Scientists have developed a new model showing that gut bacteria play an important role in how many calories people absorb. They say this means food labels may not tell us the full story.

Arizona State University researchers developed the mathematical model, known as DAMM (short for digestion, absorption and microbial metabolism), to track how food moves through the digestive tract, how much energy the body absorbs directly and how gut microbes process whatever remains. It also estimates which products of digestion are absorbed and which leave the body as waste.

In the clinical study, healthy adults followed one of two carefully designed eating plans. The first was a microbiome-enhancer diet containing substantial amounts of fibre and resistant starch; the second resembled a typical Western diet.

Despite both diets being carefully designed for the study, researchers found participants absorbed different amounts of energy. Those consuming the Western diet absorbed roughly 116 more calories per day, yet those following the higher-fibre eating plan did not report feeling hungrier.

The findings suggest that the amount of energy people obtain from food depends partly on its composition and how it moves through the digestive system, which can be influenced by differences in food processing, fibre content and microbial activity.

By accounting for the relationship between diet, human digestion and gut bacteria, the researchers say they hope to improve understanding of obesity, diabetes and other metabolic disorders. With further development, they think the approach could one day help healthcare professionals create diets tailored to individual patients.