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updated 12/10/2004 11:51:28 AM ET 2004-12-10T16:51:28

Besides eating more fruits and veggies, avoiding saturated fats and trans fats may also help prevent age-related memory loss. When it comes to the amount of fat in the diet, researchers have found that what’s good for the heart is good for the brain. In the same way that reducing levels of bad cholesterol can prevent arteries from becoming ravaged by atherosclerosis, low cholesterol levels in the diet may also help protect brain cells.

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In a study involving rat brain cells, Dr. Mark Mattson, chief of the Laboratory of Neurosciences at the National Institute on Aging in Baltimore, found that reducing cholesterol and ceramide, a form of fat, made the cells more resistant to the destructive effects of the amyloid plaque. And in a study of mice genetically engineered to develop Alzheimer's, the NIA scientists found that how much the rats ate also was significant.

“What we find is that a high-fat diet is bad for learning and memory, and the low-calorie and intermittent fasting diets preserve learning and memory,” says Mattson, whose research was presented last month at the Society for Neuroscience annual meeting in San Diego.

Although an actual cause and effect has not yet been proven, cholesterol appears to promote the production of amyloid plaque and contains an enzyme that the plaque needs to grow. It also promotes harmful oxidation and can cause damage to cell membranes.

A fishy story
While diets high in cholesterol are bad for the brain, getting plenty of omega 3 fatty acids, found primarily in fish, is vital for a healthy noggin, researchers say. In particular, a component of omega 3 fatty acids known as DHA, or docosahexaenoic acid, is key.

DHA is found in high concentrations in the brain and is needed for healthy cognitive function. It is widely believed to have an anti-inflammatory effect and is known to have a protective benefit on the heart. The most concentrated source of DHA is oily fish, such as salmon, tuna, herring, sardines and mackerel.

In an observational study conducted at Rush University Medical Center in Chicago, Dr. Martha Clare Morris, associate professor of internal medicine, found that people who ate fish once a week had a 60 percent reduction in the risk of Alzheimer’s compared with people who never ate fish. Eating fish more than once a week did not appear to provide additional benefits.

Other studies have found similar results. Hoping to learn more about the processes behind DHA's apparent benefits, Dr. Greg Cole, associate director of the Alzheimer’s Center at the University of California, Los Angeles, conducted a study in which one group of aging bioengineered mice were fed food high in DHA while another group ate a standard diet and a third group ate a diet deficient in DHA. The mice fed a diet high in DHA performed better on memory tests and had reduced levels of amyloid plaque in their brains. The mice fed a diet low in DHA performed poorly on memory tests and also showed damage in the areas where brain cells communicate.

What about toxins?
Despite the protective effects of eating fish, many people may worry about the potential dangers of fat-soluble toxins such as mercury and dioxins. Most researchers don't have an answer to this conundrum except to point out that the health benefits for populations of people who eat lots of fish, such as the Japanese, appear to outweigh the risks.

For those consumers willing to pay extra, fish oil or purified DHA may offer similar benefits, although it's unclear if they're as beneficial as eating fish itself.

Cole says the best solution would be to consume the kind of DHA used in infant formulas, which is made from farmed marine algae.

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