You work out regularly. You eat well. But you cant seem to lose any stubborn pounds.

What’s going on?Well, research published in the International Journal of Obesity suggests that it’s not as simple as getting your daily serving of fiber in the form of fruits and vegetables. In fact, researchers suggest, if you’re trying to lose weight, you should get your poop analyzed, because the bacteria in your gut might be holding you back.

“Certain bacterial species play a decisive role in weight regulation and weight loss,” said lead author Arne Astrup of Denmark's University of Copenhagen in a press release. “Now we can explain why a high fiber diet does not always lead to weight loss. Human intestinal bacteria is an important part of the answer and will from now on play a role in the treatment of the overweight.” In other words, you might be doing everything right, but your gut bacteria might not give a damn.

That's because there's two possible species of gut bacteria in humans that affect not only how much weight you gain or lose, but your physiology: Prevotella and Bacteroides. The two work in concert to orchestrate how your gut digests fiber; some people have more of these two bacteria, and others have less. The more of this bacteria tag team you have, the better your ability to lose weight.

Researchers figured this out by asking 62 overweight participants randomly assigned to follow either the "Nordic diet,” which is packed with fibrous fruits and vegetables, or the "average Danish diet," which permitted meatballs, liver paste, fried bacon, and other fatty Danish delicacies.

One would probably guess that those who followed the new Nordic diet would end up leaner — and indeed, that seemed to be the case. The new Nordic dieters lost a little more than 7.5 pounds in six months, compared to the average dieter's weight loss of just under 4 pounds.

But here's the twist: after the initial 6 months, the researchers made all of the study participants go on the new Nordic diet. They then split them up into two groups: Those who naturally had more of the Prevotella/Baceteroides combination swimming in their guts, and those who had less of it.

The researchers found that the new Nordic diet crammed with fiber, fruits, and vegetables only seemed to work best for people with more Prevotella/Baceteroides. Not only did their waistlines shrink, but they also lost more body fat compared to those with a lower ratio. Here's the kicker: It didn't matter what diet the person followed; only their gut bacteria concentration of Prevotella/Baceteroides.

So what does this mean? You could be doing everything right, but if you're not naturally blessed with high populations of Prevotella/Baceteroides in your gut, you're not going to lose weight as easily as someone who is. The authors say that this proves something we're starting to understand more: Not every diet works for everyone, and it's worth figuring out your unique biochemistry to figure out the best way to lose weight. For some, that means eating a boatload of fruits and veggies; for others, that's not going to work at all. Either way, science is clear: as gross as it sounds, it might be worth considering sending your poop to a lab.