In recent years, some research has suggested that a high-fat diet may be bad for the brain, at least in lab animals. Can exercise protect against such damage? That question may have particular relevance now, with the butter-and cream-laden holidays fast approaching. And it has prompted several new and important studies.

The most captivating of these, presented last month at the annual meeting of the Society for Neuroscience in New Orleans, began with scientists at the University of Minnesota teaching a group of rats to scamper from one chamber to another when they heard a musical tone, an accepted measure of the animals' ability to learn and remember.For the next four months, half of the rats ate normal chow. The others happily consumed a much greasier diet, consisting of at least 40 percent fat. Total calories were the same in both diets.After four months, the animals repeated the memory test. Those on a normal diet performed about the same as they had before; their cognitive ability was the same. The high-fat eaters, though, did much worse.Then, half of the animals in each group were given access to running wheels. Their diets didn't change. So, some of the rats on the high-fat diet were now exercising. Some were not. Ditto for the animals eating the normal diet.

For the next seven weeks, the memory test was repeated weekly in all of the groups. During that time, the performance of the rats eating a high-fat diet continued to decline so long as they didn't exercise.But those animals that were running, even if they were eating lots of fat, showed notable improvements in their ability to think and remember.After seven weeks, the animals on the high-fat diet that exercised were scoring as well on the memory test as they had at the start of the experiment.Exercise, in other words, had "reversed the high-fat diet-induced cognitive decline," the study's authors concluded.That finding echoes those of another study presented last month at the Society for Neuroscience meeting. In it, researchers at Kyoto University in Japan gathered a group of mice bred to have a predisposition to developing a rodent version of Alzheimer's disease and its profound memory loss.

Just why high-fat diets might affect the brain and how exercise undoes the damage is not yet clear. "Our research suggests that free fatty acids" from high-fat foods may actually infiltrate the brain, says Vijayakumar Mavanji, a research scientist at the Minnesota VA Medical Center at the University of Minnesota, who, with his colleagues Catherine M. Kotz, Dr. Charles J. Billington, and Dr. Chuan Feng Wang, conducted the rat study. The fatty acids may then jump-start a process that leads to cellular damage in portions of the brain that control memory and learning, he says.Exercise, on the other hand, seems to stimulate the production of specific biochemical substances in the brain that fight that process, he says.

Of course, lab animals are not people, Dr. Mavanji cautions, and it's not known if exercise might protect our brains in the same manner as it does in mice and rats.Still, he says, there's enough accumulating evidence about the potential cognitive risks of high-fat foods and the countervailing benefits from physical activity to recommend that "people exercise moderately," he says, particularly during periods of repeated exposure to alluring, fatty holiday buffets.