Do you know whether eggs are good for you? What about coffee, red wine, or chocolate? Most people probably have a yes-or-no impulse about each of these things, thanks to the amount of media coverage given to studies looking for health benefits or detriments of individual foods. And no matter what you say, you’re probably right, according to at least some of that science—findings often reverse or contradict one another over time, even if the conflicting studies are all methodologically sound.
“Nutritional studies are extremely difficult to do, and it’s very hard to figure out what people are actually eating, even if you try your best,” said the journalist Christie Aschwanden, speaking on a panel at the Aspen Ideas Festival, co-hosted by the Aspen Institute and The Atlantic. “If I were to ask you how many times you ate tomatoes last year and what serving size tomato you ate, it’s very difficult to answer that question.”
When studies try to set a diet or even provide food themselves, studying nutrition can still be distressingly inexact for a very relatable reason: Study participants aren’t any better at sticking to a diet than anyone else. “Even if you wanted to take a large group of people and split them into two, what often ends up happening is the two groups are actually much more similar than they’re intended to be, because you have adherence problems,” Aschwanden said.
The panel’s moderator, Corby Kummer, noted that participants often skew results just by having good intentions. “It’s really hard to think of what you actually ate with any kind of accuracy,” said Kummer, the executive director of the Aspen Institute’s Food and Society Program and a senior editor at The Atlantic. “You immediately forget, and you do what everyone does on food surveys, which is lie.”
In spite of study-to-study variation, most nutritionists and researchers agree on the broad strokes. Eating a variety of fresh, minimally processed foods and plenty of fruits and vegetables is one of the simplest ways humans can bolster their health, even if that reality isn’t as new or exciting as many journalists writing about nutrition might wish it were. (Sorry.)
New research on the variation of people’s responses to particular foods may also explain the circuitous route science has taken to establishing how certain foods affect health. “Everybody assumed there was this one diet which was somehow magic for all people, which couldn’t be further from the truth,” said Eric Topol, another panelist and the executive vice president of Scripps Research. “Finally, what we can acknowledge is that we have this unique response to food, and it’s not just the gut microbiome, but that’s a big part of the story.”
Topol said he was so interested in how the gut microbiome—the ecosystem of microorganisms that live in the human digestive system—impacts health that he signed up for a study with the Weizmann Institute of Science to spend a week measuring his own body’s response to food. What he found shocked him: Oatmeal was spiking his glucose to potentially dangerous levels, but bratwurst was rated as an A-plus food for him.
“Is it gonna change my whole nutritional plan? No,” said Topol, who, as a cardiologist, indicated a reticence to eat a bunch of sausage. “I think what it indicates is we’re chipping away at this [mystery].” More than ever, it’s looking like nutritional science is so variable because individual people respond to individual foods in vastly different ways.
Research into the gut microbiome and what it can reveal about personalized nutritional response is still in its infancy, and both Aschwanden and Topol urged caution when evaluating microbiome-testing services that are currently available to consumers, because they simply don’t have the evidence necessary to back up their use. For now, it’s wait and see—and then wait and see more.
“I think too often the public has sort of been given this view that science is a magic wand that turns everything into truth,” Aschwanden said. “But it turns out science is very often wrong on the way to being right.”