What a day of calories actually buys

Calories are the worst-behaved number your phone collects. The figure moves with your weight, your watch and the weather, and “600 active calories” carries no meaning at all on its own. It only becomes information when something is standing next to it.

The small end

A large McDonald’s fries is 480 kcal. A 10K race burns about 600. Those two sitting side by side is the entire argument about exercise and diet in one line, and it is not a flattering one.

Smaller still: a banana is 105 kcal, a slice of cheese pizza is 285. A hard hour buys you about two slices.

The far end

Where it gets genuinely interesting is the top of the scale. An astronaut’s daily ration is 3,000 kcal. A Vendée Globe skipper eats 5,000 on a day at sea, alone, racing a boat round the planet. And a polar explorer hauling a sledge needs 6,500 — more than twice what most people eat, just to stay level.

Set your own number against those and the honest answer is usually humbling. That is fine. The point of a comparison is not to flatter you; it is to tell you the truth at a scale you can hold.