A new Mayo Clinic preliminary study may explain why.
According to the preliminary study published today, specific gut bacteria may make it harder for some people to lose weight, whether or not they restrict their diets and exercise more.
“I hear about this all the time, people say, ‘I’m doing everything I can,’ and they’re not losing weight,” said Dr. Purna Kashyap, M.B.B.S., a Mayo Clinic gastroenterologist and co-senior author of the study.
Kashyap and other researchers knew that gut bacteria had a role in giving people more energy from their food. The microbes in our digestive tracts help humans gain, store and use the energy — or calories — in food.
That’s usually a helpful process, Kashyap said.
“We all want to get the maximum from what we do,” he said. “But if you are modifying your diet and you want to lose weight, you may not.”
Kashyap and the other researchers looked at 26 people on the Mayo Clinic Obesity Treatment Research Program, a rigorous, three-month weight loss program.
Program members go on a volumetric diet, which is high in fruits and vegetables and other high-volume, low-calorie foods that fill people up without — one hopes — imparting a great many calories.
A weight loss of five to fifteen percent is standard, Kashyap said — and expected. But some people don’t lose that much weight, even though the program closely monitors them to ensure they meet the program’s standards.
Kashyap’s team used stool samples to determine the gut bacteria of participants and tracked their weight loss at the same time. They were looking for a connection between weight loss and the type of bacteria they found.
Everyone’s gut bacteria are a little different, even among Midwesterners who share similar diets and environments. However, testing revealed that the gut bacteria of people who lost the weight were different than those who did not.
Specifically, one bacterium called Phascolarctobacterium was associated with successful weight loss, while another, Dialister, was more present in those who couldn’t.
The finding suggests that these bacteria help humans “use” their food differently — and one is better than the other at extracting extra energy, even from fruits and vegetables.
“The difference is small — the bacteria isn’t going to give you 500,000 extra calories a day,” Kashyap said. “But if you’re making small changes, you won’t lose as much weight. … It’s possible that the benefit is minimized somewhat.”
Both bacteria are from the same family, and higher levels of one mean lower levels of the other.
“We might have to look at diet interventions not as a one-size-fits-all,” Kashyap said.
Gut microbia with an increased ability to use certain carbohydrates were also associated with failure to lose weight.
More research is needed to determine how much of an effect the bacteria have on weight loss, and whether altering someone’s microbiome can make it easier to shed pounds.
If researchers want to target a certain gut bacterium, they can, using diet to shift things one way or another, or targeted antibiotics. However, Kashyap said more research is needed before that becomes a standard treatment.
A bigger study to try to replicate the findings is needed, he said, and the next step is to find out for certain whether some bacteria are extracting more energy from food than others.
However, he’s glad to have evidence that diet isn’t the only factor in weight loss.
“To me, the biggest problem is the stigma for people who don’t lose weight,” he said. “We look at them with suspicion.”