When Athletes Don’t Eat Enough: The Hidden Bone Crisis
Authors: Laura Cross, BSc student, Health Sciences, Carleton University | Editors: Janielle Richards, Romina Garcia de leon (Blog Coordinators) | Reviewer: Ahmad Mohammad
Date: April 3rd, 2026
Growing up as a female endurance athlete, it was an unspoken expectation that eating minimally and ‘clean’ as possible would directly result in optimized performance. As my network expanded, I realized that this mindset is widespread in athletic communities, both locally and online, and primarily among female athletes. I also noticed that many of these athletes also had a higher frequency of stress fractures and many lacked a menstrual cycle, however, this was thought to be an advantage for optimal performance. In fact, this is a frequently ignored condition called Relative Energy Deficiency in Sport (RED-S), which can silently compromise an athlete’s health for decades to come.
What Exactly is RED-S?
RED-S occurs when athletes don’t consume enough energy to fuel both their intense training and their basic bodily functions. Think of it like running a car on fumes, where at some point, something has to give. The condition was formally recognized by the International Olympic Committee in 2014, but its roots trace back to observations made in the 1970s among ballet dancers who experienced unusually high rates of stress fractures and absent or irregular periods.
The condition begins with Low Energy Availability which occurs when energy intake doesn’t meet what’s needed for energy expenditure. While our bodies are exceptionally adaptable to acute energy deficits, prolonged shortages as a result of intense athletic training and undereating can swamp these adaptive mechanisms,and in some cases, lead to RED-S.
Why the Skeleton is Affected
Females with RED-S are at high risk for stress fractures and symptoms similar to osteoporosis. Bones are metabolically expensive to maintain, and when energy is limited, the body allocates its resources to processes absolutely necessary to survival. Bone health and the reproductive system are low on this list, and their processes are severely impacted.
Research shows that even short-term energy restriction in athletes can disrupt bone metabolism within just five days. This can be measured by tracking specific blood markers, where the presence of RED-S shows increasing levels of β-CTX, which indicates bone breakdown, and decreasing levels of P1NP, a measure of bone formation. This is reminiscent of a construction crew trying to build with the demolition team simultaneously breaking down the foundations.
The Hormonal Domino Effect
The body’s response to energy deficits trigger a cascade of hormonal alterations impacting female athletes. When energy availability drops below healthy levels, the body decides to shut down many systems, including thyroid and reproductive functions. The hypothalamic-pituitary-gonadal axis, which is the hormonal network governing the menstrual cycle, becomes suppressed. Once this occurs, functional hypothalamic amenorrhea is the result, where periods are no longer active. This is a massive red flag, indicating the body is in survival mode. Paradoxically, growth hormone (GH) levels increase in RED-S, however, the body becomes resistant to its effects. Insulin-like growth factor-1 (IGF-1), which moderates many of GH’s bone-building capacities, decreases sharply. Moreover, the body downregulates thyroid hormones to conserve energy, meaning that metabolism is slowed down and the bone remodelling process is further affected.
How Estrogen and Bones are Connected
For female athletes, the loss of a regular menstrual cycle, also called amenorrhea, is devastating for bone health, and can lead to long-term challenges with conditions like osteoporosis. Estrogen plays a critical role in maintaining bone density by stimulating bone-building cells, called osteoblasts, and simultaneously suppressing bone-breaking cells, called osteoclasts. When estrogen levels nosedive due to amenorrhea, this well-regulated balance shifts dramatically towards bone loss.
The timing of this disruption is of vital importance, as women acquire approximately 95% of their total bone mass by the age of 18. This suggests that adolescents and young adults are at high risk, as having peak bone mass compromised during these critical years can result in potentially lifelong consequences.
The Long-Term Reality
While this condition lacks sufficient research regarding chronic effects, studies following women who have experienced anorexia nervosa, which shares similar behavioural and metabolic features with RED-S, found that bone density remained compromised even 21 years after weight restoration and resumption of normal menstrual cycles.
The bones with the greatest deficits include the femur and the lumbar spine, which are weight-bearing bones needed for normal mobility and support. Research shows that previously amenorrheic athletes continue to have significantly lower bone density even after their periods return, with some measurements remaining at only 85% of normal levels.
Why This Matters Beyond Athletics
RED-S is a condition which has the potential to harm athletes long-term via increasing risk for fractures, early onset osteoporosis, and compromising skeletal integrity. It is a condition which results in lower bone density, which has the capability of making menopause even more challenging due to increased bone loss. Ensuring women, especially teenagers and young-athletes, have the education and ability to spot this condition will prevent a life-time of bone issues, and this begins with recognition and intervention from coaches and practitioners. Prohibiting RED-S from occurring will not only guarantee better performance outcomes long-term, but it will also ensure a higher quality of life for many women.
