Kainic acid

High-fat diets may do more than wreak havoc on your waistline. Research has found that a diet loaded with empty calories may affect an individual's memory as well. Reducing the amount of dietary fat may improve memory and help reduce the negative effects of stress and aging on thinking and learning, recent studies suggest. Other work indicates that diets high in fats and carbohydrates could worsen cognitive losses due to sleep apnea in those prone to the condition.

Nearly two-thirds of adults in the U.S. are overweight, and 30.5% are obese, according to data from a National Health and Nutrition Examination Survey. "We are in the midst of an obesity epidemic in the United States," says Barry Levin of the Veterans Administration Medical Center in East Orange, N.J. "These new studies show that diets high in fat are a risk factor for not only heart disease, hypertension, and diabetes, but for cognitive decline as well."

Veerendra Halagappa and Mark Mattson of the National Institute on Aging, Washington, D.C., studied how a diet high in fat and sugar affected learning and memory in mice. Young adult male mice were divided into four groups by diet: normal (control); high-saturated-fat; high-sugar; and high-saturated-fat and -sugar. After four months, mice on the high-fat or the diet high in both fats and sugar had gained significantly more weight than those on the control and high-sugar diets.

To test their learning and memory, the mice completed a maze task. Halagappa found that the mice on the high-fat and high-fat, high-sugar diets could not learn and remember the maze as well as the others. "These results provide direct evidence that fast food diets, particularly a diet high in saturated fats, can have an adverse effect on learning and memory," he indicates.

Halagappa and Mattson took the work a step further by designing an experiment in which mice that had been on the four different diets were exposed to a neurotoxin called kainic acid, which is known to damage nerve cells in the hippocampus, a brain region involved in learning and memory. When mice on the control diet or the high-sugar diet were exposed to kainic acid, their learning and memory were somewhat impaired. In contrast, the memory of mice on the high-fat and high-fat, high-sugar diets severely was impaired by the neurotoxin.

"These findings show that fast food diets impaired memory acquisition in mice and made their brains more vulnerable to kainate-induced cognitive dysfunction," asserts Halagappa. "If such diets have similar effects in humans, then reducing the amount of fat and empty calories may improve one's memory and increase resistance to age- and stress-related cognitive impairment."

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