The skeptical cardiologist was somewhat disheartened to read the New York Times headline today that the PREDIMED study was flawed. I frequently reference this landmark randomized trial of the mediterranean diet when I’m citing the cardiovascular benefits of nuts and EV olive oil.
Science mag summarizes the problem which prompted a re-analysis of the study:
A months-long inquiry by the Spanish researchers and NEJM staff uncovered that up to 1588 people in the trial hadn’t been properly randomized: Some were assigned to the same diet as someone else in their household (a common feature of diet studies, but not reported in the original paper). Others, who lived in a rural area, were assigned to different diets based on the clinic closest to them—for example, one group had to pick up a liter of olive oil each week. “The investigator realized he couldn’t get people to travel as far as they needed so he made his study ‘cluster randomized,’” by clinic rather than by individual, Drazen says.
The authors reanalyzed their data without those 1588 participants and found that despite the missteps, the conclusion held: Nuts, olive oil, and fatty fish remained a net positive on heart health, though the conclusions came with somewhat less statistical oomph than in the original paper.
Here’s what I wrote about nuts and the PREDIMED study when I first started distributing Dr. P’s Heart Nuts to my patients.
The skeptical cardiologist has finally prepared Dr. P’s Heart Nuts for distribution. The major stumbling block in preparing them was finding almonds which were raw (see here), but not gassed with proplyene oxide (see here), and which did not contain potentially toxic levels of cyanide (see here).
During this search I learned a lot about almonds and cyanide toxicity, and ended up using raw organic almonds from nuts.com, which come from Spain.
I’ll be giving out these packets (containing 15 grams of almonds, 15 grams of hazelnuts and 30 grams of walnuts) to my patients because there is really good scientific evidence that consuming 1/2 packet of these per day will reduce their risk of dying from heart attacks, strokes, and cancer.
The exact components are based on the landmark randomized trial of the Mediterranean diet, enhanced by either extra-virgin olive oil or nuts (PREDIMED, in which participants in the two Mediterranean-diet groups received either extra-virgin olive oil (approximately 1 liter per week) or 30g of mixed nuts per day (15g of walnuts, 7.5g of hazelnuts, and 7.5g of almonds) at no cost, and those in the control group received small nonfood gifts).
After 5 years, those on the Mediterranean diet had about a 30% lower rate of heart attack, stroke or cardiovascular death than the control group.
It’s fantastic to have a randomized trial (the strongest form of scientific evidence) supporting nuts, as it buttresses consistent (weaker, but easier to obtain), observational data.
Despite the statistical flaws PREDIMED is still an important study demonstrating the benefits of nuts. PREDIMED was the best randomized trial data we had for nuts but there are tons of observational data which are very consistent and show a strong association between increased nut consumption and reduced mortality..
Consequently, I made up a new batch of Dr. P’s Heart Nuts in honor of the survival of PREDIMED and will be distributing them to patients today.