Two brands of low-fat margarine are unlikely to deliver the health benefits promised in advertisements, according to the Advertising Standards Authority.

Its rulings against Flora pro-activ and Benecol were made after the products' two manufacturers lodged tit-for-tat complaints about each other's promotional claims of reducing cholesterol.

But now both companies say they have amended their advertisements.

Flora's manufacturers claimed in their press adverts that it would reduce cholesterol by up to 15% within three weeks.

The makers of Benecol stated their product could achieve a 14% reduction.

But the advertising watchdog said the adverts were misleading as people would be unlikely to eat the amount of spread it would take to achieve those targets.

Lucrative market

It also said the manufacturers were not clear enough about the impact of also having a healthy diet.

The rulings will send a clear signal to others in the food industry promoting products as having an added health function.

These form part of an increasingly lucrative and competitive market.

Doctor Frankie Robinson, a nutrition scientist at the British Nutrition Foundation, says that cholesterol-reducing spreads are a fairly new weapon in the battle against heart disease.

They contain plant sterols or plant stanol ester - ingredients that occur naturally in many grains such as wheat, rye and maize. They are usually present in the diet in small amounts.

'No magic answer'

Studies have shown them to be effective at lowering cholesterol levels in the blood.

Dr Robinson said: "Therefore, these foods may be helpful for those with raised blood cholesterol levels, if the product is substituted for a standard product and eaten as part of a cholesterol-lowering diet and in conjunction with a healthy lifestyle. But they are not a magic answer."

She added that probably the most effective ways of reducing heart disease risk are to give up smoking and be more physically active.

It is also pointed out by nutritionists that cholesterol-reducing foods are more expensive than standard products, due to the high cost of obtaining plant sterol or stanol extracts.

This means they are probably out of the reach of those with the highest prevalence of heart disease - low income groups.