Running on Empty: What Runners Need to Know About Low Energy Availability

Low energy availability (LEA) happens when you don’t eat enough to support both your training and your basic body functions. It’s not just about being hungry or tired, it’s about undereating relative to what your body needs, and it shows up in more ways than you think.

And the truth is, most runners dealing with LEA aren’t doing it on purpose. Some are trying to “eat clean” or cut sugar. Others just don’t realize how much more food they need when they’re logging miles. But when the balance tips too far, the body starts making trade-offs and those trade-offs often lead to illness, injury, and performance decline.

Signs You’re Not Eating Enough for Your Training

LEA can be hard to spot because the symptoms build slowly and can be brushed off as “normal training fatigue.” But they’re worth paying attention to. Common signs include:

• Frequent colds or upper respiratory infections

• Getting injured more often — especially stress fractures or tendinopathy

• Slower recovery between runs

• Low energy, poor sleep, or feeling moody and flat

• GI issues, especially with increased training

• Missed or irregular periods in women

• Decreased performance even when training hard

  
  

This isn’t just a female athlete issue, although women are often flagged earlier because of menstrual cycle changes, men are just as vulnerable. We now group these symptoms under Relative Energy Deficiency in Sport (RED-S)  a broader clinical picture that affects bone health, hormones, metabolism, and immune function.

How It Shows Up in Runners

If you’re getting sick a lot during training blocks, struggling with minor injuries that won’t go away, or you just can’t seem to hit paces that used to feel easy, LEA might be part of the issue.

Bone stress injuries are one of the biggest red flags. We see it all the time, someone increases volume or intensity, doesn’t increase fueling to match, and suddenly they’re dealing with a tibial stress fracture. LEA also affects tendon health, delays healing, and compromises your ability to adapt to training.

If your body doesn’t have enough energy, it starts pulling resources from systems it sees as “non-essential” like bone turnover, immune support, or reproductive hormones. That’s why LEA isn’t just a nutrition issue it’s a performance and injury risk issue.

What To Do About It

Start by checking in with yourself:

• Are you eating enough before and after training?

• Are you relying on “light” meals that wouldn’t fuel a full day of workouts?

• Do you eat more when you run more?

  
  

Recovery, strength, and performance depend on adequate fuel. In the RUNsource app, we’ve pulled together resources on nutrition, sleep, and recovery, plus insight from dietitians and rehab professionals to help you figure out what your body actually needs not just what a training plan says.

📲 Check out the app for more tools on fueling, recovery, and staying strong through every training cycle.

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