In reality, human digestion is far more complex. As food journeys through your body, it interacts with trillions of microbes in your gut that fundamentally alter how much energy you actually absorb.
To bridge this gap, researchers at Arizona State University—in collaboration with the AdventHealth Translational Research Institute—have created a breakthrough mathematical model called DAMM (Digestion, Absorption, and Microbial Metabolism). This tool provides a clearer picture of how our bodies and our microscopic partners collaborate to dictate true calorie absorption.
Why "100 Calories" Isn't Always 100 Calories
Traditional calorie counting completely ignores the lower gastrointestinal tract. It fails to account for how gut bacteria ferment undigested food and fiber into new energy sources, such as short-chain fatty acids (SCFAs).
By tracking food as it moves through the entire digestive system, the DAMM model revealed a precise breakdown of where our energy actually comes from:
- The Upper GI Tract: Accounted for about 85% of usable energy, where the human body directly absorbs nutrients.
- The Lower GI Tract (Colon): Accounted for the remaining 15% of usable energy, a zone heavily driven by microbial activity.
- Short-Chain Fatty Acids: Microbes fermenting leftover material in the colon generated an average of 140 calories per day (roughly 7.4% of total usable energy) absorbed by the body.
When compared against real clinical data, DAMM estimated true calorie absorption far more accurately than the traditional Atwater method, which consistently underestimated the actual calories people absorbed.
The Fiber Paradox: More Microbial Activity, Fewer Total Calories
The DAMM model was built using data from a controlled feeding study where healthy adults ate one of two distinct diets:
- A Microbiome-Enhancer Diet: Rich in fiber and resistant starch (whole, less-processed foods).
- A Typical Western Diet: Low in fiber and resistant starch (highly processed foods).
The 116-Calorie Difference: The study revealed that participants eating the Western diet absorbed roughly 116 more calories per day than those on the high-fiber diet—even though the high-fiber group reported feeling just as full.
This highlights a fascinating digestive paradox. The high-fiber diet delivered significantly more raw fuel to the colon, causing gut microbes to go into overdrive and ramp up their production of short-chain fatty acids. Yet, because DAMM can isolate human metabolism from microbial metabolism, it proved that the high-fiber diet still resulted in fewer total calories being absorbed by the human host overall.
The Future of Personalized Nutrition
“Digestion is not just a human process—it is a collaboration between our bodies and trillions of microbes living in the gut,” explains Professor Rosa Krajmalnik-Brown, director of the Biodesign Center for Health Through Microbiomes. “DAMM gives us a powerful new way to quantify how those microbial partners contribute to human health and energy balance."
The research team—which also included ASU Professor Bruce Rittmann and lead author Taylor Davis—designed DAMM to be an evolving framework. As science learns more about the gut environment, the model can be continually updated.
Ultimately, the researchers believe DAMM will move beyond the lab to help healthcare providers map out highly personalized nutrition plans, offering a superior weapon in the fight against obesity, diabetes, and other complex metabolic disorders.
0 Comments