How Is Fat Stored & Burned as Energy in the Human Body?

If you eat more food than you need, your body will store it as fat.
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You might find yourself reaching for the fat-free and low-fat items at the grocery store in the hopes of defeating the belly flab. However, all fats are not created equal. Healthy fats are part of your daily balanced diet and a long-term source of stored fuel to keep you energized between meals. Eating more calories than you burn tips your energy balance towards weight gain and stored fat around your middle.

Fat Storage

You can blame your genes for your hour-glass, slim or bottom-heavy shape. The University of Missouri explains that the number of adipocytes, or fat cells, you have is determined early in life and is linked to the body type you inherit. Most people have developed all their fat cells by the time they are in their late teen years, but in some rare -- and unlucky -- cases, more fat cells may appear later in life. Your fat cells expand when you gain weight and shrink as you burn fat and lose weight. Where you have more fat cells is another issue. Women tend to have more fat storage around the middle, hips and thighs.

Fat for Fuel

If you've ever tried stomach crunches to slim your middle, you might have noticed that it's difficult to nudge the stored fat in one area. This is because you can't control which fat cells shrink, no matter what kind of exercise you do. The University of Missouri explains that exercises that target certain areas of your body generally do not work because they stimulate all-over fat burning, not specifically fat burning in your legs or abdomen, for example. Additionally, how much fat you burn even while at rest varies between individuals. If you are larger in size or have more muscle, you will burn more fat because your body requires more energy. Along with your bone density, your muscle mass also tends to decrease with age, slowing your body's rate of fat-burning.

Exercise Effects

The good news is that fat is one of your body's main energy sources -- and there is usually plenty of it for your body to burn. However, how efficient your body is at using up stored fat depends on your physique. A study published in the "Journal of Sports Sciences" reports that training to be in better shape boosts your muscles' capacity to use stored fat for fuel. This means that if you exercise regularly, your body will increase its fat metabolism, saving stored sugars for more long-term energy needs. The more you exercise, the better your fat cells are able to respond to hormones that tell them to release fat for energy. This explains why long-distance runners and other athletes have only 7 to 10 percent body fat, while the average person has between 15 to 20 percent body fat.

Metabolism and Weight

Your slowed metabolism may not be the best excuse for your much curvier figure. While a lower metabolic rate can lead to weight gain, notes that fat gain is usually the result of overloading on more calories than your body can burn. A slower metabolic rate is usually not responsible for less fat-burning, except in the case of an underactive thyroid gland and other illness. This is why binge dieting and depriving yourself won't work. Your body will compensate by slowing your metabolism and saving calories to survive. To successfully lose weight and keep it off, balance the amount of daily calories you eat with how much your body burns for energy for normal activities and exercise.

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