Flabby minds

BIN that hamburger now. Scientists in Canada say that a high-fat diet not only clogs arteries and piles on the pounds, it can also impair memory.

Gordon Winocur and Carol Greenwood of the Baycrest Centre for Geriatric Care in Toronto fed one-month-old rats a diet rich in either animal or vegetable fat until they were four months old. Forty per cent of their calories came from fat, but the diet was otherwise nutritionally complete. Control rats got standard lab chow, in which only 10 per cent of the calories come from fat.

From four months of age, the equivalent of late adolescence, the rats were trained to do a "delayed alternation task". They had to learn that every second time a lever was presented to them they would get a food pellet if they pressed it. Some rats quickly learned that pressing every time was pointless. The rodents also had to remember whether they had pressed the lever the last time it had appeared, which could be up to 80 seconds earlier-a long time for a hungry rat.

The researchers found that rats on either kind of high-fat diet performed much more poorly than the lean rats. "High-fat diets impair performance on virtually all our measures," says Winocur. "It's remarkable how impaired these animals are."

The researchers reckon that the fat prevents the brain taking up glucose, possibly by interfering with the action of insulin, which helps regulate blood sugar levels. High-fat diets often cause insulin resistance. Also, some people with signs of adult-onset diabetes, often caused by obesity, are known to have memory problems.

Many adolescent children get 40 per cent of their calories from fat, the researchers say. Winocur is concerned that developing neural pathways could be permanently damaged at that age. "And maybe the developing brain is much more susceptible than the older brain," he says.

New Scientist issue: 3rd March 2000

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