Daily carbohydrate, protein and energy needs
Evidence: strong
Scale daily carbohydrate to training load (roughly 3–12 g/kg/day), take 1.4–2.0 g/kg/day of protein across the day, eat enough total energy to stay above the energy-availability floor, and do not cut fat too low. Match the diet to the work, not to a fixed plan.
Not medical advice
This is a general knowledge base, not medical or dietary advice. If you are injured, unwell or weighing up a supplement or a change to your diet, speak to a doctor, physiotherapist or registered dietitian who knows your situation.
Race-day fuelling gets the attention, but it sits on top of the everyday diet, and that diet is what actually fills the glycogen stores, supports adaptation and keeps the body running. The consensus position, from the joint statement of the American College of Sports Medicine, the Academy of Nutrition and Dietetics and Dietitians of Canada, is that there is no single athlete’s diet. Intake should be matched to the training being done, day by day, rather than fixed at one set of numbers (Thomas, Erdman & Burke 2016).
Carbohydrate, scaled to the work
Carbohydrate is the fuel that runs short when the work is hard. The daily target is expressed per kilogram of body mass and scaled to training load (Thomas, Erdman & Burke 2016):
- Light training (low-intensity or skill work): 3–5 g/kg/day.
- Moderate (about one hour a day): 5–7 g/kg/day.
- High (endurance work of roughly one to three hours a day): 6–10 g/kg/day.
- Very high (three to five-plus hours a day): 8–12 g/kg/day.
For a 65 kg runner, an ordinary moderate-training day lands around 325–455 g of carbohydrate; a heavy week of marathon training pushes toward 650 g or more on the biggest days. These numbers move with the training week. An easy day and a long-run day are not the same diet, and eating high every day regardless of load is as much a mismatch as eating low on a hard day.
Protein, spread across the day
Endurance runners need more protein than the general population, both to repair training damage and to maintain muscle. The consensus range is 1.2–2.0 g/kg/day, with endurance athletes typically toward the middle and the upper end justified during heavy training or while dieting to lose weight (Thomas, Erdman & Burke 2016). For most runners 1.4–2.0 g/kg/day is a sensible working range.
How it is spread matters more than chasing a post-run window. The muscle-protein-synthesis response is maximised by servings of about 0.3 g/kg, roughly 20–40 g, so the practical advice is to spread intake across about four meals of that size rather than loading it into one (Thomas, Erdman & Burke 2016). The detail is covered under protein and recovery.
Total energy is the floor
Carbohydrate and protein targets only work if total energy intake is adequate. Eat too little overall and the body cannot meet both training and basic function, so it manages the deficit by shutting systems down. This is the concept of energy availability: the energy left after exercise, per kilogram of fat-free mass per day. Below roughly 30 kcal/kg fat-free mass per day, hormonal and other functions are disrupted, with about 45 kcal/kg as the target for healthy function (Loucks & Thuma 2003). The threshold is a gradient, not a sharp line, and the exact point varies between people (Areta et al. 2023), but the principle holds: chronic underfuelling is the floor below which everything else breaks. Sustained low energy availability is the root cause of RED-S, with bone, hormones, immunity, iron status and performance all paying the price (Thomas, Erdman & Burke 2016).
Don't cut fat too low
Dietary fat should not be slashed in the name of leanness. The consensus advises against dropping below about 20% of energy from fat, because very low-fat diets risk shortfalls in energy, fat-soluble vitamins and essential fatty acids (Thomas, Erdman & Burke 2016). Fat is part of an adequate diet, not the enemy of one.
Fuel for the work required
Intake should match the demand. The consensus frames the diet as periodised alongside training: more carbohydrate around hard and long sessions, less on easy days, with total energy kept adequate throughout (Thomas, Erdman & Burke 2016). The during-race numbers, given in absolute grams per hour rather than per kilogram, live under in-race carbohydrate; the short-term loading protocol before a long race lives under carbohydrate loading; the rapid-refuelling case sits under protein and recovery. Get the daily diet right first, and those become fine-tuning rather than rescue.