Why there’s no diet that works for everyone

It’s time to brace yourself for the season of fad foods and trendy diets to fight the holiday bulge: The time between Thanksgiving and New Year’s accounts for a fork-dropping 75 percent of the extra weight we gain during the year.

Unfortunately, as anyone who’s tried to diet knows, finding one that actually helps you shed pounds is next to impossible, and a new study has finally found out why — and it’s going to change everything we thought we knew about nutrition.

When it comes to recommending diets, doctors and nutritionists often rely on foods’ glycemic index (GI), which estimates how much a person’s blood sugar is expected to rise based on the amount of carbohydrates in the food.

Instead of GI being an intrinsic property of the food, the Personalized Nutrition Project found that blood sugar responses differ between people who ate the same thing.

“Most dietary recommendations that one can think of are based on one of these grading systems; however, what people didn’t highlight, or maybe they didn’t fully appreciate, is that there are profound differences between individuals — in some cases, individuals have opposite response to one another,” says study co-leader Eran Segal with the Weizmann Institute of Science.

Following a hunch about the lack of success with low-GI diets in many people, Segal and his team used blood sugar monitors to track 800 people over the course of a week. They recorded everything they ate, as well as their sleep patterns and exercise habits, and analyzed participants’ microbiomes through stool samples.

The differences in response to the same foods turned out to be huge, and sometimes even contradictory. For example, a middle-aged woman learned that tomatoes, commonly considered part of a healthy diet, cause her blood sugar to spike.

The study also showed that lifestyle habits affect blood sugar levels, which varied depending on whether a meal was eaten after waking up or working out.

“We chose to focus on blood sugar because elevated levels are a major risk factor for diabetes, obesity and metabolic syndrome,” Segal tells theWeizmann Wonder Wander. “The huge differences that we found in the rise of blood sugar levels among different people who consumed identical meals highlights why personalized eating choices are more likely to help people stay healthy than universal dietary advice.”

In the future, Segal predicts that nutritional recommendations will shift from general guidelines to personalized meal plans, using tools like DNA testing and microbiome analysis.