Why Daily Nutrition, Hydration, and Energy Availability Matter More Than Ever
When “Skinnier Is Faster” Fails Female Athletes
Endurance athletes put constant stress on their bodies. This means they need steady energy, proper hydration, and reliable recovery to train and perform at their best. For female endurance athletes in particular, these fueling needs are shaped by unique physiological factors. Much of the existing sports nutrition research has centered on male athletes, which has required women to adopt generalized guidance that may not fully meet their needs. The outcome has been a chronic trend toward underfueling among female endurance athletes. A 2025 review in the Journal of Eating Disorders found that, “up to 65% of ultra-endurance athletes may be at risk for REDs".
In its 2023 Consensus Statement, the International Olympic Committee defines Relative Energy Deficiency in Sport (RED-S) as a condition that occurs when an athlete doesn’t take in enough energy to support both training demands and basic bodily functions. This low energy availability can disrupt hormones, bone health, immunity, and recovery. In turn, it directly affects performance and long-term health.
Underfueling can Derail Performance and Impact Careers
The IOC RED-S Consensus Statement highlights that chronic underfueling is widespread among female endurance athletes, often stemming from time constraints, suppressed appetite from heavy training, or diet-culture pressures.
Professional cyclist Julia Borgström knows firsthand how damaging these outdated fueling beliefs can be. Early in her career, she bought into the idea that “skinnier is faster,” without understanding the long-term risks.
“I had no knowledge about what to eat or the risks in losing weight. Today I know that skinnier is not faster but healthier and happier is faster.” — Julia Borgström, professional cyclist
Borgström believes that underfueling cost her years of performance due to RED-S.
Her experience mirrors what the research now clearly shows: adequate fueling is not optional for female endurance athletes. It is foundational to optimal performance. When female athletes are able to fuel consistently day to day, not just on competition days, they set themselves up for stronger, healthier, and more sustainable success in sport.
Fueling Fundamentals for Endurance Training
Fueling isn’t just about gels on race day. An athlete’s daily diet sets the foundation for performance and recovery. Heikura et al., discusses how fueling for endurance sports extends far beyond competition days in their article, Low Energy Availability in Female Endurance Athletes. Daily energy intake is essential to support training volume, recovery, immune function, and hormonal health. Carbohydrates remain the primary fuel source for endurance performance. They replenish muscle glycogen and support sustained output during long or intense sessions. Inadequate carbohydrate intake is one of the most common underfueling patterns seen in female endurance athletes. It can lead to fatigue, poor recovery, and decreased performance.
Carbohydrates may power endurance efforts, but they’re only part of the fueling picture. Protein plays a key role in muscle repair and adaptation, particularly when spread evenly across meals and snacks throughout the day. According to the American College of Sports Medicine (ACSM), adequate protein intake helps endurance athletes support lean mass, recovery, and resilience against injury. Dietary fats also play an important role, especially during long-duration training and to promote overall hormonal health. However, they should complement, not replace, adequate carbohydrate intake.
Borgström emphasizes that learning to fuel properly was career-changing. “When I started daring to eat more and was pushed to consume more carbs on the bike, I felt like a whole new person,” she says. “I didn’t feel grumpy or sad after every ride anymore. I could train and still have a life and my long rides were not a suffer-fest anymore.”
Hydration Beyond Water: Electrolytes, Strategy, and Individual Needs
Hydration is more nuanced than simply drinking more water. According to the American College of Sports Medicine’s hydration guidelines, electrolytes, particularly sodium, play a critical role in fluid balance, nerve signaling, and muscle contraction. Replacing sodium during longer training sessions or races can help maintain performance and reduce the risk of cramping or hyponatremia.
Research also shows that effective hydration strategies need to take into account individual sweat rates, environmental conditions, training intensity, and electrolyte losses. Female endurance athletes can experience wide variability in sweat rate and sodium loss, which makes personalized hydration especially important.
Borgström herself takes a highly intentional approach to hydration — one that changes depending on whether she’s training or recovering.
“If I’m on the bike, I always plan my hydration intake beforehand and I ALWAYS use a mix of carbs and electrolytes,” she explains. “I know I lose a lot of salt through sweat, and carbs are both important for the training but also to keep hydrated.”
Off the bike, Borgström’s strategy shifts. She prefers water for staying hydrated day to day and says that she saves electrolytes for situations like “when sick, after sauna, or heat training, or when I have symptoms of dehydration.”
For Borgström, electrolytes are deployed with purpose, supporting performance, replacing meaningful sodium losses, and maintaining fluid balance when stress on the body is high. But in normal daily life, when sweat rates are lower and meals already provide adequate sodium, plain water does the job just fine. Her approach highlights an important takeaway: electrolytes are a tool, not a constant requirement.
From Practice to Performance: Fueling for a Race-Day Advantage
Hydration needs differ between training and competition. Training provides an opportunity to assess sweat losses, practice fueling strategies, and refine fluid intake, while race-day hydration should be intentional and rehearsed, not improvised.
Today, widely available online tools and app-based hydration and carbohydrate calculators make it easier to estimate sweat loss, fluid needs, and fueling targets. For athletes at any stage, they offer a practical way to start building a more intentional plan. Athletes should do homework to understand the credibility behind any online tool resource.
The science is clear and the stories echo it: fueling well is not a luxury or an afterthought for female endurance athletes, it’s the foundation. But understanding why daily fueling and hydration matter is only the first step. In Part Two, we’ll look more closely at some female-specific factors that shape these needs and how athletes can turn awareness into sustainable action.
Julia Borgström is a professional cyclist from Sweden, currently riding for Kasseien Fiets Huis. Come along for the ride through races, training, day-to-day life, and special moments.
Check out her profile on Ontheside.
