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Protein for runners: what's being used and what the research says

We report what runners are using and what the research says. We don't recommend taking any supplement. Talk to your GP or a registered sports dietitian before trying one.

Quick answer

Research suggests most runners don't need them. The international athletics federation's consensus puts daily targets for weight-stable athletes at 1.3 to 1.7 g of protein per kg of body mass[1], and the AIS says most athletes meet their targets from food[2]. The ISSN says added protein does not appear to improve endurance performance[3].

Research
Emerging (proposed)Food can meet runners' daily needs. No clear gain in race times; meta-analyses of training adaptation disagree.
Proposed by our editor; not yet confirmed by an expert reviewer.
WADA status
Permitted
Distances in the research
800 m–5K: limited research10K–half: limited researchMarathon: limited researchUltra: limited research

What are protein supplements?

Protein is found in every cell of the body. About half of it is in skeletal muscle; the rest helps build bone, cartilage, skin, blood, enzymes and hormones[2]. In Australia, meat, fish, poultry, cereals and dairy supply most of it[2].

Supplements come as powders, bars and ready-to-drink shakes made from milk proteins such as whey and casein, from egg, or from plants such as soy, pea, rice and hemp[2]. The IOC describes a typical serve as 20 to 50 g of protein and notes that products may contain other ingredients[4].

Whey comes as concentrate (70 to 80% protein), isolate (about 90%) or hydrolysate, which is broken into short chains and sold as 'pre-digested'; the AIS says the practical difference between them is small[2]. The ISSN says whey and casein have the highest leucine content of any protein source, about 11% and 9.3%, and that casein clots in the gut and is digested more slowly[3].

The AIS lists isolated protein supplements in Group A, as a sports food, and places branched-chain amino acids (BCAAs) in Group C[2][5]. The international athletics federation prefers whole foods, but says supplements can help when food is impractical, such as straight after exercise[1].

Also called: protein shakes, protein powder, whey, casein, recovery shakes.

Why are protein supplements getting attention?

Protein's role in building and repairing muscle has made it an obvious focus for athletes and coaches, and protein supplements are among the most popular supplement products[2]. A meta-analysis of 159 studies found that about 60% of athletes used a supplement of some kind; protein was among the most used, and more men than women used it[6].

Surveys of runners are few. In 119 recreational distance runners, the authors report an intake rate of 19% for carbohydrate and protein supplements, counted together[7]. In a wider sample of 220 runners, 72% of vegans used supplements, against 51% overall, but vegans didn't use more carbohydrate or protein supplements than other runners[8].

Tracer studies have suggested that endurance athletes need more protein than earlier guidance allowed[9][10], and the ISSN presents supplements as a practical way for high-volume athletes to get enough protein while keeping calories down[3].

The claims, checked against the research

  • Faster race timesNot supported

    The ISSN says added protein does not appear to improve endurance performance[3]. Adding protein to a carbohydrate drink didn't improve an 80 km cycling time trial[11], and a protein-carbohydrate drink was no faster than placebo over a 21 km run in women[12]. A 2026 meta-analysis found every significant performance effect came from trials that didn't match energy intake between groups[13].

  • Less soreness after hard runsMixed

    The ISSN says protein added to carbohydrate during exhausting exercise lowers damage markers and soreness[3]. In runners, a recovery drink with protein and antioxidants cut soreness over 6 days of training[14], but milk protein after a 15 km race didn't[15]. A systematic review found too little evidence that protein after a single bout reduces soreness[16].

  • Bigger gains from trainingMixed

    Two meta-analyses disagree. One found small extra gains in aerobic fitness, lean mass and time trials[17]; a 2025 analysis found only time to exhaustion improved, and rated most of its evidence low or very low certainty[18]. In a 10-week trial, protein raised VO2max more than carbohydrate but didn't improve endurance performance[19].

  • Quicker refuelling between sessionsNot supported

    A meta-analysis of 19 trials found that adding protein to carbohydrate didn't speed muscle glycogen restoration after exercise[20]. Another, of 13 trials, found no effect on performance in a later exercise bout[21].

  • Holding form through a hard weekMixed

    Elite orienteers who took whey around each session of a training camp ran a 4 km test faster and had a smaller rise in a damage marker[22]. Trained runners given whey before sleep during a hard week lost as much 5 km performance as those given carbohydrate[23].

  • Easier to hit protein targetsSupported

    Consensus statements see supplements as a practical option when food is impractical or inconvenient, such as straight after exercise[1][24]. In the 15 km race trial, runners who took the protein drinks as directed reached about 1.9 g/kg a day, against 1.1 g/kg on the carbohydrate drinks[15]. The AIS adds that most athletes reach their targets from food anyway[2].

How do protein supplements work?

Training raises protein needs: the AIS puts targets for athletes in heavy training at up to double those for inactive people, and says this applies to endurance athletes too[2]. Protein eaten over the day after key sessions helps the body build new proteins in response to training and replace damaged ones[1]. For distance runners, a review says the more relevant adaptation is remodelling of energy-producing (mitochondrial) and other muscle proteins, rather than muscle growth[25].

Essential amino acids, especially leucine, switch on muscle protein synthesis, and a session's effect lasts at least 24 hours[3]. In 48 endurance-trained men after 90 minutes of cycling, 30 g of milk protein maximised contractile (myofibrillar) protein synthesis but didn't raise mitochondrial protein synthesis[26]. In 36 young men after an evening ride, 45 g of casein or whey before bed raised both overnight, compared with placebo[27].

Endurance exercise also burns some amino acids as fuel. In 8 endurance-trained men, training with low carbohydrate availability raised amino acid oxidation during recovery, which the authors read as a higher protein requirement[28].

Tracer studies using the indicator amino acid oxidation (IAAO) method estimate the protein intake that maximises whole-body protein synthesis. In 6 male runners after a 20 km run, the estimated average requirement was 1.65 g/kg a day, with an upper estimate of 1.83 g/kg[9]. In 8 endurance-trained men studied a day after exercise, the figures were 2.1 and 2.6 g/kg[10].

Do protein supplements help runners?

Not clearly for race performance. The ISSN says added protein does not appear to improve endurance performance[3]. A meta-analysis found carbohydrate plus protein beat carbohydrate alone overall, but in the six trials where drinks had the same calories, time to exhaustion didn't improve[29]. On training adaptation, one meta-analysis, which included patient groups, found small extra gains in aerobic fitness, lean mass and time trials[17]; a 2025 meta-analysis found only time to exhaustion improved, with most of its evidence low or very low certainty[18].

800 m to 5K (Limited research)

Elite orienteers who took whey around each session of a hard training week ran a 4 km test faster[22]. In trained runners, protein before sleep during a hard week made no difference to a 5 km time trial[23], and 6 weeks of whey around training didn't improve a 6 km time trial more than carbohydrate did[30]. We found no protein trials at 800 m or 1,500 m.

10K to half marathon (Limited research)

In 323 recreational runners after a 15 km road race, milk protein for three days didn't reduce muscle soreness or damage markers compared with a carbohydrate drink[15]. In 11 female recreational runners, a drink with protein in place of some carbohydrate was no faster over a 21 km time trial than a carbohydrate drink or a placebo[12].

Marathon (Limited research)

In a small trial in recreational marathoners, protein during or after the race made no meaningful difference to recovery at 24 hours, though soreness and fatigue ratings were better over 72 hours[31]. We found no trials measuring marathon race times.

Ultra (Limited research)

In 28 male ultra runners, amino acids before and during a 100 km race didn't change race time, damage markers or soreness[32]. The ISSN calls the controlled evidence in ultras conflicting[33]. Finishers of a 100-mile race ate more protein than non-finishers, but that is an association, and gut problems may explain the non-finishers' lower intake[33].

Study by study

The main studies on this page. What they took is what the study gave, not advice for any individual.
StudyWho took partWhat they tookWhat was measuredWhat they found
Kloby 2020 [29]Meta-analysis30 randomised trials; about 80% men, mostly cyclistsCarbohydrate plus protein v carbohydrate aloneTime to exhaustion and time trialsBenefit overall, but none in 6 calorie-matched time-to-exhaustion trials; time trials weren't analysed by calorie matching
Zhao 2026 [13]Meta-analysis75 randomised trials, 1,206 athletesProtein supplements v placebo, carbohydrate or nothingEndurance performance, strength and recoverySome benefits, but every significant effect came from trials that didn't match energy intake between groups
Lin 2021 [17]Meta-analysis19 studies, 1,162 people, including patient groupsProtein supplements during weeks of endurance trainingVO2peak, lean mass and time trialsSmall extra gains: VO2peak 0.89 mL/kg/min higher, 0.32 kg more lean mass, time trials 29 s faster
Xiao 2025 [18]Meta-analysis23 trials, 1,146 people (78% men)Protein supplements during endurance trainingLean mass, VO2max, time to exhaustion, time trials, body fatOnly time to exhaustion improved significantly; evidence for the other outcomes rated low or very low certainty
Ten 2021 [15]Randomised controlled trial323 recreational runners (56% men, average age 44)20 g of milk protein after a 15 km race and at breakfast, plus 40 g before sleep, for 3 days, v carbohydrateMuscle soreness and damage markers (CK, LDH)No difference; in the per-protocol analysis the protein group reported more soreness at 24 hoursFunding: FrieslandCampina (dairy company)
Hansen 2015 [22]Randomised controlled trial18 elite orienteersWhey 0.3 g/kg before and after (with carbohydrate) each session of a 1-week camp, v energy-matched carbohydrate4 km run test; creatine kinase4 km run test improved, and creatine kinase rose less, with protein
Larsen 2019 [23]Randomised controlled trial32 trained runnersWhey isolate 0.5 g/kg nightly before sleep during a hard training week, v carbohydrate5 km time trial; muscle damage markersNo difference: 5 km performance fell in both groups, and damage markers rose alikeFunding: Two authors employed by Arla Foods Ingredients
Hansen 2020 [30]Randomised controlled trial24 trained runnersWhey 0.3 g/kg before and after (with carbohydrate) each session for 6 weeks, v energy-matched carbohydrateVO2max, 6 km time trial, mitochondrial proteinsVO2max and 6 km time improved in both groups, with no significant difference; one mitochondrial protein rose more with wheyFunding: Part-funded by Arla Foods Ingredients
Saunders 2018 [31]Randomised controlled trialRecreational marathoners, 4 to 8 per group; mostly women in the in-race studyGels with 20 g carbohydrate and 5 g protein during the race, or protein after it, v carbohydrateSoreness, fatigue ratings and creatine kinase over 72 hoursNo meaningful difference at 24 hours; soreness and fatigue ratings better over 72 hours
Knechtle 2011 [32]Randomised controlled trial28 experienced male ultra runners52.5 g of amino acids (20 g BCAAs) before and during a 100 km race; no placeboRace time, damage markers, sorenessNo difference in race time (after adjusting for personal bests), creatine kinase, urea, myoglobin or soreness
Gui 2017 [12]Randomised controlled trial11 female recreational runnersDrink with 2% protein and 4% carbohydrate, 6% carbohydrate, or placebo, every 2.5 km (crossover)21 km time trialCarbohydrate drink faster than placebo; protein drink no different from either
Knuiman 2019 [19]Randomised controlled trial44 recreationally active young men (40 analysed)Protein after sessions and before sleep for 10 weeks, v same-calorie carbohydrateVO2max, lean mass, simulated 10 km cycling time trialVO2max and lean mass rose more with protein; no improvement in endurance performance or muscle oxidative capacity

The key studies, in order

  1. 2006Trial10 trained male cyclists, 80 km time trial: adding 2% protein to a 6% carbohydrate drink gave no extra benefit. [11]
  2. 2007Trial23 cross-country runners, 6 days: a carbohydrate-protein-antioxidant drink lowered creatine kinase and soreness; race performance didn't differ. [14]
  3. 2011Trial28 male ultra runners: 52.5 g of amino acids before and during a 100 km race didn't change race time, muscle damage markers or soreness. [32]
  4. 2014Systematic review27 studies: little evidence that protein after one bout cuts soreness or damage markers; benefits more evident with daily training. [16]
  5. 2015Trial18 elite orienteers, 1-week camp: whey before and after each session improved a 4 km run test and limited the rise in creatine kinase, v energy-matched carbohydrate. [22]
  6. 2016Observational study5 masters and 6 younger triathletes over 3 hard days: myofibrillar protein synthesis was lower in the masters athletes. [35]
  7. 2016Trial6 male runners after a 20 km run: estimated requirement 1.65 g/kg a day, upper estimate 1.83 g/kg. Funded by Ajinomoto. [9]
  8. 2016Meta-analysis159 studies: about 60% of athletes used supplements; protein was among the most used, more by men than women. [6]
  9. 2016ConsensusJoint ACSM and dietitians' statement: 1.2-2.0 g/kg of protein a day, 0.3 g/kg after key sessions and every 3-5 hours; above 40 g per dose not shown to add more. [24]
  10. 2017Trial8 masters triathletes: 0.6 v 0.3 g/kg of protein per feeding (3 feedings) after a downhill run didn't significantly improve recovery. [36]
  11. 2017Trial11 female recreational runners, 21 km time trial: a drink with protein in place of some carbohydrate gave no benefit. [12]
  12. 2017Consensus1.4-2.0 g/kg a day suits most exercising people. Added protein doesn't appear to improve endurance performance. No controlled evidence of harm in healthy exercisers. [3]
  13. 2018Meta-analysis28 trials, 1,358 adults without kidney disease: higher-protein diets didn't change kidney filtration differently from normal diets. [45]
  14. 2018ConsensusProtein supplements give 20-50 g per serve but may contain other ingredients that raise contamination risk. Athletes are responsible for anything in their sample. [4]
  15. 2018Meta-analysis13 trials, 125 people: adding protein to carbohydrate after exercise didn't change performance in a later bout. [21]
  16. 2018TrialRecreational marathoners, 4 to 8 per group: no meaningful difference at 24 hours; soreness and fatigue ratings better over 72 hours with protein. [31]
  17. 2019Trial8 endurance-trained men a day after exercise: estimated requirement 2.1 g/kg a day, upper estimate 2.6 g/kg. [10]
  18. 2019Consensus1.3-1.7 g/kg of protein a day. Whole foods preferred; supplements useful when food is impractical. 2.4 g/kg during weight loss didn't raise kidney or bone risk. [1]
  19. 2019Expert reviewDistance running review: lists reducing fat, fibre and protein in the pre-race meal when gut problems are a risk. [44]
  20. 2019Trial8 endurance-trained men: training with low carbohydrate availability raised amino acid oxidation, suggesting a higher protein requirement. [28]
  21. 2019Trial44 young men, 10 weeks of training: protein raised VO2max and lean mass more than carbohydrate, but not endurance performance. [19]
  22. 2019Trial32 trained runners, hard training week: whey before sleep didn't reduce the drop in 5 km performance or damage markers, v carbohydrate. [23]
  23. 2019ConsensusUltra runners: about 1.6 g/kg of protein a day, up to 2.5 g/kg in demanding training. Controlled studies of protein during ultras conflict. [33]
  24. 2019Expert reviewFor distance runners, protein supports remodelling of mitochondrial and other muscle proteins; about 1.6 g/kg a day needs no supplements beyond convenience. [25]
  25. 2020Trial48 endurance-trained men after cycling: 30 g of milk protein maximised myofibrillar protein synthesis; mitochondrial synthesis didn't rise. Gatorade-supported. [26]
  26. 2020Trial24 trained runners, 6 weeks: whey didn't improve VO2max or a 6 km time trial more than carbohydrate. Part-funded by Arla Foods Ingredients. [30]
  27. 2020Meta-analysis30 trials: carbohydrate plus protein beat carbohydrate alone overall, but not in 6 calorie-matched time-to-exhaustion trials. Mostly cycling; about 80% men. [29]
  28. 2020Observational study198 protein supplements bought in Korea or from overseas: 2 contained anabolic steroids (testosterone, stanozolol). [49]
  29. 2021Meta-analysis19 trials, 160 people: adding protein to carbohydrate didn't speed muscle glycogen restoration in the 8 hours after exercise. [20]
  30. 2021Meta-analysis19 studies, 1,162 people including patient groups: protein during endurance training brought small extra gains in VO2peak, lean mass and time trials. [17]
  31. 2021Expert reviewArgues that masters athletes (over 35) are unlikely to need different amounts of protein from young athletes. [34]
  32. 2021Expert reviewSoy and wheat protein raise muscle protein synthesis less than the same amount of animal protein; more protein, blends or added amino acids may compensate. [38]
  33. 2021Observational study36 protein powders sold in Ireland: toxic elements at acceptable levels, but heavy, long-term use may slightly raise lifetime risk. [46]
  34. 2021Trial323 recreational runners after a 15 km race: milk protein for 3 days didn't reduce soreness or damage markers v carbohydrate. Funded by a dairy company. [15]
  35. 2021Survey119 recreational distance runners: the authors report 43% used vitamins, 34% minerals and 19% carbohydrate or protein supplements, counted together. [7]
  36. 2021Survey220 distance runners: 51% used supplements, 72% of vegans; vegans didn't use more carbohydrate or protein supplements. [8]
  37. 2023ConsensusLow energy availability, too little intake for the energy cost of exercise, harms health and performance in female and male athletes. [37]
  38. 2023ConsensusNo studies of female athletes' protein needs across the menstrual cycle. Suggests 1.8-2.2 g/kg a day in its text (1.4-2.2 in its summary), about 12% more in the luteal phase. [40]
  39. 2023Trial36 young men after evening cycling: 45 g of casein or whey before sleep raised overnight muscle protein synthesis v placebo, with no difference between the two. [27]
  40. 2023Expert reviewA vegan diet doesn't appear to help or harm performance, but unplanned vegan diets may fall short on protein quantity or quality. [39]
  41. 2023Trial7 women and 8 men after a 20 km run: estimated requirements 1.61 and 1.60 g/kg a day, not different by sex. [41]
  42. 2025Meta-analysis23 trials, 1,146 people (78% men): only time to exhaustion improved significantly; most evidence low or very low certainty. The authors note this contradicts an earlier meta-analysis. [18]
  43. 2026Meta-analysis75 studies, 1,206 athletes: every significant benefit of protein supplements came from trials that didn't match energy intake between groups. [13]

Who has the research been done in?

Most protein trials studied men, usually on bikes[29]. The 2025 training meta-analysis was 78% men[18], and the 2021 one included patient groups[17]. The largest running trial is an exception: 323 recreational runners with an average age of 44, 56% of them men[15].

Masters runners are barely studied. A review argues that masters athletes (over 35) keep muscle and protein metabolism similar to young athletes, so are unlikely to need different amounts[34]. Yet 5 masters triathletes (average age 53) built muscle protein more slowly than 6 younger ones over 3 hard days[35], and doubling post-exercise protein in 8 masters triathletes didn't significantly improve recovery[36].

Findings may not apply to runners with low energy availability, meaning too little energy intake for the cost of training, which the IOC links to health and performance problems in both sexes[37]; the ACSM statement says protein needs may rise for short periods when energy intake is cut[24]. Plant proteins raise muscle protein synthesis less than the same amount of animal protein[38], and unplanned vegan diets may fall short on protein[39]. We found no trials in adolescent runners.

What we know about women

The ISSN's position stand on female athletes says no studies have addressed their protein needs across the menstrual cycle or with hormonal contraceptives[40]. It reports higher protein breakdown at rest and after endurance exercise in the luteal phase, and suggests 1.8 to 2.2 g/kg a day for women at all stages (1.4 to 2.2 in its summary), about 12% more in the luteal phase, and the upper end around and after menopause[40]. In a tracer study after a 20 km run, 7 women in the mid-luteal phase and 8 men had almost identical estimated requirements, 1.61 and 1.60 g/kg a day[41].

Performance trials in women are rare: protein in a race drink didn't improve a 21 km time trial in 11 female recreational runners[12], and about 20% of participants in the main meta-analysis were women[29]. The ISSN says pre-sleep protein hasn't been shown to be specifically beneficial for female athletes who eat enough[40]. In pregnancy, the NHS advises eating some protein-rich foods every day, such as beans, pulses, fish, eggs, meat (but not liver) and nuts[42]. We found no trials of protein supplements in pregnant runners.

What the research can't tell us yet

Most trials used cycling: in a meta-analysis of protein added to carbohydrate, only four studies tested running, and about 80% of participants were men[29].

When drinks had the same calories, time to exhaustion didn't improve, but only six small trials tested this, and none used time trials[29]. Most evidence on training adaptation was rated low or very low certainty, and most of those trials didn't report how they randomised[18].

Tracer studies of protein needs are tiny, with 6 to 15 people each, and measure whole-body protein metabolism, not performance[9][10][41].

Industry money runs through this field. A dairy company funded the 15 km race trial[15]; two authors of the pre-sleep running trial worked for a whey supplier[23], which part-funded the 6-week runner trial[30]; and an amino acid maker funded the 2016 tracer study in runners[9]. ISSN protein stand authors also declare industry ties[3].

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How and when are protein supplements used in studies?

Daily targets in position stands: 1.3 to 1.7 g per kg of body mass[1], 1.2 to 1.6 g/kg in heavy training[2], 1.2 to 2.0 g/kg[24] and 1.4 to 2.0 g/kg[3]. For ultra runners, the ISSN gives about 1.6 g/kg a day, and up to 2.5 g/kg during demanding training[33]. The athletics federation says intakes above 2.5 g/kg offer no extra benefit for adaptation[1]. For comparison, the UK reference values for the general population are 55.5 g a day for men and 45.0 g for women aged 19 to 64[43].

Position stands spread protein over the day. The athletics federation describes 0.3 to 0.4 g/kg at 4 to 5 eating occasions[1], and the AIS 15 to 30 g at 3 to 5[2]. The ACSM statement gives 0.3 g/kg after key sessions and every 3 to 5 hours, and says doses above 40 g haven't been shown to add to muscle protein synthesis[24]. The ISSN describes 20 to 40 g every 3 to 4 hours, with 700 to 3,000 mg of leucine per dose[3]. The AIS describes supplement serves of 20 to 40 g[2].

Studies of runners used, for example, 20 g of milk protein after a race and at breakfast, plus 40 g before sleep, for three days[15], 0.3 g per kg before and after each session of a training camp[22], or 0.5 g/kg of whey before sleep[23].

On type, 45 g of whey and 45 g of casein before sleep didn't differ in their effect on overnight muscle protein synthesis[27], and the AIS says evidence for casein's special value at night is lacking[2]. The ACSM statement says dairy proteins seem superior to other tested proteins, largely because of their leucine[24]. Plant proteins may close the gap if people eat more, mix sources or add missing amino acids[38].

When studies gave it

After exercise: the ACSM statement describes 15 to 25 g (0.25 to 0.3 g/kg) in the first 2 hours[24]. The ISSN says benefits come from protein before or after a workout, and the effect of exercise lasts at least 24 hours[3]. In meta-analyses, adding protein to carbohydrate didn't speed glycogen restoration[20] or change performance in a later session[21].

During exercise: the ISSN describes about 0.25 g/kg of protein an hour, alongside carbohydrate, to reduce damage markers and soreness; the same stand finds no performance benefit[3]. Its ultra position stand describes 5 to 10 g of protein an hour within 150 to 400 kcal an hour[33]. Before a race, a distance-running review lists cutting protein, fat and fibre in the pre-race meal when gut problems are a risk[44].

Before sleep: the ISSN says 30 to 40 g of casein before sleep raises overnight muscle protein synthesis[3]. In runners, whey before sleep during a hard week didn't help[23], and the 15 km race trial, which found no benefit, also gave 40 g before sleep[15]. Trials in runners ran from a single race to 6 weeks of training[32][30].

What studies used. These are research protocols, not advice for any individual.
What studies usedWhenRef.
20 g of milk protein, plus 40 g before sleepAfter a 15 km race, then at breakfast and before sleep for 3 days[15]
0.3 g per kg of body mass of wheyBefore and after each session of a 1-week camp[22]
0.5 g per kg of body mass of whey isolateBefore sleep, every night of a hard training week[23]
Gels with 20 g carbohydrate and 5 g proteinDuring a marathon[31]
45 g of casein or whey30 minutes before sleep, after an evening cycling session[27]
5-10 g of protein an hour, within 150-400 kcal an hourDuring ultra-marathon racing (position stand)[33]

What are the side effects, and who should be careful?

The ISSN says there is no controlled evidence that higher protein intakes harm healthy exercising people[3]. The athletics federation says athletes eating 2.4 g/kg a day during weight loss aren't at increased risk of kidney or bone problems[1]. In a meta-analysis of 28 trials in 1,358 adults without kidney disease, higher-protein diets didn't change kidney filtration differently from lower- or normal-protein diets[45].

The AIS warns that some powders contain unneeded ingredients, some possibly harmful or banned in sport, and contaminants such as heavy metals; it notes the US consumer test behind the heavy-metal concern wasn't peer reviewed[2]. In 36 powders sold in Ireland, toxic elements were at acceptable levels, though heavy, long-term use may slightly raise lifetime risk[46].

Protein products may contain milk, soy, tree nuts and other allergens, and whey concentrate contains a little lactose[2]. The NHS notes that some people need to avoid dairy because they can't digest lactose or are allergic to cows' milk protein[47].

Protein can crowd out carbohydrate: in cyclists, a week of high-protein, lower-carbohydrate eating made a time trial take 20% longer[3].

Medicines and health conditions

The NHS advises people with chronic kidney disease to check with a doctor or pharmacist before taking nutritional supplements, which can sometimes affect the kidneys or interfere with prescribed medicine[48]. The ISSN notes that people in kidney failure benefit from protein-restricted diets, and its safety conclusions cover healthy exercisers only[3].

Whey and casein are milk proteins, which matters for anyone with a cows' milk allergy or lactose intolerance[47]. We found no NHS or gov.uk page on protein powders in September 2026. UK reference values are for the general population, and the government says anyone with a medical condition should see their GP or a registered dietitian for dietary advice[43].

Be careful if

  • You have a kidney condition: the NHS advises people with chronic kidney disease to check with a doctor or pharmacist before taking nutritional supplements[48].
  • Shakes are replacing carbohydrate-rich food: a high-protein, lower-carbohydrate diet slowed cyclists' time trials[3].
  • You're tested under anti-doping rules: protein supplements can contain undeclared prohibited substances[4][49].
  • You have a cows' milk allergy or lactose intolerance: whey and casein are milk proteins, and the NHS notes some people need to avoid dairy for these reasons[47].
  • You take several shakes a day: discussing contaminants such as heavy metals, the AIS suggests limiting protein supplements to 1 to 2 serves a day[2].

Are protein supplements allowed in competition?

Food proteins such as whey and casein are not on the World Anti-Doping Agency's Prohibited List[50]. WADA notes that most of the list's categories give examples rather than a full list[50].

The IOC notes that protein supplements may contain other ingredients that raise the risk of contamination[4], and under anti-doping rules, athletes are responsible for anything found in their sample[4]. An early analysis found undeclared prohormones in about 15% of more than 600 supplements[4]. In 198 protein supplements tested in Korea, 2 contained anabolic steroids[49].

Independent quality-assurance schemes, often called batch testing, check supplement products for prohibited substances[4]. WADA says using a product from one of these schemes can reduce, but not eliminate, the risk of an anti-doping violation[50], and the IOC says no product can be guaranteed entirely safe[4]. The AIS adds that batch testing checks for substances banned in sport, not other contaminants such as heavy metals[2].

Myth or evidence?

5 things runners hear about protein supplements. Pick an answer to see what the research says.

  1. 1.Distance runners need more protein than people who don't exercise.

    Show the answer

    Evidence. The AIS puts targets for athletes in heavy training at up to double those for inactive people, including endurance athletes[2].

  2. 2.You need protein shakes to get enough protein.

    Show the answer

    Myth. The AIS says most athletes meet their targets from food alone[2].

  3. 3.Protein before or during a race makes you faster.

    Show the answer

    Myth. The ISSN finds no clear endurance benefit[3]. In a meta-analysis, benefits appeared mainly when protein added extra calories[29].

  4. 4.Protein after a hard run cuts muscle soreness.

    Show the answer

    Mixed. A small marathon trial found better soreness ratings over 72 hours with protein[31], but the largest running trial found no soreness benefit[15].

  5. 5.Protein powders can contain contaminants or banned substances.

    Show the answer

    Evidence. The IOC and the AIS both warn of contamination risks[4][2].

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Frequently asked questions

How much protein do distance runners need each day?
The international athletics federation's consensus gives 1.3 to 1.7 g per kg of body mass a day[1], and the ISSN 1.4 to 2.0 g/kg[3]. For ultra runners, the ISSN gives about 1.6 g/kg a day, and up to 2.5 g/kg during demanding training[33].
Do runners need a protein shake to hit that target?
The AIS says most athletes reach their daily target from food and takes a food-first approach[2]. The athletics federation sees shakes as useful when food is impractical, such as straight after a session[1].
Will extra protein make me faster?
The ISSN says added protein does not appear to improve endurance performance[3]. A meta-analysis found benefits mainly when protein added extra calories: in six trials with calorie-matched drinks, time to exhaustion didn't improve[29].
Does protein after a race reduce muscle soreness?
In 323 runners after a 15 km race, milk protein didn't reduce soreness compared with a carbohydrate drink[15]. A small marathon trial found better soreness and fatigue ratings over 72 hours, but no meaningful difference at 24 hours[31].
Is a high-protein diet bad for a healthy runner's kidneys?
The athletics federation's consensus says athletes eating 2.4 g/kg a day during weight loss aren't at increased risk of kidney problems[1]. That applies to healthy athletes; the NHS advises people with kidney disease to check with a doctor or pharmacist before taking supplements[48].
Are protein supplements allowed in sport?
Yes. Food proteins are not on the WADA Prohibited List[50], but supplement products can be contaminated[4].
Is whey better than plant protein for runners?
Gram for gram, animal proteins such as whey raise muscle protein synthesis more than soy or wheat protein[38]. The AIS says eating more, or mixing plant sources, may offset this[2].
When should I have protein after a run?
Position stands describe protein soon after key sessions and then every 3 to 5 hours[24]; the ISSN says exact timing is partly a matter of tolerance[3].
Does protein before bed help runners recover?
Not in the one runner trial that tested it on its own: whey before sleep during a hard week didn't reduce the drop in 5 km performance[23]. After cycling, 45 g before sleep raised overnight muscle protein synthesis, a lab marker[27].
Do vegan runners need a protein supplement?
Not necessarily: a review found athletes can follow a vegan diet without harming performance, though unplanned vegan diets may fall short on protein[39]. Vegan runners in a survey didn't use more carbohydrate or protein supplements than other runners[8].
Do older runners need more protein?
Possibly not: a review argues masters athletes have protein metabolism similar to young athletes[34]. In 8 masters triathletes, doubling protein after a downhill run didn't significantly improve recovery[36].
Do female runners need a different amount of protein?
One tracer study suggests not: after a 20 km run, women and men had almost identical estimated requirements[41]. The ISSN suggests about 12% more in the luteal phase, but says no studies have tested protein needs across the menstrual cycle[40].
Are BCAAs as good as protein powder?
The evidence doesn't suggest so: the AIS places BCAAs in Group C[5] and calls isolated amino acids unnecessary alongside animal protein[2]. In a 100 km race, amino acids including 20 g of BCAAs didn't change race time or damage markers[32].

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Who wrote and reviewed this

Written by Grant MacMillan, Editor, RunV. Not yet reviewed by an expert.

Last checked against its references . Next review due . How pages are reviewed · How we grade research

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