THURSDAY, Oct. 1, 2003 (HealthDayNews) -- To the puzzlement of researchers, a major study finds a fat-rich diet, which clearly increases the risk of heart disease, doesn't seem to affect the risk of stroke.
"Right now, to be honest, we don't have a convincing explanation of what we find," says Dr. Ka He, who led the study while at the Harvard School of Public Health and now is an instructor in preventive medicine at Northwestern University's Feinberg School of Medicine.
And the longstanding rules for a diet rich in vegetables and fiber and low in fatty foods still apply, He says.
"We don't want readers to misunderstand, to think that they don't have to take care of dietary fat intake," He says. "They still need to watch their diet because fat intake is an important indicator of the risk of heart disease."
Nevertheless, the results of a 14-year study of almost 44,000 middle-aged men, appearing in this week's issue of the British Medical Journal, are clear: "These findings do not support associations between intake of total fat, cholesterol, or specific types of fat and risk of stroke in men."
It was a fairly rigorous study, with dietary intake assessed by comprehensive questionnaires, which also went into consumption of selected foods, such as red meat, high-fat dairy products, nuts and eggs.
But after adjusting for the presence of two other known risk factors, age and smoking, no association between dietary fat intake and the incidence of stroke was found.
Two possible explanations are offered. One is that about 20 percent of strokes occur when a blood vessel bursts rather than when a clot blocks a brain artery. These hemorrhagic strokes are not necessarily related to the artery-clogging process of atherosclerosis, fed by heavy fats, that causes heart attacks and ischemic stroke, in which a brain artery becomes blocked.
It's also possible that the unsaturated fatty acids that contribute to atherosclerosis reduce inflammation and have other favorable effects on the molecular events that can lead to ischemic stroke, the researchers speculate.
But that doesn't explain why cholesterol-lowering treatment for patients with heart disease has lowered the incidence of stroke in some trials, the report says. In the end, all He can say is that "we think further research is needed."
From a scientific point of view, says Dr. Mark J. Albert, director of the stroke program at Northwestern, the study might miss a diet-stroke association because it does not distinguish between different kinds of ischemic stroke.
"Not all ischemic strokes have the same mechanism," Albert says. "Studies that have distinguished carotid ischemic strokes, which tend to have the same mechanism as heart attacks, have found an association. Studies that lump all ischemic strokes tend not to find an association."
But whatever the scientific niceties may be, "the practical issue, even if you accept these results, is that no one is going to say, you had a stroke so it's OK to go ahead and eat a high-fat diet," Albert says. "A significant percentage of stroke patients will die of heart disease, for which diet is a major risk factor."
And in addition to eating properly, He says, "there are other factors to watch, such as exercising regularly, not smoking and controlling body weight. These are very important with respect to stroke prevention."
A rundown on stroke risk factors can be found at the American Heart Association and the National Institute of Neurological Disorders and Stroke.