The calorie values displayed on food labels are often regarded as an accurate measure of the energy the body obtains from a meal. However, emerging scientific evidence suggests that reality is far more complex, as two individuals may absorb different amounts of energy from exactly the same food.
At the center of this variation is the gut microbiome—the trillions of microorganisms that actively participate in the digestive process. A new mathematical model developed by researchers at Arizona State University in collaboration with the AdventHealth Research Institute in Florida aims to provide a more precise understanding of how food is converted into usable energy.
Known as DAMM (Digestion, Absorption and Microbial Metabolism), the model tracks the journey of food through the digestive system, measuring both the nutrients absorbed directly by the body and the contribution of gut microbes to metabolic activity.
The Limits of Traditional Calorie Counting
For more than a century, calorie calculations have relied on the Atwater system, which estimates the energy value of foods based on their protein, carbohydrate, and fat content. While the method remains a cornerstone of nutritional science, it does not account for the role of gut bacteria.
These microorganisms are capable of breaking down compounds that humans cannot digest on their own, particularly dietary fiber. During this process, they produce short-chain fatty acids, which can be absorbed into the bloodstream and provide additional energy. As a result, the calories ultimately available to the body may differ from those listed on a food label.
How the DAMM Model Works
The DAMM model evaluates digestion in stages, first estimating the energy absorbed in the upper gastrointestinal tract and then assessing the energy generated through microbial activity in the large intestine.
According to the findings, approximately 85% of usable energy comes from the upper digestive tract, while the remaining 15% is linked to processes occurring in the lower gut. Short-chain fatty acids contribute an average of about 140 calories per day, representing roughly 7.4% of total usable energy.
The Role of Diet Quality
The model was tested using data from a controlled dietary study involving healthy adults who followed two distinct eating patterns. One diet was rich in dietary fiber and resistant starch, featuring less processed foods and larger food particles. The other resembled a typical Western-style diet, characterized by lower fiber intake and a greater proportion of processed foods.
Results showed that participants following the Western-style diet absorbed an average of 116 more calories per day than those consuming the high-fiber diet. Despite absorbing less energy, individuals in the high-fiber group did not report increased hunger.
Same Meal, Different Energy Outcome
Researchers say the findings highlight how both food quality and food structure influence digestion and the way gut microbes extract energy from nutrients.
When compared with the traditional Atwater system, the DAMM model more accurately reflected the calories actually absorbed by study participants. It also captured the metabolic differences between the two dietary patterns, particularly the increased microbial activity and production of short-chain fatty acids associated with fiber-rich diets.
The researchers believe the model could improve understanding of obesity, diabetes, and other metabolic disorders. Their central conclusion is that energy extraction from food depends not only on what people eat, but also on how their unique gut microbiome processes it. Consequently, two individuals consuming the same meal may ultimately derive different amounts of energy from it.
The full study was published in the journal PLOS One.