Will Improving Your Diet a Little Bit Make You Live Longer?

The New England Journal of Medicine has an interesting new study on the association between diet quality and the risk of death. So inevitably, it’s time for the headlines to give us all a pep talk about how a healthier diet will make us all live longer.

“Even Modest Changes to Diet Can Reduce the Risk of Death”

Let’s get something straight. The risk of death is 100%. So that headline is not quite accurate. What this study actually showed is that people with a poor quality diet could reduce their risk of an earlier death with some modest improvements.

The most frequent example? Drop one serving of red meat and replace it with a daily serving of nuts or legumes (e.g. peanut butter). That sounds pretty easy.

And it might indeed be easy if you’re eating a pretty poor diet – lots of hamburgers and fries. In fact, the people who improved their diets over the course of the study were people who started with lower diet quality scores.

One aspect of this study was especially noteworthy. The researchers conducted three separate analyses, using three different measures of diet quality. They used a Mediterranean diet quality score, the more generalized Alternate Health Eating Index, and the DASH diet score. In each of these analyses, they found the same result. People who improved their diet quality over the 12 years of the study had less risk of death during those 12 years.

A Few Caveats

Buried in the paper are two important cautions about overstating what this study proves:

1. “Residual and unmeasured confounding cannot be ruled out.” In other words, the folks who improved their diets might have been different in other ways that were actually important for reducing their risks. This is a study of correlation, not causation. However, we also note that prior randomized, controlled studies of the DASH diet and the Mediterranean diet boost the credibility of findings in this new study.

2. “Because dietary data were reported by the participants, measurement errors were inevitable.” In other words, self-reported dietary data can fool us because people unconsciously fudge their answers.

And finally, it’s worth putting the roughly 14% reduction in risk of death over a 12 year period into perspective. It’s not huge, even though it’s statistically significant. That’s because you’re getting a14% reduction in a risk that’s not huge already. If you want deeper insight into interpreting such numbers, have a look at this discussion.

Bottom line: if your diet is poor and you improve it, your odds for good health improve. If your diet is good, keep it up. If you have real concerns related to health and diet, consult with a registered dietitian. RDs are the real pros.

Click here to read the study and here to read the PR from Harvard.

Eat Fish, Live Longer; photograph © duluoz cats / flickr

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July 14, 2017

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