Arizona State University researchers confirm gut microbiota modifies calorie absorption
- A clinical trial has confirmed that the human gut microbiota can modify the calories our bodies absorb from food, revealing that a diet rich in fiber allows people...
- Researchers at the University State of Arizona, including microbiologist Rosa Krajmalnik-Brown, published their work in PLOS ONE to propose a new understanding of human digestion.
- For over a century, calorie calculations have relied heavily on Atwater factors, which assign roughly four kilocalories per gram to proteins and carbohydrates and nine to fats.
A clinical trial has confirmed that the human gut microbiota can modify the calories our bodies absorb from food, revealing that a diet rich in fiber allows people to absorb roughly 116 fewer calories per day than a conventional Western diet.
University State of Arizona Researchers Publish New Digestion Model
Researchers at the University State of Arizona, including microbiologist Rosa Krajmalnik-Brown, published their work in PLOS ONE to propose a new understanding of human digestion. Instead of working alone, the human body operates alongside an internal microscopic ecosystem that actively participates in the overall metabolism.
For over a century, calorie calculations have relied heavily on Atwater factors, which assign roughly four kilocalories per gram to proteins and carbohydrates and nine to fats. However, that established formula does not capture all the transformations food undergoes inside the human body. The baseline for the new investigation came from a clinical trial published in Nature Communications that compared two distinct dietary patterns.
Fiber Diet Reduces Usable Energy Without Increasing Hunger
The trial compared a high-fiber, resistant-starch diet built to support microbial activity against a Western-style diet containing more processed foods and less fiber. Participants absorption rates shifted notably, taking in approximately 116 fewer calories each day on the microbiota-friendly diet. Crucially, those participants did not report any increase in hunger despite extracting less energy from their meals.
Investigators emphasize that this outcome does not mean consuming fiber serves as a universal weight-loss strategy. The study only identifies energy absorption differences under tightly controlled conditions. Other variables, including food processing and physical structure, also affect how much energy the body takes in.
DAMM Mathematical Model Quantifies Microbial Fermentation
To account for these microbial shifts, scientists developed a mathematical model named DAMM, representing digestion, absorption, and microbial metabolism. The model integrates gut microorganism activity directly into human energy balances. While the small intestine absorbs many nutrients, specific fibers and resistant starchy components travel onward to the colon.
Inside the colon, microorganisms ferment substances that standard human digestive enzymes cannot fully break down. This fermentation produces short-chain fatty acids that cross the intestinal wall to feed the host organism. Model estimations indicate these microbial products contributed about 140 kilocalories daily, representing 7.4 percent of usable energy.
Even though the fiber-rich diet increased the production of those microbial compounds, participants still absorbed fewer total calories overall. The energy recovered from the microbes did not offset the absorption differences recorded during earlier digestive stages. Overall statistical adjustments in the energy predictions improved from 88 percent to 96 percent when using the new model.
Rosa Krajmalnik-Brown has described digestion as a collaboration between our cells and billions of intestinal microorganisms.
Future Nutritional Applications Remain Limited by Current Uncertainty
Krajmalnik-Brown, who directs the Biodesign Center for Microbiomics and Health, notes that digestion functions as a partnership between human cells and billones of intestinal microorganisms. These microbes extract leftover nourishment and generate usable substances for the host body. The discoveries open new pathways for studying obesity, diabetes, and related metabolic conditions.
Future nutritional recommendations might incorporate individual microbiota compositions to tailor diets based on personal processing capabilities rather than food choices alone. Yet, DAMM remains strictly a research tool. The model requires evaluation across more diverse populations and varying dietary conditions before it can predict individual calorie absorption or replace current nutritional guidelines.