People who eat a handful of nuts a day have a lower risk of cancer and heart disease, according to an analysis at Imperial College London.
Eating 28g of nuts each day found to cut the risk of coronary heart disease by 30 per cent, cancer by 15 per cent, respiratory disease by about a half, and diabetes by nearly 40 per cent.
The researchers analysed the health benefits of tree nuts, such as hazel nuts and walnuts, and also peanuts (which are actually legumes). The results were similar whether the analysis looked at total nut intake or merely tree nuts or peanuts.
During the study, published in the journal BMC Medicine, the researchers analysed 29 published studies involving up to 819,000 participants, including more than 12,000 cases of coronary heart disease, 9,000 cases of stroke, 18,000 cases of cardiovascular disease and cancer, and more than 85,000 deaths.
The study found no health advantage in eating more than a small handful of nuts a day.
The study’s co-author, Dagfinn Aune, said: ‘In nutritional studies, so far much of the research has been on the big killers such as heart diseases, stroke and cancer, but now we’re starting to see data for other diseases.
‘We found a consistent reduction in risk across many different diseases, which is a strong indication that there is a real underlying relationship between nut consumption and different health outcomes. It’s quite a substantial effect for such a small amount of food.
‘Nuts and peanuts are high in fibre, magnesium, and polyunsaturated fats — nutrients that are beneficial for cutting cardiovascular disease risk and which can reduce cholesterol levels. Some nuts, particularly walnuts and pecan nuts, are also high in antioxidants, which can fight oxidative stress and possibly reduce cancer risk.
‘Even though nuts are quite high in fat, they are also high in fibre and protein, and there is some evidence that suggests nuts might actually reduce your risk of obesity over time.’
This is a meta-analysis of non-randomised prospective studies, usually used to assess the long-term effect of a particular risk factor on health.
By definition a meta-analysis represents a high level of evidence, but one must be careful in reviewing the results as the studies pooled may have methodology issues themselves.
Overall results are striking. Merely eating an additional 28g of nuts a day results in a 29 per cent decrease in coronary artery disease, a 21 per cent reduction in cardiovascular disease, 15 per cent less total cancer and a 22 per cent reduction in all-cause mortality.
An impressive 40 per cent reduction in diabetes, a major cause of cardiovascular disease and stoke, was also observed.
Before suggesting the addition of a macronutrient to the diet one must have an explanation as to why that nutrient is beneficial. In the case of nuts, we know that they contain high levels of omega-3 oils and healthy monounsaturated fats, both of which have an anti-inflammatory effect that has been demonstrated to reduce the incidence of disease.
However, it is not enough to simply pop a mouthful of nuts after a McDonald’s takeaway and think ‘job done’ — particularly if they were chocolate-covered Brazil nuts.
Furthermore, overconsumption of nuts may also contribute to weight gain, which by itself is a cause of the health outcomes positively affected by nut consumption. Nut consumption is a marker of a healthier overall diet in many cases and it is possible that this a major reason that positive results were observed.
The best way of assessing the impact of increased nut consumption on health would be a randomised controlled trial with long-term follow-up. No such trial has been carried out, save for a trial looking at the impact of the Mediterranean diet on health outcomes, of which nut consumption was a part. Suffice to say, impact was positive.
Take-home message: nut consumption has been demonstrated to improve risk profiles for cardiovascular disease, stroke, cancer and all-cause mortality but must be part of an overall healthier dietary pattern.
Research score: 4/5