Working out your metabolism and your real needs
Mifflin-St Jeor, activity level, total expenditure and target deficit, with the site's calculator.
The three tiers of your expenditure
Basal metabolic rate, what you spend at complete rest: breathing, circulation, temperature, keeping organs running. That is sixty to seventy per cent of the total.
Activity, all non-exercise movement, walking, climbing stairs, standing up, fidgeting, cooking, plus structured exercise. It is the most variable part: fifteen to thirty per cent.
The thermic effect of food, the energy spent digesting. About ten per cent of the total, but variable by macronutrient: protein costs twenty to thirty per cent of its own energy to digest, against five to ten per cent for carbohydrate and zero to three per cent for fat.
That last point is a concrete reason to favour protein in a deficit.
The Mifflin-St Jeor formula
This is the most reliable predictive formula in the general population. It works in metric; the calculator on this site converts from pounds and feet for you.
Men: basal metabolic rate equals ten times weight in kilos, plus 6.25 times height in centimetres, minus five times age, plus five.
Women: the same, minus one hundred and sixty-one instead of plus five.
Example. Woman, thirty-four, 68 kg, 167 cm. 680, plus 1,043.75, minus 170, minus 161, equals 1,393 kilocalories.
The activity coefficient
Multiply the basal rate by your activity level to get total daily energy expenditure.
| Level | Coefficient | Description |
|---|---|---|
| Sedentary | 1.2 | Desk job, little walking, no sport |
| Light | 1.375 | 1 to 3 sessions a week, or daily walking |
| Moderate | 1.55 | 3 to 5 sessions a week |
| High | 1.725 | 6 to 7 sessions, or a physical job |
| Very high | 1.9 | Athlete or heavy physical work |
Continuing the example: moderate level, 1,393 times 1.55 equals 2,159 kilocalories.
Common mistake: overestimating your level. Three training sessions a week with a desk job and four thousand steps a day is light, not moderate. When in doubt, take the level below.
Your calorie target
Fat loss: total expenditure minus fifteen to twenty-five per cent. Maintenance: total expenditure. Gaining: total expenditure plus ten to fifteen per cent.
Continuing the example: 2,159 minus twenty per cent equals 1,727 kilocalories a day, for a loss of about 0.4 kg a week.
The limits of the formula
Every predictive formula carries a margin of error of ten to fifteen per cent per individual. Metabolism varies with genetics, muscle mass, dieting history and thyroid status.
The formula is a starting point, not a truth. The correct method: work out your target, apply it for two weeks with rigorous tracking, look at the average change in weight, then adjust by a hundred and fifty to two hundred kilocalories in whichever direction is needed.
It is your body that gives the final answer, not the equation.
Do you have to count calories for ever?
No. Count for four to eight weeks to learn the orders of magnitude: what a portion actually weighs, what a spoon of oil costs, what a restaurant meal is worth.
That learning is permanent. After that, most people manage by eye with enough precision, and only count again occasionally during recalibration phases.
If counting produces anxiety or a difficult relationship with food, stop and use the visual methods in lesson 2.2, which work very well.
Exercises1
Understanding produces no change. These exercises are what makes the difference: each one has a measurable success criterion.
Working out and validating your target
Get a personal calorie target, then correct it by observation rather than by formula.
Equipment : The calorie and macro calculator on this site, a set of scales.
- 1.Work out your basal rate and your total expenditure, taking the lower activity level when in doubt.
- 2.Set your target at minus twenty per cent of total expenditure.
- 3.Apply it for two weeks, weighing daily and taking a weekly average.
- 4.Compare the two weekly averages.
- 5.Adjust by a hundred and fifty to two hundred kilocalories if the loss is zero or above one per cent of body weight.
Success looks like : After two weeks, your weekly loss sits between 0.5 and 1 per cent of your body weight.
The classic mistake : Declaring yourself moderately active with a desk job and three sessions a week. Overestimating activity level is the most common error.
Going further : Recalculate every four to six weeks, or every four to five kilos lost.
This lesson is part of Physical Transformation
16 lessons, 7 resources and the complete protocol to install the method in 12 weeks.