VEGITARIANISM IN ADOLESCENTS: RISK OR SYMPTOM?

OBJECTIF NUTRITION 75 (MARCH 2005)
by Professor Fernand Lamisse, Tours School of Medicine

What reasons cause an adolescent to become a vegetarian? Can vegetarianism in adolescents lead to deficiencies in some nutrients? Does it have an impact on sexual maturation and growth? Can it lead to eating disorders? Conversely, when examining vegetarian populations, do we find a higher incidence of adolescents with eating disorders? Although too few studies enable us to answer these questions categorically, the studies available all conclude that these behaviors, which are not without risks, must be closely monitored.

The choice of a vegetarian diet in adolescence often leads to changes in eating habits, with possible restrictions on certain food groups. Discussion of vegetarianism in adolescents therefore involves asking if this dietary lifestyle can lead to deficiencies in certain nutrients, if there is an impact on sexual maturation and growth, or if it can lead to eating disorders.

Studies conducted in adolescents often include, along with real vegetarians and vegans, subjects who do not eat red meat and are referred to as semi- or pseudo-vegetarians. A distinction is not made between adolescents who were already vegetarian and those who became vegetarian after moving out on their own. The duration of vegetarianism is rarely specified. Furthermore, labeling a subject as vegetarian is often based on the good faith of the subject describing their diet rather than on dietary investigations.

PREVALENCE AND MOTIVATIONS FOR VEGETARIANISM

There is no data available regarding this topic for France. In Sweden, studies have been mainly conducted on students, of whom 5% called themselves vegetarians. In the United Kingdom, vegetarian diets are found in approximately 5% of adults and 8% of adolescents aged 11 to 18. In the United States, the prevalence of vegetarianism is estimated at 2% of adults and 2% of children and adolescents. No studies published have mentioned the percentage of vegetarian adolescents within vegetarian families.
In three studies of the motivations of vegetarian adolescents, “concern for better health” ranked first in 67%, 39%, and 37.5% of cases, respectively. This notion of “better health” is essentially based on a lower intake of dietary fats, in particular those found in meats, in the hope of not gaining weight. Other motivations reflected a desire to lose weight (and not merely to avoid gaining it) in 25%, 19%, and 18.8% of cases respectively; ethical reasons in 15% and 14.9% of cases; religious grounds were cited in 8% of cases in one study.

NUTRITIONAL CONSEQUENCES OF VEGETARIANISM

· Possible deficiencies in vegetarian populations

The diets of 73 lacto-ovo-vegetarian adolescents were compared to the omnivorous diets of 1,891 other adolescents. The former group ate less milk, yogurt, French fries and chips, soft drinks, potatoes, and fried or barbecued foods. They ate more rice, pasta, vegetables, tea, and dietary supplements (although it is not specified whether the supplements were prescribed or taken spontaneously).  There were no differences between them and the omnivores regarding fruit, cereal, bread, alcoholic beverages, ice cream, chocolate, fast food, and coffee.
Energy intake as well as intake of iron, zinc, calcium and vitamin C in the lacto-ovo-vegetarians was not significantly different from that of the omnivores (table 1). Protein intake was lower in lacto-ovo-vegetarians than in omnivores, but was still adequate for their weight.

Despite the lack of a difference between iron and zinc intakes, a larger number of lacto-ovo-vegetarian adolescents have low serum ferritin levels (<12µg/L) and low serum zinc levels (<10.71 µmol/L). These results demonstrated that iron and zinc deficiency is more common in vegetarians than in omnivores. Higher fiber and phytate intake in lacto-ovo-vegetarians leads to a decreased bioavailability in nonheme iron and zinc. Furthermore, in the vegetarian group, the consumption of vitamin C, which could have increased the bioavailability of nonheme iron, did not differ from that of the omnivores (table 2).

· Effects on growth
The few studies available on this topic have yielded contradictory results. One study compared the height of 123 vegetarian Seventh-day-Adventist adolescents and 304 omnivorous Adventist adolescents. The vegetarians were taller, on average 2.1 cm for boys and 1.9 cm for girls, with significant differences. Another study compared the height of 19 vegetarian boys and girls with the height of an equal number of omnivorous adolescents. The vegetarians were shorter, but the differences were only significant in the boys. In a third study conducted in 15 vegetarian adolescents and 15 omnivores adolescents, no difference in height was reported.
Only one study, conducted in 16 vegetarian adolescents of both sexes compared to 44 non vegetarians, demonstrated normal sexual maturation in the boys and girls, and no difference in the age of first menarche.
There have been no studies published on the differences in bone mass between lacto-ovo-vegetarans and non-vegetarian adolescents.

VEGETARIANISM AND EATING DISORDERS

· Do vegetarian adolescents suffer from eating disorders?
A screening questionnaire for eating disorders was sent to 30 female vegetarian students and 113 female omnivorous students who were 19 years old on average. The percentages reported for each item are not given but differences are markedly significant (table 3). These results unquestionably reflect female vegetarians' desire to control their weight and the existence of eating disorders.

Another questionnaire was sent to 107 vegetarian adolescents and 204 omnivorous adolescents. The questions focused on changes in eating habits and their frequency, the ingestion of large quantities of food in short periods of time (binge eating), vomiting after eating, and the use of laxatives. The frequency of these behaviors was significantly higher in vegetarians, which suggests the existence of eating disorders in this group (table 4).

· Are adolescents with eating disorders more frequently vegetarians?

Only studies on anorexia nervosa have been reported. In a study conducted in 116 patients suffering from anorexia nervosa, of whom 63 did not eat red meat, it was found that as long as the avoidance of eating meat was maintained, weight remained lower than in omnivores and the disease lasted longer. Only four of the adolescents were true vegetarians (3%) Two other studies found a zinc deficiency in anorexia nervosa, mainly in the context of a vegetarian diet. In the first study of 46 cases of anorexia nervosa, 96% of patients did not eat red meat. The study’s authors believe that the zinc deficiency induces taste disorders and could be directly responsible for anorexia nervosa. In the second study, which involved 20 female patients suffering from anorexia nervosa, of whom 9 were vegetarians, the intake of zinc was only 62% of recommended allowances, compared to 97% in the non-vegetarians. Above all, the study’s authors have stressed the zinc losses, which are higher in the vegetarians, and secondary to greater physical activity. These losses would result in digestive lesions, which in turn disrupt the absorption of zinc and lead to a distorted sense of taste (dysgeusia) and a decrease in food intake. The study did not state whether the digestive lesions could be caused or aggravated by intense physical activity.

CONCLUSION

The number of vegetarian adolescents in France is very unclear due to inadequate epidemiological studies. Even though no studies are available on the future of adolescents who have always been vegetarians, it is likely that they are not at risk, provided that do not exclude certain food groups upon reaching adolescence. It is therefore desirable to very closely monitor the adolescent vegetarians in order to screen for the occurrence of eating disorders and the resulting deficiencies.

Bibliography

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