Nov. 10, 1998 DALLAS, Nov. 10 -- Heart-healthy components in oats may help lower high cholesterol levels and a nutrient in nuts may help prevent death from heart disease, according to preliminary research from two studies presented today at the American Heart Association's 71st Scientific Sessions.
In a 12-year study of 22,071 doctors participating in the Physicians Health Study, men whose diets contained high quantities of nuts had a decreased risk of dying from heart disease, says the study's lead author Christine M. Albert, M.D., an instructor at the Harvard Medical School in Boston.
Albert's team notes that nuts contain unsaturated fats including alpha-linolenic acid, which may help prevent fatal disturbances in the heart's rhythm.
In a study funded by Quaker Oats at Tufts University in Boston, another group of researchers examined 43 men and women eating a diet rich in oats. People on the diet had lower blood pressure and reduced blood levels of cholesterol at the end of the study. High blood pressure and high cholesterol are risk factors for heart attack and stroke.
The oat diet lowered total blood levels of cholesterol by 34 milligrams per deciliter (mg/dL), while study participants who ate a diet that substituted wheat for oats lowered their cholesterol only 13 mg/dL. The individuals' blood levels of low-density lipoprotein cholesterol (LDL or "bad" cholesterol) -- which can accumulate in blood vessels, increasing risk of a heart attack or stroke -- followed the same pattern: The oat group's LDL was 23 mg/dL lower and the wheat group's LDL was 8 mg/dL lower.
Also, the people in the oat group reduced their systolic (top number) blood pressure by 7 millimeters of mercury (mm/Hg) at the end of the six-week study compared to 2 mm/Hg for the wheat group.
"Blood pressure lowering is generally a good thing for the population. The question here is: if this dietary intervention works to reduce normal blood pressure, can we also use the same method to reduce high blood pressure?" says lead author of the oat study, Edward Saltzman, M.D., of the Energy Metabolism Laboratory at the USDA Human Nutrition Research Center on Aging at Tufts University in Boston.
Saltzman attributes the benefits of oats to its soluble fiber -- the type of dietary fiber that dissolves in water. "There are several reasons why foods such as oats that contain soluble fiber, or soluble fiber itself, could have beneficial effects on blood pressure or cholesterol. The presence of soluble fiber in foods slows the rate of digestion and absorption."
The slower digestion causes a more gradual rise in insulin levels. Insulin is a hormone that helps regulate blood sugar, but it may raise blood pressure in some individuals. "There may be other as yet unidentified factors in oats that affect the way the blood vessels react," says Saltzman.
The men and women in the study ate one of two calorie-controlled diets. Researchers determined each individual's maintenance caloric needs then gave them each 1,000 calories less than each person's maintenance level each day. The study group was given an oat-rich diet. The control group -- used as a comparison standard -- ate a diet that substituted wheat for oats.
The two diets differed mainly in the amount of soluble fiber. Oats contain more of this fiber than the same quantity of wheat. Other foods high in soluble fiber are barley, lentils, pinto beans, black beans and citrus fruits.
Saltzman stressed that his study was very preliminary and more research is needed to determine if an oat-rich diet would have the same effects in a long-term study. He says the diet needs to be strictly followed for results to be significant. "It's a hard thing to feed people for six weeks, but it's really hard to get them to follow a diet at home for a year or two," he says.
In the Harvard investigation linking nut consumption to a reduced risk of heart disease, Albert says alpha-linolenic acid, a component of nuts, may protect the heart by preventing a rhythm disturbance called ventricular fibrillation that causes sudden death. When the heart lapses into ventricular fibrillation, it cannot pump blood unless shocked into a normal rhythm with an electrical device called a defibrillator. Albert says previous studies in animals have hinted at this link as well.
Other sources of alpha-linolenic acid are unhydrogenated canola and soybean oils used in most full-fat commercial salad dressings, flaxseed and flaxseed oil and a leafy vegetable called smooth purslane which is eaten mainly in Greece. Albert stressed that her results are preliminary because the questionnaires asked only whether the physicians had eaten nuts, not what kind or how many they ate. Also, other factors of diet or risk factors for heart disease might skew the results. "Most nuts are also high in other unsaturated fats and nutrients that might contribute to reduced heart disease risk," says Albert. However, some nuts -- like Brazil nuts -- are high in saturated fats as well. Consumers need to be aware that all nuts are high in total fat and calories.
However, those questioned who ate the highest amount of nuts had the lowest risk for any heart-related death -- even after adjusting for age, exercise habits, high blood pressure, cholesterol levels, diabetes, alcohol use, other dietary habits and whether individuals were being treated for heart disease.
Saltzman's co-authors are Sal K. Das, M.A.; Andrew S. Greenberg, M.D.; Gerard E. Dallal, Ph.D.; Ernst J. Schaefer, M.D.; Susan B. Roberts, Ph.D.; and Alice H. Lichtenstein, Ph.D.
Albert's co-authors are JoAnn E. Manson, M.D.; Walter C. Willett, M.D.; and Charles H. Hennekens, M.D. Albert's study was funded by the National Institutes of Health.
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