"Macros" is short for macronutrients — the three categories of nutrients that provide energy: protein, carbohydrates, and fat. Every food is made up of these three things in different proportions. Understanding macros is the foundation of any structured approach to nutrition, whether you're trying to lose fat, build muscle, or just eat more consistently.
The Three Macronutrients
Protein
Protein is built from amino acids and is the body's primary building material — used to repair and build muscle, produce enzymes and hormones, and maintain every tissue in the body. It provides 4 calories per gram.
Unlike fat and carbohydrates, your body cannot store excess protein long-term. This means you need a consistent daily supply. The minimum for a sedentary adult is around 0.8g per kg of bodyweight, but for anyone exercising or managing body composition, the evidence points to 1.6–2.2g per kg as the optimal range.
Protein also has the highest thermic effect of food — your body burns approximately 20–30% of protein calories just through digestion, compared to 5–10% for carbohydrates and 0–3% for fat. This is one reason high-protein diets support fat loss even at the same total calorie intake.
Good UK sources: chicken, eggs, fish, lentils, cottage cheese, Greek yoghurt, tinned tuna.
Carbohydrates
Carbohydrates are the body's preferred fuel source, particularly for the brain and during high-intensity exercise. They provide 4 calories per gram. When you eat carbohydrates, they're broken down into glucose and either used immediately for energy or stored as glycogen in muscles and the liver.
There are two main types:
- Simple carbohydrates — sugars (glucose, fructose, sucrose) that digest quickly. Found in fruit, milk, and processed foods. Useful for quick energy but spike blood sugar fast.
- Complex carbohydrates — starches and fibre that digest slowly. Found in oats, brown rice, sweet potato, wholemeal bread, lentils. Provide sustained energy and keep you full longer.
Fibre — technically a carbohydrate — provides minimal calories but has significant health benefits: digestive health, blood sugar regulation, and satiety. UK adults should aim for 30g of fibre per day. Most get 15–18g.
Fat
Fat provides 9 calories per gram — more than double protein or carbohydrates. Despite decades of low-fat diet messaging, fat is essential: it enables absorption of vitamins A, D, E, and K; supports hormone production (including testosterone); insulates organs; and provides the most calorie-dense energy source available.
Types matter more than quantity:
- Unsaturated fats (olive oil, avocado, nuts, oily fish) — actively beneficial, support heart health and reduce inflammation
- Saturated fats (butter, cheese, red meat, coconut oil) — fine in moderation, but evidence links high intake to cardiovascular risk
- Trans fats (partially hydrogenated oils) — still present in some processed foods; evidence strongly links them to cardiovascular disease. Largely eliminated from UK supermarkets but worth checking labels on processed items
How Many of Each Do You Need?
There's no single answer — it depends on your goals, bodyweight, and activity level. General starting points:
- Protein: 1.6–2.2g per kg of bodyweight (for active adults)
- Fat: 20–35% of total calories (roughly 0.8–1.2g per kg)
- Carbohydrates: Fill the remaining calories once protein and fat are set
The reason protein and fat are set first is that they have functional minimums. Carbohydrates are flexible — you can go lower (keto approaches reduce them significantly) or higher (endurance athletes eat high-carb). What doesn't change is that you need adequate protein for muscle maintenance and adequate fat for hormonal function.
Use our macro calculator to get your specific targets — it calculates protein based on your bodyweight and adjusts fat and carbohydrates around your total calorie goal.
Calories vs. Macros: Do Both Matter?
Yes. Total calories determine whether you gain, lose, or maintain weight. Macro ratios determine what kind of weight you gain or lose — muscle vs fat, energy levels, satiety. You can lose weight by only tracking calories, but you'll lose more muscle and feel worse than if you also hit your protein target. Macros without calorie awareness can lead to eating the right ratios but too many (or too few) calories overall.
The most complete picture: track both. Start with your total calorie target (use our TDEE calculator to find your maintenance calories), then set your macro targets around it.
What Tracking Macros Actually Looks Like
Tracking macros doesn't mean weighing everything forever. Most people use apps (Cronometer and MyFitnessPal are popular in the UK) to log food for 4–6 weeks. After that, you develop an intuitive sense of the protein, carb, and fat content of your regular meals. You stop needing to log every meal because you've built a mental library.
The shortcut: learn the macros of your 10 most commonly eaten meals. Those 10 meals make up 80–90% of what you eat. Getting those right handles most of the work without needing to log everything else.
Once you know your targets, our meal planner generates a full week of meals that hit your exact macro goals automatically — with all the calculations done, and a shopping list built around UK supermarket ingredients.