# Energy intake (EI)

What you logged eating; the TDEE engine’s first input.

Type: biomarker · Unit: kcal/day · Domain: Nutrition & Energy Balance · Accuracy: Self-reported · Importance: Core

Also called: calories eaten, calorie intake, food log, logged calories, energy in

## In one sentence

The energy in what you logged eating today, in kilocalories, which is the first input to VT's estimate of what you burn and the one number in the record that only you can supply.

## Why it matters

Energy balance is arithmetic: what comes in, minus what goes out, is what your weight does. No device measures what comes in, so the log is the only way the arithmetic can be run, and it is the reason the TDEE engine exists at all. The log's value is as a series, not as a day: VT reads the confounder-weighted mean of your intake across a window of weeks against how your weight moved over the same window, and that relationship, not the day's total, is what it uses.

## What the research says about logs

People under-report. In the OPEN study, 484 adults aged 40 to 69 kept 24-hour recalls and food-frequency questionnaires while their true expenditure was measured with doubly labeled water: men under-reported energy by 12 to 14 percent on recalls and 31 to 36 percent on questionnaires, women by 16 to 20 and 34 to 38 percent (Subar 2003). In ten people who reported eating under 1,200 kcal a day without losing weight, measured intake was 47 percent higher than reported and activity 51 percent lower (Lichtman 1992). None of this is a verdict on you; it is why VT's engine carries a logging-consistency signal, shown as a diagnostic, and why a roughly right log kept every day is worth more to it than a precise one kept twice a week.

## How to log well

From the meal plan where one exists, with the exceptions recorded against it; weigh what you can on a kitchen scale, estimate the rest and move on. Log the late snack and the second glass. Be consistent in your own errors: an under-estimate that is the same every day cancels out of the energy-balance arithmetic, and a log that swings between careful and careless does not.

## How Vitality Tracker uses it

The TDEE engine's measured arm: average logged intake across the window minus the energy content of the weight change. The engine needs 29 of the last 36 days with both a weight and a logged intake before it reports. When your weight is steady, the engine takes a fast path, expenditure equals your mean reported intake, and compares that with its physiological prior; the ratio is the consistency diagnostic. Intake also feeds the macronutrient targets and the meal library.

## How far to trust the number

Self-reported; as good as the log. The engine's design assumes it is imperfect and says how imperfect it seems, rather than assuming it is right.

## Method

Daily kcal from the meal log; the engine's intake term is the confounder-weighted mean over the change-point-bounded window (see *[The TDEE engine](/knowledge/tdee-engine)*).

## Sources

1. Subar AF, et al. Using intake biomarkers to evaluate the extent of dietary misreporting in a large sample of adults: the OPEN study. Am J Epidemiol 2003;158:1–13. [doi:10.1093/aje/kwg092](https://doi.org/10.1093/aje/kwg092)
2. Lichtman SW, et al. Discrepancy between self-reported and actual caloric intake and exercise in obese subjects. N Engl J Med 1992;327:1893–8. [doi:10.1056/NEJM199212313272701](https://doi.org/10.1056/NEJM199212313272701)
3. Vitality Tracker, How Vitality Tracker estimates your energy expenditure, method note v1.0. [doi:10.5281/zenodo.23224326](https://doi.org/10.5281/zenodo.23224326).

## Related

- [The TDEE engine](https://vitalitytracker.app/knowledge/tdee-engine)
- [Protein, fat and carbohydrate](https://vitalitytracker.app/knowledge/protein-fat-and-carbohydrate)
- [Why log meals even if you are not trying to lose weight](https://vitalitytracker.app/knowledge/why-log-meals)
- [Why your watch's calories are not a food budget](https://vitalitytracker.app/knowledge/why-watch-calories-are-not-a-food-budget)
- [Weight](https://vitalitytracker.app/knowledge/weight)

Reviewed October 2026 · v1

Source: https://vitalitytracker.app/knowledge/energy-intake