Originally Published in The Medical Post, May 11, 2004 Volume 40 Issue 19
As more adolescents adopt a meat-free diet, solid planning can ensure they meet energy and nutrient needs
Increasing numbers of adolescents, especially girls, are adopting vegetarian diets. Their reasons for choosing a vegetarian diet vary from animal welfare, health benefits and food safety to environmental and sociopolitical concerns. Surveys suggest that approximately 8% of adolescents in the United Kingdom and 6% of older elementary and high-school students in the midwestern United States consume a vegetarian diet.
Although vegetarian diets differ, the underlying principle remains the same. The human body needs adequate calories from fat and carbohydrates, specific nutrients and proteins. This can be accomplished with solid dietary planning but many youngsters do not follow an appropriate regimen. The “all things green” philosophy, although well-intentioned, does not provide a rational basis for proper nutrition.
Vegetarian lifestyle practices usually include exercise, reduced consumption of alcohol and avoidance of cigarettes, among other health-conscious decisions. Indeed, the vegetarian lifestyle is associated with a lower incidence of type 2 diabetes, obesity and heart disease.
Rapid growth cycles in childhood and adolescence consume nutrients at a rapid rate. Well-planned vegetarian diets can provide children with all the necessary nutrients that play a role in their growth and development.
The foods and supplements required depend on the degree of vegetarianism. There are five vegetarian categories:
• Semi-vegetarian: Meat is included in the diet occasionally. Some may consume chicken and/or fish but not red meat.
• Lacto-ovo vegetarian: Avoidance of meat, but eggs and milk are included.
• Lacto vegetarian: Dairy products are included, but eggs and meat are excluded.
• Vegan: All animal products, including eggs and dairy products are excluded from the diet.
It is not necessarily the type of vegetarian diet per se but the quality, variety and amount of food consumed that is relevant.
• Macrobiotic: Whole grains, especially brown rice, are emphasized and vegetables, fruit, legumes and seaweeds are included in the diet. Animal foods are limited to white meat, or white-meat fish may be included in the diet once or twice a week.
Vegetarian adolescents should eat a diet low in saturated fat and cholesterol and high in fibre, complex carbohydrates (such as beans and vegetables) and antioxidants.
High-fibre vegetarian diets tend to include less calorie-dense foods. This may create a sense of stomach fullness before enough energy is consumed. This is problematic for adolescents because of the great energy requirements during pubertal development.
Adolescents should eat frequent meals and snacks that include energy-dense foods such as whole-grain breads, enriched cereals, nuts, peanut, almond and cashew butters, tahini, cooked legumes, soybeans, sesame and sunflower seeds, avocados and dried fruits.
Food selection must be built around the consumption of essential amino acids. Animal-source proteins contain all the essential amino acids, but plant-based foods, except for soy, do not. Adding soybean products, complementary plants (such as brown rice to legumes or nut butters to bread), dairy or eggs will compensate for this lack. It is not necessary to consume all essential amino acids during the same meal, but they should be included over the course of a day.
Rapidly growing adolescents, especially menstruating females, require iron. Fifteen to 35% of the iron within meat (heme iron) is absorbed by the intestine, compared to 2% to 20% from plant sources (non-heme iron).
Certain chemical compounds within foods will bind with non-heme iron and prevent its absorption: tannins and polyphenols in tea and coffee form iron-tannate complexes that greatly reduce non-heme iron absorption. Phytates found in legumes, nuts, seeds, grains and soy will form insoluble non-heme complexes and reduce iron absorption.
Parents can encourage their adolescent child to choose from iron-fortified cereal, whole-grain or enriched bread, pasta or grains, legumes, dried fruit, green leafy vegetables, soy products, blackstrap molasses, bulgur and wheat germ. Milk and eggs are not good sources of iron.
Vitamin C will improve non-heme iron absorption. It must be consumed with the meal because of its mechanism of action. It will prevent the formation of less soluble ferric compounds, promote non-heme iron absorption and can counteract the inhibitory effect of phytates. A 75 mg dose of ascorbic acid increases the absorption of non-heme iron by three- to four-fold.
The addition of fruits and vegetables like citrus fruit, strawberries, broccoli and tomatoes can increase the absorption by three- to four-fold. Teens should be encouraged to consume vitamin C with every meal.
Zinc deficiency can lead to growth impairment, infections, diarrhea and pneumonia. Plant sources include whole grains, cereals, legumes, wheat germ and nuts. It is also found in dairy products, shellfish and meat.
Seventy-five per cent of the calcium requirements for children and adolescents come from the consumption of cow’s milk and dairy products. In the absence of dairy, calcium-fortified foods such as soy milk, orange juice, breakfast bars, waffles, pastas and cereals can help teens meet daily requirements. Calcium-rich foods do help, but large quantities would be needed. These include kale, turnips, mustard greens, broccoli, bok choy, dried figs, blackstrap molasses and lime-processed tortillas.
Calcium supplements can be used, but food sources are better because they include extra nutrients. Vegetarian children who do not drink cow’s milk should receive at least one calcium-rich or fortified food with each meal and snack. The daily calcium requirement for adolescents is about 1,000 to 1,500 mg per day.
Our bones attain peak bone mineral density by our mid-20s. Thereafter, bone mineral density will slowly decline. It is imperative that adolescents maximize their peak bone mineral density as a means of minimizing the debilitating effects of osteoporosis in later life. The principal dietary source of vitamin D for most people is fortified milk. Those who do not consume fortified cow’s milk, soy milk or breakfast cereal are at risk for deficiency that can lead to osteomalacia in adults.
Sun exposure and a dietary intake of 200 to 400 IU will maintain a healthy bone architecture. During the winter months, many can benefit from vitamin D supplements and enriched foods.
Meat, shellfish, eggs and dairy products provide virtually the only dietary source of vitamin B12. Without supplementation, many vegetarians, with the possible exception of semi-vegetarians, will suffer from vitamin B12 deficiency. This can cause anemia and nervous system dysfunction. Indeed, it is becoming all too common to uncover macrocytic anemias on younger people due primarily to dietary deficiencies.
Fortified meat substitutes, soy beverages, nutritional yeasts and cereals are good vegetarian sources of B12. Adolescents require about 6 mcg to 9 mcg daily.
The risk of nutritional deficiencies increases with the more restrictions within the diet. With proper planning, vegetarian diets are healthful. Dieticians are a valuable resource and should be involved with the adolescent patient’s dietary planning.