Weight Loss: Here’s What Science Can (and Can’t) Tell You About the Best Way to Lose Weight

Of course, one option—and not necessarily a bad one—is to just avoid diets altogether. The goal, as registered dietitian Wesley McWhorter recently told GQ, is to focus on what you’re eating rather than what you’re restricting, and to ensure that the foods on your plate get more and more healthy over time. That can create a more sustainable pattern of better nutrition.

Weiss says he has a study coming out soon that sheds light on the question of sticking with a diet. In this new study, the best predictor of whether people followed a weight plan for the long-term was something Weiss calls “self-perceived adherence.”

“I think it has a lot to do with how well people feel,” he says. In other words, how well people think they’re doing best predicts how much weight they’ll lose.

Go With Your Gut

How individual people respond to various nutrition plans is one element of weight loss that science is still puzzling out. In the aggregate, a study can demonstrate weight loss across a group of people. But who lost weight, and who did not, might shed more light on the effectiveness of a diet than the simple average.

Eran Elinav, an immunologist at the Weizmann Institute of Science in Israel, is at the forefront of research into this topic. He’s one of the co-authors of a groundbreaking 2015 paper that followed an 800-person group that ate a total of 46,898 meals. Week to week, they monitored participants’ glucose levels, with the thinking being that people who ate foods with identical glycemic-index values would show the same spike in their blood-sugar after eating. What they found, instead, was huge variability, even in response to identical meals.

“What this told us is that this one-size-fits-all diet is probably flawed. We understood that rather than measuring foods and giving them a number, we should measure people instead,” Elinav says. It sounds simple, but people’s bodies react differently to different foods. (This likely has something to do with the gut microbiome, the mix of healthy bacteria that live in the colon and aid in our immune response.) 

Given this, a set diet plan that purportedly shows benefits isn’t exactly the right approach. In the aggregate, something like the Mediterranean diet shows benefits. At the individual level, the results aren’t always identical. “Trying to nail a one-size-fits-all diet is kind of missing the point,” says Elinav. “It might also be why different diets show different results.”

Where the science of dieting is going in the future is toward personalized nutrition. And it’s something many dietitians already intuitively know, that no one diet is going to work for everybody. It’s more likely, instead, that there are going to be a handful of diets that work for some people. The trick is identifying who those people are—and then crafting more precise dietary trials.

“I think there will be more and more well-done studies,” says Weiss. “That, I think, is what we’re headed toward.”

Sweet Potatoes, Brown Rice, and Bread