While this guy's subcutaneous belly fat is obvious, it's likely that he's storing visceral fat, too.

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If you think that belly fat is just an issue for people who are overweight, think again -- even people who are at a healthy weight and exercise regularly can have it. There's no such thing as a "perfect" body, so what's the big deal if your stomach isn't flat? It isn't just a problem of aesthetics.

There are two types of fat: visceral and subcutaneous. Visceral fat is the kind that lies far below the surface, surrounding your organs. Subcutaneous fat is just below the skin and can be easily grabbed. You can spot visceral fat via an MRI or CT scan, but there's a simple test for it at home: If you have a large waistline or you're apple-shaped, you likely have visceral belly fat.

While neither type of fat is good, visceral belly fat carries some serious health risks. According to the U.S. Department of Health and Human Services, you're at risk if you have a waistline greater than 40 inches if you're a man and 35 inches if you're a woman (a lower threshold of 35 inches for men and 31 inches for women has been recommended by the World Health Organization for people of Asian ethnicity). We aren't entirely sure why, but belly fat is linked to increased insulin resistance, which can result in type II diabetes. It can also lead to heart disease, stroke, some types of cancer, sleep apnea and premature bone density loss, and there's even evidence that it may be a factor in developing dementia.

So what causes belly fat? Heredity is one factor. Belly fat has often been called "middle-aged spread" because as you age and your metabolism slows down, extra pounds tend to accumulate across the stomach. This is probably due to changes in levels of hormones such as cortisol, which is made in the adrenal glands and helps the body process glucose, regulate metabolism and manage stress. Speaking of stress, it can raise levels of cortisol, so it might lead to increased belly fat, too.

While it can be tough to do, there are ways to get rid of belly fat -- and not just plastic surgery -- but there's no magic pill. Read on for tips.