Protein for Endurance Athletes: How Much You Actually Need

A runner logging 60 miles a week and a powerlifter squatting three times a week are usually given the same protein advice, which is to eat "enough" and stop worrying about it once the number looks reasonable on paper. That advice can leave the runner short. Prolonged aerobic exercise increases amino acid oxidation and creates repair demand across skeletal muscle and other tissues, which can push an endurance athlete's protein requirement into the same broad range used by strength athletes during harder training phases.

01Why endurance training raises the protein bill

Skeletal muscle in a well-fed, resting body contributes little amino acid fuel. The contribution can rise during prolonged exercise, especially when carbohydrate availability is low. Tarnopolsky and colleagues estimated zero nitrogen balance at 1.37 g/kg/day for endurance athletes and 0.73 g/kg/day for sedentary controls, then proposed 1.6 g/kg/day as a safe intake for endurance athletes.¹ Increased amino acid oxidation during exercise helps explain the difference. Low glycogen availability can push that contribution higher, although training volume, total energy intake, and recovery remodeling also affect the daily requirement.⁵

This is the piece missing from most endurance fueling plans, including the carbohydrate-first framework in Endurance Athlete Fueling. Carbohydrate periodization solves the fuel-availability problem during the session. It does not solve the problem of protein being consumed as fuel during the session and then still being needed afterward to rebuild collagen, myofibrillar protein, and mitochondrial protein. An athlete who nails carbohydrate targets but treats protein as a rounding error is running a caloric deficit inside their protein budget even while eating enough total calories.

02What the requirement actually looks like

Earlier sports nutrition consensus guidance placed endurance protein needs around 1.2 to 1.4 g/kg/day. The 2016 joint position from the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine broadened the athlete range to 1.2 to 2.0 g/kg/day, and the 2017 International Society of Sports Nutrition position stand recommended 1.4 to 2.0 g/kg/day for exercising adults.² Training load, energy availability, and the goal of maintaining or adding lean mass determine where an endurance athlete sits inside that wider range.

Kato and colleagues studied six endurance-trained men during a controlled three-day period totaling 35 km, including a 20 km run on the trial day. The indicator amino acid oxidation method estimated an average requirement of 1.65 g/kg/day and a recommended intake of 1.83 g/kg/day.³ The study provides a high-volume-day estimate rather than a before-and-after measure of training progression, and it does not establish the same number for women or every endurance discipline. It still gives athletes a practical reason to revisit a fixed protein target when training volume changes sharply.

03The energy availability trap makes this worse

Protein requirements do not exist in isolation from total energy intake. Some endurance athletes fall short when low energy availability, low appetite, or restrictive food choices leave too little room for protein and micronutrient coverage. This is the same dynamic behind Low Energy Availability in Female Endurance Athletes and its counterpart in men. A high-carbohydrate, low-protein day compounds the amino acid oxidation problem described above because there is less dietary protein available to replace what training used.

The fix is not to cut carbohydrate. Athletes fueling 8 to 12 g/kg/day of carbohydrate around hard sessions and races, per the ranges in Endurance Athlete Fueling, still have room for 1.4 to 1.8 g/kg/day of protein if the extra calories come from protein-dense foods rather than more carbohydrate volume. A 70 kg runner eating 3,600 calories can hit 130 g of protein, which is only 520 calories, while still running 8 g/kg (560 g, 2,240 calories) of carbohydrate for a hard training day.

04Timing and distribution still matter, just with a different backdrop

The leucine threshold logic that governs strength athlete meal planning applies to endurance athletes too, with one added wrinkle. Endurance sessions are frequently scheduled early morning, which means the pre-session meal is often skipped or minimal, and the post-session window competes with appetite suppression from prolonged aerobic exercise. Breen and colleagues gave approximately 10 g of whey protein immediately after a 90-minute cycling bout and another 10 g 30 minutes later. Myofibrillar protein synthesis was about 35% greater than with carbohydrate alone, while mitochondrial protein synthesis did not differ between conditions.⁴ The acute result supports adding protein to recovery nutrition after prolonged endurance work, although it does not prove that a specific protein dose will improve aerobic capacity over a full training block.

Pre-exercise protein evidence remains limited, and tolerance is individual. In a crossover trial of 13 recreational runners, whey doses of 0.15 and 0.4 g/kg consumed with carbohydrate 60 minutes before a 10 km run produced similar total gastrointestinal symptom burdens, although the 0.4 g/kg condition produced greater bloating.⁶ Test the chosen source and dose in training before using it in competition. Gut Training for Race Nutrition covers the broader tolerance-building process.

05Where this breaks down in practice

The most common failure pattern is treating protein as a category that gets filled by whatever is left after carbohydrate and fat. A 70 kg athlete who stops at 60 to 65 g of protein lands below 1.0 g/kg/day, even if the day's total calories and carbohydrate look appropriate. Set the protein target first as a fixed number, distribute it across meals using the meal-anchor logic in Leucine Threshold, and then fill the remaining calories with carbohydrate scaled to the training load described in Endurance Athlete Fueling.

Plant-based endurance athletes face a compounded version of the same math, since lower leucine density and lower digestibility in most plant proteins push the effective target higher, a problem covered in depth in How to Hit Your Protein Target on a Plant-Based Diet. The mechanism is identical whether the athlete runs marathons or lifts. Aerobic training just adds a second reason protein disappears from the plate, on top of every reason it already disappears from a distance runner's appetite after a hard long run.