A study has found that the “hydrogenated”, or processed, fats used to cut manufacturing costs of foods such as biscuits and cakes can alter body shape, leading to potbellies.

People who eat a lot of pastry and ready meals containing hydrogenated fats are likely to put on weight more quickly around the stomach — an area where even small deposits can accelerate ill health — than if they consume naturally occurring fats.

Previous studies have shown that hydrogenated vegetable fats can contribute to heart disease, narrowing of blood vessels and diabetes.

“If you put fat around your middle, it means more pressure on the heart and this can increase the risk of diabetes and chronic diseases. If this is what they are finding, it is very negative in terms of public health,” said Rebecca Foster, a nutrition scientist at the British Nutrition Foundation.

The research was carried out on monkeys over a six-year period by scientists at the Wake Forest University school of medicine in North Carolina.

Half of the monkeys were fed a western-style diet containing 35 calories of hydrogenated fat and the other half were given the same calorific intake of monosaturated fats.

After six years, the animals fed the hydrogenated fat diet had a 7.2% increase in body weight, compared with a 1.8% increase for those that had eaten food with monosaturated fats.

“Measuring the volume of fat using computer tomography [body scans], they deposited 30% more fat in their abdomen,” said Dr Kylie Kavanagh, author of the report, who will present her findings this week at the 66th annual scientific sessions of the American Diabetes Association.

“In equivalent diets, trans-fatty acid (hydrogenated fat) consumption increases weight gain,” said Kavanagh, adding that the six-year study of monkeys was equivalent to 20 years in humans.

Hydrogenated fat is made by heating natural fats such as soya or palm oil to 250C, then bubbling hydrogen through them. This turns the oil into a dense, waxy solid that binds food and prolongs shelf life.

Tom Sanders, professor of nutrition and dietetics at King’s College London, said: “They are easier to eat because they make food taste better.”

After previous studies highlighted the dangers of hydrogenated fat, supermarkets in Britain began to withdraw products containing it. But the substance is still present in many popular processed foods.

Elmlea Double, a popular substitute for dairy cream, contains 26% hydrogenated vegetable oil while Cookeen, widely used in pastry making, also declares that it contains the product. Hydrogenated fats are listed on the labels of many popular baked products, including Cadbury’s chocolate cake bars, Mr Kipling’s Bakewell tarts and Bramley apple pies. Pizza Express also states that its dough ball and dip retail packs contain the product.

There is no obligation for labels to show hydrogenated fat content. The Food Standards Agency recommends a daily limit of 5 grams of hydrogenated fat per day.

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