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2Nutrition science’s most preposterous result (Part II)
Studies show a mysterious health benefit to ice cream. Scientists don’t want to talk about it.
April 13, 2023, The Atlantic
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So how did the Harvard team explain away the ice-cream finding? The theory went like this: Maybe some of the people in the study had developed health problems, such as high blood pressure or elevated cholesterol, and began avoiding ice cream on doctors’ orders (or of their own volition). Meanwhile, people who didn’t have those health problems would have had less reason to give up their cookies and cream. In that scenario, it wouldn’t be that ice cream prevented diabetes, but that being at risk of developing diabetes caused people to not eat ice cream. Epidemiologists call that “reverse causation.”
To test this idea, Hu and his co-authors set aside dietary data collected after people received these sorts of diagnoses, and then redid their calculations. The ice-cream effect shrank by half, though it was still statistically significant, and still bigger than the low-fat-dairy effect that Harvard had publicized in 2005. In any event, if people who received adverse diagnoses cut back on their ice cream, you might expect that they’d also cut back on, say, cake and doughnuts. So shouldn’t there be mysterious protective “effects” for cake and doughnuts too? “There should be,” Mozaffarian said. “That’s why the finding for ice cream is intriguing.”
The new analysis was hardly a slam dunk. On paper, the yogurt and ice-cream effects still looked pretty similar. “Within the realm of statistical uncertainty, they’re identical,” Mozaffarian told me. But in the 2014 paper, he and the other authors had argued that “reverse causation may explain the findings” for ice cream. And as academia’s public-relations machinery came to life, nuance went out the window.
