Background: Recent pooled analyses supported a beneficial impact of nut consumption on health, but to our knowledge, whether nuts are associated with overall decreased mortality has not been previously reviewed.
Objectives: We aimed to systematically review prospective studies that explored the effects of nut consumption on all-cause, cardiovascular disease (CVD), and cancer mortality and quantify the size effect through a meta-analysis. We also reviewed confounding factors associated with nut consumption to assess potential clustering with other covariates.
Design: We searched PubMed and EMBASE for studies published up to June 2014. Study characteristics, HRs, and 95% CIs were generated on the basis of quantitative analyses. A dose-response analysis was performed when data were available.
Results: Seven studies for all-cause mortality, 6 studies for CVD mortality, and 2 studies for cancer mortality were included in the meta-analysis with a total of 354,933 participants, 44,636 cumulative incident deaths, and 3,746,534 cumulative person-years. Nut consumption was associated with some baseline characteristics such as lower body mass index and smoking status as well as increased intakes of fruit, vegetables, and alcohol. One-serving of nuts per week and per day resulted in 4% (RR: 0.96; 95% CI: 0.93, 0.98) and 27% (RR: 0.73; 95% CI: 0.60, 0.88) decreased risk of all-cause mortality, respectively, and decreased risk of CVD mortality [RR: 0.93 (95% CI: 0.88, 0.99) and 0.61 (95% CI: 0.42, 0.91), respectively]. Effects were primarily driven by decreased coronary artery disease deaths rather than stroke deaths. Nut consumption was also associated with decreased risk of cancer deaths when highest compared with lowest categories of intake were compared (RR: 0.86; 95% CI: 0.75, 0.98), but no dose-effect was shown.
Conclusion: Nut consumption is associated with lower risk of all-cause, CVD, and cancer mortality, but the presence of confounding factors should be taken into account when considering such findings.
Alex’s Notes: When someone mentions a plant-based diet, what comes to mind? I would bet that it is the same food groups that have been the focus of most observational studies; namely fruits, vegetables, cereal grains, and legumes. Few people would have nuts come immediately to mind, perhaps because from a nutrient standpoint they are dominated by fats rather than carbohydrates. Nonetheless, these nutrient-dense grenades truly blow away the competition.
Nuts in general have been shown to be the single most protective food group against all diet-related chronic diseases, most notably obesity and type-2 diabetes. They have been explored for their potential to modulate various neural and cognitive systems, and they have been implicated in lowering LDL-cholesterol, improving endothelial function, decreasing visceral fat, improving glycemic control, and reducing insulin resistance. Amazingly, nuts may also be cancer-protective.
To further our understanding of the relationship of nuts with health, the current study was a meta-analysis investigating the association between nut consumption and mortality.
A comprehensive search of the literature from the beginning of time to June 2014 ultimately resulted in nine studies for analysis. Importantly, studies that assessed nut consumption in combination with other food groups were excluded so as to help isolate the nut associations. Across all studies, there were a total of 354,933 individuals, 44,636 deaths, and 3,746,534 cumulative person-years.
|Eating 1 serving of nuts per day…||People in the highest quartile of nut consumption compared to the lowest quartile had a…|
|↓ risk of all-cause mortality by 27%||↓ risk of all-cause mortality by 23%|
|↓ risk of cardiovascular mortality by 39%||↓ risk of cardiovascular mortality by 29%|
|↓ risk of cancer mortality by 14%|
To put the above results into perspective, if every person in the meta-analysis were to consume one serving of nuts per day, total deaths would have been reduced by a little of 12,000 persons and total cardiovascular deaths would have been reduced by just over 3000 persons.
Unfortunately (for these associations), each additional serving of nuts per week was associated with increased fruit and vegetable intake of 10g and 13g per day, respectively, and a reduced BMI of 0.15.
That said, one of the included studies did indeed control for confounding variables and showed the association between nuts and mortality to persist. Nonetheless, the other studies did not, thus making it unclear if the observed associations were mediated by nut consumption or through the clustering of healthy behaviors in nut consumers. Moreover, we still lack information on the type of nuts and duration of consumption needed for benefits.