Nuts are packed with unsaturated fats, fibre, protein, vitamins and minerals. Previously they have had a bad press, because they were thought to be fattening, but interventional studies based on the Mediterranean diet have shown that people who ate a daily portion of nuts did not gain weight compared with those who had a nut free diet1. What is the evidence about nuts and heart disease?
The PREDIMED study
A large Spanish study (PREDIMED) took 7747 people with high risk of cardiovascular disease, but no actual disease and enrolled them on one of three diets: a Mediterranean diet supplemented with extra virgin olive oil (4 table spoons per day); a Mediterranean diet supplemented with 30g mixed nuts; and a control diet, with education to reduce their fat content. The patients were followed and observed for a major cardiovascular event (heart attack, stroke, or death from cardiovascular disease) termed the primary endpoint, up until the study was closed at 4.8 years. The authors found a 30% relative risk reduction in cardiovascular death, stroke, or myocardial infarction (composite endpoint) in the Mediterranean diet groups which had supplementary oil or nuts. This means if your risk of having a heart attack was 9%, eating nuts or oil could reduce it to 6%.
These findings were published in 2013 but article has since been retracted and revised due to deviations from the protocol with regards randomization2.
Can I trust the PREDIMED study if it was retracted?
When the PREDIMED study was first published, it was deemed ground breaking to have such a large study in the field of nutrition that followed the participants for a number of years. There has been a lots of discussion in the literature about why the study was retracted and what this means for the validity of the evidence. Does the fact that the authors had to retract and revise the analysis mean the outcome of the study can no longer be trusted?
The study authors re-analysed the data excluding 1588 participants who had not been rigorously randomised. Despite this change, there was no significant change in the results of the trial and the overall conclusions remained relatively unchanged. In people with a high cardiovascular risk, the incidence of major cardiovascular events was lower among those assigned to a Mediterranean diet supplemented with extra-virgin olive oil or nuts than among those assigned to a reduced-fat diet. However, although the relative risk appears large (30%), the absolute risk, a reduction from 4.4% to 3.4-8% in diets with nuts or oil was small.
Should I eat nuts?
If you are at risk of heart disease, you could reduce your relative risk of heart attack, stroke or death by supplementing your diet with extra-virgin olive oil (4 table spoons per day) or 30g of nuts. This is an easy change to make, and could have a significant impact on your risk. Eating nuts also provide fibre, and additional vitamins and minerals, without increasing your risk of weight gain and so are probably good for everyone without a nut allergy as part of a balanced diet.
References
1. Vadivel, V., Kunyanga, C. N. & Biesalski, H. K. Health benefits of nut consumption with special reference to body weight control. Nutrition28, 1089–1097 (2012).
2. Estruch, R. et al. Primary Prevention of Cardiovascular Disease with a Mediterranean Diet Supplemented with Extra-Virgin Olive Oil or Nuts. N Engl J Med378, e34 (2018).