Today’s episode is about a narrow question and a broad question. The narrow question is: Is ice cream secretly good for you? The broader question is about the nature of uncertainty and truth, how diet science actually works, and how bias plays a role in scientific discovery. Our guest is public health historian and journalist David Johns, who has reported on ice cream science for The Atlantic.
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In the following excerpt, Derek and David Johns discuss some of the nutrition scientists who found a link between ice cream consumption and a reduced risk of diabetes.
Derek Thompson: Dave, I think we have to start with a rumor that you heard last summer. This was a rumor about a Harvard doctoral student presenting diet research to his thesis committee, and in that research, he made a stunning confession about his conclusions. Take us into that thesis committee. What was his confession?
David Johns: Yeah, this was kind of a little tip or story that I heard from somebody kind of in the broader public health world, who I was talking to for a totally different reason, and they told me about this very funny dissertation defense that had happened at Harvard, where a doctoral student named Andres Ardisson Korat was defending his nutrition science dissertation, and he had found that consumption of ice cream—I think eating about half a cup of ice cream a day—was associated with a reduced risk of diabetes. So the idea was ice cream was somehow protective. So obviously, this was very surprising: not what a budding nutrition scientist would expect to discover. It was something that seemed to run against everything that the entire field had said before.
Thompson: So you’ve read this dissertation. You read that this isn’t the first study that has come across a similar effect. That is the idea that ice cream might actually be good for you; it might reduce your risk of getting diabetes. You reached out to Andres Ardisson Korat. Would he talk to you?
Johns: So yeah, I emailed him. I emailed him through his Tufts University email address, where he’s a nutrition scientist. He didn’t respond to me a couple times. Then, I think I tried him through LinkedIn, thinking that would go to his personal email. Nothing there. I maybe tried another time through his—I think I emailed him four times. Finally, I reached out to the Tufts press office, and I said, “Hey.” I was kind of puzzled, because I was not that long ago a postdoc. I have a degree, a PhD, in the history of public health. And when reporters call, typically, young scientists are eager to talk to journalists, because it’s like, “I know all about this particular area of research that no one else cares about.” And also because, well, it’s one of the norms of science to be transparent and to be open and to share your findings. But eventually, the Tufts press office got back to me and said, “He’s not available for this,” basically. Then I actually asked. I was like, “Why is he not available for this?” And they were like, “We could try to find out.” Basically, I never found out.
Thompson: So now we’ve got a real mystery on our hands, and like a good detective, you go digging to find corroborative evidence. And this brings us to the University of Minnesota scientist Mark Pereira. He also studied the health effects of eating dairy. And you write, “When I scroll to the bottom of Pereira’s article, down past the headline-making conclusions, I saw in Table 5 a set of numbers that made me gasp.” Dave, what made you gasp?
Johns: As a historian or academic in general, you deal more with paper records than journalists. I’m sort of a hybrid. I use journalistic methods, which are super powerful and important, and historical kinds of methods as well—obviously, in this case, writing for a popular audience. So I went into the paper records, and I was reading through the paper trail of the academic literature. It seemed to me that this one particular paper written by this guy, Mark Pereira at the University of Minnesota, as you mentioned, had kind of spawned this whole interest in this research area, which was about dairy and diabetes. And it started up just after September 11, 2001, or into the 21st century. In 2001, the then surgeon general, David Satcher, had announced we’re in an obesity epidemic.
So that was sort of the beginning of the idea that there was epidemic obesity and diabetes. So people started asking questions about: What should we eat to prevent obesity? What should we eat to prevent diabetes in particular? And it was really confusing; particularly dairy was confusing. So this guy, Pereira, had gone and researched, and his first study, which looked at dairy in this cohort of like 5,000 people, basically found that almost every kind of dairy was protective against diabetes, which was really surprising, because we were still in the end of what you might call the low-fat era, which ran more or less through the ’90s. So this idea that something with a lot of saturated fat—including whole milk and cheese—basically was protective against diabetes ran against a lot of conventional thinking. So he was super surprised about that.
As I went through the table, because I’ve got ice cream on my brain at this point, I see in the table, this Table 5, the strongest effect he found was with something called dairy-based desserts. When I later finally talked to Pereira, he was like, “Yeah, that’s mostly ice cream.” So that was a category that was like—I mean, when you eat dairy-based desserts, you’re eating mostly ice cream, maybe some pudding, Klondike bars thrown in there, but that’s ice cream too.
This excerpt was edited for clarity. Listen to the rest of the episode here and follow the Plain English feed on Spotify.
Host: Derek Thompson
Guest: David Johns
Producer: Devon Manze