SUMMARIES FOR PATIENTS
The Effects of a Mediterranean Diet on Risk Factors for Heart Disease
4 July 2006 | Volume 145 Issue 1 | Page I-11
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The summary below is from the full report titled "Effects of a Mediterranean-Style Diet on Cardiovascular Risk Factors. A Randomized Trial." It is in the 4 July 2006 issue of Annals of Internal Medicine (volume 145, pages 1-11). The authors are R. Estruch, M.Á. Martínez- González, D. Corella, J. Salas-Salvadó, V. Ruiz-Gutiérrez, M.I. Covas, M. Fiol, E. Gómez-Gracia, M.C. López-Sabater, E. Vinyoles, F. Arós, M. Conde, C. Lahoz, J. Lapetra, G. Sáez, and E. Ros, for the PREDIMED Study Investigators.
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What is the problem and what is known about it so far?
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Heart disease is the main cause of death in developed countries. However, people in some developed countries in the Mediterranean region die of heart disease less often than people in other countries. This observation has led some scientists to suggest that the Mediterranean diet may decrease death from heart disease. The Mediterranean diet is characterized by large amounts of olive oil, nuts, whole grains, fruits, and vegetables. The Mediterranean diet is made up of foods with larger amounts of "healthy" oil and fat, which contradicts traditional recommendations to prevent heart disease by decreasing oil and fat intake. The effects of a higher-fat diet on risk for heart disease compared with those of a lower-fat diet are not clear. Which, if any, components of the diet have a protective effect is also unclear.
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Why did the researchers do this particular study?
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To directly compare the effects of a Mediterranean diet and a low-fat diet on risk for heart disease.
772 older adults in Spain with diabetes or 3 or more other risk factors for heart disease, such as smoking, abnormal cholesterol level, or high blood pressure.
The researchers assessed the participants' regular diets and measured their weight, blood pressure, blood sugar level, and cholesterol level. They then randomly assigned participants to 1 of 3 groups. The first group increased consumption of vegetable fats and oils and received free virgin olive oil. The second group increased consumption of vegetable fats and oils and received free walnuts, hazelnuts, and almonds. The third group decreased consumption of all fats. After 3 months, the researchers repeated their assessments to measure the effects of the study diets on risk factors.
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What did the researchers find?
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Participants in the Mediterranean diet groups could maintain the diet better than those in the low-fat diet group. The Mediterranean diets were more effective at lowering participants' blood pressure, cholesterol levels, and blood sugar levels after 3 months.
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What were the limitations of the study?
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The researchers gave more instructions about dietary maintenance to the participants assigned to the Mediterranean diets than to the participants assigned to the low-fat diet. The study's findings might, therefore, have come from differences in the intensity of the instructions rather than the actual diets. Because the Mediterranean diets were closer to participants' actual diets, people assigned to the low-fat diet may have found it more difficult to strictly follow the diet. The study was not designed to detect differences in effect between the 2 Mediterranean diets or the effects of either diet on heart attacks and strokes.
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What are the implications of the study?
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Two kinds of Mediterranean diets reduced participants' blood pressure, cholesterol levels, and blood sugar levels after a relatively short time. The diets' effects on heart attacks and strokes remain to be proven, but the findings suggest that the Mediterranean diet might reduce risk for heart disease in high-risk people. To date, the diet has only been tested for its effect on heart disease and its risk factors in small numbers of people.
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