One of the most common beliefs about why people don't lose fat is that they don't have the metabolism for it. That is, they think there is something wrong with their metabolism, preventing them from losing fat like other people do. This is a grave mistake.
While you may not have the same genetic and metabolic gifts that the world's greatest athletes and models have, very few people have metabolic conditions that would prevent them from having a healthy body fat level. Some people can stay lean without any effort, while others have to work at it, but very few of us are doomed to fatness by our metabolisms.
That said, your baseline metabolism does tend to slow as you get older. This results in reduced energy and calorie needs, making it harder to keep active and keep the belly fat off. Our sedentary lifestyles contribute to this mess too.
You were almost surely more active when you were young than you are now. That means you almost surely burned more calories through activity each day when you were young than you do now. Combine a slowing baseline metabolism with less activity and you've got a formula for a big gut. To get rid of that gut, you need to rev up your metabolism and give it a reason to burn up some of that fat.
Cardio workouts are the most common way people try to rev up their metabolism. And they work to some extent, burning additional calories and using up fat as long as you stay on that machine or keep pounding the pavement. But step off the machine or stop striding along at speed and your metabolism quickly slows down again. You could try to keep your metabolism high by doing cardio longer, but at some point you either need to get on with the rest of your life, develop a repetitive stress injury, or bore yourself to tears. Fortunately, there's a better way.
In recent years, many researchers have concluded that cardio workouts are not the best way to rev up your metabolism. Studies show that high-intensity, highly-variable exercise works better and faster for strengthening your body, protecting your heart, and revving up your metabolism. These kinds of exercises more realistically simulate the kind of activities our bodies were designed for.
Our ancestors didn't jog for hours. No mammals do that. Instead, our ancestors lives were filled with short bursts of strenuous activity (like catching dinner) mixed with periods of rest. Their heart rates went way up then way down. Our bodies are made for that kind of activity and respond well to it.
These kinds of activities have an additional advantage when it comes to boosting your metabolism. When you engage in high-intensity activities like sprinting or lifting heavy weights, your metabolism speeds up. Your muscles also get damaged a bit. This is healthy and normal and not a problem as long as your body gets rest between intense periods.
Because your muscles get damaged by high-intensity workouts, your body needs to do repairs when you are resting. That requires energy, which boosts your metabolism. Studies have shown that your metabolic rate will be higher for as much as a day or two after a hard workout. Doing these kinds of workouts helps you burn the fat right off your belly, even when you aren't in the gym or at the track.
Many of the newer workout programs include this kind of exercise, usually called high-intensity interval training, or HIIT. If you're serious about burning fat, I strongly suggest that you look for a program that includes this kind of training in addition to, or in place of, traditional cardio workouts.