Your gut bacteria could be changing how many calories you absorb
Scientists have developed a model showing that gut bacteria play a surprisingly important role in how many calories we absorb, meaning food labels may not tell the full story. In a controlled study, people eating a high-fiber diet absorbed about 116 fewer calories per day than those eating a typical Western diet, without feeling hungrier.
Key points
- Arizona State University researchers developed a mathematical model called DAMM that tracks how food, human digestion and gut microbes interact to determine absorbed energy.
- In a controlled diet study, participants eating a Western-style diet absorbed about 116 more calories per day than those on a fiber-rich microbiome-enhancer diet.
- The model estimated that short-chain fatty acids from the colon supplied roughly 140 calories per day, about 7.4% of total usable energy from food.
The calorie number on a food label may not reflect how much energy the body actually gets, according to researchers at Arizona State University. The team has built a mathematical model called DAMM, short for digestion, absorption and microbial metabolism, that tracks food through the digestive tract, how much energy the body absorbs directly, and how gut microbes process what is left.
The researchers say the model could improve understanding of obesity, diabetes and other metabolic disorders, and with further development help health care professionals design diets tailored to individuals.
What the diet study found
In a controlled clinical study, healthy adults followed either a microbiome-enhancer diet high in fiber and resistant starch or a Western-style diet with less fiber and resistant starch. Participants on the Western diet absorbed approximately 116 more calories per day than those on the fiber-rich diet, while those on the higher-fiber plan did not report feeling hungrier.
The model estimated that short-chain fatty acids absorbed from the colon supplied an average of about 140 calories per day, roughly 7.4% of total usable energy from food. It also estimated that about 85% of usable energy came from the upper gastrointestinal tract and approximately 15% from the lower tract.
Digestion is not just a human process -- it is a collaboration between our bodies and trillions of microbes living in the gut
— Professor Rosa Krajmalnik-Brown
How DAMM compares with older methods
For more than 100 years, scientists have used Atwater parameters to estimate energy from food by assigning average calorie values to fat, carbohydrates and protein. The researchers say that approach does not account for how foods nourish gut bacteria or how those bacteria turn undigested material into usable substances.
When compared with measurements from the controlled diet study, DAMM's estimates were closer to observed calorie absorption than those from the conventional Atwater approach, which generally underestimated how many calories participants absorbed. The team says further studies are needed to test the model across different populations, eating patterns and microbiome compositions.
