Perhaps you’ve seen the latest in nut-related research tearing up your news feed? Apparently, “scientists say” that eating nuts will make you live longer. As a Licensed Scientician myself, I was doubtful of the over-simplified claims presented by most news articles, so I decided to take a closer look at the primary research.
I’m specifically picking on this article from Time, but most other articles say the same thing (and they’re likely just regurgitations of a press release). According to the article, the study is based on a huge sample of people (around 120,000), but they’re all health professionals (nurses and doctors), so it’s not exactly representative of the normal population. That aside, there are other confounding issues.
Those who reported regularly consuming nuts were less likely to die from a variety of diseases, most significantly cancer, heart disease and respiratory diseases.
Is this article actually saying that people who eat nuts don’t die from the most common causes of death? But they did die, right? Or did they live forever? Clearly, the takeaway message is that nuts prevent death.
People who ate nuts seven or more times a week, in fact, enjoyed a 20% lower death rate after four years than individuals who did not eat nuts. Nut eaters also tended to be leaner, more physically active, and non smokers.
Because they ate nuts, right? Do Peanut M&M’s count? Or do you think that people who like nuts also tend to lead a healthier lifestyle?
Prior studies found similar connections between nuts and longer life, but the large size of this study gives the association more support. How many nuts does it take to extend lifespan? That’s not clear, and the scientists say that the findings don’t imply any cause and effect relationship between nuts and later death, but the correlation is worth investigating further.
“How many nuts does it take to extend lifespan????” (I thought this paragraph was the funniest.) Ten a day? Twenty? If I eat 100 nuts a day, will I live longer than everyone else? Or will I die from a blocked bowel? I know “scientists say” that there isn’t necessarily a cause and effect relationship, but c’mon, JUST TELL ME HOW MANY NUTS TO EAT TO ATTAIN IMMORTALITY.
The research was funded by the National Institutes of Health and the International Tree Nut Council Nutrition Research & Education Foundation. But the Tree Nut Council had no part in deigning the study or reporting results. [sic]
Ah, so the authors are in the pockets of Big Nut, you say?
Now onto the actual research paper (as much fun as it was to read the bad science journalism). Most articles that mentioned this study neglected to cite the original article, so I had to do some digging, but I found the article (for free!) in the New England Journal of Medicine.
Scientific journals are written for other scientists, so I get that as a journalist (who may not necessarily have taken a science class) it’s hard to verify the evidence in the article and it’s easier to just reword whatever press release you receive. (The current state of journalism is a whole other topic that I’m not really going to discuss beyond that.) However, most people don’t have the resources (or the drive) to look up scientific articles (if they are even available to the public), so they rely on journalists to accurately describe legitimate studies. But instead, we get science journalism that is constantly contradicting itself (e.g. Egg yolks are bad!! Cholesterol! No wait, egg yolks are healthy cholesterol! Scratch that, egg consumption is linked to disease!!!) and giving bad advice. The takeaway message (promoted by the Nut Council) from this study is that eating nuts leads to longer life, but the truth is much more complicated than that.
If you actually look at the data, there are a few surprises. Here is Table 1:
According to the data, there is definitely a trend of people who “eat nuts” also living longer (although it’s not a terribly significant difference, it’s a mean of 57.5 vs 61.8 years and the error bars overlap). Although, the first thing I noticed about this table was that it only lists means–and I would be much more interested to know the median age of death instead of the mean, because the median is less likely to be skewed by outliers. (And this is why bio majors are required to take Statistics in college too.)
If you look at the other stats in Table 1, people who eat nuts also drink twice as much alcohol, are more likely to take multivitamins, exercise more, are less likely to smoke, and eat more fruits & veggies. Wait a second, scroll back to that first item…OMG you guys! NUT CONSUMPTION MAKES YOU DRINK!!! (Is that why they’re always at bars?) Or maybe, in fact, people who eat nuts just tend to do other things associated with healthy lifestyles? (Except that drinking thing. Oh wait, maybe that adds antioxidents, right? Leave my evening wine alone.)
Table 3 lists the causes of death. But it lists it in absolute numbers instead of relative percentages. I’ve taken the time to crunch the numbers below to compare the percentages of causes of death within Nut Consumption categories.
[Ed Note: Table replaced on 27Nov2013 updated math--I had incorrectly added "all causes" to the rest of the numbers and didn't account for the split in cardiovascular disease. The numbers have been updated in the paragraph below too. Thanks to commenters for pointing this out!]
The people who ate nuts less than once per week had a 38.0% chance of dying of cancer. The people who ate nuts more than five times a week had a …drumroll please… 36.2% chance of dying of cancer. WOW, what a difference. I can totally see why the author of that Time article wrote that people who are nuts were “less likely to die from a variety of diseases, most significantly cancer, heart disease and respiratory diseases.” (Although that doesn’t hold up for the cardiovascular claim.) Interestingly, people who ate no nuts were no more or less likely to die of a certain disease than the group who ate ALL THE NUTS. (That probably has something to do with the fact that people who don’t eat nuts may be more likely to have nut allergies–which doesn’t mean that they’re not otherwise leading a healthy lifestyle.)
My point is: this study seems awfully nut-focused when in fact there are a lot of different reasons that people who are disposed to eat more nuts may “live longer” (although the difference may be statistically significant, the error bars overlap too much in this area for my satisfaction).
The Tree Nut Council may not have had anything to do with this study other than funding it, but they sure as shit have a lot to do with the press releases being thrown around touting the benefits of nuts (instead of, say, just switching to a “healthier lifestyle”). The authors mention following the Mediterranean Diet but then are quick to mention that nuts are a part of that recommended diet (but gloss over the fact that the diet includes overall healthier fats and nutrients).
Aw man, I so wanted the Scientists to tell me how many pecan pies I could eat this Thanksgiving! (Or even, chocolate pecan pie? Because that has the benefit of added antioxidents, right?)