May 9, 2001 University Park, Pa. --- In the most comprehensive review yet of the available epidemiological and clinical evidence, Penn State researchers have concluded that eating tree nuts or peanuts can have a strong protective effect against coronary heart disease. Dr. Penny Kris-Etherton, distinguished professor of nutrition and lead author of the review, says, "To date, five large epidemiologic studies and 11 clinical studies have demonstrated that frequent consumption of nuts decreases the risk of coronary heart disease."
The most improvement comes with adding very small amounts of nuts – an ounce, or about three to four tablespoons, five or more times a week.
"However, you can't simply add nuts, nut butters or nut oils to your usual diet without making some adjustments," Kris-Etherton says. "You have to replace some of the calories you usually consume with nuts and substitute the unsaturated fat in nuts for some of the saturated fat in your diet."
The study was published today (May 8) in the current issue of the journal, Nutrition Reviews. Kris-Etherton's co-authors are Guixiang Zhao, a doctoral candidate and a Kligman Scholar in Nutrition; Amy E. Binkoski, doctoral candidate in Penn State's Life Sciences Consortium; Stacie M. Coval, master's degree candidate; and Dr. Terry Etherton, distinguished professor and head of the dairy and animal sciences department.
The researcher's review of the existing published epidemiologic studies shows that consuming 1 ounce of nuts more than 5 times/week can result in a 25 to 39 percent reduction in coronary heart disease risk among people whose characteristics match those of the general adult U.S. population.
Among the nuts consumed by the people who took part in the epidemiologic studies were almonds, brazil nuts, cashews, hazelnuts, macademia nuts, pecans, pistachios, and walnuts, as well as peanuts. However, the effects of specific nuts on coronary heart disease risk were not evaluated in these studies due to difficulties in classifying consumption patterns of specific nuts and because of the small number of cases in each category. In typical American diets, peanuts account for approximately half of all nuts consumed.
The 11 clinical studies reviewed by the Penn State researchers focused on the blood cholesterol-lowering effects of nuts. Collectively, these studies showed that including nuts in a blood cholesterol-lowering diet has favorable effects. However, the researchers write, "Whether the inclusion of nuts evokes a greater cholesterol-lowering response than would be expected from a typical lipid-lowering diet remains to be resolved."
Calculations conducted by the researchers using the published data suggest that nuts may contain other cholesterol-lowering constituents, but studies are needed to corroborate this. Nuts studied in clinical investigations included walnuts, almonds, macadamia nuts, pecans, pistachio nuts and peanuts.
Nuts are a rich source of unsaturated fatty acids, the "good" fats, and are low in saturated fatty acids, the "bad" fats. However, the researchers concluded that the fatty acid profile of nuts contributes to only part of the total reduction in coronary heart disease risk.
The Penn State researchers write, "Nuts are a source of plant protein dietary fiber, antioxidant vitamins, minerals and numerous bioactive substances that may have health benefits. It is conceivable, although not proven, that many nutrients in nuts may act synergistically to exert beneficial effects."
They conclude that it is appropriate to recommend inclusion of nuts in a healthy diet that meets energy needs to reduce risk of coronary heart disease. They emphasize the need to provide dietary guidance to help people understand how to plan heart healthy diets that include nuts.
Dr. Kris-Etherton notes that dietary guidance on fats has changed in recent years from removing or drastically restricting fats to substituting and replacing them with heart healthy alternatives. For example, she says, "you can cut back a little on margarine and add a small amount of slivered almonds on green beans. You can flavor a salad with a few walnuts and use less dressing. Or, you could use peanut butter instead of full fat cream cheese on a bagel."
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