Each macronutrient has a fixed caloric density: protein 4 kcal/g, carbs 4 kcal/g, fat 9 kcal/g, alcohol 7 kcal/g. Once your total daily calorie target is set, you split it across macros based on diet style. Balanced (30P/40C/30F) suits most general-fitness adults. High-protein (40P/35C/25F) is ideal during fat loss to preserve muscle. Low-carb (30P/20C/50F) suits insulin-resistant adults and those who feel better on lower carbs. Keto (25P/5C/70F) is the extreme version, with carbs restricted to under 30 g/day to induce nutritional ketosis.
Protein targets are usually expressed per kg body weight: sedentary 0.8-1.0 g/kg, recreational lifters 1.4-1.6 g/kg, serious athletes during fat loss 2.0-2.2 g/kg. For most adults aiming for body composition change, 1.6-1.8 g/kg is the sweet spot - high enough to support muscle goals, not so high as to push other macros too low. A 70 kg adult should target 112-126 g protein daily; this comes from eggs (6 g each), Greek yogurt or paneer (20-25 g per 200g serving), chicken breast (30 g per 100 g), pulses (15-20 g per cooked cup), or whey protein supplements (20-25 g per scoop).
Fat must stay above a minimum threshold for hormonal health. For most adults, 0.7-1.0 g/kg body weight is the floor - going below 0.5 g/kg for extended periods can disrupt testosterone in men and menstrual function in women. The remainder of your calorie budget after protein and fat goes to carbohydrates. For high-volume training, more carbs help recovery; for sedentary work, carbs can be lower without performance impact.