Gut microbes may convert fiber into additional calories

The group of microbes that live in the digestive tract is known as the gut microbiome. While everyone has one, some people’s microbes produce large amounts of methane, while others produce very small amounts.

Microbes and hidden energy in fiber

The study found that people whose microbes generate more methane tend to extract more energy from high-fiber foods. This may help explain why the same meal can provide a different number of calories for different individuals once it reaches the colon.

The researchers confirmed that foods rich in fiber remain beneficial. People generally absorb more calories from a typical Western diet high in processed foods, regardless of methane levels. However, the absorption of calories in a high-fiber diet varies depending on the amount of methane produced by a person’s intestines.

These findings suggest that gut methane could become a major factor in personalized nutrition – a future in which diets are tailored to the unique microbial activity in each person’s digestive tract.

“This difference has important implications for dietary interventions,” says Blake Dirks, lead author of the study and a graduate researcher at the Center for Biodesigning Health through Microbes. “It shows that people on the same diet can respond differently. Part of this is due to the composition of their gut microbiome.” Dirks is also a doctoral student in the College of Life Sciences at Arizona State University.

Learn about methane makers

Published in ISME MagazineThe study identifies the key players: methane-producing microbes known as methanogens. These microorganisms appear to be associated with more efficient digestion and higher energy absorption.

The main function of the microbiome is to break down food that the body cannot digest on its own. Microbes ferment fiber into short-chain fatty acids (SCFAs), which provide a valuable source of energy. During this process, hydrogen gas is released. Too much hydrogen can slow fermentation, but other microbes prevent this by consuming hydrogen – keeping your digestive chemistry balanced.

Methanogens are hydrogen consumers. When they feed on hydrogen, they release methane as a byproduct. They are the only microbes in the human intestine that produce this gas.

“The human body itself does not produce methane, only microbes do,” says Rosie Krajmalnik-Brown, corresponding author of the study and director of the Center for Biodesigning Health through Microbes. “So we proposed that it could be a biomarker that indicates efficient microbial production of short-chain fatty acids.”

How microbes can shape metabolism

Researchers at Arizona State University found that interactions between these microbes may directly affect metabolism. Participants who produced more methane also had higher levels of short-chain fatty acids, indicating that more energy was created and absorbed in the gut.

To test these effects, each participant followed two different diets. One included highly processed, low-fiber foods, while the other focused on whole foods and fiber. Both diets contain equal proportions of carbohydrates, proteins and fats.

The research was conducted in collaboration with the AdventHealth Translational Research Institute, which provided access to a specialist facility. Each participant spent six days in an enclosed, hotel-like room called a full room calorimeter. This environment allowed the researchers to precisely measure metabolism and methane production.

Unlike traditional methods that rely on a single breath test, this setup continuously captures methane released through breathing and other emissions, providing a more accurate view of microbial activity.

Karen D says “This work highlights the importance of collaboration between clinical translational scientists and microbial ecologists. Combining precise measures of energy balance through whole-room calorimetry with ASU’s microbial ecology expertise has made key innovations possible,” said Corbin, co-author and research associate at the institute.

Track energy and microbial activity

Data collected from blood and stool samples revealed how much energy the participants absorbed from their food and how active their gut microbes were. The researchers then compared people with high methane production with those with lower levels.

Almost all participants absorbed fewer calories while eating the high-fiber diet than on the processed diet. However, those with higher methane production absorbed more calories from high-fiber foods than those with lower amounts of methane in their systems.

A step towards personal health

The results lay an important foundation for future studies and medical applications.

This research creates a foundation for future studies and medical treatments.

“Our study participants were relatively healthy,” Dirks says. “One thing I think would be useful to look at is how other populations respond to these types of diets — people with obesity, diabetes, or other types of health conditions.”

Although the study was not intended to stimulate weight loss, some participants lost a small amount while following the high-fiber diet. Future research may explore how methanogens impact weight loss efforts or specialized nutrition programs.

“You can see how important it is to personalize the microbiome,” says Krajmalnik-Brown. “Specifically, the diet we very carefully designed to boost the microbiome for this trial had different effects on each person, in part because some people’s microbiomes produce more methane than others.”

Other members of the ASU research team include Professor Bruce Reitman and graduate researcher Taylor Davis.

This project was funded by the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health.