Nutrition: Energy Balance, Macronutrients, and Ergogenic Aids
Energy and macronutrients
Athletes need carbohydrate to fuel glycolysis and restore glycogen: roughly 6-10 g/kg body mass per day, rising toward 10-12 g/kg for heavy endurance training. Protein targets are expressed per kilogram, not as a percentage of calories: about 1.4-2.0 g/kg/day covers most resistance-training athletes, with the higher end for those in an energy deficit. Fat should supply at least 20% of energy to support hormone production and absorption of fat-soluble vitamins.
Timing and hydration
A pre-event meal 3-4 hours out with 1-4 g/kg carbohydrate tops off glycogen and settles the stomach. After training, 1.0-1.2 g/kg carbohydrate plus 0.2-0.4 g/kg protein supports glycogen resynthesis and repair. Dehydration of about 2% body mass degrades performance; replace roughly 1.25-1.5 L of fluid per kilogram of body mass lost.
Supplements and traps
Creatine monohydrate (about 5 g/day, or 20 g/day for 5-7 days to load) and caffeine (3-6 mg/kg) have the strongest evidence base. Questions love the trap that more protein is automatically better; excess is oxidized or stored, not converted into extra muscle. Remember third-party testing for banned substances, and recognize the low energy availability pattern underlying RED-S and the female athlete triad.
Worked example
A 70 kg athlete at 1.6 g/kg protein and 8 g/kg carbohydrate needs 112 g protein (about 450 kcal) and 560 g carbohydrate (about 2,240 kcal) daily. Protein is only about 16% of those 2,700 kcal, which is why percentage-of-calories framings mislead.