Metabolism

Metabolism explained: what is it and how it works

Nowadays we are often bombarded with the word ‘metabolism’. We keep hearing, reading and using the word metabolism as if it were some sort of magic word! But what is metabolism? Well, in very simple terms, metabolism is the rate at which the body burns up energy. Metabolism varies from person to person and can be slower of faster compared to a person of similar body size.

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). BMR is the rate at which the body uses up energy when at rest - e.g. when sleeping or just lying in bed.  

The more a person weighs the higher BMR will be. The metabolic rate of very heavy women is about 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.  

Average BMR

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.

 BMR: 5 important things to know 

(1)   The higher your BMR, 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 BMR 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. This means that when you eat less, your body will try to store more in order to ensure ‘survival’. Therefore, if you go on a diet, it is important that you are sensible about it and don’t suddenly restrict drastically your intake of calories.  

(3) Your BMR 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.  

(3)   Exercise is the ONLY effective way to increase your BMR
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. 

(4)     Obesity is not caused by a slow BMR