Walnuts reduce risk of mortality by almost half

Walnuts
The message that could be given based on our findings is that the consumption of more than three servings of nuts per week is associated with lower risk of cardiovascular and cancer mortality and also all-cause mortality.
Marta Guasch Ferré
According to the findings of a longitudinal study, participants who ate more than 84 grams of nuts a week reduced their risk of mortality by almost 40 per cent…

Nuts are an important component of the so-called ‘Mediterranean diet’, which also includes proportionally high amounts of fruit, vegetables, olive oil and legumes as well as moderate amounts of dairy products and wine, but relatively little red meat. Research in the past has suggested a link between frequently eating nuts and a reduced risk of Type 2 diabetes mellitus, metabolic syndrome and cardiovascular disease, with the benefits attributed to their unique nutritional composition.

A randomised controlled trial carried out in Spain, called PREDIMED, provides further evidence that nut consumption has protective effects on health. The results of the longitudinal study, comparing Mediterranean diets supplemented with extra virgin olive oil or nuts to a control group following a low fat diet, appear in BioMed Central’s open access journal BMC Medicine.

Co-author Marta Guasch Ferré is a predoctoral fellow under the supervision of Professor Jordi Salas Salvadó in the Department of Biochemistry and Biotechnology at the Universitat Rovira i Virgili. She addressed ScienceOmega.com’s questions about their findings.

"We evaluated the effect of the frequency of total nut consumption on several causes of mortality," said Guasch Ferré. "However, we thought it was important to evaluate the effect of walnuts separately given the different nutritional composition between walnuts and other nuts, such as hazelnuts and almonds. Walnuts are richer in polyunsaturated fatty acids as well as in some antioxidants than other nuts."

Surprisingly strong association
 

More than 7000 individuals between the ages of 55 and 90 took part in the trial, which found that the frequency of nut consumption was inversely related to total mortality after 4.8 year follow-up in subjects at high cardiovascular risk.

"Although our findings are in agreement with previous epidemiologic studies relating nuts to cardiovascular and all-cause mortality, and we hypothesised that there nuts would have a significant effect on mortality, we were surprised that the inverse associations between nuts and cardiovascular, cancer and all-cause mortality were so strong," Guasch Ferré told ScienceOmega.com.

In those who consumed most nuts, there was a reduction in total mortality of 39 per cent and a 55 per cent lower risk of cardiovascular mortality. Meanwhile, the overall reduction in all-cause mortality for walnut eaters was 45 per cent.

The researchers noted that people who ate more nuts tended to have a lower body mass index (BMI) and smaller waist, as well as being less likely to smoke, more likely to exercise, and more likely to have a healthy diet. So, how influential were these other aspects of participants’ lifestyles on the results?

"In our study we demonstrated that nut consumption could prevent premature mortality independently of these factors," Guasch Ferré clarified. "However, we highlight that they are equally important for longevity and improved life quality."

A serving a day...
 

28 grams of nuts were considered one serving in the study, which observed that people eating more than 84 grams per week reduced their risk of death due to cancer by 40 per cent – an association that very few studies have evaluated before – and from cardiovascular disease by 55 per cent.

"Previous studies have also shown that consuming higher amounts of nuts does not lead to an increase in body weight or increased risk of diabetes, metabolic syndrome or other chronic diseases," Guash Ferré stated. "So, it is beneficial to include, for example, a serving of nuts per day in the context of a healthy diet and lifestyle."

The nutritional profile of nuts may account for the inverse associations observed between regular nut consumption, chronic disease and mortality. Nuts are high in monounsaturated fatty acids, fibre, minerals, vitamins and many bioactive compounds, all of which are beneficial and may partly explain the health effects.

"The frequency of nut consumption has been inversely related to several chronic prevalent conditions, such as diabetes, hyperlipidemia, hypertension, obesity, metabolic syndrome, cancer, and CHD, among others," Guasch Ferré went on. "These inverse associations can be influenced by various mechanisms; nuts improve the blood lipid profile and appear to decrease insulin resistance, and there is also evidence to suggest that they can modulate inflammation, oxidative stress, and endothelial function. As a large body of evidence supports the beneficial effects of frequent nut consumption on many health outcomes, it is plausible that nuts protect against all-cause mortality as well."

Wonders of walnuts
 

Walnuts are richer in some antioxidants than other nuts and are characteristically rich in alphalinolenic acid; this is one possible explanation for the inverse relationship between walnut consumption and cancer mortality, as Guasch Ferré explained.

"Walnuts are usually consumed raw, and roasting can cause a decline in the efficacy of antioxidant capacity," she said. "It has been shown that raw walnuts, as consumed in the PREDIMED study, have a high antioxidant efficacy; this could play a beneficial role in the prevention of cancer."

It is not clear quite why nuts are able to prevent premature mortality to such an extent, or why walnuts should have a markedly stronger effect than other nuts. Given the evidence from this study and others, however, I asked Guasch Ferré what kind of public health message should be propagated concerning nuts.

"The message that could be given based on our findings is that the consumption of more than three servings of nuts per week is associated with lower risk of cardiovascular and cancer mortality and also all-cause mortality," concluded Guasch Ferré. "Although the scientific evidence regarding this issue is consistent further research would be helpful for understanding better the mechanisms by which nuts exert protective effects on health."


Read the full text of the article, 'Frequency of nut consumption and mortality risk in the PREDIMED nutrition intervention trial'...

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