Abdominal obesity comes from high blood insulin levels. To prevent blood sugar levels from rising too high after you eat, your pancreas releases insulin, which converts blood sugar to a type of fat called triglyceride. Insulin drives triglycerides into the fat cells in your belly. So having high triglycerides and a fat belly are signs of high blood insulin levels, and high blood levels of insulin constrict arteries to cause heart attacks. Insulin also acts on the brain to make you eat more and on your liver to manufacture more fat, and on the fat cells in your belly to store that fat.
The liver removes insulin from the bloodstream, but insulin causes fat to be deposited in the liver which prevents the liver from removing insulin from the bloodstream. People with fat bellies store too much fat in their livers, which prevents the livers from removing insulin, so insulin levels rise higher and higher to cause heart attacks, more abdominal obesity and eventually diabetes. If you store fat primarily in your belly, you should restrict refined carbohydrates: foods made with flour, white rice, milled corn or added sugars. See Treatment of Insulin Resistance
Fat cells in your belly are different from those on your hips. The blood that flows from belly fat goes directly to your liver, whereas the blood that flows from your hips goes into your general circulation. The livers of those who store fat in their bellies are blocked from removing insulin by the extra fat and therefore do not remove insulin from the bloodstream as effectively as the livers of people who store fat primarily in their hips. People who store fat primarily in their bellies have higher blood insulin and sugar levels, which raise levels of the bad LDL cholesterol that causes heart attacks, and lower levels of the good HDL cholesterol that prevents heart attacks.
Sit-ups are fine for strengthening your belly muscles, but don’t believe they will get rid of a fat stomach. Exercising a muscle does not get rid of fat over the specific muscles that are exercised. If it did, tennis players would have less fat in their tennis arms, but they don’t. The only way to reduce a fat belly is to lose weight overall, and any type of exercise will help you to lose weight.