Why identical diets can lead to different weight gain
A new study suggests that counting calories alone does not fully explain why some people gain weight more easily than others, even when they eat the same foods. Published recently in PLOS One, the research introduces a mathematical model called DAMM, short for Digestion, Absorption and Microbial Metabolism, developed by researchers at Arizona State University.
The model estimates not just the calories listed on food labels, but how much energy the body actually extracts after digestion and after gut bacteria do their work. That matters because most nutrition labels still rely on the Atwater system, a 19th-century method that calculates calories from the amounts of carbohydrates, protein and fat, without accounting for the trillions of microbes in the intestine. Those microbes, especially in the colon, break down fiber and resistant starch into short-chain fatty acids that can be absorbed into the bloodstream and used as energy.
According to the model, these fatty acids contributed an average of about 140 calories a day, or 7.4 percent of available energy. Overall, about 85 percent of usable energy came from the upper digestive tract and about 15 percent from the lower tract, where bacteria play a major role. Prof. Rosa Krajmalnik-Brown of Arizona State University said, “Digestion is not only a human process, but a collaboration between our body and the trillions of bacteria living in the gut.”
To test the model, the researchers analyzed data from a controlled nutrition study in which healthy participants ate one of two diets. One was high in fiber and resistant starch, with less processed foods and larger food particles. The other resembled a typical Western diet, with less fiber and more processed foods. People eating the Western-style diet absorbed about 116 more calories per day than those on the high-fiber diet, even though the high-fiber group did not report greater hunger. The researchers say the gap could matter over time, alongside exercise, sleep and genetics, and that food quality may be at least as important as calorie counts.
