One interesting finding

To drill down even deeper into the question of why such vast differences exist, the researchers designed another experiment that involved personalized dietary interventions on 26 new volunteers. The goal was to reduce post-meal blood sugar levels. The clinicians designed two sets of specialized— breakfast, lunch, dinner and up to two intermediate meals — for each person that were theorized to be a "good" diet or a "bad" diet. Every participant followed the diets for a full week. The good diets worked, and not only did they see their blood sugar levels going down, they found alterations in their gut microbiota. One interesting finding was that even though the diets were very personalized, several of the changes in the microbiota were similar for participants.

This appears to imply, the researcher said, that we're "really conceptually wrong" in our thinking about the obesity and diabetes epidemic.

We think "we know how to treat these conditions, and it's just that people are not listening and are eating out of control," Segal said, "but maybe people are actually compliant and in many cases we were giving them the wrong advice."

By using the information from the study, the researchers were able to come up with the holy grail of dieting: an algorithm that takes hundreds of factors about a person and turns them into a tailor-made meal plan. The results were pretty surprising to both the doctors and participants. “It wasn't just salad every day,” Segal told The Atlantic. “Some people got alcohol, chocolate, and ice-cream, in moderation."