Individuals with diabetes or metabolic syndrome often have conditions such as elevated blood pressure, cholesterol, or triglycerides, which can increase the risk for heart disease and stroke. Research on the association between walnut consumption and these conditions demonstrate the importance of walnuts as part of a healthy diet to help manage complications associated with diabetes and metabolic syndrome.
Continue below for a scientific summary of the research to date.
An epidemiological study representing more than 34,000 American adults suggests that those who consume walnuts may have about half the risk of developing type 2 diabetes compared to adults who do not eat nuts.1 Researchers from the University of California Los Angeles looked at data from the National Health and Nutrition Examination Survey (NHANES), in which adults (ages 18-85 years old) were asked about their dietary intake over the course of one to two days and assessed for diabetes. According to the study, the average intake among walnut consumers was approximately one and a half tablespoons per day. Doubling walnut consumption (eating three tablespoons) was associated with a 47% lower prevalence of type 2 diabetes. The study did not look at the impact of increasing walnut consumption beyond doubled intake.
Researchers from Harvard found that walnut consumption was associated with a significantly lower risk of type 2 diabetes in women compared with women who never/rarely consumed walnuts.2 The study looked at two large prospective cohorts of U.S. women: The Nurses’ Health Study (NHS) and NHS II, which followed 58,063 women (ages 52-77) in NHS (1998-2008) and 79,893 women (ages 35-52) in NHS II (1999-2009) without diabetes, cardiovascular disease or cancer at baseline. They found two or more servings (1 serving is equivalent to 1 ounce) of walnuts per week, as part of a healthy diet, was associated with a 21 percent and 15 percent lower risk of incident type 2 diabetes before and after adjusting for body mass index (BMI), respectively.
A study published in Metabolism found that short-term consumption of walnuts may improve blood lipids, by increasing apolipoprotein A concentration.3 Apolipoprotein A is the primary protein component of HDL, and is one of many factors that may be considered in a complete lipid profile when estimating cardiovascular disease risk. For this study, 15 obese subjects (ages 56-61) with metabolic syndrome were enrolled in a randomized, double-blinded, placebo-controlled crossover study in which they consumed two different isocaloric diets, one with 48 grams of walnuts daily (approximately 1.7 ounces) and one without walnuts for four days each. The results suggest that eating walnuts may have a beneficial effect on lipid metabolism even within short-term consumption.
Findings from the Yale University’s Yale-Griffin Prevention Research Center demonstrated that consumption of a diet enriched with two ounces of walnuts per day for eight weeks significantly improved endothelial function in 24 adult participants (ages 49-67) with type 2 diabetes.4 Subjects were randomly assigned to an ad libitum diet enriched with 56 grams of walnuts per day or an ad libitum diet without walnuts. Researchers compared the dietary effects on endothelial function, a measure of how well blood vessels are able to dilate resulting in increased blood flow, and a powerful predictor of overall cardiovascular risk. The same design was used in another study with 46 overweight adults with elevated waist circumference and one or more additional signs of metabolic syndrome. Findings showed that daily consumption of 56 grams of walnuts for eight weeks significantly improved endothelial function as compared with an ad libitum diet not supplemented with walnuts.5
Larger and longer-term studies, as well as studies in more diverse populations, are needed to clarify population-wide effects. In some cases, residual confounding cannot be ruled out (i.e., other lifestyle factors which are more common in adults who eat walnuts could contribute to the study results).1,3,4
1 Arab L, Dhaliwal SK, Martin CJ, et al. Association between walnut consumption and diabetes risk in NHANES [published online ahead of print June 21, 2018]. Diabetes Metab Res Rev. doi.org/10.1002/dmrr.3031
2Pan A, Sun Q, Manson JE, et al. Walnut consumption is associated with lower risk of type 2 diabetes in women. J Nutr. 2013;143(4):512-8.
3Aronis KN, Vamvini MT, Chamberland JP, et al. Short-term walnut consumption increases circulating total adiponectin and apolipoprotein A concentrations, but does not affect markers of inflammation or vascular injury in obese humans with the metabolic syndrome: data from a double-blinded, randomized, placebo- controlled study. Metabolism. 2012;61(4):577-82.
4Ma Y, Njike VY, Millet J, et al. Effects of walnut consumption on endothelial function in type 2 diabetic subjects: a randomized controlled crossover trial. Diabetes Care. 2010;33(2):227-32.
5Katz DL, Davidhi A, Ma Y, et al. Effects of walnuts on endothelial function in overweight adults with visceral obesity: a randomized, controlled, crossover trial. J Am Coll Nutr. 2012 Dec;31(6):415-23.
