Every food gets its energy from a few building blocks, called macronutrients (macros for short). Three of them supply nearly all your calories: protein, carbohydrate and fat. Fibre and alcohol count too, but most days they play a small part.
The useful bit for a beginner is the exchange rate. Each gram of a macro carries a fixed amount of energy, so grams and calories are two ways of saying the same thing.
| Macro | Energy per gram |
|---|---|
| Protein | 4 kcal |
| Carbohydrate | 4 kcal |
| Fat | 9 kcal |
| Fibre (EU labels) | 2 kcal |
| Alcohol | 7 kcal |
These are the standard conversion factors used for food labels in the EU and by the FAO. Fat packs more than twice the energy of the others per gram, which is why oils and nuts are so energy-dense even in small portions. A label that says 10 g protein, 30 g carbohydrate and 8 g fat adds up to 40 + 120 + 72 = 232 kcal.
Pick a daily energy figure, then slide the share that comes from protein and from fat. Carbohydrate takes whatever is left. The result shows grams, because grams are what you can actually weigh and read on a label.
Macros are just a way to read the same calories as protein, carbs and fat. No single split is the right one for everybody.
The European Food Safety Authority (EFSA) gives adults a reference range of 45–60% of energy from carbohydrate and 20–35% from fat. For protein it sets a reference intake of 0.83 g per kg of body weight per day, which is about 58 g for someone weighing 70 kg. That is a floor for covering needs in most healthy adults, not a target to chase, and it is shown as grams per kilo because protein needs follow body size rather than calories. EFSA also suggests 25 g of fibre a day.
The "More protein" and "Lower carb" presets in the tool above are within what people commonly eat, but lower-carb eating is one place where the research is mixed over the long term, so the tool shows a note rather than calling it better or worse. The "Lower carb" preset sits outside the EFSA ranges on purpose, so you can see how the note reacts.
This is general information, not medical advice. If you have a medical condition, are pregnant or breastfeeding, have or have had an eating disorder, or take medication (especially for diabetes or blood pressure), talk to a doctor or registered dietitian before changing how you eat. That matters most for lower-carb or higher-protein plans, which can interact with medication and with kidney or liver conditions.