Does exercise count?

What physical activity changes in your microbiome — and why the app does not ask about it.

Yes, and independently of what you eat. The clearest demonstration comes from a simple experiment: in previously sedentary adults, six weeks of endurance training raised butyrate production — the fatty acid that feeds the cells of the colon — along with the bacteria that make it, with diet held unchanged. Six weeks after the training stopped, everything had come back down. The effect was clearer in lean participants than in participants with obesity.

The work that first drew attention to the subject looked at professional rugby players, whose microbiome proved more diverse than that of sedentary controls — but they also ate entirely differently, far more protein and far more of everything. It was the controlled experiment that settled it: exercise acts, and not only the athlete's plate.

By which routes. Moving speeds up transit, changes the blood flow and the temperature of the gut, alters the circulation of bile acids and the activity of the immune system in the gut wall. Nothing spectacular taken one by one: the measured effects are real and modest, and they do not replace food — they add to it.

One reservation, for extreme efforts. A very long and very intense effort, especially in the heat, temporarily makes the gut wall more permeable: this is the marathon runner's well-known stomach trouble. It passes, and it has no known consequence for anyone training normally.

Why the app does not ask about your physical activity. Because it would change none of your figures. The app does not count grams of fiber: it counts distinct plants and the rotation of 16 categories. Someone who runs three times a week eats more, and so gets more fiber by weight — but they still have to rotate exactly the same categories, at the same pace. Exercise changes the portions, not the list. Declaring your activity would mean handing over one more piece of health data for nothing in return. Do move: it is good for your microbiome. It simply has no place in a dial that counts plants.