To my mind, the worst ads on the Internet are those cartoonish, animated ones about how to lose belly fat.

However, it turns out that belly fat is a real problem, and one of the most important indicators of whether you're susceptible to some major health issues that could easily cut years off your life.

It's not just a matter of correlation, either, where people who have lots of belly fat might also happen to have higher incidences of certain health problems. Instead, it's a matter at least partly of causation, meaning it's the excess belly fat itself that causes health issues.

Here's the danger zone. As Jane E. Brody writes in the New York Times, you want to measure your waist using a soft tape measure. (No need to cheat; you're not going to tell anyone your result unless you want to.)

If you're a man, a waist size of 40 inches is the number to be concerned about. If you're a woman, 35 inches indicates you have a problem you need to take care of.

'Visceral fat'

Obviously, there could be some variation depending on your overall height and build. And you'll note of course that these numbers don't correlate exactly to when we might think that a person has a bit of extra weight, or even a high BMI. 

But these waist sizes indicate a significant amount of "visceral fat," which gathers around your abdominal area. It turns out, it's far more dangerous than the fat you might gather around other parts of your body.

Belly fat is "essentially an endocrine organ that secretes hormones and a host of other chemicals linked to diseases that commonly afflict older adults," as Brody puts it. Also, it "has been strongly linked to a host of serious disease risks, including heart disease, cancer and dementia"--to say nothing of simple premature death, from all causes.

Among the health risks:

1. Coronary heart disease

A British study shows that women with bigger waistlines are more likely to develop coronary heart disease

2. Cancer (especially for women)

Studies in Korea and India showed women with larger waists were more likely to develop certain types of cancer. Also, a Dutch study showed women with more fat in general were more likely to get breast cancer.

3. Dementia, asthma, and diabetes

Separate California studies also showed that people "with the greatest amount of abdominal obesity in midlife were nearly three times more likely to develop dementia three decades later than those with the least abdominal fat," according to Brody.

And, another study she cites showed that great weight meant greater risk for developing asthma and diabetes.

How to lose belly fat

Okay, we understand. Belly fat is bad. So what life changes do you have to make in order to get rid of belly fat?

There's some good news and some bad news. The good news is that getting rid of belly fat is certainly possible. The bad news is that the miracle "lose belly fat" cures you might see advertised--including in those annoying website ads--simply don't work.

Instead, it's all a matter of diet and exercise. Here's a four-part plan.

1. Cut out sugar.

"Perhaps the worst offender is sugar," Brody writes, in all its forms. Cut out all soda and fruit juices to start, and avoid refined carbohydrates--white bread, white rice, basically anything that's white. Also, cut back on alcohol, "which may suppress fat-burning and add nutritionally empty calories."

2. Add protein and fiber.

This should be the easiest part, because once you start eating these things, you crave them if you skip them.

"Make sure your diet contains adequate amounts of protein and dietary fiber, including vegetables, beans and peas and whole grains," Brody writes.

3. Sleep at least seven hours.

I know, easier said than done, right? But, "in a study of 68,000 women followed for 16 years, those who slept five hours or less were a third more likely to gain 32 pounds."

4. Get more exercise, or at least just move around more.

There is study after study supporting this idea: basically, if you get a little more exercise, you'll go to work on your belly fat along with the fat all over your body.

"Obesity and abdominal obesity are associated independently with morbidity and mortality," wrote the authors of one large study in The American Journal of Medicine. "Physical activity attenuates these risks."