Hi Tom,
When you read the calorie count on a food label, do you assume that’s exactly what your body takes in?
I did, for years.
A new study suggests that isn’t quite true.
Researchers at Arizona State University have built a mathematical model, called DAMM, that follows food all the way through the highways and byways of your digestive tract. It estimates how much energy your body absorbs early on. And how much your gut bacteria add from whatever is left over.
That second part never makes it onto the label.
The calorie numbers on packaging come from a system more than 100 years old. Each gram of fat, carbohydrate, and protein gets an average calorie value, and the total is added up. It’s simple, and it’s useful. But it doesn’t ask what happens to the food that reaches your colon, or what your gut bacteria do with it.
And they do quite a lot.
Fiber and resistant starch that your own digestion can’t break down get fermented by gut bacteria into short-chain fatty acids. Some of those are absorbed into your bloodstream and used as energy.
According to the model, that adds up to about 140 calories a day. Roughly 7% of the usable energy in the diet came from what your gut bacteria made out of the food you couldn’t digest yourself.
When the researchers tested the model against real measurements from a controlled feeding study, it came closer than the traditional calorie method.
This is the part I found most interesting.
In that earlier study, healthy adults ate either a high-fiber, less processed diet or a typical Western-style diet. The people on the Western diet absorbed about 116 more calories a day.
And the people eating all that extra fiber didn’t report feeling any hungrier.
Which seems backwards at first.
The high-fiber diet gave their gut bacteria far more to work with, and they made more short-chain fatty acids. Yet overall, those people absorbed fewer calories. The upper gut took in less, and the microbes didn’t fully make up the difference.
A few caveats are worth knowing. DAMM is a research model, not a diet plan. It was tested against one small study of 17 healthy adults, and the authors say it needs testing in more people, including those with metabolic conditions, before anyone uses it to tailor diets. And, I will add, 116 calories a day isn’t a weight-loss strategy I know!
But what it does show is something I keep coming back to: Your food provides the raw materials. Your gut bacteria decide what happens next.
Which means fiber-rich, less processed foods aren’t just “good for you” in some vague way. They’re feeding a community of microbes that is doing real work on your behalf.
So, the next time you glance at a calorie label, remember it’s only half the story. The other half is happening in your gut.
Yours for better health, naturally,
Sarah Otto
Nutritionist (Master of Human Nutrition)
Goodness Lover Co-Founder
Scientific Reference:
Davis, T.L. et al. “Modeling the microbial contribution to human energy balance using the Digestion, Absorption, and Microbial Metabolism (DAMM) model.” PLOS ONE, May 2026. DOI: 10.1371/journal.pone.0347668