Gut Bacteria May Alter Calorie Intake
Scientists have developed a model showing that gut bacteria play a surprising role in how many calories the body absorbs, meaning food labels may not capture the full picture.
According to Ambassador Arjan, quoted by Science Daily, Arizona State University researchers have developed a mathematical model that investigates this aspect of digestion that is often overlooked. The model, called DAMM (abbreviation for Digestion, Absorption and Microbial Metabolism), tracks the path of food through the digestive tract, the amount of energy directly absorbed by the body, and how the remaining food is processed by gut microbes. This model also estimates which of the products of digestion are absorbed and which are excreted from the body as waste.
Researchers hope to improve our understanding of obesity, diabetes, and other metabolic disorders by considering the relationship between diet, the human digestive process, and gut bacteria. With further development, this approach could eventually help health professionals design diets tailored to each patient's condition.
"Digestion is not just a human process, but a collaboration between our bodies and the trillions of microbes that live in the gut," said lead researcher Professor Rosa Krajemalnik-Brown. The DAMM model provides us with a new and powerful method to quantitatively measure the role of these microbial partners in human health and energy balance, and also to emphasize the importance of proper nutrition of gut microbes."
For more than 100 years, scientists have been using a system based on Atwater's parameters to estimate the energy intake of people from food. This method assigns the average number of calories to each gram of fat, carbohydrate, and protein, then uses those values to calculate total energy available.
Although this approach is practical and widely used, it cannot fully explain what happens during digestion. In particular, it doesn't take into account how different foods feed the bacteria in the gut or how those bacteria convert undigested substances into substances the body can use for energy.
To better understand these interactions, the researchers based their study on a controlled diet study that examined how the gut microbiome affects human energy balance. The gut microbiome consists of a large community of bacteria and other microorganisms that inhabit the digestive tract.
In the clinical study, healthy adults followed one of two carefully designed meal plans. The first was a microbiome-enhancing diet containing significant amounts of fiber and resistant starch. Resistant starch is a type of carbohydrate that escapes normal digestion in the small intestine, allowing it to reach the large intestine, where microbes can break it down. The second diet was similar to a typical Western diet and contained lower amounts of fiber and resistant starch.
Although both diets were specifically designed for this study, the participants absorbed significantly different amounts of energy. Those who followed a Western diet consumed about 116 more calories per day than those who ate a high-fiber diet.
These findings show that the amount of energy people get from food depends to some extent on its composition and how it moves in the digestive system. Differences in food processing, fiber content, and microbial activity can all affect the final result.
The DAMM model provides a more accurate way to track the energy content of food from the moment it enters the digestive tract.
First, it examines a person's diet for protein, carbohydrates, and fat, and estimates the amount of energy that can be used in the upper digestive tract.
It then tracks the remaining material as it enters the large intestine. Here, gut microbes break down nutrients that have escaped initial digestion and produce compounds such as short-chain fatty acids. The body can absorb some of these compounds through the colon and use them as another source of energy.
According to the researchers' calculations, short-chain fatty acids absorbed from the large intestine provided an average of approximately 140 calories per day. This amount represents about 7.4% of the total usable energy from food.
More broadly, the model estimated that approximately 85% of usable energy comes from the upper digestive tract, while approximately 15% comes from the lower digestive tract, where microbes are particularly important.
These findings show why traditional caloric calculations cannot fully describe human digestion. A significant portion of the energy available to the body is affected by microbial processes that conventional food label calculations do not explicitly measure.