Metabolism: What you need to know

Metabolism refers to all the chemical processes going on continuously inside your body that allow life and normal functioning (maintaining normal functioning in the body is called homeostasis). These processes include those that break down nutrients from our food, and those that build and repair our body. 

Building and repairing the body requires energy that ultimately comes from your food. The amount of energy, measured in kilojoules (kJ), that your body burns at any given time is affected by your metabolism. If we eat and drink more kilojoules than we need for our metabolism and exercise, we store it mostly as fat. Most of the energy you expend each day is used to keep all the systems in your body functioning properly. This is out of your control.

Your metabolism has two parts, which are carefully regulated by the body to make sure they remain in balance. They are:

Catabolism – the breakdown of food components (such as carbohydrates, proteins and fats) into their simpler forms, which can then be used to create energy and provide the basic building blocks needed for growth and repair

Anabolism – the part of metabolism in which our body is built or repaired. Anabolism requires energy that ultimately comes from our food. When we eat more than we need for daily anabolism, the excess nutrients are typically stored in our body as fat.

Your body’s metabolic rate (or total energy expenditure) can be divided into three components, which are:

Basal metabolic rate (BMR) – is the amount of kilojoules (kJ) burned at rest. BMR includes the energy the body uses to keep all its systems functioning correctly. It accounts for the largest amount of energy expended daily (50-80 per cent of your daily energy use).

Energy used during physical activity – in a moderately active person (30–45 minutes of moderate-intensity physical activity per day), this component contributes 20 per cent of daily energy use.

Thermic effect of food – is the energy you use to eat, digest and metabolise food. It contributes about 5-10 per cent of your energy use

                                    Metabolism and age-related weight gain

Muscle tissue has a large appetite for kilojoules. The more muscle mass you have, the more kilojoules you will burn. People tend to put on fat as they age, partly because the body slowly loses muscle. It is not clear whether muscle loss is a result of the ageing process or because many people are less active as they age. However, it probably has more to do with becoming less active, as research has shown that strength and resistance training can reduce or prevent this muscle loss.

Looking at ways to speed up your metabolism? Here are a few tips:

Get active - it's a sure-fire way to increase the amount of muscle you have, which in turn will speed up your metabolism. Do a mixture of aerobic and resistance training for best results. And don't forget to be more active in your daily life too.

Eat little and often - there's evidence that eating small, regular meals throughout the day, rather than one or two large meals, may help to keep your metabolism ticking over. Surprisingly, around 10 percent of the calories we use each day go on digesting and absorbing food - so the more times you eat, the greater this effect is likely to be.

Eat plenty of protein-rich foods - research shows that around 25 percent of calories in a protein-rich meal may be burnt off. But make sure you choose low-fat protein foods such as lean meat, skinless chicken and low-fat dairy products.