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.
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