Scientists searching for a link between what we eat and how well we age are taking a close look at the effect of dietary fat on long term health. They speculate that a diet that leans toward vegetable fats and away from trans fat (a type found in margarine and some processed foods) may help slow the brain deterioration that leads to Alzheimer's disease. Their findings appeared in a recent issue of the journal Archives of Neurology.

Assessing diet and mental function

Researchers in Chicago recruited 815 men and women aged 65 and older. All passed mental function tests showing them to be free of the symptoms of Alzheimer's disease, and each completed a questionnaire designed to assess their usual eating habits. The researchers were looking for a connection between the amount and kinds of fat in the participants' diets and the risk of developing Alzheimer's.

Approximately four years later, the participants again completed the mental function tests. At that point, 131 people showed signs of Alzheimer's. The researchers found that those who ate the most polyunsaturated fat - from vegetable sources such as corn oil and safflower oil - were much less likely than others in the study to have symptoms of Alzheimer's. Conversely, those who consumed the most trans fat - a type produced when vegetable oil is hydrogenated, or hardened - were more likely than others to develop the disease.

How does fat make a difference?

The authors say that it is not yet known how particular dietary factors like fat might affect the aging brain. But they speculate that it may be for the same reason that polyunsaturated fat is considered 'heart healthy' and trans fat is considered unhealthy for the heart. A diet rich in polyunsaturated fats helps to control blood levels of 'bad' LDL cholesterol, while the body treats trans fat the same way it treats the saturated fat from animal sources - both contribute to elevated LDL cholesterol levels.

Advice to consumers

More research is needed to fully clarify what effect, if any, diet has on the progression of age-related diseases like Alzheimer's. But current dietary guidelines already encourage consumers to choose a 'heart healthy' diet that emphasizes vegetable fats over products made from animal fats, and limits intake of trans fats. Remember that the process used to harden vegetable oil is what raises the trans fat content of a product, so liquid oil or semi-solid vegetable oil spreads are better choices than stick margarine.