A Moment on the Lips, a Lifetime on the Hips
New research shows that annoying adage might actually be right. According to a study published by the journal Science Translational Medicine, junk food not only packs extra calories into your diet, it can also change the balance of bacteria in your gut. And this new bacteria population actually makes future weight gain easier and weight loss harder.

A shift in bacteria—which can occur in as little as 24 hours—can alter how your body will digest food, break down nutrients and store fat.

For the study at the Center of Genome Sciences at Washington University School of Medicine, mice who were given the junk food–friendly stomach bacteria gained weight, even if they were placed on low-fat diets. Researchers even found evidence that the mice passed on this bacteria to their offspring.