Basal metabolic rate is what the body uses at complete rest, and it is the largest single component of daily expenditure — typically 60 to 70 per cent of the total. The Mifflin–St Jeor equation puts a 30-year-old man of 175 cm and 75 kg at about 1,699 calories a day before any movement at all.
Exercise adds less on top of that than people expect. Jogging at MET 7 for 45 minutes at 75 kg burns about 413 calories, which is roughly 54 grams of body fat — and a meaningful part of that 413 would have been burned anyway.
Which equation, and how accurate is it?
Mifflin–St Jeor replaced the older Harris–Benedict equation in 1990 because it predicts measured resting rate more accurately across modern body compositions, and it remains the standard recommendation.
On the same 75 kg, 175 cm, 30-year-old man, Harris–Benedict gives 1,763 against Mifflin’s 1,699 — a 64-calorie difference from nothing but the choice of formula. Both are population equations, so an individual can sit 10 per cent either side of whichever one you pick.
That 10 per cent is about 170 calories on this example, which is larger than most of the adjustments people make inside a plan.
How does a MET value work?
A MET is a multiple of resting metabolism, so an activity at MET 7 uses seven times as much energy per minute as sitting still. The formula is MET × 3.5 × weight in kilograms ÷ 200, which gives calories per minute.
| Activity | Approximate MET |
|---|---|
| Sitting | 1.0–1.3 |
| Walking, moderate pace | 3.5 |
| Cycling, easy | 4.0 |
| Jogging | 7.0 |
| Running, fast | 11.0+ |
Weight is in the formula, which is why the same activity burns more for a heavier person — and why the calorie figure falls as weight comes down, in exactly the way the calorie target does.
Why is the figure an overestimate?
Because it is gross rather than net. The number includes the energy you would have burned anyway just being alive during those minutes, and that resting component has to come off before you can call it additional.
For a 45-minute session at this body weight the resting component is around 59 calories, so the true extra burn is closer to 354 than 413. Machines that report a calorie figure almost always report the gross one, and rarely say so.
Both figures are estimates in any case. MET tables are population averages that take no account of efficiency, terrain, technique or fitness, and two people of the same weight doing the same session can genuinely differ by a substantial margin.
What are the three components of daily expenditure?
Basal rate, the thermic effect of food, and movement. Basal is 60 to 70 per cent and is what the equation estimates. Digestion accounts for roughly a tenth, and it varies by what you eat — protein costs more to process than fat or carbohydrate, which is a real effect and a small one.
Movement is the rest, and only part of it is deliberate exercise. Walking, standing, fidgeting and every unplanned motion make up the bulk of it for most people, and that component varies enormously between individuals of the same size.
Why is exercise a slow route to weight loss?
Because the numbers are small relative to intake. Four hundred and thirteen calories is 54 grams of fat and about one large pastry — which is not an argument against exercising, and is an argument against treating it as the primary lever for a deficit.
What exercise does reliably is everything else: cardiovascular fitness, strength, bone density, mood, sleep and appetite regulation. It also protects lean mass during a deficit, which changes what the weight lost is made of rather than how much of it there is.
The reliable arithmetic runs the other way. Diet moves the intake side by hundreds of calories a day with less effort than exercise moves the expenditure side, which is why the evidence consistently favours diet for the deficit and exercise for everything else.
Does the basal figure change with weight?
Yes, and it is why a calorie target set once stops working. The equation has weight in it, so losing ten kilograms lowers the basal rate directly — for this example, from 1,699 to about 1,599, which then scales up through the activity factor into a larger fall in total expenditure.
That is the arithmetic behind a plateau, and it is separate from any metabolic adaptation on top of it. Recalculating every four or five kilograms restores the deficit you intended.
Questions people ask
Why does the estimate differ by sex? Because average body composition differs, and the equation is fitted to population data that reflects it. It is a statistical correction rather than a statement about any individual.
Does more muscle raise basal rate much? Modestly. Muscle is more metabolically active than fat and the difference per kilogram is smaller than most articles imply, so gaining muscle raises basal rate gradually rather than transforming it.
Should I trust my watch? As a trend, yes. As an absolute figure, it is an estimate built on the same MET logic plus heart rate, and it tends to overestimate session calories.
How is basal rate different from total expenditure? Basal is at complete rest; total is basal multiplied by an activity factor between 1.2 and 1.9. The multiplier is the largest source of error in the whole calculation, which the activity multiplier article covers in detail.
Basal rate is most of the number, the equation is a population average, and the session figure is gross. The BMR calculator applies Mifflin–St Jeor, the calories burned calculator works from MET values and body weight, and the TDEE calculator puts an activity factor on top of the basal figure.