How to avoid obesity

American researchers say most people struggling to lose weight don't realise how many calories they need to burn, which is why their efforts fail.

Experts say the key to weight control is balancing energy in (food) with energy out (physical activity). Knowing how many calories your body needs helps prevent obesity from eating more than you need.

Exercise plays an important part: it doesn't only raise your metabolism during exercise, but keeps it raised for a while afterwards, burning more calories. How much exercise you need varies with your weight, how much you eat, and what kind and amount of exercise you can do.

Aerobic exercise, such as swimming, running and cycling, makes the heart and lungs work harder to supply oxygen and gets the circulation moving.

About 3,500 calories equal a pound (about 450 g) of body fat. A 30-minute walk burns roughly 150 calories for an average person. And eating just 100 calories a day more than your body needs adds about 5 kg a year.

So 30 minutes of gentle exercise a day, together with a balance between food and exercise, is an easy, comfortable way to keep your weight under control.