~ Annie Bothma, Elite Athlete, IOPN Performance Sports Nutritionist (EQF Level 7. Masters), Running & Strength Coach
Low energy availability (LEA) is a growing concern in endurance sports, particularly for female athletes. A recent study, "The Whole-Body and Skeletal Muscle Metabolic Response to 14 Days of Highly Controlled Low Energy Availability in Endurance-Trained Females" (Caldwell et al., 2024), provides critical insights into how even a short period of LEA can severely impact performance and recovery.
This study employed a rigorous design as a randomized, double-blind, crossover-controlled trial, providing insights into the performance and physiological effects of LEA—findings that should concern every athlete.
Study Overview
Participants: 12 endurance-trained women.
Interventions: Each participant completed two 14-day conditions:
Optimal Energy Availability (OEA): 50 kcal/kg FFM/day.
Low Energy Availability (LEA): 22 kcal/kg FFM/day.
Washout Period: A three-day refueling period of optimal energy availability followed each condition.
Blinding: Participants were blinded using concentrated juice syrups to mask energy differences while maintaining identical training loads.
This robust design allowed for direct within-subject comparisons, minimizing variability and increasing the reliability of the results.
Key Findings
This study, despite its relatively short length, offers many intriguing insights. I have summarized the most significant findings and key takeaways for athletes below.
Performance Declines
A 7.8% reduction in 20-minute time trial performance.
An 18% decrease in time to exhaustion.
These impairments persisted even after the 3-day refueling period, emphasizing the lingering effects of LEA on recovery and performance.
Reduced Resting Metabolic Rate (RMR)
RMR dropped by 10.3% (~166 kcal/day) during the LEA condition (95% CI: −297 to −35 kcal/day, p = .015).
This energy conservation response can impair recovery, adaptation, and overall metabolism in athletes.
Reduced Respiratory Exchange Ratio (RER)
RER decreased by 6.6% (~−0.05) during the LEA condition (95% CI: −0.08 to −0.03, p < .001).
This shift toward fat oxidation reflects reduced carbohydrate utilization, which is less efficient for high-intensity activities.
Weight Loss Does Not Equal Improved Performance
Participants lost an average of 2.6 kg, including 0.8 kg of fat-free mass (muscle) and 1.2 kg of fat mass during the LEA condition.
Despite this weight loss, performance and power output declined, clearly demonstrating that "lighter" does not always mean "faster."
LEA Can Happen at Any Size
One of the most damaging misconceptions in sports nutrition is that low energy availability only affects athletes with low body weight or low BMI. In reality, LEA can occur at any size or BMI, as it is determined by the mismatch between energy intake and expenditure rather than absolute body weight.
Athletes at any size are at risk if they fail to fuel adequately for their training demands. Symptoms such as chronic fatigue, poor recovery, hormonal disruptions, and decreased immune function can occur regardless of an athlete’s outward appearance. This highlights the need to assess energy availability based on individual needs rather than societal or aesthetic assumptions.
Lighter Doesn’t Always Equal Faster
This study definitively challenges the common belief that weight loss inherently leads to better performance. Despite participants losing an average of 2.6 kg, including 0.8 kg of muscle mass, their performance declined. The 20-minute time trial performance dropped by 7.8%, and time to exhaustion fell by 18% (Caldwell et al., 2024).
While some studies show a potential benefit of lower body weight for speed in specific contexts (e.g., elite marathon runners), this relationship is not universal. For endurance athletes and multi-discipline sports, preserving lean body mass is crucial for supporting power output, endurance, and resilience. A lighter weight at the expense of muscle mass and energy availability often results in poorer overall performance and increased risk of injury.
The Alarming Impact of LEA
Even short-term LEA, as demonstrated in this study, can lead to significant and lasting impairments, making it critical for athletes to prioritize adequate fueling.
Athletes should be deeply concerned about the long-term consequences of chronic LEA, which include:
Hormonal imbalances affecting menstrual function and bone density.
Increased susceptibility to illness and injury.
Prolonged recovery times and reduced training adaptations.
The takeaway from this study is clear: just 14 days of LEA can derail performance, impair recovery, and disrupt key physiological systems.
Practical Recommendations for Athletes
Ensuring your body is properly fueled is essential for both performance and health. Having enough energy is fundamental for longevity in the sport. Here are some practical tips to guide you in the right direction.
Prioritize Energy Availability
Ensure your caloric intake matches your training demands, especially during periods of high training volume or intensity.
Focus on Carbohydrates and Protein
Carbohydrates
Support endurance and high-intensity training by prioritizing carbohydrates as your primary fuel source. Adequate carbohydrate intake also supports brain function and recovery.
Protein
Incorporate sufficient protein to prevent muscle breakdown, promote tissue repair, and build lean body mass. Aim for protein-rich meals and snacks throughout the day, especially post-training. Aim for 1.8-2.4 g of protein per kilogram of body-weight, depending on your goals and training volume.
Monitor for Signs of LEA
Look out for symptoms like fatigue, slow recovery, frequent illnesses, menstrual irregularities, or poor performance. These could signal inadequate fueling.
Avoid a “Lighter is Faster” Mindset
Focus on performance metrics and training consistency rather than body weight or appearance. Lean body mass and adequate fueling are key to success.
Work with a Professional
Consult a sports nutritionist to create a tailored fueling plan that supports your training, recovery, and long-term health goals.
Final Thoughts
The Caldwell et al. (2024) study is a wake-up call for endurance athletes. LEA doesn’t just compromise glycogen stores or body composition—it disrupts every system in the body, from metabolism to the nervous system. While short-term underfueling might seem manageable, even 14 days can cause profound impairments that outlast the underfueling period.
To sustain peak performance and longevity in sport, athletes must prioritize proper fueling with adequate carbohydrates, protein, and total energy intake.
Remember: lighter doesn’t always mean faster, but stronger, healthier, and well-fueled always means better.
Reach out to me at anniesathletes@gmail.com if you are struggling to meet your energy needs as an athlete.
References
Caldwell HG, Jeppesen JS, Lossius LO, Atti JP, Durrer CG, Oxfeldt M, Melin AK, Hansen M, Bangsbo J, Gliemann L, Hellsten Y. The whole-body and skeletal muscle metabolic response to 14 days of highly controlled low energy availability in endurance-trained females. FASEB J. 2024 Nov 15;38(21):e70157. doi: 10.1096/fj.202401780R.
Mountjoy M, Ackerman KE, Bailey DM, et al. (2023). International Olympic Committee Consensus Statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 57, 1073–1097. doi:10.1136/bjsports-2023-107397.
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