Your Gut's Methane-Making Microbes Could Secretly Turn Fiber Into Extra Calories

06 Nov. 2025, By D. Nield
https://www.sciencealert.com/your-guts-methane-making-microbes-could-secretly-turn-fiber-into-extra-calories

Our guts are teeming with bacteria. (Nopparit/E+/Getty Images)

We don't all respond to the same diets in the same way, and results from a new study help explain why: Gut microbes that naturally produce more methane are also able to squeeze more energy and calories out of high-fiber foods.

Everyone is different when it comes to the mix of bacteria and other microorganisms that reside in their gut, called the gut microbiome.

We already know that methane-producing microbes called methanogens can vary in abundance, which means methane (CH4) production also varies from person to person. According to this new research, these differences in our microbiomes might also have implications for how much energy we get from our food.

Led by a team from Arizona State University (ASU), the new study analyzed data from a clinical trial that put 17 participants on two diets – a low-fiber, Western-style diet, and a high-fiber diet – then measured the amount of methane produced (at both ends of the body).

Adding in data from blood and stool samples, the team found that, among those following the high-fiber diet, the people releasing more methane had also extracted more calories from their food. It suggests these high-methane microbiomes are essentially more efficient at breaking down fiber for energy.

"That difference has important implications for diet interventions," says microbiologist Blake Dirks, from ASU.

"It shows people on the same diet can respond differently. Part of that is due to the composition of their gut microbiome."

Gut microbes that break down fiber produce a range of byproducts that are converted into other compounds, such as methane (CH4) and hydrogen sulfide (H2S), which we either absorb or excrete. (Dirks et al., ISME J., 2025)

The researchers noted an increase in the levels of short-chain fatty acids (SCFAs) in the blood of the higher methane producers, particularly one called propionate. SCFAs are made when gut microbes break down and ferment fiber, and propionate has been linked to a range of health benefits, including reduced junk food cravings.

This fermentation process also creates hydrogen, which methanogens can then convert to methane. The researchers think that as the hydrogen gets converted, this helps to clear the way for more fiber to be digested.

"The human body itself doesn't make methane, only the microbes do," says microbiome researcher Rosy Krajmalnik-Brown, from ASU.

"So we suggested it can be a biomarker that signals efficient microbial production of short-chain fatty acids."

High-fiber diets have long been associated with a range of health benefits: Fiber helps keep the digestive system running smoothly, and cultivates a gut microbiome that's more resistant to damage and disease.

What this study adds is extra detail on why fiber might be more efficiently processed in certain guts that are rich in methanogens. It's not yet clear, though, whether this is beneficial or not; fiber improves digestion, but this type of microbiome also extracts more calories.

The study team suggests these methanogens may have been essential in early humans, enabling them to extract as much nutrition from their food as possible. But the foods that make up modern, Western diets tend to be far more energy-dense and fiber-poor, so this particular gut mix is way out of its element now.

It's another example of how central our gut microbiomes are to many bodily processes. Next, the researchers want to expand their experiments to look more closely at how methanogens might impact dieting, and how this works across a broader range of people.

"The participants in our study were relatively healthy," says Dirks.

"One thing that I think would be worthy to look at is how other populations respond to these types of diets – people with obesity, diabetes or other kinds of health states."

 

 

 

 

The Life of Earth 

https://chuckincardinal.blogspot.com/