Metabolism is the rate at which your body uses energy, or, burns calories. Your resting metabolism measures the number of calories required to keep your body functioning.

Energy metabolism is the body's process of breaking down nutrients and converting them to energy.

While everyone's metabolism works the same way, the rate at which it metabolizes nutrients is unique to every individual.

What is My Metabolic Rate?
Basal metabolic rate (BMR) is the rate at which your body burns calories while at rest.

To get a general idea of your BMR, multiply your weight by 10. For example, if you weigh 150 pounds, your BMR is 1,500. The actual formula looks like:

BMR = 150 x 10 kcal/lb = 1,500 kcals

This formula allows 10 kcals (commonly referred to as calories) for every pound of body weight.

This means that your metabolism can "use up" around 1,500 calories a day. If you take in more than that, you will gain weight.

But remember, this is a rough estimate and doesn't take into account other contributing factors that may influence your metabolic rate like how much you exercise.

If you're interested in a truer estimate, a qualified trainer or a registered dietitian can actually take a measurement on a device similar to a calculator that will estimate the number of calories your body burns per minute.

How Metabolism Affects Your Weight
Someone with a high metabolic rate is able to burn calories more efficiently than someone with a slower metabolic rate. Assuming these two people eat roughly the same amount of calories, the individual with a faster metabolic rate "burns up" more of the calories she eats; the person who has the slower metabolism doesn't burn all the calories taken in, so the extra calories are "saved" and then converted to fat.

Since many factors can affect your metabolism (e.g. age, your condition of health), it can actually slow down without you making any lifestyle changes. The good news is, aerobic exercise is an ideal way to increase your metabolism and combat resulting weight gain.

Aging in particular has a noticeable impact on your metabolism, due to changes in hormone balance. That doesn't mean aging makes weight gain inevitable. A 2001 study by the USDA Agricultural Research Service showed that older people can significantly improve their metabolism and fend of weight gain by participating in strength training (using weights or other resistance) exercise.

The reason both exercise and strength training can improve your metabolism? Muscle burns calories more efficiently than fat; the more muscle you have in relation to your body fat, the higher your metabolism will be.