Why so many runners are underfueled
For a sport obsessed with performance, many runners are unknowingly training with too little fuel.
They increase mileage.
They add double sessions.
They buy better shoes and track every metric.
But they still under-eat.
And over time, it catches up with them.
Low energy.
Poor recovery.
Constant fatigue.
Plateaued performance.
Injuries that won’t go away.
In many cases, this falls under something called RED-S — Relative Energy Deficiency in Sport.
And it’s far more common in endurance sports than most people realize.
The Problem: Many Runners Don’t Eat Enough For Their Training
A lot of runners still think carbohydrates are something to “control.”
But carbs are not the enemy for endurance athletes. They are the primary fuel source for performance.
The issue is that many runners fuel for how they want to look — not for how much they actually train.
There’s a huge difference between:
- running 5–10km a few times per week
- and training seriously with high mileage and intensity
Yet many people eat almost the same amount.
How Much Carbohydrate Do Runners Actually Need?
The answer depends on training volume and intensity.
General endurance guidelines often look something like this:
Light training / easy running
(5–10km easy runs, lower weekly mileage)
~3–5g carbohydrates per kg bodyweight daily
Example:
A 70kg runner = roughly 210–350g carbs/day
Moderate endurance training
(10–15km daily, workouts, moderate volume)
~5–7g/kg daily
70kg runner = 350–490g carbs/day
High-volume / marathon-level training
(20km+ days, doubles, hard sessions)
~7–10g/kg daily — sometimes even higher
70kg runner = 490–700g carbs/day
That surprises many runners.
But endurance training burns enormous amounts of glycogen.
And if glycogen stores are constantly depleted, the body starts compensating elsewhere:
- hormones get disrupted
- recovery slows down
- injury risk increases
- performance drops
What RED-S Actually Looks Like
RED-S is not just “being tired.”
It affects almost every system in the body.
Some common warning signs:
- chronic fatigue
- poor sleep
- recurring injuries
- stress fractures
- loss of strength
- getting sick frequently
- irritability or low mood
- plateaued performance
- low libido
- menstrual cycle disruptions in women
- constantly feeling cold
The dangerous part is that many runners normalize these symptoms.
They think:
“This is just hard training.”
Often, it’s underfueling.
Why It Happens So Often In Running
Running culture often rewards leanness.
Lighter is seen as faster.
And social media has only amplified this mindset.
But many runners end up trapped in a cycle:
- increasing training load
- restricting calories
- trying to stay lighter
- recovering worse
- performing worse
Elite endurance athletes are usually extremely lean because they support massive training loads — not because they chronically under-eat.
That’s a big difference.
What Actually Helps
Most runners don’t need extreme diets.
They need consistency and enough energy availability.
Some of the biggest improvements often come from:
- eating enough carbohydrates
- fueling before long sessions
- recovering immediately after hard workouts
- not skipping meals after training
- increasing intake during high-volume weeks
- sleeping properly
- monitoring iron levels
- reducing unnecessary food restriction
Useful Supplements For Runners
Supplements cannot replace proper fueling — but some can help support endurance training.
Commonly useful ones include:
- electrolytes
- carbohydrate drink mixes during long runs
- iron (only if deficient)
- vitamin D
- magnesium
- omega-3
- protein powder for recovery convenience
For higher mileage runners, intra-run fueling also becomes important:
- gels
- sports drinks
- quick carbohydrates during long sessions
Especially once sessions go beyond 90 minutes.
Performance Starts With Fuel
One of the biggest misconceptions in endurance sports is that eating less improves performance.
Usually, the opposite is true.
The runners who recover best, adapt best, and train consistently over years are often the ones who fuel properly.
Because fitness is not built only through training stress.
It’s built through recovery from that stress.
And recovery requires energy.