Macronutrients are the three nutrients your body needs in large amounts: protein, carbohydrate and fat. They are where all your calories come from, and each does a different job. "Macros" is just the shorthand. Understanding them is the difference between counting calories blindly and actually knowing what your food is doing for you.
The three macronutrients
Protein
Builds and repairs muscle, skin, hormones and enzymes. It is also the most filling macronutrient, which is why higher-protein meals keep hunger down. 4 calories per gram. Sources: meat, fish, eggs, dairy, beans, tofu. See how much protein per day and high-protein foods for weight loss.
Carbohydrate
Your body's main and preferred energy source, especially for the brain and hard exercise. Carbs range from fibre-rich whole foods to refined sugars, and that range matters far more than the total. 4 calories per gram. Sources: grains, fruit, vegetables, legumes.
Fat
Essential for hormone production, brain health and absorbing vitamins A, D, E and K. It is the most calorie-dense macro, so portions count. 9 calories per gram. Sources: oils, nuts, avocado, oily fish, dairy.
How they compare
| Macronutrient | Calories per gram | Main job |
|---|---|---|
| Protein | 4 | Build and repair, keeps you full |
| Carbohydrate | 4 | Primary energy |
| Fat | 9 | Hormones, vitamin absorption |
Notice fat has more than double the calories per gram, which is why a "small" amount of oil or nut butter adds up quickly.
What about fibre, vitamins and water?
Fibre is a type of carbohydrate your body cannot fully digest, and it is vital for gut health and fullness (how much fibre per day). Vitamins and minerals are micronutrients, needed in tiny amounts. Water and alcohol are neither: water has no calories, and alcohol provides 7 per gram but no nutrition.
Why macros matter more than calories alone
Two 500-calorie meals can do completely different things. One built on protein and fibre keeps you full and protects muscle, while one of refined carbs and fat leaves you hungry soon after. Same calories, different result. That is the whole case for looking at macros, and for judging food on more than a single number, which is the idea behind how food scoring works.
See your macros, not just calories
forme breaks every scan and meal into protein, carbs and fat against your targets, so you understand what your food is doing, not just how many calories it adds.
The bottom line
Macronutrients are protein, carbohydrate and fat, the three nutrients you need in large amounts and the source of all your calories. Protein and carbs give 4 calories per gram, fat gives 9. Balancing them, rather than only watching calories, is what makes a diet work and feel sustainable. This is general information, not personalised medical or dietary advice.