In my profession, we continually harp on the potential dangers of antibiotics use in situations where they are not needed. For example: with the common, yet extremely irritating, seasonal cold. Today I want to give you another reason to avoid antibiotics, if at all possible – your fat! A recent study demonstrated that the good bacteria present in your gut may not only help you stay thin, but may help you get leaner. Although this particular study was done in mice, the implications, based on a number of other studies, are interesting, to say the least. A set of twin mice, one fat and one lean, had their gut bacteria placed in a group of lean mice. A month later, the mice that had received the lean mouse’s gut microbes stayed lean, but the ones that got the fat mouse’s microbes got fatter, even though they ate the same diet. One potential mechanism is that it appears that mice with fattening bacteria, and obese people, have fewer and less diverse microbes in their guts, compared to lean mice and lean people. The more diverse the bacteria are the more fiber is digested, giving off short-chain fatty acids. These short-chain fatty acids cause less fat to accumulate, increase calorie burning, and increase hormones that make you feel full. Therefore, one potential player in the obesity epidemic is antibiotics. Antibiotics taken to kill problematic bacteria (or taken because last time you where sick you took them) kill the good bacteria, too, thereby lowering your microbial diversity and setting up a potential ‘fat mouse’ problem. This is something to think about. Talk to your doctor about alternatives to treatment for those irritating infections so common this time of year.