What Is a Calorie Deficit?
A calorie deficit is the gap between the energy you get from food and the energy your body uses. Understanding that gap can make your existing food log more useful.
The basic idea
Calories are a way of measuring energy. You take in energy through food and drink, while your body uses energy for basic functions, digestion, movement and exercise.
A calorie deficit happens when your average energy intake is lower than your average energy use. Your body then has to draw on stored energy, so a sustained deficit can lead to a reduction in body weight over time.
Why the numbers are not exact
Food labels, serving sizes and tracking tools all provide estimates rather than perfect measurements. Home-cooked meals can be especially difficult to log precisely because ingredients and portions vary.
Energy use is also an estimate and can change with body size, daily movement, exercise and other personal factors. The size of an appropriate deficit depends on the person, so a calculated figure is best treated as a starting point rather than a fixed truth.
How to recognise a deficit
Your food diary shows what you have recorded, but it cannot confirm a deficit by itself. You need to compare your logged intake with an estimate of your total energy use, then look at the pattern over time.
Daily body weight can move up or down for reasons unrelated to body fat, including changes in water and the amount of food being digested. A longer-term trend is therefore more informative than any single reading.
Using your food log sensibly
Consistency matters more than making every entry perfect. Record portions in a similar way, include cooking ingredients and drinks, and avoid changing your method from one day to the next.
A calorie deficit does not mean choosing the lowest possible intake. Aim for an approach that leaves room for satisfying meals, fibre, protein and a varied range of foods, then adjust your estimate according to your own longer-term trend.