What is a calorie? What to know before you start counting
The first word you run into when you start a diet is “calories”. Yet few people can explain what a calorie actually is. Before counting numbers, here’s what those numbers mean.
A calorie is a unit of energy
A calorie is a unit for the amount of energy something holds. The “kcal” on food labels is the energy needed to raise the temperature of 1 kg of water by 1 degree.
Your body gets energy from food to keep warm, keep your heart beating and move. When more comes in than you use, the surplus is mostly stored as body fat; when less comes in, you draw on those stores.
| Nutrient | Calories per 1 g |
|---|---|
| Carbohydrate | 4 kcal |
| Protein | 4 kcal |
| Fat | 9 kcal |
| Alcohol | 7 kcal |
How much do you need a day?
Needs are worked out in two steps. First find the energy you use even when doing nothing, then multiply by your activity level.
- Basal metabolic rate — the minimum energy for breathing, keeping warm and running your organs
- Total daily energy expenditure — your basal metabolic rate adjusted for activity
Surprisingly, 60–70% of the calories you burn each day go to your basal metabolism. Exercise burns less than most people think: a 30-minute walk uses about 150 kcal — not even half a bowl of rice.
How much do you need to cut to lose 1 kg?
1 kg of body fat is roughly 7,700 kcal. Eating 500 kcal less a day works out to about 1 kg in 15 days. That’s the basis for the usual recommendation of 0.5 kg a week.
| Daily cut | Expected weekly loss | Verdict |
|---|---|---|
| 250 kcal | about 0.23 kg | Slow, but easy to keep up |
| 500 kcal | about 0.45 kg | The generally recommended range |
| 750 kcal | about 0.68 kg | Recommended upper limit. Higher risk of muscle loss |
| 1,000 kcal or more | — | Not recommended |
It won’t go exactly by the numbers, though. As your weight drops, so does your basal metabolic rate, and your body adapts to save energy. It’s normal for progress to feel slower after the first few weeks.
What you miss if you only look at calories
“As long as the calories add up, it doesn’t matter what you eat” is only half true. Weight change is mostly decided by the total, but the same calories do different things in your body.
- Fullness — 500 kcal of chicken breast and 500 kcal of snacks fill you up very differently
- Keeping muscle — without enough protein, you lose muscle along with fat
- Blood sugar — the more refined a carbohydrate is, the faster it raises blood sugar
- Energy used for digestion — digesting protein uses up 20–30% of the calories it contains
How far can you trust the calories on the label?
Nutrition labels on packaged food are allowed a margin of error. The real values also change with the cooking method, portion size and shop. Restaurant menu calories vary especially widely.
So treat calories as a “rough guide”, not an “exact value”. Rather than chasing decimal points, it’s more practical to check that the big picture is right.
FAQ
Do I have to count calories every time?
For the first 2–3 weeks, it helps to learn the rough calories of foods you eat often. But nobody can count for life, so once you have a feel for it, switching to checks like “is there protein in every meal?” and “is my rice portion reasonable?” is easier to keep up.
Is it bad to eat less than my basal metabolic rate?
We don’t recommend doing it for long. It’s easy to fall short on essential nutrients, and muscle loss and metabolic adaptation increase — which actually makes losing weight harder. For weight-loss goals, this service allows down to 95% of your basal metabolic rate and never plans below that.
Can I eat back the calories I burn exercising?
Exercise usually burns fewer calories than expected, and estimates from smartwatches and similar devices are often too high. Adding your exercise burn straight back onto what you eat tends to stall weight loss.
Sources
Reading about it is one thing; applying it to your life is another.
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⚕️ This service provides general nutrition information and does not replace medical diagnosis or treatment. If you have a medical condition or take medication, please consult a professional.