Can You Get Lean with a Skinny Person’s Gut Bacteria?

In early 2013, a study showed that transplantation of fecal matter from a healthy individual into the intestine of a patient with insulin resistance (risk factor for developing diabetes), the insulin sensitivity of the patient significantly increases within 6 weeks. The mechanism for this observation, however, is unclear. Last week, in an elegant study that was published in one of the most prestigious scientific journals, Science, a group of scientists extended the findings above. Can gut bacteria determine body shape and composition?

• Over 1500 female twins between ages 21–32 were surveyed and 4 pairs of twins were selected. Twins were specifically selected so that genetic differences could be ruled out as a possible contributing factor.
• Although twins, these 4 pairs of twins were very different indeed: One was obese (BMI > 30) and the other was lean.
• Fecal matter from each twin was acquired.
• To deliver the gut bacteria from each twin to animal models, normal, healthy mice were fed with fecal matter.
• The animals’ food pellet was low in fat and high in plant polysaccharides (i.e. sugars)
• Within 35 days, animals that received fecal matter from the obese twin, had higher percentage of body fat and those that received fecal matter from the lean twin had not changed.
• As well, mice receiving the obese fecal matter were now expressing genes related to stress response while those receiving the lean fecal matter were expressing genes related to sugar breakdown.
• In a second study, animals receiving the obese fecal matter and those receiving the lean fecal matter were placed in the same cage to co-habitate. Scientists investigated whether co-habitation would result in transmission of the gut bacteria from one animal to another. Interestingly, body fat percentage in mice that had previously received the obese fecal matter decreased and the body fat percentage in mice receiving the lean fecal matter did not change! The reason for this seemingly “one-way” transmission, however, was not fully addressed.

In conclusion, it appears that the gut bacteria in lean versus obese individuals may be a contributing factor to differences in body composition. This study provides potential for future therapies using the fecal transplants for possible treatment of obesity.