Reference
Guasch-Ferré M, Bulló M, Martínez-González MA, et al. Frequency of nut consumption and mortality risk in the PREDIMED nutrition intervention trial. BMC Med. 2013 Jul 16;11:164.
Design
Observational cohort using baseline consumption of nuts as the exposure and comparing this information with mortality
Participants
As part of the PREDIMED (PREvención con DIeta MEDiterránea) study, 7,447 older participants (men aged 55–80 years and women 60–80 years) were assigned to 1 of 3 interventions: a Mediterranean diet enriched with extra-virgin olive oil (EVOO), a Mediterranean diet supplemented with mixed nuts, or advice on a low-fat diet (control diet). Although participants had no cardiovascular disease (CVD) at enrollment, they were at high cardiovascular risk because of the presence of type 2 diabetes or at least 3 of the following risk factors: current smoking, hypertension, hypercholesterolemia, low high-density lipoprotein (HDL) cholesterol, overweight or obesity, and family history of premature CVD. Participants who reported extremes of total energy intake (>4,000 or <800 kcal per day for men and >3,500 or <500 kcal per day for women) were excluded from the analysis. After those subjects with extremes of total energy intake (n= 53) and those with incomplete dietary data (lack of food frequency questionnaire) at baseline (n=78) had been excluded, 7,216 individuals were available for the present analysis.
Study Medication and Dosage
Nut consumption of participants was evaluated at baseline using a 137-item semi-quantitative food frequency questionnaire administered in face-to-face interviews by dieticians. Information on self-reported nut intake in general and walnut intake specifically was obtained. Participants reported the frequency and quantity of nut (and specifically walnut) consumption. For the purpose of this study, 28 grams of nuts was considered to be one serving.
Outcome Measures
Total mortality, cardiovascular mortality, and cancer mortality
Key Findings
During a median follow-up of 4.8 years, 323 total deaths, including 81 cardiovascular deaths and 130 cancer deaths, occurred. Nut consumption was associated with a significantly reduced risk of all-cause mortality (P for trend <0.05, all). Compared to non-consumers, subjects consuming nuts >3 servings/week (32% of the cohort) had a 39% lower mortality risk [hazard ratio (HR): 0.61; 95% CI: 0.45–0.83]. A similar protective effect against cardiovascular and cancer mortality was observed. Participants allocated to the Mediterranean diet with nuts group who consumed nuts >3 servings/week at baseline had the lowest total mortality risk (HR: 0.37; 95% CI: 0.22–0.66).
What is important about this study is that it proves that the middle ground, a balanced omnivore diet (ie, Mediterranean diet) is beneficial to health.
Practice Implications
Rohrman and Faeh provide an excellent commentary on this study, which was published in conjunction with this paper:1
“The results of this study have shown an effect of any nut consumption on all outcomes. However, although reduced all-cause and cardiovascular disease mortality were observed among consumers of walnuts and ‘other nuts,’ cancer mortality was only inversely associated with the consumption of walnuts. Nuts are rich in polyunsaturated fatty acids, but also in minerals (calcium, magnesium, potassium) and vitamins. Additionally, they contain a number of phytochemicals such as phenolic acids, polyphenols and phytosterols. Compared to other nuts, walnuts have a particularly high content of alpha-linolenic acid, and possibly also a higher bioavailability of the above mentioned phytochemicals: walnuts are usually consumed with the ‘skin,’ which has the highest content of phytochemicals, whereas this skin is usually removed from other nuts before consumption. Thus, it has been speculated that walnuts might have stronger health effects than other types of nuts. This is however in contrast to other results, for example, from a meta-analysis showing that different types of nuts had similar effects on blood lipid levels.”
The list of benefits associated with nut consumption can be expanded to include reduced risk of type 2 diabetes,2 CVD,3 and metabolic syndrome.4
The information from this current study comes as no surprise; it only confirms earlier reports. Why are we taking the time to discuss it? Because, to our continual surprise, we come across both medical and naturopathic doctors advising patients to avoid eating nuts. Such physicians seem do so due to outdated ideas about fat intake. They assume since nuts are high in fat and fat as a macronutrient is generally unhealthy for people, nuts are unhealthy. This is certainly a belief for those physicians encouraging their patients to follow a low-fat Ornish or Esselstyn type diet, that is designed to, among other things, CVD risk.
As we see in this study, to advocate nut avoidance ignores 20 years of solid science. Such low-fat advocates view dietary choices as a black/white type phenomenon: Foods are either good or bad. One is either on the “Western” diet eating junk food, sugar, agri-industry meats, pop, and hydrogenated oils, or they follow an extremely restricted diet removing, among other things, 90% of fats—including nuts. What is important about this study is that it proves that the middle ground—a balanced omnivore diet (ie, Mediterranean diet)—is beneficial to health. An omnivore diet is high in vegetables and fruits, legumes, and whole grains, but also in nuts and nut butters, and clean animal food such as omega-3 organic eggs, low-toxin fish, and occasional servings of grass-fed/grass-finished meat. In this study, eating nuts, including in a Mediterranean omnivore diet, is clearly proven to be a healthy dietary choice.
