There Really Is No 'One Size Fits All' Diet Plan, According To Study

And that could be the reason you're not losing any weight on that diet.
Alexandra Grablewski via Getty Images

Have you ever followed your doctor’s weight loss nutrition plan to a T, only to stubbornly remain at the exact same weight -- or worse, gain weight?

There’s a reason for that, according to an ambitious research project by scientists in Israel. Researchers Eran Elinav and Eran Segal of the Weizmann Institute of Science have just published the results of a large, comprehensive study in the journal Cell that found people can metabolize the exact same foods in very different ways.

What this means is that a healthy diet for one person may not be healthy for another person. Yet doctors all over the world tend to prescribe the same kinds of foods to people struggling with weight or health issues. Rather than recommend a cookie-cutter solution to weight problems, the researchers say, doctors could be more effective by recommending a personalized nutrition plan to a patient, based on the way that patient metabolizes certain foods.

"After seeing this data, I think about the possibility that maybe we're really conceptually wrong in our thinking about the obesity and diabetes epidemic,” Segal said in a statement. "The intuition of people is that we know how to treat these conditions, and it's just that people are not listening and are eating out of control -- but maybe people are actually compliant but in many cases we were giving them wrong advice."

Some fellow doctors, however, are a bit more skeptical about the pair's conclusions.

The Study

To measure how food was digested, Elinav and Segal recruited 800 people and studied them intently over the course of one week. Participants were asked to log every bite, sip, exercise session, bowel movement and sleep session on a phone app. Their blood sugar levels were measured every five minutes by a device attached to their bodies, and they turned in stool samples for gut bacteria analysis. They also gave blood samples and ate a few of the same exact meals for breakfast, so that the scientists could gauge all of the different effects the same food would have on different people.

Using all that data, Elinav and Segal mapped out which foods affected participants’ blood sugar the most. They used blood sugar as a health risk indicator because the higher blood sugar spikes and the longer it stays elevated, the more likely a person is to develop Type 2 diabetes, obesity and other facets of metabolic syndrome like high blood pressure, fatty liver disease and cardiovascular disease.

What they found was that the participants all responded very differently to foods, even after meals in which participants were eating the same exact provided foods. In the video above, the researchers explain that sushi actually caused one man’s blood sugar to spike higher than ice cream did. For another participant who had struggled to lose weight on different diets all her life, the researchers found that eating a seemingly healthy food -- tomatoes -- spiked her blood sugar.

"Examples are numerous -- some participants (in fact most participants) feature a lower glycemic response to bread with butter as compared to bread, despite its higher caloric content,” Elinav told The Huffington Post. "Some individuals’ glucose levels spike to fresh fruit while not spiking on [a] moderate amount of alcohol (a glass of beer); in some individuals pizza produces a large spike, in others it did not."

The researchers then selected 26 of the participants to see if they could provide personalized nutrition recommendations would bring down the subjects' blood sugar levels. And indeed, Elinav and Segal were able to lower blood sugar levels after recommending meals made of foods they knew wouldn’t spike individual participants’ blood sugar.

Interestingly, these dietary changes also resulted in a change in gut bacteria in the participants. That may be important because gut bacteria -- the billions of microorganisms living in our body -- help us by breaking down our food for us in our stomachs and intestines. Past studies have suggested that while we’ve all got unique communities of bacteria living inside us, depending on our environments and what we inherit, some kinds of bacteria are more helpful than others when it comes to blood sugar, obesity and diabetes. And we can perhaps influence which gut bacteria live in our intestines by eating certain kinds of foods.

Future Plans

Segal and Elinav’s research was funded by general academic grants and they received no commercial funding. But the pair said they’ve already licensed their research methods to an outside company to continue building on their findings. They want to develop a service that creates personalized nutrition plans for people with pre-diabetes, diabetes, obesity and other health complications that are linked to nutrition.

For example, because they were able to test their methods on each other, Segal and Elinav have made some personal changes to their own diets now that they know what foods spiked their blood sugar levels. Elinav found that for him, it was best to reduce both bread and beef, while beer seemed to have no effect on his blood sugar. Segal, on the other hand, has to avoid sushi and bread. Happily, he has found desserts that he can eat without guilt.

"I also found out that dark chocolate and ice cream do very little to my sugar levels, and I now eat these on a regular basis,” said Segal. Lucky guy.

Unfortunately, until the service launches, Segal and Elinav don’t have much advice to give those who want to customize their diet now, except to confirm that there really is no “one size fits all” diet that would work well for everyone.

Is it a breakthrough?

Dr. James DiNicolantonio, a cardiovascular research scientist at Saint Luke’s Mid America Heart Institute and associate editor of BMJ’s Open Heart journal, was not involved in the study and is skeptical of Segal and Elinav’s results. He says there’s little practical takeaway for patients or health care providers, and questioned their decision to measure blood sugar levels after a meal, as measuring insulin levels after a meal is a more established way of determining whether people are developing insulin resistance that can lead to type 2 diabetes.

Segal and Elinav agree with DiNicolantonio that insulin level measurements would have been helpful, too, but pointed out that only blood sugar levels can be continually measured the way they wanted for the research. They recorded over 2,000 blood sugar levels per participant with the attached device, while pricking a person for a drop of blood 2,000 times to get insulin levels would have been impossible -- or at least highly unpleasant, especially while the participants were sleeping.

Dr. Suneil Koliwad, an assistant professor at the University of California, San Francisco Diabetes Center and the Gerold Grodsky Chair in diabetes research, also had concerns about Segal and Elinav’s findings. He was wary of the study’s reliance on self-reported diet, a method of data collection that's notoriously inaccurate, especially with people who are obese or have diabetes. He also pointed out a lack of research about what a blood sugar spike may actually mean if, say, it was truly triggered by a healthy food such as a tomato.

But despite the fact Koliwad thought it was premature to be developing a consumer product based on this study, he was much more optimistic about its potential to spur future research that could one day lead to reliable consumer products and services that create personalized health plans in general.

“Potentially market ready tools that can be a great service to people who want to prevent obesity, diabetes and cancer, are on the horizon, and its going to be studies just like the one you’re asking me about that will lead us to that point,” Koliwad told HuffPost. “And that’s not too far off -- I’m talking years, not decades, and that’s very heartening to all of us who work in the field of metabolism."

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