An apple a day is far better than a baked potato if you want to reduce your risk of a heart attack, important research has found.

Scientists have discovered that there are good and bad carbohydrates. The bad, in foods such as glucose, instant rice and white bread, decrease levels of HDL (high density lipoprotein) cholesterol that safeguards against cardiovascular disease.

The discovery adds another twist to the already complicated dietary guidelines to avoid a heart attack, now the single biggest killer in the West.

The role of carbohydrates has become more important since people began adopting a low fat diet in order to reduce their cholesterol levels. While people have been eating more carbohydrates to compensate, everyone had assumed that all carbohydrates were equal.

But researchers at Hammersmith Hospital have found that some carbohydrates have lower glycaemic levels than others and those with high glycaemic levels reduce HDL-cholesterol. So, people who follow a low fat diet and compensate by eating white rice or baked potatoes, for instance, could be doing double the damage to their HDL-cholesterol levels paradoxically increasing their risk of a heart attack.

The bad carbohydrates, in order from the highest glycaemic level, are: glucose, instant rice, baked potato, white bread, wholemeal bread and sugar.

The good carbohydrates include red beans, milk and apples (Lancet, 1999; 353: 1045-8).