Public Release: 

Rat study shows high-fat diet impairs concentration and memory

Baycrest Centre for Geriatric Care

People on high-fat diets may not only be increasing their risk of heart disease -- but they may be damaging their brain function!

A study by researchers at Baycrest Centre for Geriatric Care and the University of Toronto compared the cognitive function of rats on a high-fat diet similar to what humans consume if they don't eat nutritionally, with rats on lower fat, laboratory chow. After three months, the rats on high-fat diet showed severe impairment on a wide range of learning and memory tasks relative to those animals that consumed the lower fat diet. The research also showed that glucose treatment significantly improved the memory of rats fed high-fat diets.

The findings are published in the March 2001 issue of Neurobiology of Learning and Memory (Vol.75, No.2).

"Our brain needs glucose -- essentially energy -- in order to function. When glucose metabolism is impeded by saturated fatty acids, it's like clogging the brain and starving it of energy," says Dr. Carol Greenwood, a professor in the Department of Nutritional Sciences at the University of Toronto and scientist at Baycrest Centre's Kunin-Lunenfeld Applied Research Unit.

Dr. Greenwood and Dr. Gordon Winocur, a senior scientist at Baycrest's Rotman Research Institute and professor of Psychology at the University of Toronto, have investigated the relationship of dietary factors and cognitive function in animals and humans in previous studies, published in major journals.

In this latest study, they investigated the hypothesis that if a high-fat diet can interfere with glucose use in the brain and impair cognitive function, then glucose injections would result in improved cognitive performance. If this were the case, they also wanted to determine if the glucose-enhanced performance was general in nature or specific to certain types of brain function.

"We found that when high-fat rats were injected with glucose, their cognitive function improved," says Dr. Winocur. "Most interesting was the fact that the glucose worked selectively on one part of the brain - the hippocampus." The hippocampus is located near the centre of the brain and is critical for normal memory function. It enables us to register new memories and recall those memories after a period of time.

In the study, young adult rats were divided into three dietary groups -- those fed high-fat foods derived from saturated fat (beef tallow) or polyunsaturated fat (soybean oil), and those on standard lab chow. Each of the rats underwent 21 days of training to learn a simple Go/No Go test. Basically they had to learn to alternate their response to a lever on a feeder. When it appeared the first time, they were to go and press it to be rewarded with a food pellet. When it appeared the next time, they were NOT to go and press it since they would not receive a pellet. The next time the lever appeared, they were to go and press it again to receive a food reward, and so forth. The interval delay between levers was 5, 10 and 20 seconds (to test short-term memory) and 40 and 80 seconds (to test long-term memory).

Those rats on the high-fat diet had difficulty learning the Go/No Go task and did poorly in the testing stage, especially when the interval delays were more than 20 seconds. The researchers then injected the high-fat rats with either a glucose or saline solution. Those who received the glucose showed a general improvement in performance that was greatest on the measures of long-term memory.

"While glucose administration clearly helps overcome those memory deficits associated with hippocampal function, this is not a long-term solution," cautions Dr. Winocur. "We should not fool ourselves into thinking that glucose from a glass of orange juice is all we need to protect our brains from clogging up from a high-fat diet."

Added Dr. Greenwood: "The one important message I hope people take away from this study is that modifying diet and lowering fat intake is good for your brain function."

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The study was funded by the Natural Sciences and Engineering Research Council of Canada. Baycrest Centre is an internationally renowned geriatric centre as well as an academic centre affiliated with the University of Toronto.

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