We already know that eating fatty food is bad for our physical health, but a new study shows it may have some negative consequences for our mental health, too. It may even alter our behavior. The study, published in the journal Biological Psychiatry, suggests that the way a high-fat diet changes our gut bacteria may actually have an effect on our brains, increasing the risk of depression, among other mental health problems. A healthy balance of gut bacteria (also called your microbiome), is essential for physiological functioning. Some research has shown changes in the microbiome may not only lead to digestion problems and weight issues, but it may also affect our brain.