Metabolism - What is it?

In very simple terms, your metabolism is the rate at which your individual body burns up energy. Metabolism varies from person to person. You may have a faster metabolism than normal, for a person of your size, or a slower one. See also Metabolic Typing Diet

Basal Metabolic Rate (BMR)

In order to compare one person's metabolism with another's, scientists have devised a new buzz word - basal metabolic rate (BMR). Your BMR is the rate at which you use up energy when at rest - e.g. when you are sleeping or just lying in bed. You might call it your tick over speed.

• The more you weigh the higher your BMR will be. The metabolic rate of very fat women is 25% higher than that of thin women.
• BMR is much greater in childhood than in adulthood. After the age of about 20, it drops about 2 per cent, per decade.
• People whose bodies contain a higher proportion of muscle to fat, tend to have a higher BMR than those with lower muscular proportions - all other things being equal.

What is the 'average' person's Basal Metabolic Rate?

As a very rough guide, the average person's BMR is about half a calorie per pound of body weight, per hour. So, if you weigh 140 pounds you will use up approximately 70 calories an hour or 1680 calories per day doing nothing.

The 5 things you need to know about Basal Metabolic Rate

(1) The higher the Basal Metabolic Rate, the easier it is to lose weight
All other things being equal, the more energy your body needs in order to tick over, the more food you can eat without gaining weight - or conversely, the less reduction in food you need to make in order to lose weight. Thus a high BMR tends to make dieting and weight loss easier.

(2) Your Basal Metabolic Rate decreases when you go on a diet which has fewer calories than your normal diet
In response to fewer calories, the body lowers its BMR  because it thinks there is a famine. It therefore 'slows down' in order to conserve energy. Hence the 'plateau' effect during dieting.

(3) Your Basal Metabolic Rate increases in response to increased physical activity
Not only do we use up calories doing exercise but the increased BMR continues even after we have done our exercise, often for several hours. The amount of increase varies from person to person but even a  modest increase should counteract the body's tendency to decrease BMR when we cut calories.

Note: The exact reason why physical exercise leads to an increased BMR is not known. The present consensus is that exercise preserves more of our lean body tissue. Remember, the higher our proportion of lean body tissue the higher our metabolic rate will be. 

(4) Exercise is the ONLY effective way to raise your Basal Metabolic Rate
Many diets claim to increase metabolic rate through special fat-burning exercises or fat-burning foods. The truth is, your metabolic rate falls if you start dieting and start to shed excess pounds. You may be able to reduce the extent of the fall by increased exercise but there is no evidence whatsoever that your metabolic rate will be higher than it was before you dieted.

(5) Obesity is not typically caused by a slow Basal Metabolic Rate
Except in the rare cases of serious metabolic illness it is not possible to blame your metabolism for obesity. Your metabolism certainly has an effect on how much you weigh but the main reasons lie elsewhere.

For more information
See Obesity.