People often blame their weight on a slow metabolism, but how many of us really know what it means or what it does?

Metabolism is the process by which our body converts what we eat and drink into energy. The number of calories that our body uses to carry out its basic functions such as breathing, growing and repairing cells is the basal metabolic rate. This is what is known as a person’s metabolism.

Several factors come together to dictate our basal metabolic rate:

Body size and composition

Larger people or those with more muscle burn more calories, even when resting;

Gender

Men usually have less body fat and more muscle than women of the same age and weight and will burn more calories as a result;

Age 

The amount of muscle we have tends to decrease as we age. If we carry more fat our bodies will burn less calories.

Energy needs for our body's basic functions are fairly consistent and this is not easily changed. This basal metabolic rate accounts for about 60/75 percent of the calories we burn each day.

There are two other factors that firmly decide how many calories our bodies burn each day:

Processing the food we eat

Digesting, absorbing and storing the food we eat also takes calories. This accounts for around 10 percent of the calories used each day;

Physical activity and exercise

Accounts for the rest of the calories our body burns up each day. This is by far the most variable of the factors that determines how many calories we burn each day.

Whilst it may be tempting to blame any weight-gain on our metabolism, in reality because metabolism is a natural process, our bodies generally balance it to meet our individual needs. That's why if we try starvation diets, our body compensates by slowing down these bodily processes and conserving calories for survival.

Unfortunately, the simple truth is that we gain weight as a result of eating more calories than we burn. To lose weight we need to burn more calories than we take in. This can be achieved by eating less, or increasing the number of calories we burn through exercise, or by doing both.

While we don't have much control over the speed of our metabolism, we can control how many calories we burn through our level of physical activity. Of course it stands to reason that the more active we are, the more calories we burn.

We burn more calories by:

• Regular aerobic exercise such as walking, going on bike rides and swimming;

• Strength training exercises such as weight lifting; help counteract muscle loss associated with ageing. As muscle tissue burns more calories than fat tissue, muscle mass is a key factor in weight loss;

• Our lifestyle help burn calories. Activities such as gardening, washing the car and housework burn calories and also contribute to weight loss.

There is no magic way to lose weight. It basically comes down to a direct relationship between physical activity and the amount of calories we consume. When we take in fewer calories than we burn, we will lose weight.