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Researchers publishing in JAMA Internal Medicine have examined a possible link between the consumption of nuts and changes in mortality risk in certain populations. The authors report that in the groups which they studied, people who ate more nuts had a lower mortality rate which was mainly due to a reduction in cardiovascular disease.
Ms Catherine Collins, Principal Dietitian at St George’s University Hospital Foundation Trust, said:
“Research over the past few years has shown heart-health benefits of including nuts and legumes (like peanuts) as part of a varied diet. This is probably because nuts and peanuts contribute a valuable source of protein, dietary fibres, healthy fats, vitamins B1, B6, folic acid, vitamin E, magnesium and zinc to the diet. Although almost half the weight of a peanut is fat (48%), the majority is of the heart-healthy monounsaturated and polyunsaturated types. Studies where nuts have been added to the diet (such as the European PREDIMED study), and long-term population studies have consistently shown a reduction in death from heart disease when nuts and legumes are included in the diet.
“So it’s against this background of nut research that the authors have tried to qualify the benefits of peanut intake in lower income groups, who’d be expected to have a poorer quality diet and higher risk of premature death from heart disease or stroke. Using data from two key studies, one from low income groups from the US, the other from China, the authors demonstrate statistically that, compared to those eating no peanuts in their diet, including peanuts could reduce premature mortality. Interestingly, all the low-income groups studied exceeded the 400g of fruits and vegetables daily (the ‘5 a day’ goal) also recognised as an independent factor for heart disease protection, unlike lower-income groups in the UK where less than three portions a day is the norm.
“Like many population studies the authors divided peanut intake into five groups, with non-peanut eaters forming a reference group, and peanut eaters placed into one of four additional groups, based on increasing peanut intake, for comparison. Cardiovascular disease risk and mortality were compared in each of the groups to the non-peanut eating group. Comparing the health effects of high versus low intakes is common in population studies and in this study showed those with the largest daily intake of peanuts had a 20% reduction in mortality and over 30% reduction in death from heart disease compared to non-peanut eaters. However, Chinese women assigned to the ‘highest intake’ group consumed less than 80g of peanuts or peanut products a day. In contrast, African-American women in the ‘top consuming group’ ate up to 135g of peanuts a day – 68% more peanuts than Chinese women. Studies like this mean we can’t place a value on the actual amount of nuts or peanuts needed for health benefits, just that to include some may confer health benefits.
“The authors recorded health conditions associated with premature cardiac death including diabetes, high blood pressure, smoking history and obesity. In the UK medicines to control blood pressure and diabetes are routinely prescribed to control both conditions and to reduce the risk of cardiac death. It was striking to note that in the US study, 16% of those with diabetes took no diabetes-controlling medicine whilst in African-American men over 6000 were taking diabetes medication yet only 3600 had the condition. This suggests some issues with data control of the study. For those Americans with high blood pressure, 46% were not on medication. Poor control of blood pressure and diabetes is a major contributor to heart disease risk, and without medication the effect of diet will be exaggerated.
“In African Americans only, the highest intake of peanuts (up to 170g/d) halved the risk of all-cause mortality attributed to diabetes, but peanut intake had negligable effect on other groups. The reason for this is unclear from the data provided.
“In all, this paper on peanut intake is a curate’s egg of interesting outcomes with unanswered questions regarding diet survey data and confounding heart disease risks in this group. The bottom line is to enjoy peanuts if you like them, or include beans and peas in your diet as a healthy substitute if you don’t.”
Professor Peter Weissberg, Medical Director, British Heart Foundation, said:
“This large study found that death rates from heart attacks were lower in people who eat nuts, particularly peanuts, than in those who don’t.
“However, the data do not show that the more peanuts you eat the lower the risk of a fatal heart attack, so people should not start eating large quantities of nuts, particularly salted nuts, in the hope that it will protect them from heart disease.
“The results suggest that including a modest amount of nuts as part of a well-balanced diet may be of benefit.”
Ms Gaynor Bussell, Dietitian and member of the British Dietetic Association, said:
“This is a striking study of the benefit seen in nut, mostly peanut consumption. The value of the study is that it builds on other studies showing similar results, but extends the population studies to different ethnic groups and those of low income (often difficult groups to study).
“We may never know what the beneficial components are in nuts – is it the type of fat, the fibre, or their polyphenol content? My suspicion is that it is the combination of these elements that are present in nuts. Hence the importance of concentrating on giving food-based guidance rather than trying to pick out individual nutrients. As a public health message for here in the UK, the study demonstrates how beneficial a relatively cheap and plant-based food can be. It is also a good source of protein and seems to have the health advantages even when used in the form of peanut butter!”
Dr Tim Chico, Reader in Cardiovascular Medicine and Consultant Cardiologist, University of Sheffield, said:
“One of the reasons there are so many conflicting reports about the relationship between lifestyle and health is that scientists and doctors keep committing the fatal error of confusing correlation (such as the observation that people who eat more nuts are less likely to die of cardiovascular disease) with causation (proving that eating nuts reduces cardiovascular disease). Most correlations turn out not to be causal.
“The authors of this study unfortunately commit this error; they say they have found a “substantive public health impact of nut/peanut consumption”, which they have not. To know whether there is an impact would need a study where people are given nuts and the effect on heart disease measured.
“However, it is possible that this is one of the rare occasions where an observed correlation turns out to be causal. The evidence for this comes from a different study from a few years ago in which people given a Mediterranean style diet (high in olive oil or nuts) did indeed suffer from less heart disease (see http://www.nejm.org/doi/full/10.1056/NEJMoa1200303).
“Although the current study does not prove that eating nuts definitely reduces the risk of heart disease, I think there is enough evidence to justify recommending a Mediterranean diet including nuts as part of a healthy lifestyle. However, the causes of heart disease are multiple and complex and any simplistic solution (like saying “eat more nuts”) is destined to fail.”
‘Prospective evaluation of the association of nut/peanut consumption with total and cause-specific mortality’ by Hung N. Luu et al. published in JAMA Internal Medicine on Monday 2 March 2015.
Declared interests
Prof. Christine Williams:
Member, Governing Body of the British Nutrition Foundation, 1998 –
Vice-President, British Nutrition Foundation, 2011-
Member, The Rank Nutrition Advisory Committee 2010-
Chair, UK Research Excellence Framework (REF) Sub-panel Agriculture, Veterinary and Food, 2012-2014
Director of the Governing Body of the Institute of Food Research, Norwich, 2014-
Chair, BBSRC Food Security Strategy Panel, 2014-
Member, BBSRC Research Advisory Panel, 2015-
Prof Williams’ research is primarily concerned with understanding the impact of dietary fats on human health, particularly in relation to cardiovascular disease and insulin resistance. She has provided advice to government and industry on matters relating to dietary policy and actively engages in dissemination of nutritional science to the public. In 1999 she was awarded the Royal Society of Medicine Gold Medal in Nutrition for her contribution to scholarship and education in nutrition. Between 1998-2001 she was the President of the UK Nutrition Society, she chaired the BBSRC Agri-Food Committee, 2003-2006 and is a Governor and Vice President of Council of the British Nutrition Foundation. She was Pro-Vice Chancellor (Research & Innovation) at the University of Reading, 2008-2014. In 2013 she was awarded an OBE in the Queen’s Honours list for her services to higher education and nutrition sciences.
Conflicts: In the past Christine Williams’ research has been funded by various funders including industry (Unilever, Nestle and Hoffman la Roche); during 2010-13, she acted as one of three members of Pepsico UK’s Advisory Board, advising on their nutrition and health strategy.