Gut Bacteria May Change How Many Calories Your Body Absorbs

The number of calories printed on a food package may seem like a simple measure of the energy you will get. But it does not always match the calories your body actually takes in. One reason is that digestion involves more than breaking down food. It also depends on trillions of tiny living things, called microorganisms, that live in your digestive system.

Scientists at Arizona State University have made a mathematical model to study this often overlooked part of digestion. It is called DAMM, which stands for digestion, absorption and microbial metabolism. The model follows how food moves through the digestive system, how much energy the body takes in directly, and how gut microbes handle what is left over. It also predicts which digestion products enter the body and which are passed out as waste. The study was published in the journal PLOS One, and scientists at the AdventHealth Translational Research Institute in Orlando, Florida, helped with the project.

The researchers hope the model will improve understanding of conditions such as obesity and diabetes. With more work, it could someday help doctors design diets for individual patients. Professor Rosa Krajmalnik-Brown said digestion is a partnership between our bodies and the microbes in our gut, and that it matters to feed those microbes properly.

For more than 100 years, scientists have estimated the energy in food with a system based on Atwater parameters. It gives an average number of calories for each gram of fat, carbohydrate and protein and adds them up. The system is practical and widely used, but it does not take into account how different foods feed gut bacteria, or how the bacteria turn undigested material into substances that the body can use for energy.

One example is short-chain fatty acids. Microbes in the colon make them when they break down fiber and other food parts that were not absorbed earlier in the digestive system.

In a controlled study, people who ate a high-fiber diet absorbed about 116 fewer calories per day than people who ate a typical Western diet, and they did not feel hungrier.