Normal flora in the gut is an essential proponent to intestinal health. Variations and changes in the gut flora, ie dysbiosis, can lead to numerous conditions such as inflammatory bowel disease, irritable bowel syndrome, colon cancer, obesity, diabetes, depression, anxiety, autism, and anorexia nervosa. A number of factors can influence the intestinal microbiota such as antibiotics, probiotics, prebiotics, synbiotics, xenobiotics, alcohol, genetics, and mood.

To gain better insight into the role of intestinal flora in adiposity, Bäckhed et al. used germ-free mice and colonized their intestines with fecal material from mice nourished with a normal diet and Western diet.¹ After providing each group with the same amount of food, mice with microbiota from the Western diet developed increased adiposity compared to the normal diet.¹ This finding was replicated in fecal samples from twins discordant for obesity. Mice that were colonized with the healthy microbiota did not gain additional adipose tissue while the mice colonized with the obese microbiota gained additional adipose tissue.² These findings suggest that the increased adiposity phenotype can be transmissible via enteric microbes.

Germ-free mice have a higher stress response. In a study in which researchers colonized germ-free mice with specific pathogen-free (SPF) microbiota, Bifidobacterium infantis, or pathogenic Escherichia coli, the impact on stress was affected. The SPF and Bifidobacterium infantis cultured mice had decreased impacts on stress while the group colonized with pathogenic Escherichia coli had increased stress.³ An interesting finding was related to the age of the mouse, in that change could be instituted early in the life of SPF mice but not later.³

Anorexia nervosa (AN) is a severe psychiatric disorder characterized by extreme weight dysregulation and high rates of anxiety. It affects both men and women (in the United States, 0.3% and 0.9%, respectively). AN also has the highest mortality rate of all psychiatric illnesses and relapses are frequent. Both weight dysregulation and altered behavior, ie stress/anxiety, are dominant traits of AN but are also believed to be impacted by intestinal flora.⁴ To test the effects of nutrition, a preliminary study was undertaken in patients with AN.⁴ Fecal samples were taken from subjects who were: 1) AN patients <75% of their ideal body weight (IBW); 2) same AN patients refed over 4 weeks until they were >85% of their IBW; and 3) healthy controls.⁵ AN patients in the first and second groups (same patients) had a decrease in intestinal microbiota diversity compared to healthy controls (p <0.02) but were not statistically different from time points 1 and 2.⁵ This is an interesting finding as many diseases often have a decreased microbiota diversity. These AN patients were also asked to complete Beck Anxiety Inventory and Beck Depression Inventory questionnaires, both of which were statistically significant in correlation with microbiota diversity: the higher the depression/anxiety, the decreased the microbiota diversity.⁶

• Characterization and correlation of composition and diversity of intestinal microbiota with adiposity and stress measures.
• Functional influence of microbiota on adiposity.
• Behavioral impact of AN microbiota on mice.
• Physiologic changes in mice mirroring AN through caloric restriction.
• Effect of fecal transplant product in AN patients.

Fecal microbiota transplantation, also known as microbiome replacement therapy, may be used in clostridium difficile infection.⁷ It has been attempted in metabolic syndrome and ulcerative colitis with varying degrees of success.^8,9