How to Recognize Underfueling and How to Fix It

You might go out for a run and immediately feel exhausted after just a mile or two. Sometimes, it just isn’t your day, and that’s fine. It can be easy to brush off at times. However, if this becomes a constant occurrence, it’s a sign that something else might be wrong.If you begin experiencing symptoms like the following, they could be signs pointing to a common running ailment called Low Energy Availability, or LEA.sleep difficultygastrointestinal problemsfrequent illnessesrecurring bone stress injuriesirregular menstrual cycles. changes in your mooddifficulty concentrating. Overall, your runs, and even day-to-day life begin to feel tiring due to a lower sense of wellbeing.“I work with some athletes who know exactly what feels good and what feels bad, to the point where they can tell you everything that’s happening minute to minute,” says Jason Machowsky MS, RD, CSSD, CEP, CSCS, in The Runner’s World Guide to Nutrition and Fueling. “Other people just don’t necessarily have that body awareness.”In situations like that, Machowsky likes to have runners keep a subjective wellness log. You could ask questions like:How do you feel in the morning? How did you sleep? What’s your energy like during the day? What's your energy like during your runs? Then you can start looking for patterns.“Once you notice those patterns, compare them with your nutrition and your training log to start putting the pieces together,” he says. identifying what's really driving how you feel.What is Low Energy Availability? Because running is an endurance sport, athletes burn calories much faster than the average person. So runners require a higher caloric intake. If you consistently under-replenish, this caloric deficit combined with the exertion that comes with running can lead to LEA.LEA can lead to long-term conditions, such as relative energy deficiency in sport, or RED-S.“RED-S is a syndrome that encompasses harmful effects on systems throughout the body, including negative health outcomes such as reduced bone density, reproductive dysfunction, and gastrointestinal problems,” says Kristen Whitney, MD, a sports medicine specialist and medical director of Boston Children’s Hospital Injured Runner’s Clinic. “It also includes performance effects like decreased training response, endurance performance, and muscle strength.”It is possible for LEA to develop unintentionally due to a lack of knowledge. Missing a meal after a run or forgetting to eat breakfast happens to everyone, but if it becomes a regular habit, it could certainly impact your health.Spot and Prevent Symptoms EarlyIt is important as a runner to pay close attention to your body and recognize when something does not seem right. If you notice that your performance is declining for no obvious reason, or even if you’ve been experiencing random mood shifts, it could be LEA in the early stages of development. Catching the symptoms early allows for a quicker route to recovery, and can prevent LEA-related injuries that significantly impact performance.Additionally, using a nutrition plan that is catered toward you and your body’s needs is beneficial. Everyone responds differently to certain foods, so the more individualized your nutrition is, the better.Try to remain consistent in fueling. Studies have shown that exercise can suppress appetite signals, so it can be harder to tell when you are ready to eat, leading to a possible caloric deficit and overall poor performance. To avoid this, try to fuel as consistently as possible by consuming three meals as well as snacks throughout the day.“If you are experiencing chronic fatigue, lack of focus, or persistent headaches it might be a sign that you need to change your fueling,” Ellen Davis, RD, a sports dietitian in West Des Moines, Iowa, with The Performance Collective previously told Runner’s World.Fueling before and after training is also essential to avoiding LEA. Once again, it is helpful to use a personalized nutrition method and try to get a few prerun snacks as well as a solid postrun meal.A good prerun meal contains a balance of macronutrients, including protein and healthy fats, along with complex carbs. A smaller prerun snack should focus mostly on carbs.“Simple carbs will provide an increase in blood glucose without feeling like your food is jumbling around in your stomach. Protein, fiber, and fat can linger in digestion, therefore leading someone to feel like they ate too much before their workout,” Katelyn Greenleaf, RD, a dietitian in Gainesville, Florida says.New York-based dietitian Frances Largeman-Roth, RDN and the International Society of Sports Nutrition recommends aiming for a 3:1 or 4:1 carbohydrate-to-protein ratio. Protein will help repair and build muscles by stimulating protein synthesis.Casey Healey has been running for 11 years and brings that firsthand experience to the Runner’s World team as a summer 2026 editorial intern. Hailing from Scranton, PA, Casey is now a rising senior at Villanova University, where she plans to graduate with a degree in Communications. She also serves as Co-Sports Editor of her school newspaper, The Villanovan. Outside of running, she enjoys skiing, iced coffee, and walking her mini schnauzer, Winnie.