Relative Energy Deficiency in Sport: The Hidden Costs of Under-Fueling on Menstrual and Bone Health

Relative Energy Deficiency in Sport (RED-S) and the Triad

Relative Energy Deficiency in Sport (RED-S) is a term used to describe the subsequent effects of chronic under-fueling in athletes [1]. It explains how low energy availability negatively impacts athletes across all genders, with consequences for metabolism, cardiovascular health, bone health, and immunity [1,2]. This syndrome includes what was originally known as the “female athlete triad,” composed of energy deficiency, menstrual dysfunction, and low bone density [3]. In simple terms, when an athlete consistently expends more energy than they consume, the body conserves the leftover energy by downregulating reproductive and skeletal functions [3].

Menstrual Dysfunction (Amenorrhea) in Athletes

Among athletes with menstrual cycles, amenorrhea (loss of periods) is often the first warning sign of the triad [3]. “Athletic amenorrhea” usually refers to secondary amenorrhea, where someone who previously menstruated stops for three or more consecutive months [3]. Secondary amenorrhea can be commonly found in lean or endurance sports athletes such as distance running, gymnastics, or ballet, with rates of up to 30–70%, compared to only 2–5% in the general population [3,6]. By contrast, primary amenorrhea is the failure to begin puberty by age 15–16. This form of amenorrhea is less common, but may appear in young athletes with delayed development [3].

In nearly all of these cases, the mechanism is functional hypothalamic amenorrhea (FHA). FHA occurs when the hypothalamus suppresses release of GnRH (Gonadotropin-releasing hormone, a hormone that stimulates sex hormones in the ovaries) to the reproductive tract due to energy deficiency or stress [3]. This shuts down ovarian estrogen production [3]. Importantly, athletic amenorrhea reflects an energy imbalance, but not necessarily weight loss [2]. Athletes may appear lean or “normal weight” while still being under-fueled [2]. Common contributing factors include: chronic calorie deficit, high exercise volume/intensity without adequate rest, rapid or prolonged weight loss, very low body fat, or high psychological stress [2,6].

Bone Health: The Silent Crisis

Bone loss is one of the most serious consequences of RED-S [3]. Adolescence and early adulthood are critical years for building peak bone mass [8]. Estrogen deficiency during these years disrupts bone formation, leading to low bone mineral density (BMD) [3]. These changes often go unnoticed until a stress fracture occurs [3].

For example, Rickenlund et al. (2005) found osteopenia in 22–50% of amenorrheic athletes when compared with 12% of non-athletes [5]. Amenorrheic athletes in particular often have bone density comparable to much older women [5]. Not surprisingly, these deficits translate to injuries: young athletes with even mild bone loss have a 3–4.5 times higher risk of stress fractures compared to peers with normal BMD [3].

Performance and Hormonal Trade-Offs

Hormonal suppression from amenorrhea also impairs cardiovascular and metabolic health [5]. Low estrogen contributes to endothelial dysfunction and unfavorable cholesterol profiles [5]. Energy deficiency can also cause fatigue, poor focus, immune suppression, and mood changes as the body struggles to cope [6].

Ironically, the very behaviors athletes may use to enhance performance, such as relentless training and strict dieting, often actually harm it [6]. VanHeest et al. (2014) studied junior elite swimmers and found that those with ovarian suppression slowed down across a season, while their peers with regular cycles improved [7]. Amenorrheic swimmers’ 400m times declined by ~10%, compared with an 8% improvement in eumenorrheic (regularly menstruating) swimmers [7].

Prevention and Treatment

The good news is that RED-S and the triad are preventable and treatable [1,2]. The first step is education: athletes, coaches, and parents must recognize amenorrhea and extreme leanness as warning signs rather than a sign of hard work [6]. Sports programs that emphasize fueling, recovery, and rest are important to prevent unhealthy patterns [6].

Treatment of RED-S focuses on restoring energy balance [2]. This usually means increasing caloric intake and/or reducing training until energy availability improves [2]. A sports dietitian can tailor nutrition to add calories, emphasize carbohydrates for fuel, ensure sufficient protein, and maintain adequate calcium and vitamin D [8]. Studies show that when energy intake rises (and training load is reduced), most athletes resume menstruation within months [8]. Bone metabolism also gradually normalizes once energy balance is restored [3].

Conclusion

RED-S and the female athlete triad show that health and performance go hand-in-hand [1]. Regular menstrual cycles and strong bones are indicators that an athlete’s body is fueled properly [2]. By prioritizing balanced nutrition, recovery, and open dialogue about menstrual health, athletes can remain strong, resilient, and protected from the long-term consequences of RED-S [6].

References:

1. Hackney AC et al. Relative Energy Deficiency in Sport (RED-S): Scientific, Clinical, and Practical Implications for the Female Athlete. 2022.

2. American Academy of Family Physicians. Relative Energy Deficiency in Sport (RED-S). Am Fam Physician. 2022.

3. Ackerman KE et al. The Female Athlete Triad: A Clinical Guide. 2012.

4. L’Heveder AL et al. Menstrual Cycles and Performance in Elite Athletes: A Longitudinal Study. Frontiers in Sport and Active Living. 2024.

5. Rickenlund A et al. Amenorrhea in Female Athletes Is Associated with Endothelial Dysfunction and Unfavorable Lipid Profile. J Clin Endocrinol Metab. 2005.

6. Mehta J, Thompson B, Kling JM. The Female Athlete Triad: It Takes a Team. Cleve Clin J Med. 2018.

7. VanHeest JL et al. Ovarian Suppression Impairs Sport Performance in Junior Elite Female Swimmers. Med Sci Sports Exerc. 2014.

8. Mokhtar SA et al. Influence of Adolescents’ Physical Activity on Peak Bone Mass. J Public Health Res. 2016.

9. Fox H. Women’s health in sport: How can research gap be bridged and findings put into practice? Sky Sports. 2023.