There are pluses and minuses to vegetarian diets. On the positive side, they provide more fiber and less fat than traditional American fare, but they carry an increased risk of deficiencies in vital nutrients such as calcium and protein. And the regimen is very popular among sufferers of anorexia nervosa.
An October 16, 1998 Scripps Howard News Service article appearing online at ABC News.com cited a University of Minnesota study finding that vegetarian teenagers have a greater tendency to develop eating disorders than their meat-eating counterparts. The study, first reported in the 1997 Archives of Pediatrics & Adolescent Medicine, indicated that twice as many teenage vegetarians than non-vegetarians said they dieted frequently, and four times as many said they purged, according to Scripps Howard. However, the study drew no conclusions regarding cause and effect.
Nevertheless, a survey of 116 anorexic patients cited by Scripps Howard indicated that 54 percent avoided red meat; only four percent had done so before their illness. Similarly, research into the food habits of 131 young adult women reported in the International Journal of Eating Disorders found that 34.3 percent were vegetarians whose diets were significantly more restrictive than the rest of those studied1.
Three studies conducted at the University of California, Davis suggest there is a biological basis to vegetarianism among anorexics. One caveat: they all involve rats, and, therefore, the results may not apply to the more complex human animal.
The first study2 investigated the effect of vagotomy, tropisteron, and an amino acid-imbalanced diet on appetite. The vagus nerve is important in several aspects of gastrointestinal function3, including amino acid, glucose, and fatty acid metabolism4.
The investigators surgically severed the vagus nerve below the diaphragm in half the rats (VAGX)5. The others were given a “sham” operation in which the vagus was left intact6. These groups were further subdivided into those given either a saline injection (VEH) and those given tropisteron (TROP), a blocker of serotonin at the brain’s number 3 receptor7. All TROP and VEH groups were either fed a normal diet (BAS) or an amino acid-imbalanced diet (IMB) deficient in the amino acid isoleucine8.
Previous research had shown that IMB diets induce anorexic behavior in rats, and that TROP injections restored normal eating9. There were two trials. In both, it was found that vagotomy lessened the anti-anorexic effect of TROP10. After 3 hours, the greatest decrease in appetite was found in the IMB-fed sham group pre-treated with saline (sham-VEH)11. During this same time period, the IMB-fed sham group pre-treated with TROP increased its intake to 66.4 percent of baseline feeding (BAS)12. But after 6 hours in trial 1, and 9 hours in trial 2, IMB intake was 70.7 percent of BAS in the sham-VEH group, but only 61 percent of BAS in the VAGX-VEH and the VAGX-TROP groups13.
The researchers concluded that the vagus nerve is involved in the anorexic response to IMB diets, and that intact vagus function is required for the full anti-anorexic effect of TROP14.
The second study15 employed the serotonin antagonist ondansetron (OND), which is more specific to the number 3 receptor16. The researchers found that low doses of OND fully restored IMB feeding to control levels, demonstrating that the anorexic pathway employs the number 3 receptor, not the number 4 as previously hypothesized17.
The third study18 investigated taste preferences among rats exposed to IMB diets and another serotonin-3 blocker (let’s call it TROP2). The animals were given either a VEH (saline) injection or a TROP2 injection19. Then each rat was conditioned with one of four diets: IMB; IMB flavored with saccharin (IMB-SAC); a normal diet (COR); or a normal diet flavored with saccharin (COR-SAC)20. For three days thereafter, all animals were allowed to choose between COR and COR-SAC diets21.
There was no significant difference between the groups in food intake over the entire three-day period22. During the first two days, however, the preference for saccharin was lowest for rats pre-treated with VEH and IMB-SAC, but by the third day, their appetite for saccharin had returned23. On the first day, rats pre-treated with COR or COR-SAC ate more than those pre-treated with IMB and IMB-SAC24. However, on the second and third days, rats pre-treated with IMB and IMB-SAC ate more than the others25.
The researchers hypothesize that the VEH/IMB-SAC rats developed a taste aversion to saccharin when fed the imbalanced diet, but their aversion had disappeared by the third day of the experiment26. In addition, say the researchers, the increased appetite, on the second and third days, of the rats pre-treated with IMB and IMB-SAC may have been due to compensation for their decreased intake while being conditioned on amino acid-imbalanced diets 27. They conclude that animals conditioned on amino-acid imbalanced diets will not choose a proper diet over a protein-deficient one until after they have actually experienced its benefits28.
Taken together, these studies demonstrate that anorexia in laboratory animals can be manipulated with drugs, diet, and/or surgery. Although the biological mechanisms underlying these phenomena are not fully understood29, this research may some day benefit humans.
Scripps Howard cites a series of Roper Polls over the last 10 years indicating that approximately one percent of Americans are vegetarians. The data distinguish between those who occasionally eat chicken or fish (5-10 percent), and purists who eschew all animal products (e.g., eggs and milk).
The article strongly suggests that anyone embarking upon a vegetarian diet get competent nutritional counseling. According to research cited by Scripps Howard, most people in the U.S. get 70 percent of their calcium from dairy products. Physicians, according to the article, are particularly concerned that girls who avoid dairy products can develop calcium deficiencies.
Calcium is a mineral essential to developing and maintaining healthy bones. Older women are particularly vulnerable to calcium deficiencies, which are associated with osteoporosis and arthritis.
An additional concern cited in the article is that people who eat no meat run the risk of developing protein and iron deficiencies. Vegetarian sources of iron, according to Scripps Howard, include apricots, bran flakes, and spinach.