 Not eating walnuts make double our risk of dying from heart disease compared to at least one serving a week. But walnut consumption may only drop our cholesterol levels about 5%. How can we get a 50% drop in cardiac mortality from just a 5% drop in cholesterol? Walnuts must have some other heart-protecting benefits besides just lowering cholesterol, such as improving arterial function. This review found five clinical trials analyzing the effect of nut consumption on the ability of our arteries to relax and open normally, considered an excellent barometer of underlying vascular health. Even after controlling for other risk factors, 80% of those with better-than-average arterial function survived cardiac event-free over the years, whereas 80% of those with below-average dilation didn't. And so what effect do nuts have? All three studies on walnuts showed an improvement in endothelial function, in arterial function—this so-called flow-mediated dilation measured in the arm. The one study on pistachios also found a positive effect, but the one study on hazelnuts was a wash. A subsequent study on hazelnuts, though, did find a significant improvement in arterial function, so the data on hazelnuts is mixed. Whereas two subsequent walnuts studies, however, confirmed walnuts' benefits. So, eight studies to date on nuts in berycul artery function, and seven out of eight showed a significant improvement in arterial function. One showed negligible effect, and none found nuts made things worse. Half of the studies, though, used the added walnuts to replace foods in the diet, known to have a negative effect on endothelial function. For example, in this study, walnuts replaced meat and dairy, which have been shown to be detrimental, so no wonder arterial function got better. When you do a study like that, you can't tell if the benefits you're seeing is because you're adding good stuff or getting rid of the bad. And in three of the other studies, nuts replaced olive oil, which tends to lead to a worsening of endothelial function, thereby exaggerating the beneficial effects of the walnuts from here to here. But the other four studies, like this one, that just added nuts as a snack or with a meal without replacing any specific foods, found nuts significantly improved arterial function. And given their association with longevity, I encourage everyone to eat an ounce of nuts a day, unless of course you're allergic. Only about 1% of people report nut allergies, but still that's a significant downside of nut consumption for millions of Americans.