Trans fats could be bad for the brain...

A high-fat diet could harm the brain. And trans-fats, such as those found in margarine, and which are often used to increase the shelf-life of foods, are the worst culprits, suggests a new study.

Ann-Charlotte Granholm of the Medical University of South Carolina in Charleston, US, says she became concerned about trans-fats after seeing how they are made.

Hydrogen is bubbled through an oil, and metals such as zinc and copper are added to made it solid at room temperature. The resulting greyish fat is then bleached and coloured to make it look more appealing, she says.

Zinc and copper are known to build up in the brain of people with Alzheimer’s disease, she says, and there are signs that high fat diets could contribute to the risk of this disease. “I became concerned about what these fats were doing to our children, who are given French fries at school every day.”

Granholm compared rats on a high-fat diet of about 12% soybean oil with those on a high trans-fat diet, containing 10% hydrogenated fat and 2% cholesterol, so that any effects seen could be attributed to the type of fat, not the weight of the animals.

It is hard to compare this level directly with human diets, but this sort of proportion would be considered to give a high risk of heart disease in humans, she says.

Rats on the high trans-fat diet showed learning difficulties, she reports. When the animals were required to remember the position of hidden platforms in a water-filled maze, the animals on the trans-fat diet learned more slowly and made more errors, particularly as the task was made harder. They are about five times worse at the task, she says, than those animals on the soybean oil.

The brains of the animals also showed signs of damage in a region called the hippocampus, which is important for learning and memory. “The high trans-fat diet may cause loss of a neural protein,” she says. She also found that the brains of rats on this diet showed signs of inflammation.

This is a pilot study, stresses Granholm, and it is not clear yet whether these changes are temporary or reversible.

Barry Levin, an expert on obesity from the Veterans Affairs Medical Center in East Orange, New Jersey, adds: “We must regard these as preliminary studies.”

There may be many factors involved - insulin levels, obesity, lack of exercise - rather than the fats themselves. “And we all work on rats, so we can not necessarily extrapolate this to humans.” But he agrees that there are many reasons to be cautious about a high fat diet.

Granholm suggests preferentially eating natural foods, rather than those with additives to increase shelf life. “A longer shelf-life may make for a shorter life span for humans,” she cautions.

Current UK recommendations for trans fats are 4.4g per day for women, the same amount detected by Which? in a KFC meal. A McDonalds McNuggets and regular fries meal contains 3g, while 2.5g came in for Saxby’s short pastry, the same as for Tesco’s gluten-free toffee fudge shortbread.

Of the 30 products tested, a Sainsbury’s treacle tart bought from the bakery counter, a McVitie’s Penguin biscuit and Morrisons pork pie were bottom of the table with 0.2g of trans fat per portion.

In Europe Which? pointed out that McVities have removed trans fatty acids from biscuit dough, but they are still present in cream fillings. UK retailer Sainsbury’s has already switched to low trans-fat pastry (although 1.8g found in its puff pastry minced beef pie), and while KFC branches run directly by KFC use oil that contains trans fats, the franchised shops use non-hydrogenated vegetable oil.

For more information, the European Food Safety Authority have published a detailed report on trans fatty acids.

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