I have not previously discussed studies performed on mice or any other animal. With regard to diet, we simply have not found an animal model which correlates with human metabolism and eating behavior. One thing we know is that farm animals are consistently fattened up with carbohydrates but until now, I have not been inclined to tout animal studies.
With regard to gut microbes possibly contributing to obesity and diabetes, there are some very compelling studies in mice. Jeffrey Gordon of Washington University in St. Louis has performed some of the best. He and his partners raised baby mice in a sterile environment so that their intestines would be free of bacteria. He then inserted intestinal microbes from obese women into some of the mice and microbes from their lean twin sisters into others. The mice were then fed the same diet in equal amounts, yet the ones receiving bacteria from obese women gained more weight and more body fat than those with bacteria from a thin twin. When this experiment was performed with the animals moved to the same cage, they all remained lean. The mice with microbes from obese women had apparently eaten the feces of their lean roommates (a common mouse behavior) repopulating their guts with obesity preventing bacteria. One final twist was to repeat the experiment in which fat and lean microbe mice were placed in the same cage. This time they were fed “junk food” chow and the obese microbe mice once again became fat. The unhealthy food apparently caused the bad microbe population to prosper and did not allow the healthy microbes from feces to get established and thrive.
These are fascinating studies which strongly suggest a cause and effect relationship between gut microbes and obesity at least in mice. Moving beyond mice, recent clinical evidence in humans is now showing that healthy bacteria can reduce inflammation and oxidative stress which can increase insulin sensitivity and thus reduce the chance of diabetes. More next time.