Where your calories go

Your calories go four places. Resting burn keeps you alive and takes about 55 to 70 percent of the day. Digesting food takes about 10 percent. Everyday movement and exercise share the rest, and the workout is often the smallest slice.

Isn’t exercise where you burn calories?

It’s the part you can see. A treadmill counts calories as you go, and a watch closes a ring. Nothing tells you what your liver spent today, so most people picture their burn as mostly workouts and a little background.

It’s closer to the other way round. Think of your home’s power bill. The hair dryer is loud, you know exactly when you used it, and it feels expensive. The heating runs quietly all day and costs far more. Your workout is the hair dryer. Your resting burn is the heating.

The four parts, for two real-sized people

Take a 35 year old woman who is 5 foot 5 and 170 pounds (77 kg) and walks about 6,000 steps a day. The Mifflin-St Jeor formula puts her resting burn at about 1,470 calories, and her whole day at about 2,020.

Now a 40 year old man, 5 foot 10 and 200 pounds (91 kg), who walks 4,000 steps a day and lifts weights three hours a week. His resting burn is about 1,820. Digesting food is about 230, everyday movement about 140, and the lifting about 100 calories a day once it’s spread over the week. That’s about 2,290 in all, and his three gym sessions are about 4% of it.

Resting burn: the part that never stops

Your resting burn is what your body spends lying still, awake, after a night’s fast. It pays for the work you never think about. Over nine hours of sleep, your heart beats about 30,000 times at a resting pace, and you breathe the whole time.

Not all of you burns at the same rate. In a 2010 study that matched MRI scans of 131 adults to their measured burn, a kilogram of heart or kidney burned about 440 calories a day, brain about 240 and liver about 200. A kilogram of muscle burned about 13, and a kilogram of fat about 4.5. Per pound, that’s about 200 calories for heart or kidney, about 6 for muscle and about 2 for fat. Pound for pound, your organs outspend your muscle 15 to 35 times over.

That’s why resting burn follows size. In the 1990 study behind the Mifflin-St Jeor formula, built on 498 adults, every extra kilogram of weight added about 10 calories a day, and each year of age took off about 5.

Strong Resting burn is measured in labs from the air you breathe, and the formulas are fitted to hundreds of those measurements.

Digesting food: a tax on every meal

Your body spends energy breaking food down and storing it. A 2004 review put it at about 10% of the calories you eat on a mixed diet. Each nutrient pays a different rate.

The difference is real and small. On 2,000 calories a day, moving from 20% to 30% of your calories as protein adds roughly 35 calories of digesting cost. Protein’s bigger gift is how full it keeps you, which the same review links to its high digesting cost.

Everyday movement: the part that varies most

This is everything you do that isn’t a workout: walking to the car, standing at the stove, pacing on a call, fidgeting. Researchers call it non-exercise activity (NEAT).

In a 1999 Mayo Clinic study, 16 adults ate 1,000 calories a day more than they needed for eight weeks. Two thirds of the rise in their daily burn came from everyday movement, not exercise. Some people raised it a lot and some barely at all, and that explained a tenfold difference in how much fat they stored.

Steps are the easiest way to see this part. Walking at about 3 miles an hour costs about 3.8 times your resting rate in the 2024 Compendium of Physical Activities. At about 100 steps a minute, the pace researchers use as the line for moderate walking, that works out to about 2 calories for every pound you weigh per 10,000 steps, on top of resting. At 150 pounds that’s about 300 calories, and at 220 pounds about 440. Your activity level turns your steps into the number calculators use.

Moderate The step costs are well measured. How much everyday movement changes when you eat more or less comes from small studies.

Exercise: smaller than it feels

A 155 pound person burns about 630 calories in nine hours of sleep and about 110 running one mile at 6 miles an hour, by the 2024 Compendium’s values. An hour of ordinary weight training at 180 pounds costs about 205 calories on top of resting.

And the body makes up for some of it. In a 2021 study of 1,754 adults, only about 72% of the extra calories burned in activity showed up as extra calories burned that day, because resting burn dipped to compensate. The Hadza, hunter-gatherers in northern Tanzania whose men walk about 7 miles a day, burn about the same each day as Westerners of the same size. In a study of 332 adults in five populations, daily burn rose with activity at the low end and then levelled off at the high end.

For someone sitting most of the day, more movement adds real calories. For someone already very active, adding more buys less than the numbers suggest. Either way the workout is a small slice, which is why food sets most of a deficit.

Where the energy is stored

Your blood carries only about 4 grams of sugar at a time, about a teaspoon. Your liver keeps more than 80 grams in reserve as glycogen to top it up, and your muscles hold more for their own use. Fat is the long-term store. The old rule says each pound you lose is worth about 3,500 calories. It fits people with a lot of fat to lose, and overstates it for leaner people.

Glycogen is stored with three to four parts water. When you cut calories, you use some glycogen and lose its water with it. That’s why the first week of a diet drops the scale fast, and why a big, carb-heavy day can push the scale up overnight with no new fat.