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How might adding a few nuts to one’s daily diet, in this case about 4 walnuts, almonds and hazelnuts cut one’s stroke risk nearly in half? Well olives and nuts are plant foods, and as such packed with antioxidants, raising the antioxidant level of our bloodstream, resulting in lower fat oxidation and free radical DNA damage, but what’s happening inside people’s arteries?

Researchers measured the amount of atherosclerotic plaque in the neck arteries going to the brain in folks who for years were eating the added nuts, or added extra virgin olive oil, or neither to their daily diets. In the control group, the plaque got worse, which is what happens when one continues to eat an artery-clogging diet, but there were no significant changes in the added extra virgin olive oil group, and the plaque in the added nut group appeared to get better. The nuts appeared to induce a regression of the disease, or at least a significant delay in the progression. Now the nut group was still suffering strokes, but only half as many, perhaps because the reduction in plaque height within the arteries on extra nuts was indicating a stabilization of the plaque rendering them less likely to rupture.

Adding nuts to our diet may also improve endothelial function, boosting the ability of our arteries to dilate naturally by about 30%. If you look at the baseline adherence to Mediterranean diet principles, and control for things like smoking and exercise, there were only two factors significantly associated with reduced heart attack and stroke risk, more vegetables and more nuts. No significant association with the olive oil or the wine or the fish or cutting back on soda and cookies. Among the individual components, only increased consumption of vegetables and nuts were related to reduced cardiovascular events.

On the one hand, cutting stroke risk in half just by eating a handful of nuts a day is pretty amazing, but those in the added nut group didn’t appear to live any longer overall. And other studies have suggested that frequent nut consumption may extend life, for example the Harvard health professionals studies, involving a whopping 3 million person-years of follow-up over decades, found nut consumption associated with fewer deaths from cancer, heart disease, respiratory disease, and most importantly fewer deaths overall, confirmed by all the other big major prospective studies, as of 2014, with a new one just published. 17,000 people followed for 5 years and those who ate nuts had less than half the risk of dying.

Maybe this is just because people may eat nuts instead of meat, eggs, and dairy, and that’s why they live longer? No, since vegetarians that frequently eat nuts also have a dramatically reduce risk compared to those that don’t.

So what’s going on here? Did they just not wait long enough? Well, just because people were randomized to the nut group didn’t mean they actually ate more nuts, and those randomized to the other groups didn’t necessarily stay away. If you re-analyze the data comparing the death rates of those who actually ate more nuts to those who actually didn’t, nut consumption was indeed associated with significantly reduced risk of death. If you do the same kind of post hock analysis with olive oil, even with the extra virgin, there is no benefit in terms of living longer. This is consistent with how Ancel Keys, the so-called Father of the Mediterranean diet, viewed olive oil. He thought of its benefit more as a way of just replacing animal fats, anything to get people to eat less lard and butter.

What are the best kind of nut? The greatest benefits were attributed to walnuts, particularly it seems, for preventing cancer deaths. Those eating more than three servings of walnuts a week appeared to cut their risk of dying from cancer in half.

Now it’s just a matter of communicating the research to the public. All the major cancer groups emphasize a more plant-based diet, remarkably consistent with the World Health Organization guidelines for healthy eating. The far-reaching positive effects of a plant-based diet—including walnuts—may be the most critical message for the public.

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Scientists are not yet certain whether walnuts act as a cancer chemopreventive agent, an effect which may be a result of the fruit's high phenolic content, antioxidant activity, and potent in vitro antiproliferative activity.[23]

Compared to certain other nuts, such as almonds, peanuts and hazelnuts, walnuts (especially in their raw form) contain the highest total level of antioxidants, including both free antioxidants and antioxidants bound to fiber.[11]"