Should Marathon Runners Increase Protein? What a 2025 Review Found

When you’re training for a marathon, mileage is only part of the equation. What you eat affects how well you train, recover, and hold pace late in a long run.

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Carbohydrate remains the main performance nutrient for endurance because it’s your body’s preferred energy source for muscles and the brain. But a new 2025 systematic review suggests protein deserves more attention during marathon prep, not just after training.

The study in plain English

This 2025 systematic review and meta-analysis (published in Frontiers in Nutrition) looked at whether protein supplementation improves body composition, endurance performance, and training adaptations.

What researchers analysed

• 23 randomised crossover trials
  
  

• 1,146 adults, from sedentary individuals to trained endurance athletes
  
  

• Trial length: 6 to 26 weeks
  
  

• Protein sources included milk, soy, casein, collagen, whey, and beef
  
  

• Daily protein intake during trials typically ranged from 1.2g to 2.3g per kg of body weight
  
  

For context, the general Recommended Dietary Allowance (RDA) for protein is 0.8g/kg/day. The article also notes that endurance athletes may benefit from targeting around 1.0g to 1.6g/kg/day depending on training load.

What the results mean for runners

1) Body composition: a small lean mass benefit

Protein supplementation slightly increased lean (fat-free) mass. For runners doing higher mileage while also trying to keep strength training in the week, that matters. A bit more lean mass can support better durability across a long training block.

Notably, supplementation did not meaningfully change fat mass or overall body weight.

2) VO2 max: no meaningful change for trained athletes

Protein didn’t produce a meaningful VO2 max improvement for well-trained endurance athletes.

However, sedentary participants saw larger VO2 max improvements than active participants, which suggests boosting protein may be more noticeable when you’re starting from a lower fitness base.

3) Time to exhaustion: the clearest performance win

This was the standout finding. Across the trials, protein supplementation improved time to exhaustion, meaning participants could sustain a given intensity for longer.

Carbs still matter most for running fuel, but adding protein can be a smart way to build resilience so you can hold on a little longer when fatigue builds.

A practical protein target for marathon training

Instead of guessing, use your body weight to set a simple daily range.

A common endurance target from the article is 1.0 to 1.6g/kg/day. That means:

• 70kg runner: 70 to 112g/day
  
  

• 80kg runner: 80 to 128g/day
  
  

If you want help translating targets into a plan, use the GymNation nutrition calculator to estimate your needs and structure your day around them.

Food-first, supplements when needed

You do not need supplements to benefit from higher protein. Many runners can reach targets with:

• Protein at each meal (breakfast included)
  
  

• A protein-rich snack after training
  
  

• Protein paired with carbs around harder sessions
  
  

Supplements can help when appetite is low, time is tight, or you struggle to hit your range consistently, but they are a convenience tool, not a requirement.

Don’t forget strength training

The lean-mass finding matters most when you pair higher protein with consistent strength work. If your goal is to stay strong through peak mileage, a structured strength option can keep you consistent without overthinking programming.Try Strength Development

Bottom line

For marathon runners, carbohydrate stays the priority for performance fuel. But this 2025 review suggests higher protein intake, including supplementation, may offer small lean-mass gains and a meaningful improvement in time to exhaustion. If you want to run stronger for longer, protein is worth treating as part of your performance plan, not just a recovery detail.

Source: runnersworld.com

The opinions shared in the blog articles are solely those of the respective authors and may not represent the perspectives of GymNation or any member of the GymNation team.