Trans-fats are the worst culprits, suggests a new study.

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.

Granholm presented the results of the study, which showed that trans-fats adversely affected rats’ learning ability, at the Society for Neuroscience meeting in San Diego, US, on Monday.

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.

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.