NUTRITION AND DIET-RELATED PROBLEMS

ADOLESCENT MEDICINE

00954543 /98 $8.00

+ .OO

NUTRITION AND DIET-RELATED PROBLEMS Elizabeth C. Miller, RD and Christopher G. Maropis, MD

Adolescence is a time that may be best defined by the growth spurt. Except for infancy, the most rapid physical growth occurs during this time. This period of rapid growth is accompanied by cognitive, emotional, and hormonal changes, and these changes create specific nutritional needs. Because of the greater need for nutrients during this time, adolescents are vulnerable to inadequate nutritional intakes. In addition, negative family, peer, or media influences may further jeopardize an already marginal diet. This article focuses on proper adolescent nutrition. Eating habits that are characteristic of this age group, along with factors that influence eating behavior, are addressed, as well as the issues of obesity, vegetarianism, sports nutrition, and eating disorders. NORMAL NUTRITION Nutrient Requirements

As mentioned previously, adolescence is a time of dramatic change. In addition, adolescence is a time of tremendous variability among peers. The most marked differences among age-matched adolescents are noted by studying metabolic rate, onset of growth spurt, growth rate and maturation level, and amount of physical activity. Because of these variations, there are few existing experimental data regarding optimal nutrient intakes for this age group. The recommendations that do exist are based on child or adult allowances, which are then extrapolated according to typical adolescent growth rates. Moreover, these recommendations are classified by chronologic rather than maturational age, so they serve only as guides, particularly if looking at large populations of adolescents. For this reason, if an adolescent presents with a nutritional issue, his or her case must be individFrom the Department of Family Medicine (CGM), and the Medical Dietetics Division (ECM), The Ohio State University College of Medicine and Public Health, The Ohio State University Medical Center (ECM) and the Department of Athletics, The Ohio State University (ECM, CGM), Columbus, Ohio PRIMARY CARE VOLUME 25 *NUMBER 1 6 MARCH 1998

193

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MILLER & MAROPIS

ualized because a recommended dietary allowance chart probably is not representative or Energy

Energy needs for adolescents, like nutrient requirements, vary according to sex, height, weight, pubertal development, and physical activity level. One exception to this is the fact that energy requirements for all adolescents are highest during the growth spurt.I6National surveys indicate that energy intakes are below the RDA for most adolescents, particularly older males, blacks, and adolescents from low-income families.” In addition, a study of the School Breakfast Program (SBP) and the National School Lunch Program (NSLP) found that the energy that these programs provided for adolescent boys fell short of the RDA.Io The existing energy intake recommendations (Table 1) are based on median energy intakes of adolescents followed in longitudinal growth s t ~ d i e s .There ’~ is no factor appended for illness, stress, or other variations.6zAnother perhaps more sensitive way to estimate energy needs for adolescents is by calculating calories per unit height. These needs are 10 to 19 kcal/cm for 11- to 18-year-old females and 13 to 23 kcal/cm for 11- to 18-year-old males.@ Carbohydrates

Regardless of age, carbohydrates should provide the majority of energy in the diet. Current recommendations note that 55% of the energy intake in an adolescent’sdiet should come from carbohydrate sources, with the bulk coming from complex carbohydrates such as pasta, grains, and Most adolescents are able to achieve this overall goal, but they do so using simple sugars that frequently are found in high-calorie, low-nutrient snacks.38 Protein

During this critical time of positive nitrogen balance, dietary protein is needed to ensure proper growth and development of the body. As with energy intake, protein needs are dependent on growth and maturation rather than chronologic age. Current recommendationsfor protein are that it constitute 15%to 20% of total caloric intake in adolescents’ diets.%As is the case with energy intake, however, some argue that the best index of protein needs may be related to the amount of protein per unit height. Using these guidelines, the protein needs are 0.27 to 0.29 g/cm for adolescent females and 0.29 to 0.32 g/cm for adolescent males.24 Fat

Fat is the most calorie-dense nutrient. The amount of total fat in the average adolescent’sdiet is greater than 35%,which is in excess of the National Cholesterol Education Program (NCEP) goal of less than 30%.3,36,45,54,75 In addition, most surveys reveal that 13 to 15%of total calories come from saturated fatty acids (SFAS), which also is in excess of the NCEP goal of less than 10%.3,45,75 Recommended amounts of polyunsaturated and monounsaturated fat are 10% and 10% to 15% of total calories, respectively; the recommended amount of cholesterol for this age group is less than 300 mg per day.45,54,75

+

0.0-0.5 0.5-1 .O 1-3 4-6 7-1 0 11-14 15-1 a 19-24 25-50 51 11-14 15-1 8 19-24 25-50 51 + 1st trimester 2nd trimester 3rd trimester 1st 6 months 2nd 6 months

6 9 13 20 28 45 66 72 79 77 46 55 58 63 65

Weight, kg 60 71 90 112 132 157 176 177 176 173 157 163 164 163 160

Height, cm 320 500 740 950 1130 1440 1760 1780 1aoo 1530 1310 1370 1350 1380 1280

REE" kcalld

1.70 1.67 1.67 1.60 1.50 1.67 1.60 1.60 1.55 1.50

650 a50 1500 1aoo 2000 2500 3000 2900 2900 2300 2200 2200 2200 2200 1900 +O 300 300 + 500 + 500

1oa 9a 102 90 70 55 45 40 37 30 47 40 38 36 30

+ +

Per Day*

Per kg

Average Energy Allowance, kcalt Multiples of REE

'Calculation based on Food and Agriculture Organization of the United Nations equations, then rounded. t l n the range of light-to-moderate activity, the coefficient of variation is ? 20%. *Figure is rounded. REE = Resting Energy Expenditure (From Recommended Dietary Allowances, ed 10. Copyright 1989 by the National Academy of Sciences. Courtesy of the National Academy Press, Washington, DC; with permission.)

Lactating

Pregnant

Females

Males

Children

Infants

Category

Age, Y. or Condition

Table 1. MEDIAN HEIGHTS AND WEIGHTS AND RECOMMENDED ENERGY INTAKE

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MILLER & MAROPIS

As discussed subsequently, there are many reasons why adolescents eat too much fat in their diets, but one need not look any further than our federal breakfast and lunch programs to see why this is so. In the SBP, the average amount of SFAs is 14%, with only 4% of the programs offering less than 10% SFAs. In addition, 83% of all public and private schools participate in the NSLP. The typical NSLP lunch, however, is 38% total fat and 15% SFAs, with only 1%of schools offering lunches that are less than 30% total fat. Both the SBP and NSLP are in accordance with current cholesterol recommendations, providing only 73 mg and 88 mg of cholesterol, respectively.1° Fiber Fiber-containing foods are an important part of the diet because they usually are low in fat and cholesterol and therefore may aid in the prevention of obesity as well as chronic maladies such as specific cancers, cardiovascular disease, and type I1 diabetes.81There is not a lot of research available regarding optimal amounts of fiber intake in the diet, but a good rule is to use the adolescent’s age plus 5 g per day up to age 20 years to calculate how much fiber should be in the daily diet.3 For instance, a 10-year-old youngster would need 10 + 5 = 15 grams of dietary fiber each day. Good sources of fiber include raw fruits and vegetables and whole grains. Calcium

Controversy still surrounds the amount of calcium that should be in the diet. There is no argument, however, that calcium requirements are highest during the growth spurt, pregnancy, lactation, and later adult life.46For instance, regarding the growth spurt, the neonatal skeleton contains about 25 g of calcium whereas the adult skeleton contains around 1200 g of calcium.35For normal mineralization and calcium accumulation to occur during adolescence, about 400 to 500 mg of calcium must be added per day during Bone mineral deposition rates decrease later, as do calcium requirement^.^^ Because peak adult bone mass largely is achieved by age 20 years, optimal calcium intake during adolescence is critical for maximizing and maintaining peak adult bone mass and minimizing the risk of osteoporosis in later life.46Over 80% of adolescent females and over 40% of adolescent males, however, are deficient in calcium.3sOne of the reasons for this is that youth often forego milk for carbonated beverages, which are high in phosphorous. Milk provides about 250 to 300 mg of calcium per 8-oz glass. This increased phosphorous intake alters the calcium-tophosphorous ratio and impairs calcium absorption.28 As of 1989, the RDA for children under 11 years of age was 800 mg of calcium per day.I3These levels jumped to 1200 mg per day for 11- to 18-year-01ds.I~ Newer evidence from the National Institutes of Health, however, suggested that between 500 and 1000 mg of calcium should be added to the current RDA, based mostly on the fact that the mean daily calcium intake for adolescents is between 700 and 900 mg of c a l ~ i u m . ” ,Key ~ ~ ,and ~ ~ Key35since have advised that the recommended elemental calcium intake for adolescents should be 1400 to 1600 mg per day to ensure a positive calcium balance and maximum bone-mass a c ~ r e t i o nThis . ~ ~ implies that an average adolescent should supplement his or her diet with 500 to 750 mg of calcium every day. Although milk is widely recognized as an excellent source of calcium, there

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are alternatives for persons who either do not enjoy or cannot tolerate milk. Yogurt provides between 350 and 400 mg of calcium per 6- to 8-02 serving. One ounce of cheese contains approximately 150 mg of calcium. Calcium-fortified foods such as crackers, orange juice, and cereal bars are becoming more readily available and can be excellent nondairy sources of calcium. Iron

Iron deficiency is very common during adolescence. Younger males are at risk during peak growth, and older females are at risk because of iron losses during menses and poor dietary intake.38Others at risk are adolescents from lowincome families, pregnant females, vegetarians, and athlete^.'^,^^,^^ Iron requirements are heightened during adolescence because of increases in lean body mass, blood volume, and hemoglobin c o n c e n t r a t i ~ n .For ~ ~ ,males, ~ ~ once the growth rate decreases, so does the need for dietary iron. In females, however, iron requirements remain high until menopause. To ensure adequate iron intakes of 12 mg per day in males and 15 mg per day in females as listed in Table 2, all adolescents must be advised to eat ironfortified bread and cereal, lean red meat, and other iron-rich f o o d ~ .In~addition, ~,~~ plant foods with nonheme iron should be eaten with vitamin C to enhance iron bioavailability, and all pregnant teens should supplement their diets with iron to meet their increased needs of 30 mg per day.13.38 Zinc

Zinc is necessary for healthy growth of skeletal and muscle tissue and for sexual maturation in a d o l e s c e n ~ e . There ~ ~ , ~ ~is evidence that zinc levels are compromised during For instance, the SBP provides less than one fourth of the RDA for all age groups, and the NSLP falls short of the RDA for most age groups during adolescence.1oThe current RDA for zinc is 12 mg for females and 15 mg for males.l3 Vitamins

Proper vitamin intake is essential during this critical time of rapid growth and change. Greater energy demands, particularly during the growth spurt, necessitate more thiamin and riboflavin in the diet, which serve to release energy from carbohydrate sources. Vitamin B,, folate, and vitamin B,, are required for the increased DNA and RNA metabolism that occurs with increased tissue synthesis. Vitamin D is vital for rapid skeletal growth, and vitamins A, C, and E are needed to ensure the maintenance of new cell^.^*,^^ Although the need for vitamins is crucial during this time, surveys have found that certain vitamin intakes are inadequate. Vitamin A intake, which is essential for reproductive success, has been found to be inadequate during a d o l e s c e n ~ e . ~ , ~ ~ , ~ Vitamin C intake has been found to be low, particularly in those who avoid fruits and vegetables, and in those who smoke, diet excessively, or come from lowincome fa mi lie^.^^,^^ Regarding folic-acid intake, one study found that anywhere between 10% and 50% of adolescents had low folacin levels.55Those most at risk were pregnant teens and those from low-income fa mi lie^.^,^^,^^ RDAs for vitamins are listed in Table Z.I3

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Table 2. FOOD AND NUTRITION BOARD, NATIONAL ACADEMY OF SCIENCESNATIONAL RESEARCH COUNCIL, RECOMMENDED DIETARY ALLOWANCES,* REVISED 1989 Fat-SolubleVitamins

Category lnlants Children

Males

00-0 5 05-1 0 1-3 4-6 7-1 0 11-14 15-1 8 19-24 25-50

Females

51 + 11-14 15-1 8 19-24 25-50 51 +

Pregnant Lactating

Water-Soluble Vitamins

Vitamin Vitamin Vitamin Vitamin Age, Y. A, D, E, K, or Weightt, Heightt, Protein, Condition kg cm g pg RE* pgg m g a - ~ ~ l lpg

1st 6 months 2nd 6 months

6 9 13 20 28

60 71

13 14

90 112 132

45 66 72

157 176 177

79 77

176

16 24 28 45 59 58 63

46 55

173 157 163

63 46 44

58 63 65

164 163 160

46 50 50

375 375 400 500 700 1000 1000 1000 1000 1000 800

7.5 10 10 10 10 10 10 10 5 5 10

3 4 7 7 10 10 10

5 10 15 20 30 45 65 70

10 10 8

80 80 45

6

800

10

8

55

800 800

8 8

60 65

60 65

800 800 1300

10 5 5 10 10

8 10 12

65 65 65

62

1200

10

11

65

Vitamin C, mg

Thiamin, mg

Riboflavin,

30

0.3

35 40 45 45 50 60 60 60 60 50

0.4 0.7 0.9 1.o 1.3 1.5 1.5 1.5 1.2 1.1

60 60 60 60

1.1 1.I 1.1 1.0

70 95

1.5 1.6

1.3 1.3 1.3 1.2 1.6 1.8

90

1.6

1.7

mg 0.4 0.5 0.8 1.1 1.2 1.5 1.8 1.7 1.7 1.4 1.3

*The allowances, expressed as average daily intakes over time, are intended to provide for individual variations among most normal persons as they live in the United States under usual environmental stresses. Diets should be based on a variety of common foods in order to provide other nutrients for which human requirements have been less well defined. See text for detailed discussion of allowances and of nutrients not tabulated. tWeights and heights of Reference. Adults are actual medians for the US population of the designated age, as reported by NHANES II. The median weights and heights of those under 19 years of age were taken from Hamill PW, Drizd TA, Johnson CI, et al: Physical Growth: National Center for Health Statistics Percentiles. Am J Clin Nutr 32:607-629, 1979. The use of these figures does not imply that the height-toweight ratios are ideal. SRetinol equivalents, 1 retinol equivalent = 1 pg retinol or 6 pg p-carotene. See text for calculation of vitamin A activity of diets as retinol equivalents. §AScholecalciferol. 10 pg cholecalciferol = 400 I Uof vitamin D. lla-Tocopherol equivalents. 1 mg d-a tocopherol = 1 a-TE. See text for variation in allowances and calculation of vitamin E activity of the diet as a-tocopherol equivalents. 11 NE (niacin equivalent) is equal to 1 mg of niacin or 60 mg of dietary tryptophan.

FACTORS INFLUENCING DIET HABITS Family

The predominant influence on an adolescent’s eating behavior is the family unit. The family conveys food attitudes and preferences that have long-lasting affects. Those adolescents who eat with their families on a regular basis have better diets. Because of changes in family structure, however, with more single parent families and more working mothers, family meals occur less frequently. This may be adversely affecting the food choices of teenagers. This is evidenced by the fact that adolescents from dysfunctional families often use food as a vehicle to express dissatisfaction with parental authority. Examples of such behavior include food binges, food aversions, fad diets, and skipped meals.64

NUTRITION AND DIET-RELATED PROBLEMS

Water-Soluble Vitamins Niacin, mgNEll

Vitamin B,, mg

Folate, P9

Minerals Vitamin B,,, P9

Phos- MagneCalcium, phorus, sium, mg mg mg

180 180 180 180 400 280

0.3 0.5 0.7 10 1.4 2.0 2.0 2.0 2.0 20 2.0 2.0 2.0 2.0 2.0 22 26

800 800 800 1200 1200 1200 800 800 1200 1200 1200 800 800 1200 1200

260

2.6

1200

17 20 19 19 15 15 15 15 15 13 17 20

0.3 0.6 1.o 11 1.4 1.7 2.0 2.0 2.0 2.0 1.4 1.5 1.6 1.6 1.6 22 2.1

25 35 50 75 100 150 200 200

20

2.1

5 6 9 12 13

200 200 150

199

400

600

40 60 80 120 170

iron, mg

Zinc, mg 5 5 10 10 10 15 15 15 15 15 12

300 500 800 800 800 1200 1200 1200 800 800 1200 1200 1200 800 800

270 400 350 350 350 280 300 280 280 280

6 10 10 10 10 12 12 10 10 10 15 15 15 15 10

1200 1200

320 355

30 15

1200

340

15

Iodine, Selenium, vg cg 40 50 70 90 120 150

10 15 20 20 30 40

15 19

150 150 150 150 150 150 150 150 150 175 200

50 70 70 70 45 50 55 55 55 65 75

16

200

75

12 12 12 12

For this reason, parents should aim to be positive role models for their kids. Although parents cannot control what their children consume outside the home, they can control what their children consume in the home. They can do this by stocking the kitchen with nutritious foods and limiting the availability of lownutrient snacks. Moreover, parents should encourage family meals in a relaxed and loving environment free from volatile issues. The television should be turned off during these meals to encourage interaction." Peers The early teen years are a time when parental dependency loosens and peers play a larger role in the life of an adolescent. The peer group defines what is socially acceptable regarding many things such as learning, fashion, music preferences, and food and beverage choices. Adolescents crave the approval of their peers, so even the foods they select must conform to this peer pressure. Certain symbolic meanings attributed to foods must be positive or strong. Otherwise, food selection will be considered unacceptable by the peer group, and an adolescent will be less likely to partake in it.64 Media

The media probably are the most negative influences on eating behavior. In addition to the entertainment and information they provide, the media also carry

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MILLER & MAROPIS

advertisements. The purpose of an advertisement is to entice a consumer into purchasing something. All advertisers know that the adolescent population is a coveted market. For this reason, advertisers strive to appeal to the weaknesses of peers, particularly regarding their need for approval and their need to fit in. Advertisers for appearance-related products are notorious for recruiting sports stars and fashion models as their spokespersons. Similar images are depicted in food advertisements to influence the food choices of teens.64 Of all the media, television has had the greatest impact on adolescents. The typical adolescent has witnessed 100,000 television food commercials. The majority of these food commercials depict healthy, athletic, and attractive young people partaking in junk foods, soft drinks, or beer.@In addition, food-related messages on the most popular television programs often refer to alcoholic beverages, sweets, and other low-nutrient snacks. These food-related messages rarely depict balanced, sit-down meals and often serve to meet an attractive, younger television character’s emotional or social needs. So the message that is typically presented is a contradictory one-slender, attractive people eating in ways that are guaranteed to lead to 0besity.3~ EATING HABITS Irregular Meals

Adolescents are notorious for skipping meals, and adolescent females are more likely to skip meals on a regular basis.65 They do so for a number of reasons. One may be that frequent snacks preclude the necessity of a meal. Whatever the reason, breakfast is the meal most missed, with about 12% of adolescents not eating breakfast on any given day.I0Other surveys have shown that 50% or more of adolescents admit to not eating breakfast at all or eating breakfast less than twice a ~ e e k . ’The ~ , fact ~ ~ that adolescents often skip meals is of major concern particularly because studies have shown that those students who ate breakfast scored higher on comprehensive tests and had lower absentee rates, while those who did not eat breakfast showed signs of delayed cognition, especially in their information-retrieval~ p e e d . ~ ~ , ~ ~ Snacks

Over 90% of adolescents snack and over half admit to eating at least five times a Only 38%of these teens, however, report partaking in nutritious An adolescent’s typical snack is high in calories and low in nutrients, commonly called ”junk food.”38These junk foods also are high in fat, simple sugars, and sodium and low in fiber, calcium, iron, and vitamin A.38,62 These snacks do provide, however, about one third of total daily energy intake, so if they are wisely chosen snacks can actually be an asset to an adolescent‘s diet.6,38An example of a wisely chosen snack is a fruit or vegetable with milk or juice. Fast Food

With more and more fast-food franchises available, an increasing number of adolescents are eating away from home.54As a matter of fact, over 80% of fastfood restaurant visits are by people younger than 18years of age.53Although many

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fast food restaurants are starting to incorporate more nutritious food items into their menus, the vast majority of restaurants still provide foods that are too high in total fat, SFAs, cholesterol, and In addition, these fast foods often are low in calcium, iron, vitamin A, riboflavin, and folate.62Adolescents who frequent fast-food restaurants need to be educated to limit the amount of deep-fried foods they eat and to supplement fast food with fresh fruits and ~ e g e t a b l e s . ~ ~ ADOLESCENT OBESITY AND BEING OVERWEIGHT

Obesity and being overweight in the United States have reached epidemic proportions. The incidence has been increasing gradually over the past 10 years: Today it is estimated that one in every three Americans is ~verweight.'~ Concurrently, adolescent obesity has increased. According to the most recent National Health and Examination Survey (NHANES III), which was completed from 1989 to 1991, 22% of adolescent youths are overweight. This is a significant increase from the NHANES I1 study (1976 to 1989), in which the prevalence of being overweight was 19.9%for boys and 15.8%for girls. The US Department of Health and Human Services has recommended a target for adolescent obesity of 15% or less.71,77 As we drift further from this recommendation, our awareness is heightened to the clinical, emotional, and social effects of adolescent overweight and obesity. There is no generally accepted definition of obesity for adolescents.Body mass index (BMI) commonly is used in both research and clinical practice to determine health risk as a function of weight. The major criticism of BMI (weight in kg divided by height in m2)is that it does not distinguish between lean mass and fat mass. Once a high BMI has been determined, however, a brief review of exercise habits and physical observation should differentiate the overlean patient from the overfat patient. The National Center for Health Statistics defines ovemveigkt as a BMI equal to or greater than the 85th percentile of men and women of the same age. Severe overweight is defined as a BMI greater than or equal to the 95th percentile. Men are considered overweight if their BMI is 27.3 or higher, and severely overweight with a BMI of greater than 31.1. Women's categoric definitions are similar, with BMI cutoff points of 27.3 and 32.3 respectively." The term obese has been defined a number of different ways. Researchers often use greater than 120% of "desirable" body weight (as determined by the Metropolitan Life Insurance Height and Weight Tables or weight recommendations published by the US. government).',*Adults with a BMI of at least 30 are considered to be at high health r i ~ k . Caution 5~ must be practiced if using adult methods of weight assessment for adolescents, as growth often is not complete by the teenaged years, especially for males. Overweight adolescents are more likely to become overweight adult^.'*^^^ As a result, these adolescents are at higher risk for the well-documented physical complications of being overweight, such as dyslipidemia, certain forms of cancer, and cardiovascular disease.46The Bogalusa Heart Study was an epidemiologic study of cardiovascular disease risk factors beginning in childhood. Adolescents ages 13 to 17 years were surveyed from 1976 to 1988 and again as young adults (aged 25 to 31 years) from 1988 to 1991. Overweight in this study was determined to be a BMI greater than the 75th percentile. Of the 192 young adults who were overweight, 57% had been overweight adolescents, with the highest predictive value (62%) found for black females. Additionally, the overweight cohort was found to have a significantly increased prevalence of cardiovascular risk factors such as hypertension, hyperlipidemia, and hypergly~emia.~~

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MILLER & MAROFIS

A second risk factor among overweight adolescents is on increased mortality rate. The Harvard Growth Study of 1922 to 1935 collected anthropometric data on over 3000 schoolchildren from ages 13 to 18 years. These subjects were measured annually until they were graduated from high school. Follow-up over the next 55 years revealed that adolescent overweight predicted future adverse health conditions, including an increased mortality rate from coronary heart disease, stroke, and colorectal cancer, that were independent of adult In addition to the potential medical complications, being overweight during adolescence also has social and economic consequences. Gortmaker et alZ6studied over 10,000 young people from ages 16 to 24 years. At follow-up 7 years later, those who were overweight during the initial assessment were significantly less likely to be married and had lower household incomes and higher rates of household poverty.26The adolescent years are socially and emotionally awkward for many youth, but overweight and obese individuals have additional difficulties coping with the turmoil of teenage years. Adolescent obesity is correlated with lower self-esteem and often results in clinical depression.60Without treatment, many overweight adolescents may turn to food for comfort, which potentially can exacerbate their weight problems, creating a negative cycle of depression, weight gain, and further depression. The etiology of being overweight in adolescents is unclear and multifaceted. Weight gain is the result of a chronic energy surplus in which energy intake is greater than energy expenditure. Although energy intake and energy expenditure can be manipulated, genetic influences are less malleable. The genetic effect of obesity is poorly understood and studies are inconclusive. It has been reported that a child has an 90% chance of becoming obese if both parents are obese, and a 60% chance if only one parent is obese.9 Investigators acknowledge, however, that it is difficult to discriminate between genetic and environmental influences. Thus, there are two controllable components to the energy balance equation: food (energy intake) and activity (energy expenditure). Weight loss usually results if one or both of these components is altered enough to create a consistent energy deficit. The eating patterns of adolescents have dramatically changed over the past 20 Nutrient deficiencies and undernutrition are no longer the primary foci of public health professionals. With the exception of iron, calcium, and zinc, the typical diet of US adolescents meets or exceeds 100% of the RDA for most nutrients. In comparison with the US Dietary Guidelines, adolescents consume an excessive amount of fat, saturated fat, and sodium. The Continuing Survey of Food Intake by Individuals, conducted by the US Department of Agriculture in 1989, found that the average fat intake of adolescents was 35%,with over 13% of total calories from saturated fat sources.74The recommended fat and saturated fat intake for both adults and adolescents is no more than 30% and 10%of total calories, respe~tively.’~ The distribution of nutrients may be significant because dietary fat is more efficiently converted to body fat than carbohydrate or protein. Some data suggest that the percentage of calories from fat, independent of total calorie intake and activity level, may contribute to overweight in adolescent^.^^ It is of interest to note that as adolescent obesity has increased over the past 20 years, diet analysis data from the three NHANES studies have indicated that calorie intake has remained stable. Although these data may be affected by the difficulty of obtaining accurate diet information, all age groups showed a slight decline in calorie consumption with the exception of 16- to 19-year-old males and fern ale^.'^,^^,^ Although diet habits undoubtedly are an important consideration in the cause of being overweight, physical inactivity may be a stronger predictor. Physical activity affects energy expenditure in two ways. Activity of any kind burns more calories than sedentary behavior for the same period of time. Second, and more

NUTRITION AND DIET-RELATED PROBLEMS

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significantly, physical activity promotes increased lean body mass. Lean body mass (or fat-free mass) is directly related to basal metabolic rate. Because muscle tissue contains mitochondria and is metabolically active (adipose tissue is not), increased lean mass results in a higher basal metabolism, which accounts for up to 70% of total energy expenditure. Physical activity and the thermic effect of food represents the remaining 30%.61 There are no data available to estimate the prevalence of inactive youths. Recent studies have documented, however, that less than 25% of the US population participates in regular exercise.66One possible explanation for adolescent inactivity is an increased amount of time spent watching television. Several studies have documented a positive association between hours of television viewing and incidence of obesity in both adolescents and adults. Gortmaker et al:5,27 found that in 1990 the average youth (ages 10 to 15 years) watched 4.8 hours of television each day; 33% of the youths sampled watched more than 5 hours each day. Even if baseline characteristics were controlled (e.g., whether the child was initially overweight, mother’s education, gender, household poverty) a strong, linear relationship was found between hours spent watching television and incidence of obesity. Established treatment of adolescent obesity emphasizes diet modification and physical activity. Fad diets and nutrition misinformation are rampant in today’s society. Ideally a nutrition professional, such as a registered dietitian, should educate adolescents on basic nutrition principles. Educational efforts to teach young people to eat more healthfully, read nutrition labels, and understand the importance of food variety promote long-term diet compliance. Simply handing an overweight youth a sample 1800-calorie diet plan is insufficient and results in poor adherence. In addition to life-long diet changes, the overweight youth must implement regular physical activity. Because motivation and compliance with an exercise program often are difficult, lifestyle exercise such as taking the stairs instead of the elevator and walking or biking to work or school can be an effective starting point in conjunction with diet modification.21 Like many other illnesses, disease prevention is preferred to disease treatment. Exercise may have the most significant impact in preventing excessive weight gain. Not only does exercise increase calorie expenditure, it reduces the amount of available sedentary time. Family involvement in regular athletic activity and supervision of inactivity are essential in the prevention of adolescent obesity.21 SPORTS NUTRITION AND ADOLESCENTS Regular physical activity and participation in organized sports have numerous benefits for adolescents. Improved self-image, reduced cardiovascular disease risk factors, and enhanced socialization skills are a few of the known advant a g e ~ . ~ ~ ,Low ~ ~ , levels ~ ~ , 6 of * physical activity have been associated with negative health behaviors such as cigarette smoking, low dietary intake of vegetables and fruits and greater television watching.49 Adolescence is a period of rapid growth requiring additional calories and nutrients for normal development and maturation. Young people who are athletically active have even greater energy demands, yet these youth often are not concerned with good nutrition or are more inclined to follow harmful nutrition practices in hopes of enhancing sports pe~formance.~~ Although adolescents are more active than adults, activity level often rapidly decreases during the high-school years. A 1995 survey found that 72% of ninthgrade students had vigorously exercised three times in the past week and 55% of twelfth-grade students had practiced this level of activity.I2The US Surgeon Gen-

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MILLER & MAROPIS

era1 reported in 1996 that approximately one half of youths aged 12 to 21 years reported participating in regular physical activity, while one fourth reported no physical activity.66 Energy

Considering that a moderately active adult of average height and weight usually requires 2000 to 2500 calories per day, energy intake of the active youth is remarkably high. It is not unusual for a young male to require more than 4000 calories daily to compensate for both growth and activity. Significant weight loss in appropriate-weight adolescents is abnormal and should be a cause for concern. Weight gain is normal and is the result of bone and muscle development. Adolescents need a variety of foods to provide the calories and nutrients required for anabolic growth and activity. Carbohydrate

Carbohydrate is the primary substrate for energy production. The young athlete needs to consume grains, breads, cereals, fruits, starchy vegetables, and dairy products daily in order to maximize glycogen storage.20A high-carbohydrate diet (60% to 70% of total calories) every day is preferred to the typical "carbohydrate loading" regimen that is higher in fat and protein for the first 2 to 3 days and then significantly increases carbohydrates in the few days before competition. This diet can be impractical for the athlete who competes several times each week or practices daily, and is not recommended. Protein

Protein needs for active young people are only slightly higher than for sedentary youth. Although additional protein is beneficial for muscular growth in conjunction with exercise, protein supplementation usually is not necessary. If calorie intake is adequate, the typical American diet provides enough protein (15% of total calories) for the active adolescent.zoIn very active adults, research has shown that protein intake above 1.8g per kg is either oxidized for energy or excreted in the Because excess protein is excreted in the urine, very high-protein diets may promote fluid loss and dehydration. Vitamins and Minerals

The recommended dietary intake of vitamins and minerals does not increase with athletic activity. Specific nutrients such as calcium, iron, vitamin C, and zinc, however, do have recommendations that increase as a function of age and rapid growth. Supplementation can fill the gaps of a poor diet but will not act as an ergogenic aid to performance. Nutrient deficiencies that are of special concern for young athletes include calcium and iron. Calcium

Calcium requirements increase by 50% during adolescence. The RDA for both females and males ages 11 to 24 years is 1200 mg each day. Because males tend

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to consume a greater amount of food to meet their calorie needs, a calcium deficiency is uncommon. Women, however, are notoriously calcium-deficient. Most women require fewer calories than men and therefore consume less food. Young women also are much more likely to restrict their calorie intake and frequently omit milk and dairy products from their diet. According to the USDA's Continuing Survey of Food Intake by Individuals, teenaged girls meet only 64.6%of their calcium r e q u i r e m e n t ~ ? ~ As , ~previously ~ mentioned, adequate calcium intake is required to maximize bone-tissue mineral deposition. Additionally, athletes who are chronically calcium-deficient may be more prone to stress fractures as a result of low bone mineral density. Calcium supplementation often is warranted with adolescents, but increased consumption of dairy products and calcium-fortified foods should be encouraged. Iron

Iron also deserves attention when discussing the adolescent athlete. Iron deficiency is more likely to occur during any period of rapid growth, because of accelerated erythropoesis.2nIn addition, athletes often have hemoglobin concentrations that are at the low end of the normal range. This phenomenon has been termed sports anemia and results from an increased plasma volume. Poor dietary intake and increased gastrointestinal blood loss also may contribute to iron deficiency in athletes. Iron depletion without anemia can reduce exercise capacity signifi~antly.~~ Women, again, are at much greater risk for anemia for two reasons: increased dietary requirements (15 mg versus 10 mg for males) to compensate for iron losses during menstruation and low consumption of iron-rich foods such as red meat, eggs, and green vegetables. Iron supplementation is appropriate for those athletes with clinically diagnosed anemia; however, iron supplementation frequently causes constipation. Low hemoglobin levels often can be improved with an increase in dietary iron and vitamin C to enhance absorption. Although iron and calcium deficiencies are relatively common (especially in women), other nutrient deficiencies are uncommon. Adolescents need to be encouraged to consume a varied diet representing all food groups. A daily multivitamin/multiminera1 can complement a poor diet but generally is not necessary. Fluid

Like most adults, active adolescents frequently do not consume enough fluid. Excessive fluid losses and suboptimal fluid consumption result in early fatigue and dehydration. Young athletes are at greater risk for heat exhaustion and heat stroke because they are inefficient thermoreg~lators.~~~ Fluid replacement after exercise should be at least 2 cups of water for every 1 Ib of weight lost during activity. To maintain adequate hydration throughout exercise, 4 to 6 oz of water or a diluted sports beverage should be consumed every 15 to 20 minutes.2nUrine that is pale in color and voluminous indicates euhydration. Adolescents need to be educated on the dangers of dehydration and encouraged to drink past the point of thirst satiety. Pre- and Post-exercise Nutrition

A mix of high-carbohydrate, moderate-protein, and low-fat foods with ample fluid consumption provides a day-to-day healthy eating plan for active youths.

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The pregame and postgame meals, however, also are important to maximize athletic performance. The pregame meal should be approximately 400 to 500 calories of high-carbohydrate foods (fruits, starchy vegetables, breads, and grains) and should be consumed at least 4 to 6 hours before competition to allow adequate time for digestion. Because fat and protein take longer to digest, meals containing high-fat meats are more likely to cause abdominal distress and will not provide energy-yielding carbohydrate. Caffeine-containingbeverages should be minimized, as they often have a diuretic effect and may contribute to dehydration. Two to three hours before competition a carbohydrate-based snack of approximately 200 to 300 calories is appropriate if the athlete desires.20Foods such as a bagel, a cereal bar, or a piece of fruit can serve to settle a nervous athlete’s stomach, delay feelings of hunger, and top off energy reserves. Although the pregame meal receives much attention from young athletes, it remains controversial. Long-term daily nutrition habits have a much greater impact on athletic performance. Exercise often produces an anoretic effect and as a result, many athletes experience difficulty eating after activity. The importance of the postgame meal is frequently overlooked. Muscle glycogen is more efficiently resynthesized within 4 hours after exercise completion. Athletes should consume carbohydrate-containing foods within this time period.31Commercial carbohydrate-replacement drinks, which are more concentrated than dilute sports beverages, are available at most health food stores and may be favorable to solid food consumption for athletes who have a depressed appetite after activity. ADDITIONAL NUTRITION CONCERNS Vegetarianism

Vegetarians can be classified as vegans, lactovegetarians, or lacto-ovovegetarians. Vegans consume no food of animal origin, whereas, lacto- or lacto-ovovegetarians abstain from meat but will eat dairy products or both dairy products and eggs, respectively. A vegetarian lifestyle has shown many positive health benefits such as lower weight, lower serum cholesterol, and reduced mortality rates from certain forms of cancer.19Adolescents who choose to follow a vegetarian diet need to emphasize food variety. Traditionally, protein intake was thought to be suboptimal among vegetarians. It appears, however, that vegetarians, like omnivores, often eat much more protein than they actually require. Vitamin D, calcium, and vitamin B,, may be deficient in the diets of vegans, and it is recommended that a reliable food source or supplement of each of these nutrients be consumed regularly.32The American Dietetic Association has found vegetarian diets to be “healthful and nutritionally adequate when appropriately planned” for both adults and adolescent^.^^,^^

Eating Disorders

To effectively discuss the nutritional, medical, and psychological sequelae of eating disorders would require an entire supplement and is beyond the scope of this article. Therefore, we have chosen a brief overview with particular attention to the adolescent population. Eating disorders such as bulimia nervosa and anorexia nervosa are common among adolescents. Although the typical adolescent patient is a Caucasian female, eating disorders pervade all ages, ethnic groups, and sexes.77Athletes are at higher

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risk for eating disorders, especially those involved in weight-classed or aesthetic sports such as wrestling, gymnastics, and ballet.67 Anorexic patients fear weight gain and frequently consume around 500 calories each day.30This chronic malnutrition results in numerous nutrient deficiencies, an emaciated appearance, and medical complications such as ammenorhea, lowered blood pressure, and d e h y d r a t i ~ n Bulimia .~~ nervosa is a cycle of food binges with subsequent purges using laxatives, diet pills, or vomiting. Each binge can range anywhere from 1000 to 20,000 calories.3oThese patients may have a normal to moderately high weight but are also at risk for ammenorhea as well as mouth sores and bloody diarrhea.56 Eating disorders are complex illnesses with an unknown cause. Adolescents who suffer from an eating disorder frequently have emotional and psychological disorders, although some research suggests a genetic or biologic susceptibility. The most successful treatment uses a multidisciplinary approach, incorporating a physician, a dietitian, a psychologist, and appropriate family members. SUMMARY

Several dramatic changes make adolescence a nutritionally vulnerable period of time. Family, peers and the media influence the eating habits of this age group which often adopts poor eating habits like meal skipping, snacking and frequenting fast food restaurants. This may lead to obesity or disordered eating patterns, both of which are associated with increases in morbidity and mortality. In addition, certain adolescents with special nutritional needs, such as vegetarians or athletes, may be at risk for undernutrition. For these reasons, adolescents need to be better educated about the critical role nutrition plays and how it is vital to ensure optimal health, growth and development. References 1. 1983 Metropolitan height and weight tables. Stat Bull Metrop Insur Co 64:2, 1984 2. Allen JG, Overbaugh KA: The adolescent athlete, part 111: The role of nutrition and hydration. J Pediatr Health Care 8:250, 1994 3. American Dietetic Association: Position of the American Dietetic Association: Child and adolescent food and nutrition programs. J Am Diet Assoc 96:913, 1996 4. Bailey LB, Wagner PA, Christakis GJ, et al: Folacin and iron status and hematological findings in Black and Spanish-American adolescents from urban low-income households. Am J Clin Nutr 35:1023,1982 5. Bar-Or, 0:Temperature regulation during exercise in children and adolescents. In Gisolfi CV, Lamb DR (eds): Perspectives in Exercise and Sports Medicine, vol2. Indianapolis, Benchmark Press, 1989, p 335 6. Bigler-Doughton S, Jenkins RM: Adolescent snacks: Nutrient density and nutritional contribution to total intake. J Am Diet Assoc 871678, 1987 7. Brabin L, Brabin BJ: The cost of successful adolescent growth and development in girls in relation to iron and vitamin A status. Am J Clin Nutr 55:955, 1992 8. Bray GA (ed): Obesity in America. NIH publication no. 79-359 Bethesda, MD. National Institutes of Health, 1979, p 4. 9. Brouchard D, Perusse L: Genetics of obesity. Annu Rev Nutr 13:337, 1993 10. Burghardt JA, Devaney BL, Gordon AR: The school nutrition dietary assessment study: Summary and discussion. Am J Clin Nutr 61:252S, 1995 11. Calfas KJ, Taylor WC: Effects of physical activity on psychological variables in adolescents. Pediatric Exercise Science 6:406, 1994 12. Centers for Disease Control: Youth Risk Behavior Surveillance, United States, 1995. MMWR CDC Surveil1 Summ 45:SS4,1996

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13. Committee on Dietary Allowances, Food and Nutrition Board, National Research council: Recommended Dietary Allowances, ed 10. Washington, National Academy Press, 1989 14. Dallman PR Biochemical basis for the manifestation of iron deficiency. Annu Rev Nutr 6:13, 1986 15. Daniel WA Jr: Nutritional behavior. In Adolescents in Health and Disease. St. Louis, Mosby, 1977, p 234 16. Daniel WA Jr: Nutritional requirements of adolescents. In Winick M (ed): Adolescent Nutrition. New York, John Wiley & Sons, 1982, p 19 17. Daniel WA Jr, Bennett DL: Dietary intakes and plasma concentrations of folate in healthy adolescents. Am J Clin Nutr 28:363, 1975 18. DiPietro L, Mossberg HO, Stunkard AJ: A 40-year history of overweight children in Stockholm: Life-time overweight, morbidity, and mortality. Int J Obes Relat Metab Disord 18:585,1994 19. Dwyer J T Health aspects of vegetarian diets. Am J Clin Nutr 48712, 1988 20. Dyment PG (ed): Sports medicine: Health care for young athletes. Elk Grove Village, IL, American Academy of Pediatrics, 1991 21. Epstein LH, Valoski A, Wing RR, et al: Ten-year follow-up of behavioral, family-based treatment for obese children. JAMA 264:2519, 1990 22. Fisher M: Medical complications of anorexia and bulimia nervosa. Adolescent Medicine: State of the Art Reviews 3:487, 1992 23. Gazzaniga JM, Burns TI: Relationship between diet composition and body fatness, with adjustment for resting energy expenditure and physical activity, in preadolescent children. Am J Clin Nutr 199:21, 1993 24. Gong EJ, Heald FP: Diet, nutrition, and adolescence. In Shils ME, Young VR (eds): Modern Nutrition in Health and Disease. PA, Lea & Febiger, 1988, p 969 25. Gortmaker SL, Dietz WH, Cheung LWY: Inactivity, diet and the fattening of America. J Am Diet Assoc 90:1247, 1990 26. Gortmaker SL, Must A, Perrin JM, et al: Social and economic consequences of overweight in adolescence and young adulthood. N Engl J Med 329:1008,1993 27. Gortmaker SL, Must A, Sobol AM, et al: Television viewing as a cause of increasing obesity among children in the United States. Arch Pediatr Adolesc Med 150:356, 1996 28. Guenther PM: Beverages in the diets of American teenagers. J Am Diet Assoc 86:493, 1986 29. Guo SS, Roche AF, Chumlea WC, et al: The predictive value of childhood body mass index values for overweight at age 35. Am J Clin Nutr 59:810,1994 30. Herzog D, Copeland P: Eating disorders. N Engl J Med 319:683,1988 31. Ivy J: Muscle glycogen synthesis after exercise and effect of time of carbohydrate ingestion. J Appl Physiol64:1480, 1988 32. Janelle KC, Barr SI: Nutrient intakes and eating behavior scores of vegetarian and nonvegetarian women. J Am Diet Assoc 95:180, 1995 33. Kaufman L: Prime-time nutrition. Journal of Communication 30:37, 1980 34. Kennedy E, Goldberg J: What are American children eating? Implications for public policy. Nutr Rev 53:111, 1995 35. Key JD, Key LL Jr: Calcium needs of adolescents. Curr Opin Pediatr 6:379, 1994 36. Kimm SY, Gergen PJ, Malloy M: Dietary patterns of US children: Implications for disease prevention. Prev Med 19:432,1990 37. Kreipe RE: Eating disorders among children and adolescents. Pediatr Rev 16:370, 1995 38. Lifshitz F, Tarim 0, Smith MM: Nutrition in adolescence. Endocrinol Metab Clin North Am 22:673, 1993 39. Looker AC, Sempos CT, Johnson CL, et a1 Comparison of dietary intakes and iron status of vitamin-mineral supplement users and nonusers, aged 1-19 years. Am J Clin Nutr 46:665, 1987 40. Macdonald I: Food and drink in sport. In Ding JB (ed): British Medical Bulletin A Series of Expert Reviews: Sports Medicine. New York, Churchill Livingstone, 1992, p 612 41. Meyers AF, Sampson AE, Weitzman M, et al: School breakfast program and school performance. Am J Dis Child 143:1234, 1989 42. Must AP, Jaques PF, Dallal GE, et al: Long-term morbidity and mortality of overweight adolescents: A follow-up of the Harvard Growth Study of 1922 to 1935. N Engl J Med 327~1350-1355,1992

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Address reprint requests to Elizabeth C. Miller, RD The Ohio State University Medical Center 842 Doan Hall Department of Nutrition 410 W. 10th Avenue Columbus, OH 43212-1228