Researchers say different diets work better on different people, depending on what kind of bacteria they have in their gut.

Have you ever known someone who seems to lose weight simply by thinking about dieting?

Meanwhile, you can follow expert advice for weeks and months, only to lose maybe 1 pound for every 5 pounds they lose?

It’s frustrating, right?

And it can be that thing that convinces you that dieting isn’t worth it.

It turns out that for some people… it might not be.

At least, not in the traditional sense.

A recent study out of Denmark analyzed feces samples of 57 people who were following either a New Nordic diet (lots of fruit, vegetables, fiber, and whole grains) or an average Danish diet.

Researchers found that people with a higher proportion of Prevotella intestinal bacteria compared to Bacteroides intestinal bacterial lost an average of about 7 pounds when following the New Nordic diet as opposed to the traditional Danish diet.

For those with less Prevotella, there was no weight loss difference between the two dieting groups.

The gist of the research was pretty simple.

Traditional dieting advice worked for participants with certain gut bacteria levels.

But for 50 percent of the study participants, that same advice was essentially useless.

Mads Fiil Hjorth, a study researcher and assistant professor at the Department of Nutrition, Exercise and Sports at the University of Copenhagen, explained, “The study shows that only about half of the population will lose weight if they eat in accordance with the Danish national dietary recommendations and eat more fruit, vegetables, fibers, and whole grains. The other half of the population doesn’t seem to gain any benefit in weight from this change in diet.”

Healthline spoke about the study results with Kristin Kirkpatrick, MS, LD, RD, a licensed, registered dietitian and wellness manager at the Cleveland Clinic Wellness Institute.

“I agree 100 percent that there is no one-size-fits-all approach to weight management and weight loss,” she explained. “I’ve found with my own patients that some individuals may work well with one approach but not with others. That’s why it’s so important that clinicians find as personalized of an approach as possible with their patients.”

It’d be great if there were hard and fast rules to losing weight that everyone could follow. But that’s simply not the case.

“I think this is just another reminder of how powerful our gut is,” Kirkpatrick explained. “And how much it controls the rest of our health. Poor diet and bad lifestyle choices can severely impact our gut microflora. This study can solidify even further why our gut health should be a top priority.”

Still, she recognizes that more research needs to be done.

“I’d love to continue seeing studies on gut health and how lifestyle choices and various diets impact our gut.,” she said. “While this study is a step in the right direction, we need to always think more high level and get people to eat more real food and less manufactured calories. That is, after all, the first step toward living long and better lives.”

While the results are interesting, is it as simple as sending a fecal sample to a lab to find out which dieting options might be best for you?

Well, not yet.

“These results show that people having a high abundance of Prevotella-to-Bacteriodes bacteria in their gut lose more weight when consuming a high amount of dietary fibers, while people with a low abundance of Prevotella-to-Bacteriodes bacteria do not lose additional bodyweight by consuming additional fibers,” Hjorth told Healthline.

“There currently exists no ready-to-use test kit on the market that can tell consumers which of these groups they belong in, but something is being designed at the moment,” he said.

So you might not be able to find out which group your own gut bacteria places you in today.

That can make it harder to choose a diet specifically suited to your needs.

But Kirkpatrick explains there’s still plenty that can be done to pinpoint what is and isn’t working for you.

“I’d suggest that anyone currently failing to find success in their dieting efforts should sit down with their physician or dietitian and go through every aspect of life that may impact the lack of results they are seeing,” she said.

“Are they getting enough sleep? Are they surrounded by supporting family and friends? What are they eating (and not eating) and when? Sometimes even just the timing of meals can make a difference in weight loss impact. And there are other important factors to consider as well, like age, gender, disease status, and physical activity.”