Eating fatty food appears to take an almost immediate toll on both short-term memory and exercise performance, according to new research on rats and people.
Other studies have suggested that long-term consumption of a high-fat diet is associated with weight gain, heart disease and declines in cognitive function. But the new research shows how indulging in fatty foods over the course of a few days can affect the brain and body long before the extra pounds show up.
To determine the effect of a fatty diet on memory and muscle performance, researchers studied 32 rats that were fed low-fat rat chow and trained for two months to complete a challenging maze. The maze included eight different paths that ended with a treat of sweetened condensed milk. The goal was for the rat to find each treat without doubling back into a corridor where it had already been. The maze was wiped down with alcohol, so the rat had to rely on memory rather than sense of smell.
All of the rats studied had mastered the maze, finding at least six or seven of the eight treats before making a mistake. Some rats even found all eight on the first try.
Then half the rats were switched to high-fat rat chow (comprised of 55 percent fat), while the remaining rats stayed on their regular chow (which had 7.5 percent fat). After four days, the rats eating the fatty chow began to falter on the maze test — all of them did worse than when they were on their regular chow. On average, the rats on the fatty diet found only five treats before making a mistake. The rats who stayed with their regular food continued the same high level of performance on the maze, finding six or more treats before making a mistake.
Half of the rats had also been trained to run on a treadmill. After only a few days on the high-fat diet, the rats performed 30 percent worse on the treadmill. After five days of testing, the treadmill performance of the rats eating fatty foods had declined by half. The study results appear in The Faseb Journal, which is the journal of the Federation of American Societies for Experimental Biology.
“We expected to see changes, but maybe not so dramatic and not in such a short space of time,’’ said Andrew Murray, the study’s lead author and a lecturer in physiology at Cambridge University in Britain. “It was really striking how quickly these effects happened.’’
Although the human data aren’t yet published, the researchers have also performed similar studies of high-fat diets in healthy young men who then performed exercise and cognitive tests. Dr. Murray said he is still reviewing the data, but the short-term effect of a fatty diet on humans appears to be similar to that found in the rat studies.
It’s not clear why fatty foods would cause a short-term decline in cognitive function. One theory is that a high-fat diet can trigger insulin resistance, which means the body becomes less efficient at using the glucose, or blood sugar, so important to brain function.
Fatty foods appear to have a short-term effect on exercise performance because the body reacts to high fat content in the blood by releasing certain proteins that essentially make the metabolism less efficient. “It’s thought to be a protective mechanism to get rid of excess fat,’’ Dr. Murray said. “But it was making muscles less efficient at using oxygen and fuel to make the energy needed to run.’’
The findings are particularly relevant to people who may not worry about binging on fatty foods because they exercise regularly.
“Exercise is a good way of burning it off, because you’re burning the calories off,’’ Dr. Murray said. “But in terms of actually trying to put in a good time if you’re running, it will limit your performance.’’