Michael R. Kohn
This chapter focuses on energy and nutrient requirements as well as deficiency states that develop during adolescence. Adolescent obesity is discussed in Chapter 32.
Nutrition is an essential component of total adolescent health care. Two important transformations occur during adolescence that may cause significant changes in a teenager's nutritional needs. Growth in height and weight and changes in body composition are greater and more rapid than at any other time in life, except during infancy. In general, there is also a significant change in the adolescent's eating habits and food consumption. Adolescents have been found to have the highest prevalence of any age-group for unsatisfactory nutrition. Adolescents are known to reduce regular breakfast consumption, increase consumption of prepared foods, snacks, fried foods, nutrient-poor foods, and sweetened beverages and have a significant increase in portion size at each meal. This is associated with a decrease in the consumption of dairy products, fruits, and vegetables. Furthermore, sodium intake is far in excess of recommended levels, whereas calcium and potassium intakes are below recommended levels (Gidding et al., 2005).
Health care providers should assess nutritional status and provide appropriate nutritional counseling as part of health supervision visits. The MyPyramid Food Guide (www.MyPyramid.gov) is a helpful educational tool that can be used to assist teenagers in improving their diets (Figs. 6.1 and 6.2). MyPyramid incorporates recommendations from the 2005 Dietary Guidelines for Americans that was released by the United States Department of Agriculture (USDA) and United States (U.S.) Department of Health and Human Services (HHS). The Dietary Guidelines for Americans provides authoritative advice for individuals 2 years of age and older on how proper dietary habits can promote health and reduce risk of major chronic diseases. MyPyramid was developed to promote dietary guidance and increase the awareness of the health benefits from simple and modest improvements in nutrition, physical activity, and lifestyle.
Potential Nutritional Problems
All of these factors contributed to the findings of the Food and Drug Administration's (FDA) Ten State Nutritional Survey in the 1960s (U.S. Department of Health, Education and Welfare, 1972), the National Health and Nutrition Examination Survey (NHANES) during 1971–1974 (National Center for Health Statistics [NCHS], 1979), the NHANES III study in 1988–1994 (National Center for Health Statistics,
1994), and the National Health and Nutrition Examination Survey, 1999–2002. These surveys concluded that the highest prevalence of unsatisfactory nutritional status occurs in the adolescent age-group. Of particular note were deficiencies in the intake of calcium, iron, riboflavin, thiamine, and vitamins A and C.
FIGURE 6.1 USDA new food pyramid. (From U.S. Department of Agriculture Center for Nutrition Policy and Promotion. www.mypyramid.gov. April 2005.)
Assessing the nutritional status of an adolescent should be part of a comprehensive health evaluation. This becomes even more important in adolescents who are identified as nutritionally at risk. Such adolescents include those with nutritionally related medical conditions, dietary deficiencies, or those with conditions that predispose them to inadequate nutrition. Nutritional assessment requires repeated measurements of nutritional status over time. Methods used in the nutritional assessment of adolescents include dietary and clinical evaluation, measurements of body composition and laboratory data.
Dietary information can be obtained from a food record kept by the teenager, a dietary history obtained from a nutritionist, a 24-hour recall, or a diet questionnaire. Figure 6.3 is an example of a diet questionnaire for adolescents. Simple screening questions that are quick and easy to ask include the following:
FIGURE 6.2 USDA new food pyramid, example for 16-year-old male. (From U.S. Department of Agriculture Center for Nutrition Policy and Promotion. www.mypyramid.gov. April 2005.)
Helpful screening questions used in older adolescents and young adults (followed by the associated sensitivity and specificity for disordered eating) include the following (Anstine and Grinenko, 2000):
Each of these questions appears to have a very high correlation with the score on the Eating Attitudes Test (EAT-26). This screening test examines attitudes and behaviors regarding food, weight, and body image and has been validated for use in adolescents.
the height in meters or BMI = kg/m2. The BMI is easily determined, is highly reliable, and has a correlation of 0.7 to 0.8 with body fat content in adults. The correlation coefficient of BMI with body fat content in children and adolescents is 0.39 to 0.90. Adolescents who are overweight or deemed at risk for overweight have a BMI between the 85th and 95th percentiles for age and gender, and those who are obese have a BMI exceeding the 95th percentile for age and gender. BMI values in adolescents are listed in Chapter 1 (Figs. 1.25and 1.26). BMI-for-age charts are available at www.cdc.gov/growthcharts/.
may be a better predictor of the sequelae associated with adult obesity. A WHR >1.0 in adult men or >0.8 in adult women has been shown to predict complications from obesity, independent of BMI. It should be noted that the WHR has not been evaluated in all ethnic groups.
FIGURE 6.3 Diet questionnaire for adolescents. (Adapted from Fomon S. Nutritional disorders of children: prevention, screening, and follow-up [DHEW Publication (HSE) 78–5104]. Rockville, MD: U.S. Department of Health, Education, and Welfare, Health Services Administration, 1976.)
The clinical evaluation includes examination of skin, eyes, lips, tongue, gums, teeth, hair, and nails. The following is an illustrative list of clinical findings and possible nutritional causes.
Laboratory tests helpful in assessing nutritional status include hemoglobin, hematocrit, ferritin, serum protein, and albumin.
Dietary reference intakes (DRIs) represent the new approach to providing quantitative estimates of nutrients used to plan and evaluate diets for healthy people. The DRIs are a set of four nutrient reference values that have replaced the 1989 recommended dietary allowances (RDAs).
The DRIs cover the following groups of nutrients:
Energy requirements are determined by basal metabolic rate, growth status, physical activity, and body composition. Energy requirements of adolescents vary depending on the timing of growth and pubertal development. As such, energy needs are based on height because it provides a better estimate of total daily caloric recommendations. Suggested caloric intakes are listed in Table 6.2, but these will vary widely according to body size and activity level.
Protein provides 4 kcal of energy in each gram. Protein requirements are based on the amount of protein needed to maintain existing lean body mass and the increase in additional lean body mass with growth and development. Protein requirements are highest during the peak height velocity. Most teenagers' diets exceed the RDA for protein.
Carbohydrates provide 4 kcal of energy in each gram. Carbohydrates are the primary source of dietary energy. Carbohydrates should make up approximately 50% of the daily caloric intake. However, no more than 10% to 25% of calories should come from sweeteners (sucrose and high fructose corn syrup). Beverages with caloric sweeteners, sugars and sweets, and other sweetened foods that provide little or no nutrients are negatively associated with diet quality and can contribute to excessive energy intakes. In fact, 12% of all carbohydrates consumed by adolescents come from the added sweeteners in soft drinks.
Carbohydrate-containing foods include grain products, fruits, and vegetables. Approximately 25 to 35 g of fiber should be consumed daily. Fiber is found in whole grain foods, fruits, vegetables, legumes, nuts, and seeds.
Glycemic index (GI) classifies carbohydrate foods on the basis of the response they bring about in the body, specifically the effect on blood glucose. The GI of foods is
ranked according to this “glycemic response”. The index ranges from 0 to 100; with glucose or other reference standard being 100. Hence, the lower the GI, the lower the expected rise in blood sugar for a given food. In general, foods are classified into low GI (<40), moderate GI (40–70), and high GI (>70).
Alcohol provides 7 calories of energy in each gram and can also be a significant source of calories.
Fat provides 9 kcal of energy in each gram. Adolescents require dietary fat and essential fatty acids for many vital functions in the body. A teenager's diet should contain no more than 30% of calories from fat. Most adolescents' total and saturated fat intake is greater than that recommended.
There is an increased need for iron in both males and females during adolescence because of the rapid growth, and increase in muscle mass and blood volume. In addition, females require increase in iron because of menstrual losses. High-iron foods include lean red meats, spinach, green vegetables, and fortified cereals. Nonheme iron, present in plant sources is less bioavailable, but its absorption can be enhanced by concurrent intake of vitamin C.
Calcium, which is important for attaining skeletal health, is particularly important during adolescent growth and development. Requirements for dietary calcium increase substantially during periods of peak velocity of growth and accrual of bone-mineral content. Adolescents tend to eat a diet deficient in calcium. The DRI for calcium for 9- to 18-year olds is 1,300 mg/day (Table 6.3). Many Adolescents have inadequate calcium intakes, in part due to the substitution of carbonated beverages for milk. It is highly likely that current high levels of soft drink consumption are replacing the drinking of milk. Data from the U.S. Department of Agriculture Continuing Surveys of Food Intakes by Individuals indicate a drop in milk intake among adolescent girls from 72% on a given day in 1977 to 1979 to 57% in 1994.
Those adolescents not taking in adequate calcium from food sources may need to take supplemental calcium such as calcium carbonate, citrate, lactate, or phosphate (absorption varies from 25%–35%). Optimal absorption of the calcium supplements occurs when no more than 500 mg/dose is taken with food. In addition to dairy products, calcium is found in tofu, salmon and sardines, darkgreen leafy vegetables, and calcium-fortified foods (such as orange juice).
Zinc is needed for adequate growth, sexual maturation, and wound healing. The RDA for zinc was set at 8 mg/day for adolescents 9 to 13 years old and 9 mg/day and 11 mg/day for females and males 11 to 14 years old, respectively. Good food sources of zinc include lean meats, seafood, eggs, and milk.
Vitamin requirements increase during adolescence, especially for vitamin B12; folate; vitamins A, C, D, and E; thiamine; niacin; and riboflavin (Table 6.3). It has been shown that supplements of antioxidant vitamins (A, C, E, and β-carotene) probably reduce the risk of cardiovascular disease and certain cancers, but there is no current recommendation to prescribe them routinely.
Guidelines for Nutritional Therapy
Adolescents may be vegetarian because of ecological, economic, religious, or philosophical beliefs. Teens who are vegetarians (but not choosing to be vegan) are likely to have an adequate nutritional intake. Nutritional counseling may be of benefit to ensure adequate intake of energy, protein, and micronutrients as well as to assess the need for supplements.
Types of Vegetarians
Semivegetarians eat milk products and limited seafood and poultry but no red meat.
Lactovegetarians consume milk products but no eggs, meat, fish, or poultry.
Ovolactovegetarians consume milk products and eggs but no meat, fish, or poultry.
Vegans consume vegetable foods only and no foods of animal origin (i.e., no eggs, milk products, meat, fish, or poultry).
Fruitarians consume raw fruit and seeds only. Examples of such fruits include pineapple, mango, banana, avocado, apple, melon, orange, all kinds of berries, and the vegetable fruits such as tomato, cucumber, olives; and nuts.
Further information is available from the Vegetarian Resource Group on their Web site: http://www.vrg.org/.
Supplemental Needs of Vegetarians
Potential nutritional issues with vegetarian diets include macronutrient and micronutrient deficiencies such as those of protein, fat, vitamin B12, iron, zinc, calcium, and vitamin D.
Semivegetarians, lactovegetarians, and ovolactovegetarians have no need for supplements if attention is paid to dietary composition. Vegans may need supplemental riboflavin and vitamins B12 and D.
Adequate protein intake has been a traditional concern for vegetarians; however, vegetarians usually meet or exceed protein requirements (except for vegans). There is also mounting evidence that the practice of eating complementary proteins in the same meal is unnecessary.
There is no uniform need for supplements, but vegetarians are at increased risk for iron and zinc deficiencies. Vegetarians may need up to 50% more zinc in their diet since phytate (found in plants) and calcium hinder zinc absorption.
Teens with lactose intolerance are at risk of inadequate calcium intake. Some adolescents with lactose intolerance can tolerate small amounts of milk products including aged cheese or yogurt with active cultures. There are many nondairy foods high in calcium including green vegetables, such as broccoli and kale; fish with edible bones, such as salmon and sardines; calcium-fortified orange juice; and soymilk. Currently, there are a variety of lactose-reduced dairy products in the supermarket including milk, cottage cheese, and processed cheese slices. Teens often find lactase enzyme replacement pills or liquid helpful.
There is limited information available regarding the nutrition needs in pregnant adolescents. Energy requirements are greater for pregnant adolescents than for nonpregnant adolescents. Younger adolescents may require higher energy intake than older women. Pregnant adolescents should not consume less than 2000 kcal/day and in many cases their needs may be higher. The best gauge of adequate energy intake during pregnancy is satisfactory weight gain. Goals for weight gain are based on prepregnancy weight, height, age, stage of development, and usual eating patterns. Young pregnant women who are below an optimal weight are advised to gain more weight than overweight women.
Folate is essential for nucleic acid synthesis and is required in greater amounts during pregnancy. Recent research suggests that taking folic acid before and during early pregnancy can reduce the risk of spina bifida and other neural tube defects in infants. Because these defects occur early in gestation, it is advised that women of childbearing age and those who are capable of becoming pregnant consume 400 µg/day of folic acid. The DRI for folate during pregnancy is 600 µg/day. Good sources of folate include leafy dark-green vegetables, legumes, citrus fruits and juices, peanuts, whole grains, and some fortified breakfast cereals.
The calcium recommendation during pregnancy is 1,300 mg/day for adolescents. Since most nonpregnant adolescent females consume significantly less than the recommended amount of calcium, pregnant teens should
either add calcium-rich foods to their diet or take calcium supplementation.
Dietary counseling can be one of the most important interventions for a pregnant adolescent to ensure a healthy pregnancy and a healthy baby. Teens should be encouraged to obtain their nutrients from food. A low-dose vitamin–mineral supplement is recommended for pregnant adolescents who do not regularly consume a healthy diet. Teens should be counseled against dieting during pregnancy.
Risk for Iron and Zinc Deficiency
Both male and female adolescent athletes are at risk for iron deficiency. Athletes (especially menstruating females and those involved in endurance sports such as distance running) should be screened for low hemoglobin or hematocrit levels. Serum ferritin can be helpful in determining loss of iron stores and need for supplementation. A ferritin level of <16 µg/L corresponds with depleted iron stores. For the athlete who is not anemic but has low iron stores, 50 to 100 mg of elemental iron daily (ferrous gluconate 240 or 325 mg twice daily or ferrous sulfate 325 mg daily or twice daily) should be recommended. For the anemic athlete, 100 to 200 mg of elemental iron daily (ferrous gluconate 325 mg three times daily or ferrous sulfate 325 mg twice daily), should be given. Laboratory measurements should be repeated after 2 to 3 months to document response to therapy. Athletes with iron deficiency anemia may also be zinc deficient. Education regarding good dietary sources of zinc and iron should be provided.
Sodium and Potassium
Athletes need increased intake of sodium and potassium. This requirement will generally be met as they increase their calorie intake.
The active athlete who engages in 2 hours/day of heavy exercise needs 800 to 1,700 extra calories/day beyond the recommended minimum for age, sex, height, and weight. According to the American Dietetic Association, the approximate distribution of calories should be carbohydrates, 55% to 60%; proteins, 12% to 15%; and fats, 25% to 30%.
Attention must be given to hydration before and during activity.
Avoid any major weight restriction during the adolescent growth spurt. Alterations in diet to cause rapid weight gain or loss should be discouraged. Eating disorders are prevalent among athletes (especially female athletes), especially in those involved in running, swimming, diving, gymnastics, or dance (Chapter 33). Therefore, carefully question all athletes regarding body image, desired weight, and amenorrhea. The female athlete triad (amenorrhea, disordered eating, and osteoporosis) should be suspected in an athlete with secondary amenorrhea.
Diets that are chronically high in carbohydrate are not recommended. For optimal performance, the athlete should train lightly or rest 24 to 36 hours before competition. On the day of competition, the athlete may consider a high-carbohydrate, low-fat meal 3 to 6 hours before an event and an optional snack 1 to 2 hours before the event. Foods high in carbohydrates (60% to 70%) have also been recommended after competition to replace glycogen stores. However, Hawley et al. (1995) pointed out that a diet of 5,000 kcal/day that is only 45% carbohydrate is sufficient to restore muscle glycogen within 24 hours. An initial “depletion phase” consisting of vigorous workouts and low-carbohydrate eating before competition is also no longer recommended.
Ergogenic Nutritional Supplements
The word “ergogenic” is derived from the Greek word ergon, which means “to increase work or potential for work.” Anecdotal reports suggest that compounds such as bee pollen, caffeine, glycine, carnitine, lecithin, brewer's yeast, and gelatin improve strength or endurance. However, scientific research has failed to substantiate these claims.
Teen athletes who are considering the use of nutritional supplements should be aware that the effects of long-term supplement use have not been studied. In addition, supplement use can be quite costly. Most athletes can maximize their performance through consistent, appropriate training and attention to adequate nutrition rather than relying on supplement use (http://www.drugfreesport.com/choices/supplements/). See Chapter 83 for further discussion on herbal therapies.
For Teenagers and Parents
http://www.mypyramid.gov/index.html. USDA web site that customizes food pyramids based on age, sex and exercise levels.
http://www.mayohealth.org. Nutrition section from Mayo Clinic.
http://www.fda.gov/fdac/features/795_teenfood.html. How to read a food label.
http://www.vrg.org. Vegetarian Resource Center.
http://www.eatright.org. American Dietetic Association Web site.
http://www.kidshealth.org/teen/food_fitness. Exercise and nutrition site for teens.
http://www.foodsafety.gov. U.S. Food and Drug Administration site on nutrition and food safety.
http://www.nal.usda.gov/fnic/etext/fnic.html. U.S. Department of Agriculture (USDA) food and information center.
For Health Professionals
http://www.mypyramid.gov. MyPyramid from USDA.
http://www.vrg.org. Vegetarian Resource Center.
http://www.americanheart.org. American Heart Association diets.
http://www.nutrition.org. American Society for Nutritional Sciences.
http://www.iom.edu/topic.asp?id=3708. Food and Nutrition Board home page with sections on RDIs.
http://www.drugfreesport.com/choices/supplements. Nutritional supplements, NCAA sponsored site.
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