There are a lot of factors that go into determining an animals weight and metabolism. However, due to the growing obesity rate in (mostly) first world countries the cause(s) of obesity are of particular interest. Scientists are discovering that it may not be simply a matter of calorie count, and that the effects of obesity are multifaceted. A key component lies in the environment of the gut, particularly the gut’s microbes. A recent study on rats (the link to this very interesting article is below) found that certain microbes can send information via the vagus nerve that result in weight gain. Pretty interesting that these small microbes play such a vital role.