Background: Epidemiologic studies have shown inverse associations between nut consumption and diabetes, cardiovascular disease (CVD), and all-cause mortality, but results have not been consistent.
Objective: We assessed the relation between nut intake and incidence of type 2 diabetes, CVD, and all-cause mortality.
Design: We searched PubMed and EMBASE for all prospective cohort studies published up to March 2013 with RRs and 95% CIs for outcomes of interest. A random-effects model was used to pool risk estimates across studies.
Results: In 31 reports from 18 prospective studies, there were 12,655 type 2 diabetes, 8862 CVD, 6623 ischemic heart disease (IHD), 6487 stroke, and 48,818 mortality cases. The RR for each incremental serving per day of nut intake was 0.80 (95% CI: 0.69, 0.94) for type 2 diabetes without adjustment for body mass index (BMI); with adjustment, the association was attenuated [RR: 1.03; 95% CI: 0.91, 1.16; NS]. In the multivariable-adjusted model, pooled RRs (95% CIs) for each serving per day of nut consumption were 0.72 (0.64, 0.81) for IHD. 0.71 (0.59, 0.85) for CVD, and 0.83 (0.76, 0.91) for all-cause mortality. Pooled RRs (95% CIs) for the comparison of extreme quantiles of nut intake were 1.00 (0.84, 1.19; NS) for type 2 diabetes, 0.66 (0.55, 0.78) for IHD, 0.70 (0.60, 0.81) for CVD, 0.91 (0.81, 1.02; NS) for stroke, and 0.85 (0.79, 0.91) for all-cause mortality.
Conclusions: Our meta-analysis indicates that nut intake is inversely associated with IHD, overall CVD, and all-cause mortality but not significantly associated with diabetes and stroke. The inverse association between the consumption of nuts and diabetes was attenuated after adjustment for body mass index. These findings support recommendations to include nuts as part of a healthy dietary pattern for the prevention of chronic diseases.
Alex’s notes: Nuts are an incredible food. They are rich in unsaturated fatty acids, fiber, vegetable-protein, and minerals such as magnesium and potassium. They are also high in polyphenols and other beneficial antioxidant compounds. Previous research has concluded that eating nuts most days of the week reduced the risk of heart disease by about 35%, and considering that the American College of Cardiology predicts that the number of people diagnosed with some form cardiovascular disease (CVD) will reach 25 million people in the U.S. alone, nuts could save over 8 million people. Then you add in diabetes, which has a worldwide prevalence of 6.4%, and the potential benefits of nuts for its prevention, and you have one true superhero food.
But enough of the depressing talk; let’s get to the meta-analysis at hand. It looked at 31 reports of CVD, diabetes, and mortality from 18 studies with participants aged 20-87 years old and follow-up periods ranging from four to 30 years. Overall, in an unadjusted model nut consumption was associated with a lower risk for everything, but when adjusted for BMI, age, and gender, nut consumption only reduced the risk of CVD, stroke in women, and all-cause mortality. In my opinion, that’s still pretty damn good. Interestingly, BMI was the sole factor attenuating the beneficial effects of nuts on diabetes, suggesting that your best path to health is getting lean. Speaking of which, the individuals who did eat nuts were leaner, exercised more frequently, smoked less, and ate more vegetables, fruits, fish, and dairy.
The above is actually one of the main downsides to this meta-analysis. Observational studies cannot exclude the effects of some unknown or residual confounding factors attributable to other dietary and lifestyle factors because nut eaters tend to be healthier in general. Additionally, there are so many types of nuts that these findings should be interpreted as the average associations with a variety of nuts. Regardless, it is still likely that nuts are beneficial in and of themselves. The Mediterranean diet is commonly praised for its health benefits, and the addition of an ounce of nuts (almonds, hazelnuts, and walnuts) per day significantly reduced blood pressure, risk of metabolic syndrome, and incidence of diabetes compared with a low-fat variation.
My favorite nuts are macadamias and I shall continue to eat them daily with joy.