30 Jul 2003

Bored with the same old foods you tend to eat? Consider adding more fish and some specific plant products. Two recent studies suggest that not only would this liven up your diet, but it might also lower risk of developing Alzheimer's disease somewhat, at least indirectly.

In what editorialist Rob Friedland, of Case Western Reserve University in Cleveland, Ohio, calls "a remarkable prospective study," researchers from Rush-Presbyterian-St. Luke's Medical Center followed 815 middle-aged and elderly Chicagoans for an average of four years, assessing the group for development of Alzheimer's disease. These data were correlated with food intake data, particularly with intake of fish. Writing in the Archives of Neurology, Martha Clare Morris and her coauthors found that people who ate fish at least once a week had a 60 percent reduced risk of developing Alzheimer's compared to subjects who rarely or never ate fish (relative risk 0.4; 95 percent CI, 0.2-0.9).

The researchers also took a closer look at the dietary effects of some of the specific n-3 polyunsaturated fatty acids (PUFAs) that have been found to be neuroprotective in animal studies. Based on nutrient estimates from the diet questionnaires study participants filled out, the researchers extrapolated estimates of consumption of these PUFAs from fish, as well as from nuts and salad oils. They determined that total intake of PUFAs was associated with a decreased risk of Alzheimer's, as was docosahexaenoic acid individually. Neither eicosapentaenoic acid nor alpha-linolenic acid intake were associated with risk of Alzheimer's disease in the overall study population, but alpha-linolenic acid was protective in people with an apoE E4 allele.

The fascinating story of lipid homeostasis and Alzheimer's disease is just beginning to unfold. In the current JAMA, David Jenkins of the St. Michael's Hospital in Toronto, Canada, describes a prospective clinical trial to compare the efficacy of newer dietary recommendations for reducing cholesterol to older recommendations and to a commonly prescribed cholesterol-lowering drug. The newer guidelines suggest that a diet high in plant sterols, viscous fibers, soy protein, and nuts may lower cholesterol more effectively than a diet simply low in saturated fat.

The study population of 46 men with high cholesterol was broken into three groups. For a month, all subjects ate a low-fat, high-whole-wheat diet. In addition, one group took lovastatin, and another added plant sterols (from enriched margarine), soy protein (from various foods), viscous fibers (oats, barley, psyllium), and almonds to their diet. Consistent with previous research, the control group (low-fat, whole wheat) saw only an 8 percent reduction in LDL cholesterol, while the lovastatin group saw a 31 percent reduction in LDL. Surprisingly, the group following the newer guidelines saw a 29 percent drop in LDL.

"Is it time to make dietary recommendations?" asks the subtitle of Friedland's editorial. He concludes that, "Dietary intake is best considered from the point of view of diet patterns, rather than individual foods. A high antioxidant/low saturated fat diet pattern with a greater amount of fish, chicken, fruits, and vegetables and less red meat and dairy products is likely to lower the risk of AD, as well as that for heart disease and stroke."—Hakon Heimer

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