Fast foods, cookies and ice cream, sodas and energy drinks -- Americans eat a lot of processed foods high in fats and simple sugars. Not surprisingly, this type of diet can lead to weight gain and is one of the main culprits in the obesity epidemic in this country. But, is there more to this story? The foods you eat serve as food for the community of microorganisms that inhabit your digestive tract. Those microbes have their own food "preferences," metabolizing different types of food molecules and releasing their byproducts, which your body may absorb. Scientists have hypothesized that a high-fat, high sugar diet actually alters the composition of the microbial community that inhabits the beginning of the large intestine, which contributes to obesity. Because of the difficulties of carrying out experiments on humans, scientists have used mice as an animal model in which to test this hypothesis.