Every January, fat's in the crosshairs of health columnists, fitness magazines, and desperate Americans. This year, PopSci looks at the macronutrient beyond its most negative associations. What's fat good for? How do we get it to go where we want it to? Where does it wander when it's lost? This, my friends, is Fat Month.

Troublesome tummies.

Belly flab has long been used to body-shame people into joining various weight loss programs. In recent years, though, a real reason to shed inches off your waist has emerged: to stay healthy. Research suggests that a wide waist increases risk for cardiovascular disease, diabetes, and cancer. Even if you're otherwise at a healthy weight for your height, excess abdominal fat significantly raises your likelihood of developing all of those diseases.

This seems to relate to where our bodies regulate weight. We think of our metabolism as a whole-body phenomenon, but the reality is that particular organs determine whether we gain or lose weight. If body fat is concentrated in areas that influence those organs, it can be much worse for your overall health.

Fat is not created equal

There are two kinds of fat in this world, and none of them are "skinny fat." One is subcutaneous, the layer of fat cells under your skin but not quite inside your body cavity. This fat is pretty healthy—we all have some, and we all need it. Your body uses fat to store fuel. The other, more dangerous kind, is visceral fat. These are fat cells accumulated inside the body, in and around your organs.

Belly flab tends to be of the visceral variety, especially in men. Women generally gain weight around the butt and hips, because it seems to be evolutionarily advantageous to have this extra layer around the baby-making area. Unfortunately, there's no advantage to a potbelly if you don't plan on carrying a baby.