Gut microbes may convert fiber into extra calories, study suggests - Video

Scientists at Arizona State University have discovered that certain microbes in the human gut, known as methanogens, influence how efficiently individuals extract calories from high-fiber foods. Published in The ISME Journal, their research highlights that people whose gut microbiomes produce more methane absorb more energy from fiber-rich diets, suggesting a novel biomarker for personalized nutrition.

The gut microbiome, the community of microorganisms living in the digestive tract, breaks down food components the body cannot digest alone. One key function is fermenting dietary fiber into short-chain fatty acids (SCFAs), an important energy source. Methanogens consume hydrogen produced during this fermentation, releasing methane gas as a byproduct and maintaining chemical balance. This microbial activity appears to enhance energy absorption.

In collaboration with the AdventHealth Translational Research Institute, researchers enrolled participants who followed two controlled diets of equal macronutrient content but differing in fiber: a processed, low-fiber diet and a whole-food, high-fiber diet. Each participant spent six days inside a whole-room calorimeter-a sealed chamber that continuously measured metabolic rates and methane emissions via breath and other routes-allowing precise tracking of energy use and microbial methane production. Blood and stool samples were collected to assess metabolism, microbial activity, and SCFA levels.

Results showed that participants generally absorbed fewer calories from the high-fiber diet than from the processed diet. However, individuals with higher methane production absorbed significantly more calories from fiber, linked to elevated SCFAs in the gut. Methane production may thus serve as an indicator of efficient fiber fermentation and calorie extraction.

Lead author Blake Dirks noted that these findings emphasize how the gut microbiome shapes individual metabolic responses to diet, underscoring the potential for personalized nutrition interventions to optimize health outcomes based on microbial composition.

REFERENCE: Blake Dirks, Taylor L Davis, Elvis A Carnero, Karen D Corbin, Steven R Smith, Bruce E Rittmann, Rosa Krajmalnik-Brown. Methanogenesis associated with altered microbial production of short-chain fatty acids and human-host metabolizable energy. The ISME Journal, 2025; 19 (1) DOI: 10.1093/ismejo/wraf103