A combination of poor nutrition, lack of (or ineffective) physical exercise, stress and sometimes genetics can cause fat to settle in the abdomen, therefore belly fat may be a major problem for you.
More fat is required of women then of men because of the pregnancy issue. Women are considered healthy with a body fat range of 20-24%, where men are considered healthy at 14-17%. Without proper body fat, your body is incapable of maintaining a pregnancy. Plus, you may simply be genetically predisposed to carrying more fat in your belly, then say, your best friend. Everyone is built differently.
Cortisol and Belly Fat
Not only does stress cause you to dive head first into a gallon of mint chocolate chip ice cream, but it also triggers your body to produce the hormone cortisol. Stressing once in a while isn't going to give you a gut, but chronic stress, and therefore high cortisol levels, has serious consequences. Cortisol triggers a desire to eat, and causes your metabolism to slow, thus burning fewer of the calories that you just took in.
Cortisol also causes visceral fat to be produced and stored. This is the fat that surrounds your organs, is deep in the abdomen and causes more health problems. Needless to say, getting control of your stress could be the key to getting started as you fight belly fat.
It's this visceral fat that is directly related to heart disease and diabetes, among other major health risks. Unfortunately, it builds over decades and is also the hardest to work off.
Work it Off
You have probably done thousands of crunches as you try to eliminate the fat on your belly. While crunches do make your abdominal muscles stronger, they do not help you burn fat in your abs. A total body regimen is necessary to burn fat all over your body, because unfortunately, fat can't just be evicted from that one stubborn place. Here are the components of a complete workout regimen:
Intervals: The quickest way to burn body fat is to work intervals into your cardio routine. Long, slow cardio sessions rarely give the results that you are hoping for. Whether you run, swim or bike you must add intervals that push you to your limit. For 2 or 3 of your sweat sessions, complete intervals in a 2:1 ratio. In other words, complete 2 minutes of "active rest", a slow jog, lower speed, minimal resistance -- the speed that you could handle for a long stretch. Complete 1 minute of a high enough interval that you are pushed to your max. Then it's back to the rest period. Stick with the ratio: 1 minute active rest, and a 30 second sprint, etc.
Strength Training: Total body toning, either with body weight exercises, machines or dumbbells will strengthen muscles. The more lean muscle mass you hold, the more calories you burn just sitting around.
Nutrition: Do your best to cut some calories from your diet -- even just 200 a day, and be sure that the fats that you consume are healthy fats from lean meats, nuts, and low-fat dairy. Eliminate unhealthy fats like butter, fried foods, mayonnaise and full-fat cheeses.