Calories Decide Weight, Macros Decide Composition
Total calories determine whether weight goes up or down. The split between protein, carbohydrate and fat determines what that weight is — whether a deficit costs you muscle, and whether a surplus adds mostly muscle or mostly fat.
The order of decisions matters: set calories from your goal, set protein from body weight, set fat to a healthy minimum, and let carbohydrate take whatever is left.
Setting Protein First
Protein is the one macro with a hard floor. Below roughly 1.6 g per kg, muscle retention in a deficit suffers measurably. Research on resistance-trained people supports 1.6–2.2 g per kg, with the higher end during aggressive dieting. At 4 calories a gram, an 80 kg person eating 1.8 g/kg spends 576 calories on protein — a fixed cost before anything else is allocated.
Fat Has a Floor Too
Fat below about 20% of calories impairs hormone production and the absorption of vitamins A, D, E and K. A range of 20–35% suits almost everyone. Within it, the choice between higher fat and higher carbohydrate is largely preference — adherence beats optimisation.
Carbohydrate Absorbs the Rest
Carbohydrate is not essential in the biochemical sense — the body can produce glucose from other sources — but it is the preferred fuel for hard training. Cutting carbohydrate lowers training performance before it lowers fat, which is why very low-carb diets tend to suit endurance walkers better than sprinters and lifters.
Common Splits
| Approach | Protein | Carbs | Fat | Suits |
|---|---|---|---|---|
| Balanced | 30% | 40% | 30% | General health, most people |
| Higher carb | 25% | 55% | 20% | Endurance athletes, high training volume |
| Higher fat | 30% | 25% | 45% | Preference, appetite control |
| Cutting | 40% | 35% | 25% | Fat loss with muscle retention |
| Ketogenic | 25% | 5% | 70% | Specific medical or personal reasons |
Meal Distribution
Muscle protein synthesis responds to roughly 25–40 g of protein per meal, with diminishing returns above that. Spreading protein across three or four meals produces a better response than the same total in one or two — though total daily protein remains far more important than timing.
Frequently Asked Questions
Do I need to hit macros exactly?
No. Within 5–10 g of protein and fat targets is fine; carbohydrate has the most latitude. Precision beyond that produces stress without results.
Should I use total body weight or lean mass for protein?
Total weight for people at ordinary body fat levels. Lean mass is more accurate for anyone significantly overweight, where total weight overstates the requirement considerably.
Is fibre counted in carbohydrate?
Total carbohydrate includes fibre, though fibre contributes roughly 2 calories a gram rather than 4. Aim for 14 g of fibre per 1,000 calories regardless of the split chosen.