Written by Dr Emily Jevons on behalf of Enertor

Bio: Emily is a Registered Nutritionist with a PhD in Exercise Metabolism & Nutrition. She specialises in endurance sport and disordered eating, currently she’s working with a range of athletes from professional cyclists to our everyday heroes like you and me! Emily also is an avid runner and triathlete herself balancing work and being a mum trying to get the most out of her training by recovering well!

You're training consistently, eating what you'd call “clean,” and still picking up niggle after niggle. Before you blame your shoes, your stride, or bad luck, it's worth asking a different question: are you fuelling enough for the training you're doing?

As runners we’re always looking for the extra 1% but if we’re not fuelling our training or recovering well, we’re losing more than any of those 1% additions will ever gain! Under fuelling is one of the most overlooked causes of running injury, and it's far more common than most runners realise. A lot of the time, under fuelling is unintentional. Studies suggest that low energy availability affects anywhere from around 1 in 5 to well over half of athletes, depending on the sport. Squeezing in training around a busy lifestyle or lack of appetite after training (which is completely normal by the way!) are both examples of why we can end up unintentionally under fuelling, let’s look at what it means in more detail.

What under fuelling actually means

Under fuelling, also known as low energy availability, isn’t just about eating too little overall. It’s about not eating enough relative to how much you’re training. You can eat what looks like a normal, “healthy” diet and still be running an energy deficit if your mileage has crept up faster than your intake. We can also end up under fuelling if not getting the right balance of macronutrients e.g. not consuming enough carbohydrate to support our energy needs.

Why it raises your injury risk

When your body doesn’t get enough fuel to cover training demands, it starts deprioritising functions that aren’t immediately essential including bone remodelling, tissue repair, and hormone regulation. Over time, this shows up as a higher risk of stress fractures, tendon problems, and injuries that take longer to heal than they should. This pattern is well documented in the sports science literature as Relative Energy Deficiency in Sport (RED-S/REDs), and it affects recreational and competitive runners alike.

Signs you might be under fuelling

A few common signs worth paying attention to:

•       Ongoing fatigue that doesn’t lift with rest

•       Getting ill more often than usual

•       Irregular or absent menstrual cycle (for female runners)

•       Performance plateauing or dipping despite consistent training

•       Minor injuries that heal more slowly than expected

None of these are a diagnosis on their own, but if a few sound familiar, it’s worth a conversation with a qualified sports nutritionist or dietitian.

Practical tips to minimise under fuelling from a nutritionist…

1.    Fuel around your sessions, not just across your day.

Eating enough overall doesn’t help much if it’s poorly timed around training and don’t fear carbohydrate before or after your run, they’re not just for race day!

2.    Rest days still need fuel.

Recovery, not just running, costs energy. Rest days are a time for your body to refuel from the training the day before and prepare for the following day’s training.

3.    Build a recovery routine that works for you after training.

Refuelling with both carbohydrate and protein can kick start the recovery process. If you struggle with appetite after your sessions, I recommend trying a shake or smoothie which can be easier to stomach.

Supporting your body’s recovery isn’t only about what’s on your plate, reducing unnecessary impact stress on already-fatigued tissue matters too, which is where good recovery habits across the board good recovery habits across the board (nutrition, sleep, and the right support underfoot to reduce unnecessary impact stress) all add up.

Nutrition should be part of your training, not separate. Pairing the right fuelling strategy with the right recovery support is one of the most overlooked ways to stay injury-free this season.

 

Further reading:

Kerksick CM, Arent S, Schoenfeld BJ, et al. International Society of Sports Nutrition Position Stand: Nutrient Timing. Journal of the International Society of Sports Nutrition, 2017; 14:33.

Loucks AB. Low Energy Availability in the Marathon and Other Endurance Sports. Sports Medicine, 2007; 37(4–5): 348–352.

Rogers MA, Appaneal RN, Hughes D, Vlahovich N, Waddington G, Burke LM, Drew M. Prevalence of Impaired Physiological Function Consistent with Relative Energy Deficiency in Sport (RED-S): An Australian Elite and Pre-Elite Cohort. British Journal of Sports Medicine, 2021.

Heikura IA, Uusitalo ALT, Stellingwerff T, Bergland D, Mero AA, Burke LM. Low Energy Availability Is Difficult to Assess but Outcomes Have Large Impact on Bone Injury Rates in Elite Distance Athletes. International Journal of Sport Nutrition and Exercise Metabolism, 2018.

Cupka M, Sedliak M. Hungry runners - low energy availability in male endurance athletes and its impact on performance and testosterone: mini-review. Eur J Transl Myol, 2025.