On food packaging, calories often appear straightforward. You glance at the label, see a number, and understand the energy intake. However, once food enters the body, deciphering calorie significance becomes considerably more complex.
Our intestines host trillions of microorganisms involved in digestion, and their activity can affect how many calories are actually absorbed. Therefore, the calorie count displayed on a product’s packaging doesn’t fully represent the actual energy our body obtains.
Researchers have successfully developed a mathematical model to estimate energy dynamics post-meal, taking into account the contribution of gut microorganisms. The findings from this study have been published in the journal PLOS One.
Scientists at Arizona State University have created a mathematical model named DAMM, an acronym for Digestion, Absorption, and Microbial Metabolism.
This algorithm operates by tracking the journey of food through the digestive system. It determines which nutrients are directly absorbed by the body, which are then passed to the large intestine, and how the gut microbiota interacts with these remaining substances.
The research team collaborated with experts from AdventHealth’s Translational Research Institute (TRI) in Orlando, Florida. According to the researchers, this novel model will empower scientists to gain a deeper understanding of obesity, diabetes, and metabolic diseases in general.
“Digestion isn’t just a human process; it’s a collaboration between our bodies and the trillions of microbes living in our gut,” explained Professor Rosa Krajmalnik-Brown from Arizona State University. “DAMM offers a powerful new way to quantify how these microbial partners influence human health and energy balance, highlighting the importance of nourishing our gut flora.”
For over a century, a method known as the Atwater system has been used to measure food calories. This system calculates caloric content based on the levels of protein, carbohydrates, and fats present in food items.
While the Atwater system is effective for calorie estimation, it overlooks the process where gut bacteria break down indigestible materials like fiber into short-chain fatty acids, which can be absorbed.
It’s plausible that this bacterial process accounts for why similar diets can affect individuals differently. The new model was constructed using data from a controlled diet study involving healthy adults, who followed one of two dietary plans.
One diet was rich in fiber and resistant starch, contained fewer processed foods, and featured larger food particles.
The other diet mirrored a more typical Western eating pattern, characterized by low fiber and a high proportion of processed foods.
Individuals on the Western diet absorbed approximately 116 more calories per day than those following the high-fiber diet. Interestingly, the group consuming the high-fiber diet did not report feeling increased hunger.
These results align with a growing body of evidence suggesting that fiber not only impacts digestion but also modifies microbial behavior and the way the body extracts energy from food.
The DAMM system tracks food in stages. Initially, it estimates the energy absorbed in the upper gastrointestinal tract. Subsequently, the model monitors remaining food in the large intestine, where microbes continue to break down substances not previously digested.
During this microbial activity, short-chain fatty acids are produced. These compounds can enter the bloodstream and provide additional energy. The model indicates that short-chain fatty acids contributed roughly 140 calories daily on average, representing about 7.4% of the total available energy.
Approximately 85% of absorbed energy comes from the upper digestive tract, while about 15% originates from the lower tract, where microbial activity plays a central role.
The model also incorporates methane production by specific microbes known as methanogens, enabling researchers to achieve a more comprehensive view of the body’s energy flow.
When researchers compared the DAMM model to the traditional Atwater approach, the new model more accurately reflected the actual calories absorbed by individuals during the diet study.
The model also captured the discrepancies observed between the two diets. The high-fiber diet resulted in more material reaching the large intestine, leading to higher levels of short-chain fatty acid production by microbes.
These findings corresponded with data gathered from blood and stool samples collected during the clinical study. Professor Bruce Rittmann, director of the Biodesign Swette Center for Environmental Biotechnology and an emeritus professor of Environmental Engineering at Arizona State University, commented on the significance.
“The DAMM model’s uniqueness lies in its quantitative link between human metabolism and the metabolism of microbes in the colon, in a way that aligns with clinical study outcomes and provides fundamental insight into how the microbial community interacts with the human body,” Rittmann stated.
Scientists continue to investigate the intricate processes involved in digestion. As new discoveries emerge, researchers plan to expand the model to incorporate additional connections.
“The DAMM model is more than just a tool for characterizing a diet,” said co-author Taylor Davis from Arizona State University. “It’s a concept designed to evolve. As we learn more about the interplay between diet, metabolism, and microbes, new data can be integrated into the model, allowing it to grow with our understanding.”
About the Author
