A calorie is a unit of energy
Food carries energy; your body spends energy — on staying alive, digesting, moving, training. A calorie (technically a kilocalorie, kcal) is just the unit both sides are measured in, the same way meters measure distance. Kilojoules are the same idea in a different unit, and the app speaks both.
The balance
Compare energy in against energy out over time and there are only three states:
- Deficit — you eat less than you burn; the body draws the difference from its stores and weight trends down.
- Balance — intake matches expenditure; weight holds.
- Surplus — you eat more than you burn; the extra is stored and weight trends up.
Every diet with results — keto, fasting, low-fat, anything — works through this equation. The wrappers differ; the physics doesn't.
Why it doesn't feel that simple
Because neither side of the equation sits still. Your expenditure shifts with activity and adapts as your body changes; intake estimates carry error; water masks fat changes on the scale for days at a time. The equation is true over weeks and noisy over days — which is exactly why the app works with trend weight and a continuously measured expenditure instead of any single day's numbers.
The takeaway
You don't need to feel the balance — you need to measure it. Log intake, weigh in, and let the trend tell you which of the three states you're actually in.