digest
Introduction
Have you ever taken a good hard look at what a nut looks like? Take the walnut for example. Doesn't it look like a wrinkled old person? Or I guess the wrinkled version of a nut. How can something that can't even keep up its own youth help us achieve longer life and stave off death? Well, I analyzed 15 studies to find out. I based the majority of my investigation on this meta analysis of 20 studies. Then I broke out as many of the studies I could get my hands on from this meta analysis and looked at each study individually.
This is Nuts!
So when we look at the overall nut consumption as we see here in this forest plot, you'll see two striking results. To explain this a bit, you can see all the studies listed on the left side and then the study results are indicated numerically on the right. We can focus our attention on the actual forest plot, which includes the study results shown as black squares in the middle. If the squares move squarely to the left, haha, pun intended, that means that there's reduced risk of all-cause mortality, aka death, from nut consumption. The overall diamond at the very bottom is a good summary result of all the studies combined. And clearly, you can see that there is reduced risk of death when consuming nuts.
That's the first striking result, but the second is actually found by looking at the individual studies listed in the graph. Notice how not a single study shows an increased risk of mortality from nut consumption. That means that we can be reasonably certain that nuts at least have no relationship to mortality and won't harm us, at least based on these data. But this doesn't tell us specifically about walnuts, and there are always imperfections with meta-analyses of associative studies.
On the second point, this analysis included studies that at least accounted for age, education, family history of disease, body weight, smoking, alcohol, physical activity, and, well, some dietary factors. But anything beyond that can be quite heterogeneous. Meaning that some studies might adjust for saturated fat intake while other studies might adjust instead for red meat intake. Yet another study might adjust for added sugar intake, which leads to differences in the results from study to study. This still informs on the overall association between nut consumption and mortality regardless of what factors are accounted for. But we would need a more critical eye on some of these individual studies to get a better picture of the true result. Now, I'm not going to bog this down too much more with methodological considerations, but it's something I do want to point out.
Another way of assessing the impact that nut consumption can have is to look at another type of analysis called a dose-response relationship. On the horizontal axis, you can see increasing nut consumption. On the vertical, you have the risk of death. The lower the lines go, the lower the risk of death. This is pretty revealing because it speaks to how much the relationship plateaus as you get to greater consumption. As you can clearly see, we see an initial dip in all-cause mortality risk up until about 15 grams of nut consumption, and then the risk mostly plateaus. That means that for the vast majority of the benefit, one would want to consume around 15 grams of nuts per day, which is only about half a serving.
Walnuts, Perhaps?
Let's turn our attention to walnuts, though. We know that total nut consumption is linked to reduction in all-cause mortality. But there are many different types of nuts, and walnuts are one of the most prominent. Just as a quick lesson, when it comes to dissecting data, if you're looking at an overall group like total nut consumption, it's still entirely possible that a particular nut could have a negative health consequence and the other nuts simply make up for it, which leads to an overall reduced mortality risk. So technically, we'd probably want to do individual analyses for each nut, but let's focus on walnuts for the time being.
Getting into walnuts specifically is going to lead to a bit of a surprising relationship. While we've been focused on walnuts, I actually cover more on peanuts and peanut butter and the relationship that different nuts have with cardiovascular disease, cancer, and even kidney disease mortality in my full analysis. That full analysis in video and article format, plus an accompanying podcast, can be accessed as a Physionic Insider along with all of my analyses and live sessions with me. If you're interested, check out the Physionic Insiders using the link in the description.
The short of it is that studies specifically focused on walnut consumption indicate a robust reduced mortality relationship with walnut consumption. That is certainly true when looking at men and women combined. But interestingly, when you split the data by sex, the benefit is roughly the same for women and men, with possibly a slightly earlier benefit at lower consumption for women. We can see that evidenced by the lines going down from the 1.0 dotted line, which indicates a neutral relationship. If the confidence intervals, which are the lines that come out of the squares and dots attached to each line, cross that dotted line, then there is no identified relationship. You can see that for women, there's a continued reduction in mortality risk. But for men, it only seems to appear around greater consumption. Either way, we see that the total nut relationship also applies to walnuts. So walnuts, much like total nuts, are linked to reduced total mortality risk.
An Exciting Nuance: Healthy Diet
There's one surprising aspect to all this, and I think it's important to acknowledge. One consideration for any of these analyses is that the benefit of walnut consumption, or anything consumed, is only beneficial if a person has a relatively poor diet. It makes sense that if you were to add a health food to a poor diet, regardless of what that health food is, you would see improvements in things like mortality. It's also possible that you can experience something like reverse causation, where people with healthier diets may consume more walnuts and therefore experience improvements in their mortality risk.
Fortunately, we can lean on data like this where the researchers have separated out poor diet quality from high diet quality based on a composite score designed by researchers called the AHEI, or Alternate Healthy Eating Index. Participants are split by their AHEI score, which is determined by the amount of vegetables, fruit, whole grains, nuts, and legumes, omega-3 fats, and polyunsaturated fats that they consume, as well as the amount of sugar-sweetened beverages, processed meats, trans fats, and more that they consume. The higher the score, the better their diet quality is based on these criteria. This is not a perfect index, but it does give something to separate data by, which is informative. And what you'll notice again: if the lines move to the left, that's reduced mortality risk. Regardless of diet quality, walnut consumption still tracks with reduced mortality risk. That means that if you already have a pretty healthy diet, adding walnuts on top of that diet may provide additional protection from premature mortality.
We covered the amount of total nut consumption needed to get the biggest bang for your buck when it comes to mortality, but that doesn't mean it translates directly to walnut consumption. Unfortunately, the way the data is broken out for the walnut-specific study we've been focused on is not as exact as the dose-response curve we discussed earlier for total nut consumption. Still, the best guess is that consuming walnuts, even as little as two to four times per week, with a little more robust evidence for the higher end of that range, is linked to mild but consistent reduced mortality risk.
The servings in this study were outlined as a standard serving, which is 28 grams. If you do the math on that and average it out over a week, the previous dose-response curve looking at total nut consumption is roughly in line with what we're talking about here with walnuts. If you eat one 28-gram serving three to four times per week, that's roughly 14 to 15 grams every day across seven days. So in short, the lower threshold of notable mortality benefit would still be in line with half a serving per day of walnuts, around 15 grams per day.
Isn't that nuts? Come on. I had to throw that pun in there. That's just too easy. There's plenty more absolutely crazy health science to uncover right here. Thanks as always for tuning in. I hope you have a great day. I'll catch you in the next one. See you.