People who are overweight or prone to gaining weight easily sometimes blame a slow metabolism for their bodies not expending calories quickly. But before pointing the finger at your metabolism, you should understand exactly what it is, what affects it and how you can raise it.

When most people talk about metabolism, they are referring to the rate at which their bodies burns energy, which is provided in the form of calories by food they eat. The two main types of metabolism are basal metabolic rate and resting metabolic rate.

Basal metabolic rate (BMR): Your body needs energy simply to exist. Every time your heart beats or you take a breath, you burn calories. BMR is the minimum level of energy required to sustain your body's vital functions, such as breathing and brain activity, while awake, and does not account for physical activity.

The number of calories required for basal metabolism varies with sex, age, body size, lean body mass (muscle) and hormones. Because of the increased activity of cells undergoing division, younger folks have a higher (faster) metabolic rate than older people. In addition, as a result of a greater percentage of muscle tissue in the male body, men generally have a 10-15 percent faster BMR than women.

Resting metabolic rate (RMR): This is similar to BMR but refers to the rate at which you burn energy or calories at rest. Resting metabolism makes up about 50 to 75 percent of your caloric expenditure each day and is proportional to your body size and surface area, so taller, heavier individuals have a higher RMR than shorter, lighter people. In addition, people with more muscle have higher RMRs because muscle processes more calories than fat.

The Influence of Physical Activity

Physical activity, such as exercise, also has a great effect on your overall metabolic rate, boosting it both during the workout and afterward. Research proves that during vigorous exercise, metabolic rates can increase as much as 10 times the resting value. Physical activity can account for between 15 percent and 30 percent of your daily caloric burn, depending on the intensity and duration of the activity.

Other Considerations

Even your digestive process burns calories and increases metabolism. So just eating and processing food accounts for about 10 percent of your overall caloric expenditure.

Climate also can play a role in determining your metabolism, as studies show that the RMR of people in tropical climates or very cold environments is generally five percent to 20 percent higher than those in more temperate locations. With these temperature extremes, the body has to work harder simply to maintain its core temperature.

Increasing Your Metabolism

The reality is that RMR accounts for the majority of your caloric expenditure, and several things out of your control, such as genetics, sex, hormones and age, determine it.

The good news, however, is that you can increase your metabolism through exercise. The combination of regular cardiovascular activity and strength training will result in a body with more muscle and less fat, which produces a higher metabolism because even at rest, your muscles actively use more calories than fat tissue does. As a result, your metabolism speeds up to provide your muscles with energy. The more muscle you have the higher your metabolism will be. Therefore, the best thing to do to raise your metabolism is to get and stay active.