A high-fat diet appears to make you dumber, but exercise makes you smarter. At least if you're a rat.
That's what researchers at the University of Minnesota and the VA Medical Center found, according to studies presented in October in New Orleans at the annual meeting of the Society for Neuroscience.
In one experiment, researchers housed 30 rats in containers that had two compartments, which the rat could freely go between. Ten of the rats were allowed to use a running wheel whenever they wanted. Ten were put on a treadmill for 45 minutes a day, five days a week. And 10 rats were sedentary.
The rats were trained with 30 trials in which a light went on and a tone sounded that would be followed five seconds later by a mild shock to the rat's feet. The shock lasted five seconds. But the rats could escape the shock by crossing over to the other compartment.
The result: After five weeks of exercise, the rats on the running wheels or the treadmills were more likely to figure out that they could escape the shock by running over to the other compartment. And they were more likely and quicker to get to the safe side before the shock began.
The sedentary rats were more likely to just to sit there and endure the shock.
Another finding: The farther members of the exercising rat team ran, the better they were at avoiding the shocks. One particularly high-performing rat voluntarily clocked nearly 40 kilometers, or close to 25 miles, on the running wheel during
"Rats, they love running wheels," said Vijayakumar Mavanji, a researcher with the VA and the U of M Department of Food Science and Nutrition. The research team also included ChuanFeng Wang, Catherine Kotz and Charles Billington.
Another experiment by the group tested the effect of a high-fat diet on 17 rats. For four months, 10 rats were fed a normal diet and seven were fed a high-fat diet -- food containing 45 percent saturated fats.
Then about half the rats in each group were given access to a running wheel, while half were allowed to remain sedentary. For the next seven weeks they were given the foot-shock test.
The result: The rats on the high-fat diets did worse than the others in avoiding the foot shocks.
But after hitting the running wheel for seven weeks, the high-fat rats wised up and did about as well as those on a standard diet in figuring out how to avoid the shocks.
According to Mavanji, high-fat diets may impair memory formation and retention, by leading to fatty acids getting into a part of the brain called the hippocampus.
But for the rats, exercise appears to reverse that cognitive decline.
Maybe the exercise increases the size of the hippocampus, as studies on humans have shown. Or maybe the rat workouts are leading to biochemical changes in the brain or the formation of new neurons or synapses that offset the impact of the fatty diet.
Mavanji said the data are still preliminary. He said researchers still need to find out if it's actually the exercise that helps the rats' brains or if it's a byproduct of the treadmill workouts, like lower body weight or the lower food consumption that was seen in the running rats.
Humans shouldn't see the findings as permission to eat fatty foods thinking they can offset any effect on their brains by exercising, Mavanji said.
"We won't suggest anyone should eat high-fat food," he said.
Richard Chin can be reached at 651-228-5560. Follow him at twitter.com/RRChin.