Issue 133 Item 3 Nuts, Peanut Butter Consumption Associated with Lower Diabetes

Eating nuts and peanut butter has been associated with lowered risk of type 2 diabetes in women during 16 years of follow-up in a large study of nurses (83,000) in the United States at the Harvard School of Public Health Researchers found that consuming one tablespoon of peanut butter or 28g (handful) of peanuts or other nuts five or more times a week is associated with a 20-30 per cent reduced risk of developing type 2 diabetes.

Relative risk for women who ate nuts never or almost never was 1.0. It was 0.92 for those eating a 28-gram portion of nuts less than once a week and 0.84 for those consuming a portion once to four times a week. Relative risk for women eating portions five or more times a week was 0.73.

Researchers studied nut and peanut butter consumption in a cohort of 83,818 women from 11 states who participated in the Nurses’ Health Study. The women were aged from 34 to 59 years. They had no history of diabetes, cardiovascular disease or cancer at baseline in 1980, when they completed a validated dietary questionnaire.

Results indicate there were 3,206 new cases of type 2 diabetes among participants during 16 years of follow-up.

The finding of lower risk with nut and peanut butter consumption was independent of known risk factors for type 2 diabetes: age, obesity, family history of diabetes, physical activity, smoking and dietary factors, say investigators from Harvard University and Brigham and Women’s Hospital in Boston, Massachusetts.

It also persisted within strata defined by levels of body mass index, smoking, alcohol use and other diabetes risk factors.

The researchers explain that the mechanisms by which specific types of dietary fat affect insulin sensitivity are not well understood. Research indicates fatty acid composition of the phospholipids in skeletal muscle cell membranes is related directly to insulin sensitivity.

"A specific fatty acid in cell membranes could influence insulin action through altering insulin receptor binding or affinity and influencing ion permeability and cell signalling," they suggest. "Changes in dietary fatty acid composition alter fatty acid composition of the phospholipids in cell membranes, perhaps modulating insulin action and sensitivity."

Peanuts contain mainly good unsaturated fat and are low in saturated fat, characteristics which are associated with lower risk of type 2 diabetes. Many peanut butters contain a high percentage of peanuts, have a very small amount of salt and sugar for taste, and have undetectable levels of trans fats even though labels list partially hydrogenated oil as a minor ingredient.

Nuts also contain fiber and magnesium which decrease insulin resistance and have been inversely associated with risk of type 2 diabetes. Peanuts have more plant protein than any other nut. They are also rich in vitamin E, folate, potassium, zinc, phytosterols and antioxidants, which are thought to be important to health.

Nuts may also protect against type 2 diabetes through other mechanisms, the investigators add, so that other constituents such as vitamins, mineral, antioxidants and plant protein, or interactions among these factors, could play an important role.

Dr Frank Hu, associate professor of Nutrition and Epidemiology at Harvard School of Public Health and an author of the study, said: "Given the observed inverse association between nuts and risk of coronary heart disease as well as type 2 diabetes, it is advisable to recommend regular peanut butter and nut consumption as a replacement for refined grain products or red or processed meats, which would avoid increasing caloric intake."

The researchers concluded that the data, combined with other clinical and epidemiological data, support potential benefits of increasing nut consumption in reducing type 2 diabetes risk.
JAMA, 2002; 288: 2554-2560.