A series of animal studies helps clarify the effects of high-fat diets and obesity on learning and memory.
First up: the “typical” American fast-food diet. M.H. Veerendra Kumar and colleagues at the National Institute on Aging found that mice fed a diet high in fat, or high in fat and sugar, had impaired memory acquisition and were more vulnerable to stress-induced cognitive dysfunction. If such diets have similar effects on humans, the authors say, then reducing the amount of fat and “empty calories” may improve memory and increase resistance to age-and stress-related cognitive impairment.
Separately, John Morley and colleagues at St. Louis University found that obese mice that were fed a high-fat diet (10 percent fat) for seven months had impaired performance on two learning and memory tasks. In work by David Gozal of Kosair Children’s Hospital Research Institute in Louisville, Ky., memory deficits were seen in rats fed a diet high in fat and refined carbohydrates, in comparison to rats that ate less fat and more complex carbohydrates. Cognitive function was impaired even further in rats that were exposed to intermittent hypoxia, a model for sleep apnea. The combination of “bad high fat, high sugar, and sleep apnea together are a major disaster for the brain,” Gozal says.
In another study, Ann-Charlotte Granholm of the University of South Carolina investigated the effects of trans-fat, which she called “the Trojan Horse fat” because it is not listed explicitly on food labels (subtracting unsaturated and saturated fat content from total fat tells you how much trans-fat is in a product). Her group found that rats fed a diet that included 10 percent hydrogenated coconut oil, but which were not overweight, made significantly more mistakes on a working memory task. Errors increased as the task became more difficult. The findings have important implications to school-age children eating diets high in trans-fat, she says.