Food labels make calories seem simple. Check the package, look at the number, and you know how much energy you’re getting.
However, once inside your body, calories become more complicated to understand.
In the intestine, there are trillions of microorganisms involved in digesting food, which might influence the number of calories absorbed.
So, the calories on your food label don’t tell everything about the actual intake of energy.
Researchers managed to develop a mathematical model that estimates energy dynamics after eating, taking into account the contribution of microorganisms.
A closer look at digestion
Researchers at Arizona State University created a mathematical model called DAMM, short for digestion, absorption, and microbial metabolism.
This particular algorithm is based on tracking the progress of food in the digestive system to identify what nutrients are absorbed directly by the body, what enters the large intestine, and what the gut microbiota works with after that.
The team collaborated with experts at the AdventHealth Translational Research Institute (TRI) in Orlando, Florida.
According to the researchers, this new model will allow scientists to better comprehend the nature of obesity, diabetes, and metabolic diseases in general.
“Digestion is not just a human process — it is a collaboration between our bodies and trillions of microbes living in the gut,” said Professor Rosa Krajmalnik-Brown at ASU.
“DAMM gives us a powerful new way to quantify how those microbial partners contribute to human health and energy balance, and also point at the importance of properly feeding our gut microbes.”
Traditional calorie counts have limits
For over a century, the way to measure the caloric value of food has been through a technique referred to as the Atwater method.
This technique measures the caloric content depending on the levels of proteins, carbohydrates, and fats contained in the foods.
The Atwater method is effective in calculating caloric contents. However, this technique ignores the process carried out by the intestinal bacteria in breaking down indigestible substances such as fiber into short chain fatty acids that can be absorbed.
It is possible that this bacterial process accounts for the different effects that similar diets may have on individuals.
What the study showed
The new model was built using data from a controlled diet study involving healthy adults. Participants followed one of two eating patterns.
One diet was rich in fiber and resistant starch, featuring less processed foods and larger food particles.
The other reflected a more typical Western diet with lower fiber levels and more processed foods.
People eating the Western diet absorbed about 116 more calories per day than those eating the high-fiber diet. Even so, the high-fiber group did not report feeling hungrier.
The findings add to growing evidence that fiber affects much more than digestion. It also changes how microbes behave and how the body extracts energy from food.
The calories you never see
DAMM tracks food in stages. It first estimates how much energy is absorbed in the upper digestive tract.
The model then follows leftovers into the colon, where microbes continue breaking down material that escaped earlier digestion.
During that process, microbes produce short-chain fatty acids. These compounds can enter the bloodstream and provide additional energy.
According to the model, short-chain fatty acids contributed an average of about 140 calories per day, roughly 7.4% of total usable energy.
About 85% of usable energy came from the upper gastrointestinal tract, while about 15% came from the lower gastrointestinal tract, where microbial activity plays a central role.
The model also includes methane production by specialized microbes known as methanogens, giving researchers a more complete picture of energy flow inside the body.
A better match to real-world results
When researchers compared DAMM with the traditional Atwater approach, the newer model came closer to matching the amount of calories people actually absorbed during the diet study.
The model also reflected differences between the two diets. The fiber-rich diet delivered more material to the colon, where microbes produced higher levels of short-chain fatty acids.
This pattern matched observations from blood and stool samples collected during the clinical trial.
Professor Bruce Rittmann directs the Biodesign Swette Center for Environmental Biotechnology and is a Regents Professor of environmental engineering at ASU.
“What is truly unique about the DAMM model is that it quantitatively links human metabolism to the metabolism of the microorganisms in the colon in a way that matches the results from the clinical study and provides fundamental insight into how the microbial community works in partnership with the human host,” said Rittmann.
What comes next
Scientists are still working to better understand the complex processes involved in digestion.
As new discoveries emerge, researchers plan to expand the model to capture more of those connections.
“The DAMM model is more than just a tool for characterizing diet,” said study first author Taylor Davis, an ASU graduate research assistant.
“It’s a framework designed to evolve. As we discover more on how diet, metabolism and the microbes interact, the new insights can be incorporated into the model, allowing it to grow with us as we learn.”
The full study was published in the journal PLOS One.
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