Belly fat is the accumulation of abdominal fat that results in an increased waist size. Many people have a problem with too much belly fat, and a variety of factors can cause you to get a bigger midsection. People often put on more belly fat when we become middle-aged, after pregnancy, or when they eat or drink too much. They don't call it a beer belly for nothing. But no matter what the cause, a bulging belly is something we all want to eliminate. One of the most common causes of belly fat is simply eating too much and moving too little.