Harvard Study Shows a Serving of Peanuts or a Half Serving of Peanut Butter Eaten Daily Significantly Cuts Risk of Gallstones

Jul 7, 2004

Harvard School of Public Health researchers report that consuming a one-ounce serving of peanuts or other nuts (about 160 calories per serving) five or more times a week is associated with a 25% reduced risk of cholecystectomy, or removal of the gallbladder. Consuming a half-serving, or one tablespoon, of peanut butter (about 95 calories) five or more times a week is associated with a 15% reduced risk. Small, daily servings of peanuts and peanut butter have previously been shown to reduce the risk of heart disease and type 2 diabetes as well. This important study is published in the July 2004 issue of American Journal of Clinical Nutrition.

Although gallstone disease is a major source of morbidity in developed countries, little attention has been given to how specific foods affect this condition. In Western populations, an estimated 80% of gallstones are cholesterol stones. Gallstones are associated with high triglyceride levels and low “good” HDL cholesterol levels, which are also risk factors for heart disease.

In the study, researchers observed an apparent “threshold effect” of peanut, peanut butter and nut consumption. A significant reduction in risk of cholecystectomy was observed only in women who ate nuts or peanut butter almost daily. Despite being calorie-dense, this study and others show that frequently consuming peanuts, peanut butter, and nuts does not increase body mass index. Frank Hu, MD, PhD, Associate Professor of Nutrition and Epidemiology at Harvard School of Public Health and an author of the study writes in the paper, “…the women who consumed more nuts tended to weigh less. This indicates that the energy contained in nuts tends to be balanced by decreased intakes of other sources of energy or by increased physical activity.” Food frequency questionnaires show how many women were eating “nuts” five or more times per week. Of the 83,000 female nurses who were followed for an average of 16 years in the Nurses’ Health Study, 749 women ate peanut butter almost daily compared to 82 for peanuts and 32 for other nuts.

The paper states that in addition to the well-documented benefits of healthy mono- and polyunsaturated fats in peanuts and nuts, other bioactive components may play a role. Peanuts and nuts are rich sources of dietary fiber, which may contribute to reducing the risk of gallstones by improving insulin sensitivity and decreasing recirculation of bile acids. A one-ounce serving of peanuts contains about two and a half grams of fiber.

Peanuts, nuts and peanut butter are rich sources of magnesium, which also could explain reduction in risk of cholecystectomy. The paper suggests that dietary magnesium plays a role in improving insulin sensitivity, thereby reducing the occurrence of gallstones. They also contain phytosterols, which may help lower blood cholesterol, and help reduce the risk of gallstones.

The Peanut Institute is a non-profit organization that supports nutrition research and develops educational programs to encourage healthful lifestyles.