People who regularly eat nuts appear to live longer, according to the largest study of its kind.
The findings, published in the New England Journal of Medicine, suggested the greatest benefit was in those munching on a daily portion.
The US team said nut eaters were likely to also have healthy lifestyles, but the nuts themselves were also contributing to their longer lifespan.
Source: BBC News, 21st November 2013
This is an unusual one for the Bad PR blog – published research, and in a very respectable journal too. We even get tempered quotes from advocacy groups urging more study:
The British Heart Foundation said more research was needed to prove the link.
All well and good so far. Yet, there’s an interesting and potentially confounding factor, which the BBC covers late in their story:
The study was funded by the US National Institutes of Health and the International Tree Nut Council Nutrition Research & Education Foundation.
Aside from having one of the most awkwardly-named foundations I’ve ever seen, it’s clear to see how the provenance of the research may influence its findings.
Crucially – and somewhat surprisingly – missing from the BBC article was a link to the actual study being discussed, which is available on the NEJM website. In it, the potential flaws of the study are outlined:
Because nut intake was self-reported, some measurement error is inevitable.
The study didn’t look at nut consumption, so much as reported nut consumption. A minor flaw, and of course the resulting statistical inaccuracy would be relatively consistent (or, at least, consistently unpredictable) across the full range of respondents – however, clearly this isn’t the same as directly measuring nut intake and its effects on health.
Similarly, the direct benefits of a but-heavy diet is something the data can’t confidently prove:
Given the observational nature of our study, it is not possible to conclude that the observed inverse association between nut consumption and mortality reflects cause and effect.
While it’s commendable that the study made this clear in the discussion, it is only to be expected of a scientific study accepted into a major journal. And, of course, the equivocation over the direct causal relationship isn’t something that makes it into the press release, and isn’t what makes it into the media reporting.