The key takeaway
Calories measure energy. They do not measure how nutritious, satisfying or enjoyable a food is.
What is a calorie?
Food labels usually show energy in kilocalories (kcal) and kilojoules (kJ). In everyday conversation, “calories” normally means kcal. Your body needs this energy for basic functions and movement.
Protein and carbohydrate provide about 4 kcal per gram. Fat provides about 9 kcal per gram. These values help explain why portion sizes and ingredients change a meal’s energy content.
Read the portion as well as the number
Compare products using the per-100-g column, then work out the amount you actually eat. A packet’s suggested serving may be different from your usual portion.
| Label example | Your calculation |
|---|---|
| 200 kcal per 100 g; you eat 150 g | 200 × 1.5 = 300 kcal |
| 80 kcal per 100 ml; you drink 250 ml | 80 × 2.5 = 200 kcal |
Energy is only part of the picture
Two meals with similar calories can offer different amounts of protein, fibre and vitamins. A varied pattern of eating matters alongside energy intake.
Use calories as one piece of information, not a score for whether food is good or bad. You can include foods for pleasure as well as nutrition.
Try this at your next shop
Pick two familiar foods and compare their per-100-g energy and usual portions. Then notice protein and fibre. The aim is to understand what you are buying, not to find the smallest possible number.
Put it into practice
Sources & further reading
These sources support the general information and explain the wider context. Practical examples are illustrative.
Our editorial approachGeneral educational information for adults. Estimates are not a diagnosis or a personalised diet. For pregnancy, breastfeeding, eating-disorder concerns, medical conditions or medication-related questions, seek qualified guidance. Read the full disclaimer.