Glossary
What is energy balance?
Updated 2026-08-16By Chris RichardsAll terms
Definition
Energy balance is the relationship between energy in (food and drink) and energy out (rest, movement, training, digestion) over time. A deficit, maintenance, and a surplus are three readings of the same scale.
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Your estimate
kcal / day maintenance estimate · BMR 1,419
Estimate only — verify with a weight log over 2–3 weeks. Not medical advice.
Definition
Energy in is what you eat and drink. Energy out is BMR plus NEAT plus exercise plus the cost of digesting food. When in is below out, stored energy covers the gap. When in is above out, the extra is stored. When they match on average, weight holds.
Both sides are estimates. Labels have tolerances. Equations describe populations. That is why Hall’s modelling of energy imbalance treats weight change as a curve, not a straight line from “3,500 calories = 1 pound”.
How to read it without a lab
Hold intake roughly steady for three weeks. Weigh daily under the same conditions. Compare weekly averages. Flat is maintenance. Down is a deficit. Up is a surplus. Recalculate after a large weight change — a smaller body burns less.
The mistake people make
Arguing that “calories in, calories out is too simple” and then ignoring the average. Hormones, sleep, and medication change the out side; they do not repeal the accounting. Measure the trend instead of debating the slogan.
A day of 3,400 kcal after six days at 1,900 can still be a weekly deficit. A day of 1,200 after a weekend of unlogged oil can still be a surplus. The unit is the week, then the month. The maintenance calorie calculator is a starting hypothesis for the in side, not a verdict.
FAQ
Is calories in, calories out true?
As an accounting identity over a long enough window, yes. As a prediction that 500 calories a day equals a pound a week forever, no. Expenditure changes as you do.
Why does the scale disagree with my log?
Usually timescale (water), under-logged intake, or an overstated activity factor. Trust three weeks of averages over either a calculator or a single morning.
Sources
- [1] Hall KD, Sacks G, et al. “Quantification of the effect of energy imbalance on bodyweight” (2011) — The Lancet 378:826–837 (PMID 21872751)
- [2] Body Weight Planner — National Institute of Diabetes and Digestive and Kidney Diseases (NIH)
General nutrition information, not medical advice. Calorie and macro targets are estimates — talk to a doctor or a registered dietitian before changing your diet, especially if you are pregnant, managing a health condition, or have a history of disordered eating.
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