Q & A: A Role for Bacteria in Eating Disorders?

Q. I’ve been reading about the potential role that gut bacteria might play in obesity, and I wonder if there’s any indication that they might be important in eating disorders as well. (B.B., New York City)

A. You’re absolutely correct about a surge of new studies regarding the potential role of the gut’s microbial biome (as it’s called) in many aspects of health and disease, and in obesity research in particular (link). For easy-to-read introductions to this area, you might also want to read “Bacterial Ecosystems Divide People Into 3 Groups, Scientists Say,” in the April 20, 2011 issue of The New York Times, and “Germs Are Us” in the October 22, 2012 issue of The New Yorker magazine.

Studies suggest that at least some obese individuals harbor different microbial colonies than do thin individuals, and that these differences might contribute to the maintenance of obesity. In recent research, when mice whose intestines were sterilized of microbes were transplanted with the biota of obese vs. thin individuals and fed standard-issue mouse chow (high-fiber, vegetarian feed), those mice receiving microbes from obese individuals gained more weight than those receiving microbes from thin individuals. However, these differences are strongly influenced by differences in diet–when the mice had access to fattening foods they gained weight – fatty foods trumped differences in gut microbes. Nevertheless, the results of these experiments suggest that differences in microbial gut colonies not only result from obesity, but that differences in microbial colony composition might also contribute to maintaining obesity. The exciting possibility exists -still unproven and in need of further experiments- that manipulating human gut microbe colonies, for example, by administering carefully designed probiotics, might help some obese individuals lose weight–as long as they can stay away from high-fat diets (Science 341, 1241214 (2013).

When it comes to eating disorders per se, there’s no evidence that differences in gut microbe colonies might contribute to causing these conditions. However, it’s entirely possible that starvation might alter gut microbe colonies. For example, a recent study found 11 new, never-before-reported species of bacteria in stool samples from patients with anorexia nervosa (Eur J Clin Microbiol Infect Dis DOI 10.1007/s10096-013-1900-2).

Another interesting question is whether manipulating gut microbes might actually help patients with anorexia nervosa regain weight. Of course, yogurt-containing foods, particularly the low-fat or nonfat varieties, are wonderfully healthy, often contain active probiotic elements, i.e., assortments of microbes that are good for you, and are highly recommended to be included in patients’ diets. (One caveat is that while yogurt can be a nutritious food choice, yogurt-containing foods also include a lot of high-calorie and high-fat bars and candies.)

One intriguing small study found that patients with anorexia nervosa treated with yogurts sustained better immune-system marker improvements compared to patients receiving non-fermented milk. Patients receiving the yogurt achieved higher ratios of CD4a to CD8b cells in blood and increased production of IFN-g by PHA-stimulated peripheral blood mononuclear cells (Eur J Clin Nutr [2002, 56 Suppl 4:S27-33]). However, this finding is still far from demonstrating that yogurts might be engineered to contain bacteria more beneficial than those in already available commercial yogurts for nutritional rehabilitation and weight gain in eating disorder patients. No controlled trials have tested this idea, and to my knowledge at this point yogurts are not yet being marketed at your local supermarket or health food store that claim better results for weight gain–but there’s always tomorrow.

—J.Y.