Gut bacteria and calories: body absorbs less energy on a high-fiber diet

How much energy the body extracts from food appears to depend partly on gut bacteria. Researchers at Arizona State University and AdventHealth's Translational Research Institute in Orlando developed a mathematical model called DAMM for this purpose. They compared it with measurements from a controlled diet study in healthy adults. The findings were published in the journal PLOS One, and ScienceDaily reported on them on Oct. 12.

The study compared two eating plans: one rich in fiber and resistant starch, and a more processed, lower-fiber Western-style diet. On the Western diet, participants absorbed about 116 more calories per day on average. Participants on the high-fiber diet did not report feeling hungrier. Short-chain fatty acids produced by microbes in the colon supplied about 140 calories a day on average, or roughly 7.4 percent of usable food energy, according to the study.

“Digestion is not just a human process,” said co-author Rosa Krajmalnik-Brown. The model estimated calorie absorption more accurately than the conventional Atwater method, which generally underestimated it. The authors stress, however, that DAMM is a research framework rather than a ready-to-use method for personal diet plans. Further studies are needed to test whether the results hold across other populations, eating patterns and microbiome compositions.