Education on the glycemic index of foods fails to improve treatment outcomes in a behavioral weight loss program

Eating Behaviors 6 (2005) 145 – 150

Education on the glycemic index of foods fails to improve treatment outcomes in a behavioral weight loss program Robert A. Carels*, Lynn A. Darby, Olivia M. Douglass, Holly M. Cacciapaglia, Sofia Rydin Department of Psychology, Bowling Green State University, Bowling Green, OH 43403, USA Received 6 July 2004; accepted 31 August 2004

Abstract The glycemic index (GI) may play an important role in weight management by helping to control appetite and insulin levels. The impact of adding education on the GI of foods to a behavioral weight loss program (BWLP) was examined. Fifty-three obese, sedentary participants were randomly assigned to receive either a BWLP or a BWLP+GI education. Pre- and posttreatment weight loss, body fat, and diet were assessed. Weight loss and body fat were assessed at 1-year posttreatment. GI education had no significant impact on weight loss treatment outcomes at posttreatment or 1-year follow-up. Average weight loss was 7.6 kg ( pb0.05). Participants in the BWLP+GI education group had significantly greater GI knowledge ( pb0.05) and consumed foods with a lower average daily GI ( pb0.05), than participants in the BWLP at posttreatment. At 1-year posttreatment, participants regained 59% of their posttreatment weight loss and 34% of their lost body fat. GI education did not improve BWLP treatment outcomes in this investigation. D 2004 Elsevier Ltd. All rights reserved. Keywords: Glycemic index; Weight loss; Diet; Treatment

1. Introduction Numerous scientific articles have been published on the scientific and clinical utility of the glycemic index (GI; Pawlak, Ebbeling, & Ludwig, 2002; Raben, 2002). The GI is a physiologically based measure * Corresponding author. Tel.: +1 419 372 9405; fax: +1 419 372 6013. E-mail address: [email protected] (R.A. Carels). 1471-0153/$ - see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.eatbeh.2004.08.005

146

R.A. Carels et al. / Eating Behaviors 6 (2005) 145–150

of how quickly carbohydrates are broken down during digestion (Ludwig, 2002). The GI refers to the bincremental area under the glucose response curve after an amount of carbohydrate from a test food relative to that of a control food is consumedQ (Ludwig, 2002). A low-GI diet may contribute to weight loss by influencing insulin levels, appetite, and metabolism (Ludwig, 2002). Several recent studies report a positive impact of a low-GI diet on ratings of hunger and caloric intake (Ludwig et al., 1999), resting energy expenditure and nitrogen balance (Agus, Swain, Larson, Eckert, & Ludwig, 2000), and fat loss (Bouche, Rizkalla, Luo, & Veronese, 2002). Despite the GI’s increasing popularity, its utility in clinical settings and its benefit to obese individuals attempting to lose weight are matters of debate (Pawlak et al., 2002; Raben, 2002). The effect of high- and low-GI diets on weight loss in ad libitum studies has been understudied. The current investigation hypothesized that a behavioral weight loss program that included GI education (BWLP+GI) would have superior treatment outcomes when compared a BWLP. Weight loss and body fat at 1-year posttreatment were also assessed.

2. Methods 2.1. Participants Fifty-three obese, sedentary participants recruited through local advertisements were randomly assigned to receive a BWLP or BWLP+GI education (Table 1). Participants were included if they were (a) obese (body mass index (BMI)N30 kg/m2), (b) sedentary, (c) nonsmokers, and (d) cleared for participation by their physician. Participants were excluded if they had (a) cardiovascular disease, (b) musculoskeletal problems, (c) insulin-dependent diabetes or uncontrolled Type II diabetes, and (d) elevated resting blood pressure (N160/100 mmHg). All procedures received human participants review board approval. 2.2. Study design At baseline and posttreatment, participants completed assessments of body weight and composition, and diet. The program was administered in small groups over 20 weekly sessions. BWLP participants met weekly for 60–75 min, while BWLP GI group participants met for 90–120 min.

Table 1 Demographic and baseline characteristics Demographics Age, years Gender Women, Income b$30,000 College degree Working full time Blood pressure med.

BWLP

BWLP+GI

Total

M (S.D.)

M (S.D.)

M (S.D.)

43.5 (9.83)

43.4 (9.02)

43.4 (9.37)

N (%)

N (%)

N (%)

23 (88.5) 6 (23.1) 8 (30.1) 23 (88.5) 8 (30.8)

21 (77.8) 6 (22.2) 14 (51.8) 17 (63.0) 4 (14.8)

44 12 22 40 12

(83.0) (22.6) (41.5) (75.5) (22.6)

R.A. Carels et al. / Eating Behaviors 6 (2005) 145–150

147

2.3. Interventions 2.3.1. Behavioral weight loss program The BWLP was based on the LEARN program which is an empirically supported approach to weight management devoted to achieving gradual weight loss, increased physical activity, and reduced energy and fat intake (Brownell, 2000). The LEARN program’s nutritional information was consistent with the GI education in this investigation. However, the LEARN program’s discussion of carbohydrates is quite limited and makes no reference to the GI or GI-related constructs. 2.3.2. Glycemic index education The GI education component was a combination of didactic instruction, individual activities, and out-of-class assignments. The GI education materials emphasized eating a low-fat, low-GI diet. Participants received a copy of the book, The New Glucose Revolution (Brand-Miller, Wolever, Foster-Powell, & Colagiuri, 2003). Participants were instructed on (1) carbohydrate consumption and glucose and insulin levels, (2) computing the GI, (3) physical characteristics of carbohydrates and the speed of digestion, (4) the GI and health, (5) low-GI foods, hunger, and satiety, and (6) on low-GI cooking. 2.4. Measures 2.4.1. Body weight Body weight and fat estimates were obtained using a digital scale and leg-to-leg bioelectrical impedance (BF-350e; Tanita, Arlington Heights, IL). 2.4.2. Dietary assessment Participants recorded food intake over four days at baseline and at posttreatment. Average daily GI and glycemic load (GL) were determined for the food records from published tables (Brand-Miller et al., 2003; Foster-Powell, Holt, & Brand-Miller, 2002). The GL was determined by multiplying the carbohydrate content of a food by its GI value; this value was then summed for all food items consumed in each day. Estimates for total calories, calories from fat, saturated fat, carbohydrates (including values of the carbohydrate content of foods), and protein were calculated using Nutribase 2001 Professional Nutrition software (Phoenix, Arizona). 2.4.3. GI knowledge A 14-item measure was created to assess GI knowledge. The questionnaire included questions on the assessment of GI, the physical characteristics of low- or high-GI foods, and common high- or low-GI foods. The number of correct responses were summed (a=0.86). 2.4.4. Data analysis Baseline differences between the treatment groups were assessed using ANOVA and v 2. Pre- and posttreatment effects were evaluated using two-way repeated measures ANOVA with treatment groups as the between group factor. Weight loss, body composition, and diet were used as dependent measures. One-year posttreatment effects were also examined using repeated measures ANOVA.

148

R.A. Carels et al. / Eating Behaviors 6 (2005) 145–150

3. Results 3.1. Background characteristics and adherence The BWLP participants had significantly greater baseline body fat than the BWLP+GI participants, F(1,52)=7.84, pb0.01 (Table 1). Forty participants (75.5%) completed the study. Participants in the BWLP group attended a significantly greater number of sessions (15.6) than participants in the BWLP GI group (13.1), F(1,40)=6.79, pb0.01. Compared to the BWLP participants, posttreatment GI knowledge was significantly greater in the BWLP+GI participants, t(40)=45.1, pb0.05. 3.2. Changes in body weight and body composition There were no significant pre- to posttreatment differences between the BWLP and BWLP+GI groups in body weight, BMI, or body fat. From pre- to posttreatment, average weight loss was 7.6 kg, F(1,40)=44.29, pb0.01, BMI decreased by 2.6 kg/m2, F(1,40)=53.2, pb0.01, and average body fat decreased by 8.6%, F(1,40)=28.53, pb0.01 (Table 2). 3.3. Changes in dietary intake From pre- to posttreatment, there was a significant decrease in total calories, F(1,34)=105.2, pb0.01 (Table 3). The percentage of daily energy derived from carbohydrates, F(1,40)=17.24, pb0.01, and protein increased, F(1,40)=20.34, p=0.01. The percentage of energy derived from fat, F(1,40)=31.9, pb0.01, and saturated fat decreased, F(1,40)=12.2, pb0.01. From pre- to posttreatment, there was a significant time by treatment group interaction for the average daily GI of the diet, F(1,40)=4.36, pb0.05; the BWLP did not change, but the BWLP GI group significantly decreased the average daily GI of the diet, t(40)=2.49, pb0.05. Conversely, when expressed as the average daily GL, the time by treatment group interaction was not significant F(1,40)=3.06, pb0.09. The GL was significantly lower for both groups at posttreatment, F(1,40)=31.9, pb0.01. In addition, when GL was computed accounting for total energy intake (GL, g/1000 kcal), there were no BWLP versus BWLP+GI group differences. Table 2 Pre- and posttreatment health outcomes and GI knowledge BWLP

BWLP+GI

Combined

%

Pre

Post

Pre

Post

Pre

Post

M (S.D.)

M (S.D.)

M (S.D.)

M (S.D.)

M (S.D.)

M (S.D.)

96.6 (15.9) 34.4 (4.3) 41.9 (5.5) 6.9 (2.2)

101.2 (16.3) 38.0 (13.4) 42.5 (4.0)

94.1 (15.1) 35.5 (13.4) 38.7 (6.8) 11.5 (1.6)

102.8 (18.5) 37.6 (10.4) 44.1 (4.2)

95.2 (15.3) 35.0 (10.2) 40.3 (6.3) 9.5 (2.9)

Weight loss and body composition Weight (kg) 104.8 (21.2) Body mass index 37.2 (5.1) Body fat (%) 45.8 (3.9) GI knowledgeb

BWLP: behavioral weight loss program; GI: glycemic index. a pb0.05 (pretreatment compared to posttreatment). b pb0.05 (posttreatment: BWLP different from BWLP+GI education).

7.4a 6.9a 8.6a

R.A. Carels et al. / Eating Behaviors 6 (2005) 145–150

149

Table 3 Pretreatment–posttreatment changes in diet BWLP Pre Total calories Carbohydrates (%) Protein (%) Fat (%) Saturated fat (%) GI GL GL, g/1000 kcal

BWLP+GI Post

Pre

Combined Post

Pre

% Post

M (S.D.)

M (S.D.)

M (S.D.)

M (S.D.)

M (S.D.)

M (S.D.)

2272 (454) 48.1 (7.4) 14.7 (2.8) 37.4 (5.4) 9.7 (2.5) 56.0 (2.9) 153.5 (48.9) 67.6 (11.7)

1659 (433) 53.2 (4.9) 16.6 (3.4) 32.3 (6.1) 8.3 (2.1) 56.5 (4.3) 117.7 (31.1) 70.9 (11.0)

2580 (607) 49.9 (5.1) 14.4 (2.5) 35.4 (5.1) 9.2 (2.0) 54.7 (3.8) 180.2 (65.5) 69.8 (12.2)

1674 (586) 53.9 (6.6) 18.1 (3.3) 29.1 (1.3) 7.1 (2.7) 51.5 (4.7) 112.2 (51.7) 67.0 (18.1)

2443 (559) 49.1(6.2) 14.5 (2.6) 36.3 (5.3) 9.4 (2.2) 55.2 (3.5) 168.4 (59.5) 68.9 (11.8)

1667 (516) 53.6 (5.9) 17.4 (3.4) 30.5 (5.9) 7.6 (2.5) 53.7 (5.1) 114.7 (43.3) 68.8 (15.3)

31.8a 9.2 20.0a 16.0a 19.1a 2.7b 31.9a 0.2

BWLP: behavioral weight loss program; GI: glycemic index. a pb0.05 (pretreatment compared to posttreatment). b pb0.05 (treatmenttime interaction); GI lower in BWLP+GI at posttreatment compared to BWLP.

3.4. One-year posttreatment Of the 40 participants completing the intervention, 39 participants (97.5%) completed the 1-year follow-up. One participant who was 7-months pregnant was excluded from data analyses. Therefore, posttreatment data were available for 38 participants. Weight and body fat were collected at 1-year posttreatment. There were no significant differences between the BWLP and BWLP+GI groups on weight or body fat. There were significant within subject effects for body weight, F(1,36)=17.02 pb0.05, and percent body fat, F(1,36)=15.31 pb0.05. From the end of the intervention to 1-year posttreatment, pair–sample t-tests indicated that total body weight, t(37)=6.00, pb0.05, and body fat, t(37)=3.41, pb0.05, increased significantly. Participants regained 4.5 kg (59%) of their weight loss and 1.3% (34%) of their body fat loss. However, paired t-tests indicated that body weight, t(33)=2.96, pb0.05, and body fat, t(33)=3.08, pb0.05, remained significantly lower at the 1-year follow-up compared to pretreatment values.

4. Discussion The addition of GI education to a BWLP did not improve treatment outcomes. On average, participants lost 7.6 kg of their body weight and 3.8% of their body fat (i.e., baseline minus posttreatment). However, by 1-year posttreatment, participants had regained 59% of their lost body weight and 34% of their lost body fat. Several factors may account for the nonsignificant findings between treatment groups. All participants learned a variety of self-control strategies. While adopting a low-GI diet is likely to provide longer satiation and fewer cravings, BWLP participants who did not receive GI education may have learned to inhibit eating in response to mild feelings of hunger and craving. Alternatively, the emphasis placed on GI education during the program may have been insufficient to influence intervention outcomes. While participants in the BWLP GI group received 30–45 min of weekly GI education, they also received 45–60 min of weekly instruction on exercise, nutrition, and psychological factors associated with weight loss.

150

R.A. Carels et al. / Eating Behaviors 6 (2005) 145–150

Compared to the BWLP group, the BWLP+GI group demonstrated a significant increase in GI knowledge and were eating a lower GI diet by the end of treatment. Nevertheless, statistical significance is not synonymous with clinical significance; the participants may have needed to lower the average daily GI of their diet more drastically to influence treatment outcomes. Also, a low GI intervention successful at lowering GL (not GI) demonstrated significantly better weight loss when compared to an energy-restricted, reduced-fat diet (Ebbeling, Leidig, Sinclair, Hangen, & Ludwig, 2003). Although the GL was lower in this intervention at posttreatment, the treatment groups did not significantly differ in GL at the end of treatment. Finally, participants in the treatment group attended significantly fewer sessions than the control group, producing a potential bias against detecting treatment group differences. While eating a low-GI diet may favorably influence weight-related factors, such as resting energy expenditure, nitrogen balance, and blood glucose regulation (Agus et al., 2000), it did not improve weight loss treatment outcomes beyond that of a BWLP, which emphasized eating a low-calorie, low-fat diet and increasing physical activity. The effectiveness of low-GI diets on enhancing weight loss and long-term weight maintenance is still unclear.

References Agus, M. S., Swain, J. F., Larson, C. L., Eckert, E. A., & Ludwig, D. S. (2000). Dietary composition and physiologic adaptations to energy restriction. American Journal of Clinical Nutrition, 71, 901 – 907. Bouche, C., Rizkalla, S. W., Luo, J., & Veronese, A. S. G. (2002). Five week low glycemic index diet decreases total fat mass and improves plasma lipid profile in moderately overweight nondiabetic men. Diabetes Care, 5, 822 – 828. Brand-Miller, J. C., Wolever, T. M. S., Foster-Powell, K., & Colagiuri, S. (2003). The new glucose revolution. New York. Brownell, K. D. (2000). The LEARN Program for weight management 2000. Dallas, TX7 American Health Publishing. Ebbeling, C. B., Leidig, M. M., Sinclair, K. B., Hangen, J. P., & Ludwig, D. S. (2003). A reduced-glycemic load diet in the treatment of adolescent obesity. Archives of Pediatrics and Adolescent Medicine, 157, 773 – 779. Foster-Powell, K., Holt, S. H. A., & Brand-Miller, J. C. (2002). International table of glycemic index and glycemic load values: 2002. American Journal of Clinical Nutrition, 76, 5 – 56. Ludwig, D. S. (2002). The glycemic index: Physiological mechanisms relating obesity, diabetes, and cardiovascular disease. JAMA, 287, 2414 – 2423. Ludwig, D. S., Majzoub, J. A., Al-Zahrani, A., Dallal, G. E., Blanco, I., & Roberts, S. B. (1999). High glycemic index foods, overeating, and obesity. Pediatrics, 103, 261E – 266E. Pawlak, P. B., Ebbeling, C. B., & Ludwig, D. S. (2002). Should obese patients be counselled to follow a low-glycemic diet? Yes. Obesity Reviews, 3, 235 – 243. Raben, A. (2002). Should obese patients be counseled to follow a low-glycemic index diet? No. Obesity Reviews, 3, 245 – 256.