Writing in 1988 in the American Journal of Clinical Nutrition, Dwyer reviewed studies of the previous five years and concluded that elderly people also should be especially cautious about adopting vegetarian diets because their bodies may absorb vitamin B12 poorly. Ovo-vegetarians, who eat eggs but no dairy foods or animal flesh, and vegans may have inadequate vitamin D and calcium. Inadequate vitamin D may cause rickets in children, while inadequate calcium can contribute to risk of osteoporosis in later years. Vegans must guard against inadequate calorie intake, which during pregnancy can lead to low birth weight, and against protein deficiency, which in children can impair growth and in adults can cause loss of hair and muscle mass and abnormal accumulation of fluid. According to the Institute of Food Technologists and the American Dietetic Association, if appropriately planned, vegan diets can provide adequate nutrition even for children.
Some experts disagree.
Gretchen Hill, Ph.D., associate professor of food science and human nutrition at the University of Missouri, Columbia, believes it's unhealthy for children to eat no red meat. While meat is well-known as an important source of iron, Hill says it may be even more valuable for copper and zinc. Copper not only helps build the body's immunity, it builds red blood cells and strengthens blood vessels. Children can't meet their zinc needs without eating meat. Also, vegetarian women of childbearing age have an increased chance of menstrual irregularities, Ann Pedersen and others reported last year in the American Journal of Clinical Nutrition.