Nutrition · 3 min read
Resting metabolic rate and total daily energy expenditure are often used interchangeably. They are not the same, and the difference matters when a calorie target is being set from either one.
By Chris Gkoufas, DVOTION
Daily energy expenditure is usually described in four parts.
Resting energy expenditure is the energy used to keep organs functioning, maintain temperature and support breathing and circulation at complete rest. In an RMR test this is measured directly.
The thermic effect of food is the energy cost of digesting and processing what you eat. Activity expenditure covers everyday movement outside training. Exercise expenditure covers training itself. None of these three is measured by an RMR test. Each is estimated.
If resting expenditure is the largest share of the total for most people, then getting it wrong propagates through everything built on top of it.
A deficit set against an over-estimated requirement is larger than intended. That is a common reason a nutrition plan becomes difficult to sustain: the plan was not badly designed, the number underneath it was wrong.
Measuring the resting component narrows the error in the largest term. It does not eliminate error in the others.
Activity and training expenditure are estimated from reported training volume, session type, occupation and daily movement. These are reasonable estimates, and they are still estimates. Two athletes reporting the same weekly training can expend meaningfully different amounts of energy doing it.
This is why a total daily figure derived after an RMR test is presented as a range rather than a single number, and why it is described as estimated in the report.
Treat the measured resting value as fixed for the period between tests, and treat the daily total as a hypothesis to be tested.
Set a starting intake from it, then review against measured change in body mass, how training is tolerated, and recovery, over a few weeks. If body mass moves faster or slower than intended, the estimated components were off, not the measurement.
A repeat measurement after a period of changed intake or training shows whether resting expenditure itself has moved, which prediction equations cannot show.
They are closely related but measured under different conditions. Basal metabolic rate requires stricter conditions, typically an overnight stay. Resting metabolic rate is measured after a period of rest and a fasting protocol, and is the figure used in practice.
When something has changed enough to expect the value to have moved — a substantial change in body composition, a sustained change in intake, or a large shift in training load.
You can produce an estimate by applying an activity factor, and that estimate carries the uncertainty of the factor you choose. The report sets out the assumptions used so the estimate can be adjusted as your circumstances change.
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