This discovery may prove why some people can follow a diet to the letter and still gain weight.
A new study published in the journal Cell found the problem could be in how diets approach blood sugar levels.
Spikes in blood sugar are linked to heart problems, obesity and diabetes.
It's largely believed that every person's blood sugar will respond the same way to the same foods. Yet the study, which used roughly 800 participants, found that their blood sugar reacted differently to the same diets.
Researchers used the findings to develop an algorithm that predicts how blood sugar levels would react to different foods.
From there, a group of participants were given a personalized "good diet" and a "bad diet" to follow for a week each. And what was on those individualized diets might surprise you.
One of the researchers told the Atlantic the good diets weren't "just salad every day. Some people got alcohol, chocolate, and ice-cream, in moderation." Foods that a dietician probably wouldn't recommend.
The good diets led to significantly lower blood sugar levels and decreased other factors linked to Type 2 diabetes.
Some critics argue the algorithm was never directly compared against other measures though, like the glycemic index, so more research may be needed.
Still, some say the study could change what we know about so-called healthy foods. The researchers say they hope to do another test of the algorithm, this time over the course of a year.
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