Protein for endurance athletes and runners: how much do you need?

Protein is usually linked with lifting weights, but endurance training also breaks down and rebuilds muscle, mitochondria and red blood cell proteins. Runners and cyclists who under-eat protein may recover more slowly and adapt less to training. The good news is that most people can hit their target with ordinary food.

What it is

Dietary protein supplies amino acids, including the essential amino acids the body cannot make. Leucine in particular acts as a signal to switch on muscle protein synthesis. Protein comes from meat, fish, eggs, dairy, soy, legumes and grains. Supplements include whey and casein (from milk), and plant powders such as soy and pea. Whey is rapidly digested and rich in leucine.

Does it raise VO2max?

Training raises VO2max, not protein itself. A meta-analysis by Lin and colleagues (Clinical Nutrition, 2021) of 19 studies found that protein supplementation during endurance training gave a small extra gain in VO2peak, about 0.9 mL/kg/min more than training alone, alongside a little more lean mass and slightly better time trial times. For context, training by itself improved VO2peak by about 3.7 mL/kg/min in these studies. A 2025 meta-analysis of 23 trials (Xiao et al.) found no significant overall effect on aerobic capacity, but it did find better time to exhaustion, and a small possible lean-mass benefit mainly in untrained people. So protein helps you adapt to training, it does not replace it (see how to improve VO2max).

Does it improve endurance performance?

The International Society of Sports Nutrition position stand (Jäger et al., 2017) says endurance athletes should focus first on enough carbohydrate for performance, and that adding protein may help offset muscle damage and promote recovery. The joint position of the Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine (Thomas et al., 2016) similarly treats protein as part of an overall fuelling plan, and recommends a registered dietitian for a personalised approach.

The bigger question is how much. Older recommendations for endurance athletes were about 1.2–1.4 g per kg per day. Kato and colleagues (2016) used the indicator amino acid oxidation method in trained male runners after a 20 km run and estimated an average requirement of 1.65 g per kg and a recommended intake of 1.83 g per kg per day, higher than the older figures. It was a small study of six men, but it fits the ISSN's 1.4–2.0 g per kg range for most exercising people.

How it is used in studies

From the ISSN position stand:

• Daily total: about 1.4–2.0 g per kg of body weight per day for most exercising individuals. For a 70 kg runner, that is about 100–140 g a day.
• Per serving: about 0.25 g per kg, or 20–40 g of high-quality protein, with roughly 700–3000 mg of leucine.
• Spacing: evenly distributed every 3–4 hours across the day.
• Timing: before or after training both work. The anabolic effect of exercise lasts at least 24 hours, so there is no narrow "window", although it likely fades with time.
• Before bed: 30–40 g of casein increases overnight muscle protein synthesis.

After long or hard sessions, combining protein with carbohydrate covers both repair and glycogen refuelling.

Side effects, safety and anti-doping

The earlier ISSN position stand (Campbell et al., 2007) concluded that 1.4–2.0 g per kg per day, as part of a balanced diet, is not harmful to kidney function or bone metabolism in healthy, active people. People with kidney disease, liver disease or other medical conditions, and anyone on a prescribed diet, should talk to their doctor or dietitian before increasing protein. Powders can cause bloating, especially lactose-containing whey in people with lactose intolerance. Protein powders are a known source of contamination with banned substances, so athletes who compete should use third-party tested products. This page is not medical advice.

Who might benefit

• High-volume runners, cyclists and triathletes, especially on double days.
• Athletes eating less to lose weight, who need protein to protect muscle (see VO2max and body weight).
• Older athletes, since the ideal serving size depends on age (see VO2max and ageing).
• Plant-based athletes, who may need slightly larger servings to reach the same leucine content.
• Anyone combining endurance with strength training for runners.

A protein shake is a convenience. If your meals already provide enough, powder adds little.

Bottom line

Endurance athletes need more protein than sedentary people, roughly 1.4–2.0 g per kg per day, spread through the day. Protein supports recovery and gives small extra gains from training, but carbohydrate is still the main performance fuel. Food first, powder if it is convenient. Compare other options on the supplements page, such as creatine.

Sources

• Jäger R, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20. doi:10.1186/s12970-017-0177-8
• Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine joint position statement: nutrition and athletic performance. Med Sci Sports Exerc. 2016;48(3):543–568. doi:10.1249/MSS.0000000000000852
• Kato H, et al. Protein requirements are elevated in endurance athletes after exercise as determined by the indicator amino acid oxidation method. PLoS One. 2016;11(6):e0157406. doi:10.1371/journal.pone.0157406
• Lin YN, et al. Protein supplementation increases adaptations to endurance training: a systematic review and meta-analysis. Clin Nutr. 2021;40(5):3123–3132. doi:10.1016/j.clnu.2020.12.012
• Xiao Y, et al. Effects of protein supplementation on body composition, physiological adaptations, and performance during endurance training: a systematic review and meta-analysis. Front Nutr. 2025;12:1663860. doi:10.3389/fnut.2025.1663860
• Campbell B, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2007;4:8. doi:10.1186/1550-2783-4-8