Short‐Term Severe Low Energy Availability in Athletes

Many athletes and coaches believe that losing body weight can boost the power-to-body mass ratio and enhance performance. However, this review highlights the risks of short-term severe low energy availability (LEA) (consuming less than 30 kcal per kilogram of fat-free mass per day) especially in female athletes.

Short-term severe LEA triggers the body to conserve energy, disrupting critical physiological systems such as hormone production (including reproductive and thyroid hormones), metabolic rate, and protein turnover in connective tissues. If these effects aren’t reversed, they can lead to long-term issues like menstrual dysfunction, weaker bones, higher injury risk, and reduced exercise performance.

Recent research shows that even short periods of severe LEA can suppress muscle growth, increase stress hormones, impair immune function, and directly reduce power, sprinting, and endurance abilities—even if body mass decreases.

These findings challenge the common belief that cutting weight always improves performance. Instead, they emphasize the importance of carefully balancing energy intake and training needs on an individual basis to protect health and optimize athletic success.

Key Takeaway

Elite athletes need enough energy and nutrients to support not only their training and performance but also essential bodily functions like temperature regulation, reproduction, and cell repair. When energy intake is too low, the body prioritizes vital processes over others, which can lead to adjustments such as reduced reproductive function to conserve energy.

Causes of Low Energy Availability

• High training loads can unintentionally lead to LEA

• Poor or misunderstood sports nutrition knowledge

• Eating low energy-dense foodsLow appetite and digestive system limitsIntentional energy restriction to reduce body mass or fat before competition

• Emphasis on leanness or low body weight

• Participation in weight-class and leanness-focused sports

• Frequent dieting and body weight fluctuations

• Use of unhealthy or extreme weight-control practices

• Pressure from social media to maintain an ideal body shape

• Pressure and body-shaming from coaches

Effects of Low Energy Availability

Key Vocabulary: BMD, Bone mineral density; BMR, Basal metabolic rate; FFA, Free fatty acid; FSH, Follicle‐stimulating hormone; HPO, Hypothalamic‐pituitary‐ovarian; IGF‐1, Insulin‐like growth factor 1; LH, Luteinizing hormone; ROS, Reactive oxygen species; T3, Triiodothyronine.

HPO Axis (Hypothalamic-Pituitary-Ovarian Axis)

Disruption of the HPO axis affects reproductive health, leading to menstrual irregularities or amenorrhea in females, and may reduce fertility and hormonal balance in both sexes. This also signals the body is conserving energy by down-regulating reproduction.

Whole Body Metabolism and Hormones

1. Lower BMR (Basal Metabolic Rate) means that the body lowers its resting energy expenditure to conserve energy.

2. Lower T3 (Triiodothyronine) is further decreases metabolism.

3. Leptin is a hormone that signals energy availability to the brain. When it drops, appetite is reduced, and there are more metabolic adaptations.

4. Lower growth hormone potentially impairs tissue repair and growth.

5. ICF-1 (Insulin-like Growth Factor 1) is important for muscle and bone growth. When ICF-1 levels decrease, recovery and training adaptions are compromised.

   
   

Inflammation and Immune Function

Too high levels of immune cell ROS (Reactive Oxygen Species) can damage cells and tissues. Furthermore, increased cortisol can suppress immune function and increase muscle breakdown.

Nutrient Availability

This shift indicates the body relies more on fat as fuel during LEA, but this can affect high-intensity exercise performance, which typically requires carbohydrates, potentially reducing power and endurance.

Skeletal Muscle

Reduced muscle repair and increased breakdown harm strength, endurance, and recovery, making it harder for athletes to maintain or improve performance.

Bone Metabolism

Lower P1NP (Procollagen Type 1 N-Terminal Propeptide) is a marker that bone formation has decreased, indicating less new bone growth. This increases the risk of bone loss and stress structures, especially dangerous for athletes who rely on strong skeletal health.

Effects of Low Energy Availability on Performance

Citation

Jeppesen JS, Hellsten Y, Melin AK, Hansen M. Short-Term Severe Low Energy Availability in Athletes: Molecular Mechanisms, Endocrine Responses, and Performance Outcomes-A Narrative Review. Scand J Med Sci Sports. 2025 Jun;35(6):e70089. doi: 10.1111/sms.70089. PMID: 40539747; PMCID: PMC12180388.