Metabolism is the rate at which your body breaks down the nutrients in food to produce energy, and a 'metabolic rate' is the energy used in a day to keep the body functioning, i.e. the heart beating and lungs breathing for example. This is sometimes called the basal or resting metabolic rate.

Results from studies consistently show that overweight people use more energy to keep their bodies working. This is because they have a larger body with bigger organs and muscles and therefore use up more oxygen.

However, slim and obese people have been shown to have similar metabolic rates, after taking into account differences in body size.

Metabolic rate can depend on the composition of the body; muscle requires more energy to function than fat, so a body high in muscle will have a faster metabolic rate. As we get older, we tend to gain fat easier and lose muscle, which is why metabolic rate tends to decrease with age.

Men tend to have a higher basal metabolic rate than women because they have a larger percentage of lean muscle tissue.

Each of us has a different level of physical activity and therefore uses varying amounts of energy throughout the day. The total amount of energy used is made up of your basal metabolic rate and your energy needs, determined by how active you are.

There is no quick-fix to speed up your metabolic rate. In the long-term, the only way to increase metabolic rate is to improve body composition. This means increasing muscle and decreasing fat, by being physically active and having good nutrition.