Ben Alter, MA, ND
Subheadline
How chronic low energy availability disrupts metabolism, hormones, recovery, immune function, and performance—and why recreationally active individuals may be especially vulnerable.
Short Description
This article explores Relative Energy Deficiency in Sport (RED-S), a frequently overlooked consequence of chronic under-fueling that can impair metabolic health, hormone balance, recovery, immune function, and physical performance. It examines how RED-S commonly affects recreationally active individuals and provides practical strategies for restoring energy availability, resilience, and long-term health.
Introduction
Most “fit” people I meet are surviving, not thriving. They train, track, and grind… yet feeldrained, inflamed, nursing nagging injuries, or always coming down with something.
One of the most common (and overlooked) reasons is simple: they’re under-fueled. The dominant story says we should always be chasing a calorie deficit for better body composition. But if the goal is sustainable health, energy, and performance, the body requires adequate fuel, and that fuel needs to be nutrient-dense so you can both power the engine and clear the metabolic waste it produces.1
Even though the obesity epidemic is framed as a disease of excess, deficiency runs just as rampant, especially in people who appear “fit” and active.²⁻³ Sports medicine has a name for this: Relative Energy Deficiency in Sport (RED-S). This isn’t just an “elite athlete” problem. In many ways, it’s more common in “normal active” people – parents who train early, professionals squeezing workouts between meetings, and weekend warriors stacking big sessions on top of a high-stress life.4-5
Let’s unpack what RED-S really is, how it shows up, and what it takes to get the system back online.
What Is RED-S, Really?
In plain language, RED-S means you’re not eating enough for what your body is being asked to do. In sports science terms, RED-S is driven by low energy availability – there isn’t enough energy left over for basic physiology after you subtract the calories burned in exercise.6-7
Put simply:
- Energy availability = what you eat – what you burn in training.
- When that “leftover” pool is too small, the body starts down-regulating energetically costly functions to keep you alive.6-8
The International Olympic Committee (IOC) defines RED-S as impaired physiological and psychological functioning caused by prolonged or severe low energy availability, affecting metabolism, hormones, bone health, immunity, cardiovascular function, and performance.6-9 RED-S evolved from the older Female Athlete Triad model (low energy availability, menstrual dysfunction, and low bone mineral density) and now clearly applies to both males and females.9-10 It is well-documented in endurance athletes and increasingly recognized in team sports and recreationally active individuals.4,6-11
It’s important to know that RED-S is most often unintentional. It does not always start with a deliberate diet or weight-loss plan. It commonly develops when people underestimate how much energy and stress their training, steps, work, and life actually add up to – and their daily nutrition simply does not keep up.6-12
How the Body Compensates When Fuel Is Too Low
The body is not a calculator; it is a complex psychoneuroendoimmune system wired for survival. When energy availability stays low, vital organs are protected first and the body starts cutting costs everywhere else.6-8
Some of the most common consequences of under-fueling include:
Metabolic changes
- Reduced resting metabolic rate to conserve energy.6-8
- Increased energetic efficiency: you burn fewer calories doing the same activity, making fat loss harder over time.8-13
- Weight-loss plateaus or even weight gain despite “doing everything right.”6-8
Hormonal and reproductive changes
- Disrupted reproductive hormones (menstrual irregularities in women, reduced testosterone in men).6-9
- HPA-axis disruption with chronically elevated stress-hormone signaling (e.g., cortisol).6-8
- Altered thyroid and other metabolic hormones, further slowing metabolism and affecting mood and energy.8-14
Bone and tissue health
- Reduced bone formation and bone mineral density, increasing stress-fracture and osteoporosis risk.6-9
- Impaired protein synthesis and recovery, leading to greater muscle breakdown and slower repair.6-8
- Greater susceptibility to sprains, strains, and overuse injuries.6-11
Immune and blood factors
- Higher illness susceptibility and more frequent “coming down with something.”6-8,15
- Worsening symptom flares in patients with underlying autoimmune disease.16
- Blood changes such as reduced iron availability and anemia risk, directly impairing endurance and stamina.6-8
Performance and nervous system effects
- Increased fatigue, irritability, low mood, anxiety, and sleep disturbance.6-9
- Autonomic nervous system imbalance, often reflected in lower heart-rate variability.17
- Blunted training response and plateaued or declining performance despite high effort.6-8
- The symptoms that feel random or disconnected usually share a common driver – a chronic fuel deficit that amplifies stress across the entire system.6-8
Why “Eat Less, Move More” Becomes a Trap
The standard fat-loss narrative is simple: “calories in vs calories out.” On a spreadsheet, it makes sense. In a human, it often backfires.
Yes, a calorie deficit can produce short-term weight loss. But when patients stack:
- More training
- More daily movement
- More life and work stress
- Less food…
they drive the system toward low energy availability (RED-S) and chronic stress physiology rather than sustainable fat loss. This is especially true when that deficiency pattern is maintained for months to years, or repeated over time in chronic “yo-yo” dieters.6-18
Research and clinical experience converge on a few key points:
- Low energy availability is the central driver of RED-S, even in the absence of a formal eating disorder.6-19
- A commonly cited threshold is ≤30 kcal/kg fat-free mass/day in women and ≤20-25 kcal/kg fat-free mass/day in men, below which multiple endocrine and metabolic disturbances have been demonstrated.6-21
- True energy requirements are highly individual, varying with age, sex, sport, training load, and non-exercise stressors.6-22
- The longer someone remains in a low-availability state, the deeper the adaptations: chronic fatigue, recurrent injury, low bone mineral density, and persistent hormonal disruption.6-23
By the time the scale finally moves (if it ever does), the cost in resilience, recovery, and endocrine health can already be substantial.6-18
How RED-S Presents in Recreationally Active Patients
Most non-elite patients don’t walk into a doctor office and say, “I have RED-S.”
Their chief complaints are typically:6-11,24
- “I’m wired but tired—exhausted all day, then stimulated at night.”
- “My metabolism feels broken.”
- “I can’t lose weight despite exercising lots and cutting calories.”
- “I’m always dealing with a nagging injury or coming down with something.”
- “My libido is gone.”
- “I used to feel strong, now I struggle.”
If a patient maintains any degree of active lifestyle, RED-S should be on the differential.6-11
These complaints map directly onto the multisystem consequences described in RED-S literature: dysregulated stress response, un-restorative sleep, impaired tissue repair and recurrent injury, down-regulated immune system, suppressed hypothalamic-pituitary-gonadal axis function, as well as psychological and cognitive symptoms.6-9,24-25
It’s also helpful to know that RED-S exists on a continuum: from optimal energy availability → subclinical low EA → clinically significant dysfunction.6-24 Patients do not need to check every box to warrant intervention.
Why Recreationally Active Individuals May Be at Greater Risk
Paradoxically, recreationally active individuals may be more vulnerable than elite athletes with structured support.4-5
Contributing factors:4-18
- Less structured fueling and limited access to sports nutrition expertise.
- Less intentional recovery programming (sleep, planned rest days, deloads).
- Higher allostatic load from work, family, commuting, and financial stress layered on top of training.
- Persistent cultural exposure to “eat less, move more” and physique-focused messaging that normalizes under-fueling.
Meanwhile, early RED-S signs are frequently misattributed to:
- “Just getting older”
- “Needing to tighten up the diet”
- “Not grinding hard enough”
This often leads patients to double down on caloric restriction and training intensity, further deepening the deficit.18
Clinical Management: Principles of Recovery
RED-S is an adaptation to chronic under-fueling, not irreversible pathology. The system can re-regulate if inputs change.6-26
There are three core pillars to recovery: reduce excessive training load, restore energy availability, and address psychological/behavioral stressors.9-26
1. Facilitate True Rest (Not Pseudo-Rest)
Rest is not simply replacing an intense workout with something “lighter.” It is creatingphysiologic space for deep repair and rebalancing of hormones and the nervous system.27
Recommendations:
- Real deload: temporarily reduce training volume and/or intensity by at least 30–50%, notmerely take a few scattered “rest days.”27
- Sleep optimization: prioritize 7–9 hours of consistent, high-quality sleep, which directlysupports GnRH pulsatility, anabolic hormone release, and immune function.6-27
- Extended recovery phase as needed: if RED-S signs have persisted for months, plan atrue recovery block of 1–2 weeks (or more) with training load cut by at least 50%.27
Research on RED-S and overtraining syndrome demonstrates substantial symptom overlap and reinforces that performance typically improves when training load is strategically reduced and fueling is restored.9-28
2. Restore Energy Availability (Fuel the System)
The most important piece of RED-S recovery is raising energy availability: increasing energy intake relative to total expenditure.6-27
Recommendations:
- Increase total energy intake: more food, more frequently – not just adjust macronutrient ratios.26-27
- Ensure adequate carbohydrate availability: especially around and after training sessions, as low carbohydrate availability can independently worsen RED-S and impair training adaptation.9-28
- Address common micronutrient deficiencies: if there has been a deficit of macronutrients (calories), there has likely been a deficit of micronutrients such as iron, calcium, vitamin D, B-vitamins, and trace minerals.6-11
The goal is to match fuel to output so the body no longer has to choose between basicphysiologic function and training demands.6-26
3. Support Nervous System Regulation
While RED-S is defined by energy availability, the autonomic nervous system regulates how that energy is allocated.6-17
Recommendations:
- Down-shift sympathetic overdrive: restore parasympathetic tone, which directly supports digestion, hormone regulation, and tissue repair.6
- Simple, repeatable interventions: breath work, non-sleep deep rest (NSDR), time outdoors, social connection, and morning sunlight all demonstrate benefits for HRV, sleep quality, and stress resilience.27
- Reduce stimulant dependence: moderate caffeine intake and limit late-night screen exposure, both of which perpetuate sympathetic activation.27
The highest-yield intervention is often the least sexy: more real food, more real rest, less chronic overdrive.
The Identity Shift Required for Recovery
For many high-output patients, the most difficult aspect of RED-S recovery is not eating more or resting more. It is the prerequisite shift in mindset necessary to engage with life differently and support re-balancing.
Examples of helpful narrative shifts include:
- “I’m training for my sport” → “I’m training for life”
- “I need to feel good now” → “I’m investing in my future self”
- “My body is failing me” → “My body is protecting me”
- “I need to earn my meal” → “I am deeply nourishing myself to thrive”
- “My activity makes me feel good” → “I am innately worthy of all the goodness in life”
RED-S is not a moral failure or lack of discipline. It is simply a mismatch between energy outputs and inputs. While calories are an important input, so too are love, connection, and fulfillment.
RED-S resolves when energy inputs match demands. The real clinical challenge is helping patients believe they deserve that balance.
References:
1. Micronutrient deficiencies in obesity. Adv Nutr. 2012;3(1):1-7.
2. Impact of micronutrient deficiencies on obesity. Nutr Rev. 2009;67(10):559-572.
3. The malnutrition of obesity: micronutrient deficiencies that promote diabetes. ISRNEndocrinol. 2012;2012:103472.
4. REDs: “But I’m not an elite athlete?” NHD Magazine. Published August 3, 2025.Accessed May 12, 2026. https://www.nhdmag.co.uk/blog/red-s-but-im-not-an-eliteathlete
5. Under-fueling in athletes and active people. Cornell Health. Accessed May 12, 2026.https://health.cornell.edu/sites/health/files/pdf-library/RED-S.pdf
6. Relative energy deficiency in sport (RED-S). PMC. 2022;9724109.
7. Relative energy deficiency in sport. Wikipedia. Updated September 2, 2006. AccessedMay 12, 2026.
8. Endocrine and metabolic repercussions of relative energy deficiency in sport. Curr OpinEndocr Metab Res. 2019;9:56-65.
9. 2023 International Olympic Committee’s (IOC) consensus statement on relative energydeficiency in sport (RED-S). Br J Sports Med. 2023;57(17):1073-1098.
10. The IOC consensus statement: beyond the Female Athlete Triad—Relative EnergyDeficiency in Sport (RED-S). Br J Sports Med. 2014;48(7):491-497.
11. Energy availability and RED-S risk factors in competitive CrossFit athletes. Front Nutr.2021;8:698049.
12. Relative energy deficiency in sport: a cross-sectional study of non-elite recreationalathletes. PMC. 2026;12916108.
13. Low energy availability score overview. Vitality Blueprint. Accessed May 12, 2026.
14. Relative energy deficiency in sport (REDs). Endocr Rev. 2024;45(5):676-733.
15. Effects of exercise on immune function. Gatorade Sports Science Institute. AccessedMay 12, 2026.
16. Exercise and autoimmune disease: evidence-based, low-impact approaches.Autoimmune Institute. Published February 4, 2026.
17. Cardiovascular consequences of relative energy deficiency in sport. Am Coll Cardiol.Published December 19, 2022.
18. Reasons for and consequences of low energy availability in female and male athletes:social environment, adaptations, and prevention. Sports Med Open. 2020;6(1):44.
19. Relative energy deficiency in sport (REDs). National Eating Disorders Association.Updated November 9, 2025.
20. Can we measure low energy availability? My Sport Science. Published January 14, 2025.
21. Low energy availability (LEA) in male athletes: a review of the literature. Sport J.Published October 20, 2024.
22. Relative energy deficiency in sports (RED-S). German J Sports Med. 2024;4.
23. Energy deficiency suppresses bone turnover in exercising women with menstrualdisturbances. J Clin Endocrinol Metab. 2019;104(8):3131-3139.
24. Understanding RED-S: the hidden health risk in athletes. Fly Nutrition. Published June 1, 2025.
25. The state of play on relative energy deficiency in sport (REDs): psychological aspects.Nicky Keay Fitness. Published March 17, 2024.
26. Navigating REDs recovery while staying in the game. Project REDs. Published May 8,2026.
27. Relative energy deficiency in sport (REDs): awareness, identification, and management.NSCA Coach. Published November 18, 2025.
28. Overtraining syndrome (OTS) and relative energy deficiency in sport (RED-S): a clinicalcomparison. Front Sports Act Living. 2021;3:751315.
Author Bio:
Benjamin Alter, ND, is a licensed naturopathic doctor, educator, and co-founder of Alter Health. He specializes in evidence-informed lifestyle medicine, helping individuals prevent and reverse chronic disease through whole-food, plant-based nutrition, behavior change, exercise, stress management, and restorative sleep. Dr. Alter is passionate about empowering patients with practical, sustainable strategies that address the root causes of illness while optimizing metabolic health, longevity, and overall well-being. He also educates healthcare professionals and the public on the transformative role of lifestyle medicine in modern clinical practice.
