelings and thoughts during the last month. Items were scored and totaled according to instructions provided by the authors, with higher scores reflecting higher perceived stress. Rosenberg’s Self-esteem Scale (RSS) is a widely used measure of self-esteem (Rosenberg, 1965). Items were scored according to Rosenberg’s original instructions. Higher scores indicate lower self-esteem. Statistical analysis Participants with complete responses to the TFEQ restraint scale were included in the analysis, and were grouped according to their restraint scale scores, based on quartiles established in a previous study of this population (unpublished). Those with scores of 0 –5 on the TFEQ restraint scale (the first quartile) were grouped as ‘low restraint’; scores 6 –12 (the second and third quartiles) as ‘medium restraint’ and scores 13 –21 (the fourth quartile) as ‘high restraint’. Group comparisons among the low, medium and high restraint groups were made by ANOVA. When significant F ratios were present, Duncan’s multiple range test was used to determine which means were significantly different. For comparisons of population proportions, chisquare ðx2 Þ was used. Stepwise multiple regression analysis was used to determine which characteristics independently
J.A. McLean, S.I. Barr / Appetite 40 (2003) 185–192
predicted dietary restraint scores, and discriminant analysis was used to examine variables that differentiated women with regular and irregular menstrual cycles. The statistical analysis was achieved through computer programs available in the Statistical Package for the Social Sciences, Personal Computer version 10.0 (SPSS Inc., 1999, Chicago, IL). Cases with missing values for variables other than the TFEQ restraint scale were excluded from analysis on a case-wise basis. The level of significance was set at P , 0:05 and comparisons were two-tailed.
Results Of 1350 questionnaires distributed, 761 (56%) were returned. A printing error resulted in the loss of 95 responses, and of the remaining 666, 596 (44% of distributed questionnaires) had complete responses to the TFEQ restraint scale. Just under 32% ðn ¼ 189Þ of women had low scores for restraint, 44% ðn ¼ 262Þ had medium restraint scores, and 24% ðn ¼ 145Þ had high restraint scores. Participants grouped according to restraint scores Descriptive and lifestyle characteristics Physical and lifestyle characteristics of women grouped according to their TFEQ restraint scale scores are presented in Table 1. Age, height, weight, BMI (kg/m2) and best BMI (calculated from weight given as ‘best weight’) were similar among the three groups. Highest BMI was higher in women grouped as having high or medium scores for restraint when
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compared to women in the low restraint group. Lowest BMI differed only between women with low and medium scores for restraint with the former group having lower values. Compared to women with low and medium scores for restraint, women with high restraint scores reported more hours of weekly exercise. Alcoholic beverage use did not differ among groups nor did the prevalence of vitamin or mineral supplementation. Women with high restraint scores tended to be more likely to smoke and to use more caffeinated beverages although the group differences were not significant ðP , 0:10Þ: The likelihood of following a lacto-ovo or vegan diet, however, increased significantly as the level of dietary restraint increased. With regard to vegetarianism, additional analyses were done to compare the 47 women who identified themselves as being vegetarian (i.e. excluding meat, fish and poultry) to the non-vegetarian women ðn ¼ 549Þ: Vegetarians were found to weigh more than non-vegetarians (60.4 ^ 12.5 vs. 57.1 ^ 9.5 kg, t ¼ 2:17; P ¼ 0:03), exercise more (5.5 ^ 6.2 vs. 3.5 ^ 3.6 h/wk, t ¼ 3:4; P , 0:001) and were more likely to smoke cigarettes (17.0 vs. 5.8%, x2 ¼ 9:5; P ¼ 0:002). A higher percentage of the vegetarian participants had a history of eating disorders (17.1 vs. 3.1%, x2 ¼ 17:9; P , 0:001). They also had higher restraint scores (11.4 ^ 5.6 vs. 8.4 ^ 5.2, t ¼ 3:8; P , 0:001) and self-esteem scores (indicating lower self-esteem) (2.0 ^ 1.9 vs. 1.4 ^ 1.5, t ¼ 2:2; P , 0:05). Weight fluctuation and dieting history Weight fluctuation and dieting history of participants grouped according to restraint scores are presented in
Table 1 Physical and lifestyle characteristics (mean ^ SD) of women with low, medium and high scores for dietary restraint Characteristic
All subjects ðn ¼ 596Þ
Restraint Low ðn ¼ 189Þ
Age (yr) Height (cm) Weight (kg) BMI (kg/m2) Highest BMI (kg/m2)d Lowest BMI (kg/m2)g Best BMI (kg/m2)h Exercise (h/wk) Caffeinated beverages (cups/d) Alcoholic beverages (drinks/wk) Cigarette smokers Vegetarian Using vitamin/mineral supplements a b c d e,f g h i
21.5 ^ 3.9 164.7 ^ 7.2 57.4 ^ 9.8 21.1 ^ 3.0 22.6 ^ 3.8 19.8 ^ 2.5 20.0 ^ 2.0 3.6 ^ 3.9 1.1 ^ 1.1 1.1 ^ 1.8 6.4% 7.9% 35.8%
21.2 ^ 3.3 164.7 ^ 7.4 56.4 ^ 10.9 20.8 ^ 3.8 21.9 ^ 4.1e 19.4 ^ 2.8e 20.0 ^ 2.3 3.2 ^ 3.5e 0.9 ^ 1.0 1.3 ^ 2.1 5.9% 3.7% 35.8%
a
Medium ðn ¼ 262Þ 21.6 ^ 3.4 164.5 ^ 6.6 57.8 ^ 9.2 21.3 ^ 2.6 22.7 ^ 3.3f 20.0 ^ 2.4f 20.2 ^ 1.9 3.4 ^ 3.1e 1.0 ^ 1.1 1.0 ^ 1.6 4.6% 7.3% 35.5%
b
High ðn ¼ 145Þ
F ratio (or x2 )
P
1.118 0.113 1.351 1.515 6.356 3.806 2.475 5.867 2.657 1.413 x2 ¼ 5:3 x2 ¼ 13:4 x2 ¼ 0:03
0.328 0.893 0.260 0.221 0.002 0.023 0.085 0.003 0.071 0.244 0.071 0.001 0.986
c
21.7 ^ 5.2 164.9 ^ 8.0 57.8 ^ 9.0 21.2 ^ 2.5 23.3 ^ 4.0f 19.8 ^ 2.2e,f 19.8 ^ 1.9 4.6 ^ 5.3f 1.2 ^ 1.2 1.2 ^ 2.0 10.4% 14.5%i 36.4%
Score 0–5 on the TFEQ restraint scale (Stunkard & Messick, 1985). Score 6–12 on TFEQ restraint scale. Score 13–21 on TFEQ restraint scale. Calculated from weight given as ‘highest adult weight’. Means differ significantly between values in rows not sharing a common superscript (by one-way ANOVA and Duncan’s multiple range test). Calculated from weight given as ‘lowest adult weight’. Calculated from weight given as ‘best adult weight’. Percentages differ significantly among groups (chi-square).
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Table 2 Weight fluctuation and dieting history of women with low, medium, and high scores for dietary restraint Characteristic
Presently trying to lose weight Ever tried to lose weight History of eating disorders Weight fluctuatione,f a b c d e f g,h
All subjects ðn ¼ 596Þ
44% 74.5% 6.4% 1.5 ^ 2.0
Restraint Low ðn ¼ 189Þa
Medium ðn ¼ 262Þb
High ðn ¼ 145Þc
15.3% 49.7% 1.2% 1.1 ^ 1.4g
45.0% 80.3% 1.4% 1.5 ^ 1.5g
80.3% 96.5% 13.7% 2.1 ^ 3.0h
x2 or F
P
x2 ¼ 139:0 x2 ¼ 101:9 x2 ¼ 35:7 F ¼ 8:57
0.000 0.000 0.000 0.000
Score 0–5 on the TFEQ restraint scale (Stunkard & Messick, 1985). Score 6–12 on TFEQ restraint scale. Score 13–21 on TFEQ restraint scale. Percentages differ significantly among groups (chi-square). Number of times .5 lbs lost during the past two years. Mean ^ SD. Means differ significantly between values in rows not sharing a common superscript (by one-way ANOVA and Duncan’s multiple range test).
Table 2. In response to the question, “Are you presently trying to lose weight?” a significant difference was found among restraint groups with over 80% of women with high scores for restraint responding “yes”. A difference was also found in response to the question, “Have you ever tried to lose weight?” Over 90% of women in the high restraint group reported having tried to lose weight at some point. History of an eating disorder was also markedly higher in women in the high restraint group compared to those in the low or medium restraint groups. Of all women who provided this history, 77% were in the high restraint group. Finally, weight fluctuation (the number of times more than 5 lbs was lost) was higher in the previous 2 years in women with high scores compared to those with low or medium scores for restraint. Menstrual cycle characteristics Three hundred and ninety-four women reported that they were having menstrual cycles and were not using oral contraceptives. For these women, the proportions reporting irregular cycles were compared by restraint group (Fig. 1). The prevalence of self-reported menstrual cycle irregularity in women with high restraint (34.7%) was double that of women with low and medium scores (17.1 and 17.0%,
Fig. 1. Prevalence of self-reported menstrual cycle irregularity among women grouped according to scores on the TFEQ restraint scale (Stunkard & Messick, 1985). Scores in the low, medium and high restraint groups were 0– 5, 6–12, and 13 and above, respectively. Percentages differed significantly among groups (x2 ¼ 13:4; P ¼ 0:001).
respectively). This difference persisted when the analysis was repeated after excluding women who reported a history of an eating disorder: the prevalence of menstrual irregularity among women with high, medium and low restraint was 32.5%, 14.6 and 16.1%, respectively (x2 ¼ 12:0; P ¼ 0:003). No differences among restraint groups were detected in self-reported cycle length. In separate analyses, the women who reported irregular menstrual cycles were compared to those reporting regular cycles. It is notable that those reporting irregular cycles ðn ¼ 84Þ were comparable to those with regular cycles ðn ¼ 310Þ in terms of BMI (20.7 ^ 3.1 vs. 21.1 ^ 3.2 kg/m2) and hours of weekly exercise (3.1 ^ 3.1 vs. 3.3 ^ 3.5 hr/wk). However, they were more likely to smoke cigarettes (8.3 vs. 3.2%, x2 ¼ 4:1; P ¼ 0:042) and tended to be more likely to follow vegetarian diets (13.1 vs. 7.4%, P ¼ 0:10). Scores on the TFEQ restraint subscale were significantly higher in women reporting irregular cycles than in those reporting regular cycles (10.3 ^ 6.0 vs. 8.2 ^ 5.1, P ¼ 0:001), but the two groups did not differ in terms of scores on the TFEQ hunger and disinhibition subscales. Perceived stress scores did not differ between groups, while self-esteem scores were higher (1.9 ^ 1.8 vs. 1.5 ^ 1.5, P , 0:05), indicating lower self-esteem. Discriminant analysis revealed that restraint score was the only variable that significantly differentiated between women reporting regular and irregular menstrual cycles (Wilks’ Lambda Exact F ¼ 13:8; P , 0:001). Sixty percent of cases were correctly classified as regularly or irregularly menstruating. Eating behavior, perceived stress and self-esteem Participants’ scores on the TFEQ subscales, the PSS and RSS are presented in Table 3. There were no group differences on the TFEQ hunger subscale. All other scales differed among groups, and scores were highest in the high restraint group, reflecting higher perceived disinhibition, perceived stress, and lower self-esteem.
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Table 3 TFEQa subscale, PSSb, and RSSc scores (mean ^ SD) for women with low, medium and high scores for dietary restraint Characteristic
All subjects ðn ¼ 596Þ
Restraint d
TFEQ restraint TFEQ disinhibition TFEQ hunger Perceived stress Self-esteem
8.6 ^ 5.3 6.2 ^ 3.7 6.4 ^ 3.1 26.2 ^ 7.6 1.5 ^ 1.6
e
F
P
1865.1 34.7 2.10 13.1 18.7
0.000 0.000 0.124 0.000 0.000
f
Low ðn ¼ 189Þ
Medium ðn ¼ 262Þ
High ðn ¼ 145Þ
2.7 ^ 1.6g 4.8 ^ 3.3g 6.1 ^ 3.0 25.0 ^ 7.2g 1.1 ^ 1.5g
8.8 ^ 2.0h 6.3 ^ 3.6h 6.5 ^ 3.0 25.5 ^ 7.4g 1.4 ^ 1.5h
16.1 ^ 2.3i 8.1 ^ 3.8i 6.8 ^ 3.4 28.9 ^ 7.9h 2.2 ^ 1.8i
a
TFEQ ¼ Three-Factor Eating Questionnaire (Stunkard & Messick, 1985). PSS ¼ Perceived Stress Scale (Cohen et al., 1983). c RSS ¼ Rosenberg Self-Esteem Scale (Rosenberg, 1965). Lower scores reflect higher self-esteem. d Score 0–5 on TFEQ restraint scale. e Score 6–12 on TFEQ restraint scale. f Score 13–21 on TFEQ restraint scale. g,h,i Means differ significantly between values in rows not sharing a common superscript (by one-way ANOVA and Duncan’s multiple range test). b
Regression analysis Stepwise linear regression was conducted to determine which variables were independently associated with the dietary restraint score (Table 4). The final model included presently and previously trying to lose weight, history of an eating disorder, BMI, highest BMI, self-esteem score, menstrual regularity, and exercise. Variables that did not enter the equation included the number of times . 5 lbs had been lost in the past 2 years, vegetarianism, smoking, best BMI, lowest BMI, perceived stress, disinhibition and hunger.
Discussion This study of female university students revealed associations between dietary restraint and several variables related to efforts to control body weight. We also detected associations between restraint and menstrual irregularity, with potential long-term health implications. Before discussing these results, possible limitations of the study should be addressed. One limitation was the composition of the particular sample, which included
students recruited from biochemistry, human nutrition, psychology, family science, nursing and human kinetics classes. Compared to students in other disciplines, these students may have had a higher level of interest in health issues. This possibility, and the modest response rate, must be borne in mind when considering to whom the results might be generalized. A second limitation relates to the use of self-report data, and that some variables were assessed with single questions (e.g. smoking, vegetarianism, menstrual regularity) rather than validated scales. This is of greatest concern for menstrual regularity, as the associations between cognitive dietary restraint and irregular menstrual cycles were a major finding of the study. Limited data from a subset of participants suggest that the question used to assess menstrual regularity was reasonably reliable and valid. Women in the present study who reported regular menstrual cycles (among other criteria) were recruited to participate in an additional study. During the course of that study (McLean et al., 2001a), they completed the questionnaire again and kept menstrual cycle records for up to 3 months. Cycles were again reported to be ‘regular’, and only one woman was excluded because her recorded cycles did not meet the criterion for normal length (intervals of 21– 35
Table 4 Stepwise multiple regression of variables associated with dietary restraint score Variable entered at each step
B ^ SE
Standardized beta
t ðpÞ
Model R2
Constant Presently trying to lose weighta Previously tried to lose weighta Diagnosed or treated for eating disordera Menstrual regularityb BMI (kg/m2) Highest BMI (kg/m2) Rosenberg self-esteem scorec Exercise (h/wk)
21.77 ^ 2.61 4.41 ^ 0.55 3.03 ^ 0.65 4.37 ^ 1.43 21.55 ^ 0.60 20.65 ^ 0.16 0.42 ^ 0.14 0.42 ^ 0.15 0.17 ^ 0.07
–
20.68 (0.497) 8.03 (,0.001) 4.66 (,0.001) 3.06 (0.002) 22.59 (0.010) 24.06 (,0.001) 3.02 (0.003) 2.79 (0.006) 2.44 (0.015)
0.295 0.354 0.392 0.411 0.426 0.444 0.455 0.466
a b c
1 ¼ no, 2 ¼ yes. 1 ¼ irregular, 2 ¼ regular. Higher scores reflect lower self-esteem.
0.398 0.238 0.135 20.113 20.354 0.269 0.124 0.107
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days). Although this does not demonstrate reliability and validity of the question for those reporting ‘irregular’ cycles, it should be recognized that misclassification of menstrual regularity would likely attenuate the observed associations, rather than inflate them. Finally, rigid and flexible control dimensions of dietary restraint have recently been identified (Westenhoefer, Stunkard, & Pudel, 1999), and some data suggest that rigid control, but not flexible control, may be associated with eating disorder symptomatology (Stewart, Williamson, & White, 2002). This assessment tool was not available when our data were obtained, so we cannot determine whether the associations we observed were associated primarily with flexible or rigid control dimensions of restraint. In this study, irregular menstrual cycles were reported by a greater percentage of women with high restraint scores than with low or medium restraint scores; menstrual irregularity was independently associated with restraint score; and restraint score was the only variable that differentiated women with regular and irregular cycles. Although our results are self-reported, they concur with the findings of several studies in which menstrual cycle characteristics were directly monitored (Barr et al., 1994a, b; Lebenstedt et al., 1999; Schweiger et al., 1992). In these previous studies conducted with women who self-reported ‘regular’ cycles, an association was found between cognitive dietary restraint and subclinical ovulatory disturbances such as anovulation and short luteal phase cycles, which can occur within cycles of normal length. The present study differs from previous studies of restraint and the menstrual cycle in that instead of assessing subclinical disturbances that wouldn’t be evident to women, clinical disturbances (i.e. menstrual irregularity) were assessed. Establishing that dietary restraint has an independent association with menstrual irregularity requires consideration of potential confounding by other variables that may influence the cycle. These are discussed below, and include relative weight, exercise, vegetarianism, history of an eating disorder, and personality characteristics such as perceived stress and self-esteem. As has been observed by others (Tuschl et al., 1990b; Van Loan & Keim, 2000), women in this study with high scores for restraint had similar relative weights to those with low restraint scores. Although menstrual irregularity has been associated with unusually low body weight and with obesity (Clark et al., 1995; Rogers & Mitchell, 1952), BMI did not differ among women with low, moderate or high restraint scores in the present study, nor did BMI differ between those reporting regular and irregular cycles. Thus, relative weight did not confound the associations between restraint and menstrual irregularity. Several studies have suggested that the prevalence of menstrual disturbances is higher among women athletes than among sedentary women (Warren, 1992), and women with high restraint scores in the present study did report more hours of exercise. However, prospective studies in
which exercise was increased gradually do not support a causal role for exercise in menstrual dysfunction (Rogol et al., 1992), and short-term studies have demonstrated that normal release of luteinizing hormone (required for normal cycles) is maintained even when exercise is increased dramatically, provided that energy availability remains adequate (Loucks, Verdun, & Heath, 1998). In our study, hours of weekly exercise did not differ between women with regular and irregular cycles, suggesting that exercise did not confound the association between restraint and the menstrual cycle. Women with high restraint, however, may use exercise as an additional weight management strategy. Women commonly report weight management as a motivation for exercise (Biddle & Fox, 1998), and in a recent study, exercise was the most frequently reported weight loss practice among women (Neumark-Sztainer, Sherwood, French, & Jeffery, 1999). Women with high restraint scores were more likely to identify themselves as vegetarian, and associations between vegetarianism and menstrual irregularity have been reported in the literature (Barr, 1999). These studies, however, had a number of potential biases, including failure to control for oral contraceptive use and the possibility of a recruitment bias (vegetarians with menstrual disturbances might be more likely than those with normal cycles to volunteer for a study on this topic). A study that controlled these potential biases demonstrated that healthy vegetarian women do not have a higher prevalence of subclinical menstrual disturbances (Barr et al., 1994a). Thus, vegetarianism per se is unlikely to have confounded the association between restraint score and menstrual irregularity. Although our study was not designed to characterize vegetarian and non-vegetarian women, we did detect a number of differences between these two groups that are relevant to the suggestion that women with high restraint scores use a variety of strategies to control weight. In addition to higher restraint scores, vegetarian women had lower self-esteem, were heavier, exercised more, were more likely to smoke, and had a greater history of weight fluctuation and eating disorders, all of which support an association between vegetarianism and concern about body weight. However, vegetarianism did not enter the regression equation for restraint score, suggesting that the difference in restraint score between vegetarians and non-vegetarians was explained by associations with other variables that also differed between these groups. Our findings regarding vegetarian women are in contrast to much of the literature, which often reports that vegetarians are leaner and less likely to smoke cigarettes (Dwyer, 1988; Dwyer, Mayer, Dowd, & Mayer, 1974; Freeland-Graves, Greninger, Graves, & Young, 1986), and to common beliefs. These differences may be explained by the fact that many studies of vegetarians have used large groups such as Seventh Day Adventists who also practice other health promoting behaviors (Hunt, Murphy, & Henderson, 1988; Key, Thorogood, Appleby, & Burr,
J.A. McLean, S.I. Barr / Appetite 40 (2003) 185–192
1996) or have had exclusion criteria which would have excluded many of our subjects (Barr et al., 1994a). This study did not intentionally recruit vegetarian women, which suggests that those included may be more representative of young vegetarian women than study volunteers described in other studies. Our finding that women with high restraint scores were more likely to be vegetarian likely reflects another socially acceptable way to control calorie and fat intake. As Gilbody suggested, vegetarianism may legitimize food avoidance (Gilbody, Kirk, & Hill, 1999). All characteristics assessed in relation to weight fluctuation and dieting history, including being diagnosed with or treated for an eating disorder, differed among women with low, medium and high scores for restraint. Many of these variables also entered the regression equation for restraint score. As dietary restraint reflects the cognitive attempt to control or limit food intake, the relationship between restraint group and dieting is not surprising, and has been reported by others (Barr et al., 1994a; Laessle et al., 1989; Schweiger et al., 1992; Tuschl et al., 1990b). The difference in prevalence of an eating disorder diagnosis between women with high scores and those with medium or low scores for restraint is also not unexpected as there were no exclusion criteria for participation. Women with eating disorders would most likely score high on any instrument assessing restrictive attitudes towards food intake. Importantly, the association between restraint and menstrual irregularity did not result from including these women, as the association persisted when they were excluded from analysis. Women with high restraint scores scored higher on the PSS. It could be hypothesized that those who perceive events in their lives as more stressful experience more negative feelings with regard to their weight and attempt to limit food intake to reduce their sense of dissatisfaction. Alternately, higher restraint may lead to a general feeling of stress, which is subsequently extrapolated into other situations. Although stress is known to be associated with menstrual cycle disturbances (Harlow & Matanoski, 1991), PSS scores were not independently associated with restraint scores, nor did PSS differ between women with regular and irregular cycles. Accordingly, perceived stress does not appear to explain the relationship between restraint and menstrual irregularity. Finally, women with high restraint scores had lower selfesteem, and self-esteem was independently associated with restraint score. While our data are cross-sectional, it has been hypothesized that low self-esteem predates the onset of eating disorders and is a necessary prerequisite for their development (Silverstone, 1992). Empirical evidence to support this has been obtained (Button, Sonuga-Barke, Davies, & Thompson, 1996). Accordingly, low self-esteem may increase women’s sensitivity to current cultural pressures to be thin, and therefore, susceptibility to dietary restraint. Although women reporting irregular menstrual
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cycles did have lower self-esteem, self-esteem scores did not differentiate women with regular and irregular cycles. The association between high levels of dietary restraint and menstrual irregularity has potential health implications for women. In addition to the obvious impact on fertility, bone health may be affected. High levels of dietary restraint may act as a subtle but frequently experienced stressor, activating the hypothalamic –pituitary– adrenal axis and leading to increased secretion of the stress hormone, cortisol. Recent studies (Anderson, Shapiro, Lundgren, Spataro, & Frye, 2002; Mclean et al., 2001a) have confirmed that cortisol secretion is increased in women with high scores for dietary restraint. Corticotropin releasing hormone may interfere with menstrual function by inhibiting gonadotropin secretion (Barbarino et al., 1989); menstrual dysfunction, whether marked or subtle, affects circulating sex steroids and is known to lead to bone loss (Prior, Vigna, Schechter, & Burgess, 1990; Rigotti, Neer, Skates, Herzog, & Nussbaum, 1991). In addition to affecting menstrual function, cortisol has the potential to adversely affect calcium homeostasis and inhibit bone formation through a number of mechanisms (Reid, 1997). Elevated cortisol, even within the normal range, is associated with lower values for bone mineral density (Dennison et al., 1999; Greendale, Unger, Rowe, & Seeman, 1999; Raff et al., 1999). Finally, we recently observed that restraint scores were an independent negative predictor of lumbar spine bone mineral density in young women (McLean et al., 2001b). In conclusion, our results support the concept that high levels of dietary restraint are not innocuous. Although restraint scores were the only variable that differentiated women with regular and irregular menstrual cycles, our data cannot exclude the possibility that associated behaviors and characteristics may act synergistically or additively in affecting menstrual cycle function.
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