Everybody knows that fast food —an industry that does a swift business in North America—isn’t good for you. It’s dangerous for your heart and adds on unwanted pounds. Yet in spite of all the evidence of its detriment, the high-fat diet remains a firmly-rooted staple for Americans. In surveys conducted ten years ago, the average American was taking in 40 percent of their protein via fat. This number, says Dr. Carol Greenwood, nutrition expert and associate professor at the University of Toronto’s Baycrest Centre for Geriatric Care, has dropped some in the last decade because of an increased awareness of the harm fat causes. But, she adds, "You will still find plenty of people out there with this kind of high fat-intake."
The extra pounds and increased potential for heart disease aren’t the only pitfalls of a high-fat diet. Research conducted by Dr. Greenwood and her colleague, Dr. Gordon Winocur, have also shown that a high fat diet could be bad for the brain as well.
Much of Greenwood and Winocur’s research has looked at the impact of diet on adult-onset or Type II diabetes. It’s relatively well established that a high-fat diet increases the risk of coming down with diabetes, but that same diet may also be having a negative impact on thinking abilities. "What we know from our animal studies is that the chronic consumption of high fat diets is associated with cognitive deficits," says Greenwood. "That is, diets and lifestyles that are consistent with an increased risk of diabetes development are also consistent with cognitive impairment."
Greenwood and Winocur discovered that rats fed a low-fat diet (roughly 10 percent of their caloric intake) have better memory than those fed a high-fat diet (roughly 40 percent of caloric intake, which, remember was what most of us were taking in when these things were last comprehensively studied ten years ago).
In a study published in the March 2001 issue of the journal Neurobiology of Learning and Memory, Greenwood and Winocur have pinpointed what they believe is so detrimental about high-fat diets to cognition: glucose. Or rather, a lack of glucose.
Their hypothesis is that a high-fat diet impairs glucose metabolism in the brain. And why would that matter? Probably for two reasons.
"For memory processing there is a double need for glucose," says Greenwood. "It is important for brain function because when the brain is performing memory tasks, glucose is needed to support the energy of the neuron. When brain cells are working, they’re actively firing and that’s a high energy-demanding process. So they need glucose for that."
Also, she adds, "we know that the neurotransmitter that predominantly subserves a lot of memory function is acetylcholine, and glucose is necessary to produce the acetyl part of that."
To test their hypothesis, Greenwood and Winocur administered glucose to rats already showing memory deficits from a high-fat diet. These rats showed substantial improvement on cognitive tasks after the glucose was administered. Particularly affected were tasks involving hippocampal function, an area of the brain responsible for long and short-term memory.
Greenwood and Winocur point out that rats on a low-fat diet showed no gains from the glucose supplement, which would seem to further the point.
Dr. Winocur has cautioned the public not to make what could be an obvious logical step to compensating for a poor diet with an increased amount of glucose. That is to say, a glass of orange juice is not going to make up for a daily lunch of burgers and fries.
And if you think that being young makes you exempt, think again. The study was actually conducted on very young rats, which were fed the high-fat diet starting at the age of one month for a period of three months, or into the equivalent of early adolescence.
“Developing brains are much more susceptible to any kind of disruption,” says Winocur, which is one reason the team chose this age group. “What’s remarkable is that these very young animals that were on the diet for only three months saw such devastating effects of cog functions.”
There is an alarming increase, adds Greenwood, in the numbers of cases of Type 2 diabetes in younger and younger populations.
“If kids are consuming these kinds of diets,” says Greenwood, “then they are at risk.”
Greenwood and Winocur have lately been applying a study to look at the effect of dietary neglect and high fat diet on the aging brain.
“I wouldn’t be at all surprised,” says Winocur, “if an aged brain was even more vulnerable to this effect than a young brain.”