Nuts contain mostly unsaturated fat, which may be beneficial for glucose and insulin homeostasis. In a prospective cohort study, Jiang and colleagues examined the impact of nut and peanut butter consumption on the risk of developing type 2 diabetes.

The Nurses' Health Study, a survey of 121,700 registered nurses, assessed dietary information in 1980, 1984, 1986, 1990, and 1994, using a food-frequency questionnaire that included a question to determine frequency of nut consumption. In the analysis, the authors included only respondents with no diabetes at baseline and considered factors such as body weight, cigarette smoking, and family history of diabetes. The outcome measure was development of type 2 diabetes. In relating diabetes to nut consumption, the authors created four categories of consumption frequency: those who consumed nuts never or almost never, less than once a week, one to four times a week, or at least five times a week.

The authors documented 3,206 incident cases of type 2 diabetes during 1,282,892 person-years of follow-up in the 16 years from the 1980 baseline. The age-adjusted relative risk of diabetes was 0.55 percent when comparing women who ate nuts at least five times a week with those who never or almost never ate nuts. Because women who ate nuts generally weighed less than those who did not eat nuts, the body mass index (BMI) was the strongest confounding variable in multivariate analysis. The relative risk was attenuated when BMI was added to the analysis, revealing a statistically significant trend toward decreased risk. No other factors modified these results, and controlling for propensity scores still showed a lower diabetes risk in those who ate nuts. The authors noted similar results for peanut butter consumption.

This study correlates with other recent findings that a diet high in saturated fats decreases insulin sensitivity compared with diets containing monounsaturated fats. The authors conclude that there is an inverse relationship between nut consumption and type 2 diabetes risk. Nut consumption appears to have other benefits, including an inverse relationship with cardiovascular disease. Consumption of nuts in this study was not associated with weight gain.