Under eating while weight training

RED-S: The Dangers of Underfueling (Under Eating while Weight Training)

This article will cover the dangers of under-fueling, describing a serious issue in sport and performance that impacts pros and joes alike. Your body is a miraculous machine. Even if you don’t provide it with enough fuel, it doesn’t just stall out on the side of the road. Instead, it starts to rob the bank of metabolic tissue to pay the energy expenditure bill. After a while, you start to really deplete your body’s savings. If you don’t replenish it, your body starts to suffer.

RED-S: The Danger of Under-Fueling

By: Jeremy Partl, Registered Dietitian

You’re putting in hard work in the gym. The endorphin rushes you get from lifting something heavy, sprinting, or just breaking a sweat keep you coming back. There’s something special about it . . . and you just want more.

However, if you’re training frequently, it’s crucial to make sure that you’re actually giving your body the nourishment it needs—overtraining and under-fueling can have serious health consequences.

This article will cover the dangers of under-fueling, describing a serious issue in sport and performance that impacts pros and joes alike. After giving you a primer, I will explore the root causes of what is now referred to as Relative Energy Deficiency in Sport (RED-S) and discuss the potential consequences. I will finish up by providing commentary on how to ensure that you are appropriately nourishing your body to fuel optimal performance and health.

A Primer

The importance of proper fueling for sports has been well-recognized as a cornerstone of athletic health and performance for decades.

For years, however, coaches and medical professionals have observed what the American College of Sports Medicine (ACSM) has coined the Female Athlete Triad: adolescent and young adult female athletes presenting with declining performance, increasing amounts of injuries and stress fractures, and difficulties getting through games and practices. [1],[2] The term describes the interrelationship between menstrual dysfunction, low energy availability (with or without an eating disorder), and decreased bone mineral density (BMD).

The Triad is represented by a continuum where an athlete could present at any point along each spectrum, from having optimal energy availability (EA), eumenorrhea, and optimal bone health, to having low EA with or without an Eating Disorder, functional hypothalamic amenorrhea, and osteoporosis.[3]

The underlying cause of the Triad was found repeatedly to be a result of low energy availability, a mismatch between dietary energy intake, and the expenditure required for exercise and physiological functions, such as growth, muscle recovery, and homeostasis.[4],[5]

Essentially, there was a mismatch between the energy going in versus the work that was being done. Over time, whether acute or chronic, this negative energy balance was wrecking the performance and health of athletes across the world.

Operationally, energy availability (EA) is defined as follows:[6]

Energy Availability (EA) = Energy Intake (EI) (kcal) − Exercise Energy Expenditure (EEE) (kcal)/ Fat Free Mass (FFM) (kg)

From the outside, this looks like it only accounts for what you eat and how you move your body, but the exercise energy expenditure is calculated as the additional energy expended above that of daily living during the exercise bout, and the overall result is expressed relative to fat-free mass to account for metabolic processes.

The evidence suggests that optimum EA for healthy physiological function is typically achieved at an EA of 45 kcal/kg FFM/day.[7],[8] While there may be differential responses between the various body systems, many of these systems are substantially impacted at an EA <30kcal/kg FFM/day, making it historically a targeted threshold for diagnosis for low-energy availability.[9] This tends to be the level where you are forcing your body to run at a deficit, resulting in slow destruction and/or reduced efficiency.

The prominence of the Female Athlete Triad illustrates the importance of properly fueling activities in all populations and the inherent dangers of under-fueling. Perhaps young girls are more exposed to the unrealistic ideals of body image and performance, but low energy availability is a concern for anyone who is trying to train hard while under-eating. The underfed athlete is a false image for anyone who is trying to make the most of their hard work.

Your body is a miraculous machine. Even if you don’t provide it with enough fuel, it doesn’t just stall out on the side of the road. Instead, it starts to rob the bank of metabolic tissue to pay the energy expenditure bill. After a while, you start to really deplete your body’s savings. If you don’t replenish it, your body starts to suffer.


In 2014, the International Olympic Committee (IOC) published a consensus statement entitled ‘” Beyond the Female Athlete Triad: Relative Energy Deficiency in Sport (RED-S).”[10] Recognizing that the issues were more complex and wide-ranging and the fact that male athletes are also affected, they needed a more appropriate terminology.

The syndrome of RED-S refers to “impaired physiological functioning caused by relative energy deficiency and includes, but is not limited to, impairments of metabolic rate, menstrual function, bone health, immunity, protein synthesis, and cardiovascular health.”[11], [12]

This new classification brought a heightened awareness of the potential consequences of under-fueling, going beyond the field and court.

However, it’s important to note that RED-S has a large impact on performance as well, with potential consequences shown below:

For the lay population (and even most professional agencies), calculating energy availability is a very tricky test. At present, there is no standardized protocol for undertaking an assessment of EA in free-living athletes that is sensitive, reliable, time-efficient, and cost-effective. Thus, the screening and diagnosis of RED-S have been simplified in many cases to using a clinical assessment tool such as the one developed by the IOC.

Still, screening and diagnosis can be difficult, as symptomatology can be subtle. Professionals have to be on the lookout for early warning signs of disordered eating habits, weight loss, lack of normal growth and development, endocrine dysfunction, recurrent injuries and illnesses, decreased performance or performance variability, and/or mood changes.

Depending on the classification of the athlete’s status, athletes may be prevented from any participation at all (red light/high risk), may be cleared for sports participation only with supervised participation and a medical treatment plan (yellow light/moderate risk), or allowed to fully participate (green light/low risk).

Treatment of RED-S is a team effort that usually involves professionals such as physicians, dietitians, physiologists, athletic therapists or trainers, and therapists or psychologists as needed. The focus is on correcting the relative energy deficit through increasing energy intake and/or decreasing energy output.

Barbell Logic and RED-S

Up to this point, I’ve primarily been talking about athletes participating in sports like soccer, rowing, gymnastics, etc. You may be wondering why I have brought this up to the readers of Barbell Logic. Well, I believe that this is an important concept to be aware of and something that must be prevented to optimize our health.

Although any athlete can suffer from RED-S, it does not discriminate between age, sex, sport, or physical ability. Furthermore, those at particular risk are those in judged sports with an emphasis on the aesthetic or appearance (i.e., bodybuilding), weight category sports (i.e., powerlifting), and endurance sports.

We live in a society that glorifies and even reinforces weight loss (yes, Fitbits and Apple watches, I’m talking to you). Individuals tend to be more concerned by not overconsuming, rather than considering how much their body actually needs. And, with traits like perfectionism and ultra-competitive nature more common in society, individuals tend to seek out and implement drastic measures to gain any advantage they can. Thus, I don’t believe that this concept is anything that should be overlooked by our readership.

When it comes to cutting weight for a meet, prepping for a physique show, or just going through intense training cycles, athletes need to put a larger focus on adequately nourishing the body. However, these are the times when we sacrifice our health to reach these goals. I will not say that it’s something that can’t be done on a very infrequent basis, but when the goals become to stay at the lowest weight class you can, stay stage-lean all year round, or push the pedal to the medal all year long, it’s likely that it jeopardizes health for the sake of achieving success in sports.

Keeping the Balance

Finding that balance between optimizing performance and body composition while maintaining your health can take work and is more of a skill than people think. It requires getting data from your body, listening and deciphering that information, and sometimes seeking outside perspectives and help.

Just like when you have a weak muscle that causes your other muscles to compensate and typically results over time in injuries, your body must be in balance to avoid compensating and starting to deteriorate your health.

What can you do to find that sweet spot?

  • Avoid prolonged calorie deficits and weight loss phases.
  • Monitor fiber and protein intake to make sure that it does not prevent you from getting adequate calories.
  • Pay attention to hunger and fullness cues.
  • Improve satisfaction in your diet by adding more components, tastes, and textures to meals.
  • Balance out meals by including protein, carbohydrates, and fats with each meal, and avoid cutting out food groups.
  • Watch out for problems with digestion.
  • Create awareness around your sleep quality and quantity.
  • Monitor your mood and emotional states.
  • Get a full lab panel done at least once per year.
  • Include rest days, deloads, and time off from training.

Check in, check often, and check off self-care.


[1] Otis, C. L., Drinkwater, B., Johnson, M., Loucks, A., & Wilmore, J. (1997). American College of Sports Medicine position stand. The female athlete triad. Medicine and Science in Sports and Exercise, 29(5), i-ix.

[2] Nazem, T. G., & Ackerman, K. E. (2012). The female athlete triad. Sports health, 4(4), 302-311.

[3] STAND, P. (2007). The female athlete triad. Med. Sci. Sports Exerc, 39(10), 1867-82.

[4] STAND, P. (2007). The female athlete triad. Med. Sci. Sports Exerc, 39(10), 1867-82.

[5] De Souza, M. J., Nattiv, A., Joy, E., Misra, M., Williams, N. I., Mallinson, R. J., … & Matheson, G. (2014). 2014 Female Athlete Triad Coalition Consensus Statement on treatment and return to play of the female athlete triad: 1st International Conference held in San Francisco, California, May 2012 and 2nd International Conference held in Indianapolis, Indiana, May 2013. British journal of sports medicine, 48(4), 289-289.

[6] Loucks, A. B., Kiens, B., & Wright, H. H. (2011). Energy availability in athletes. Journal of sports sciences, 29(sup1), S7-S15.

[7] Loucks, A. B., & Heath, E. M. (1994). Induction of low-T3 syndrome in exercising women occurs at a threshold of energy availability. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 266(3), R817-R823.

[8] Loucks, A. B., & Thuma, J. R. (2003). Luteinizing hormone pulsatility is disrupted at a threshold of energy availability in regularly menstruating women. The Journal of Clinical Endocrinology & Metabolism, 88(1), 297-311.

[9] Burke LM, Deakin V. (2015) Clinical sports nutrition. 5th edn: McGraw-Hilll Education


[10] Mountjoy, M., Sundgot-Borgen, J., Burke, L., Carter, S., Constantini, N., Lebrun, C., … & Ljungqvist, A. (2014). The IOC consensus statement: beyond the female athlete triad—relative energy deficiency in sport (RED-S). British journal of sports medicine, 48(7), 491-497.

[11] Mountjoy, M., Sundgot-Borgen, J. K., Burke, L. M., Ackerman, K. E., Blauwet, C., Constantini, N., … & Sherman, R. T. (2018). IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. British Journal of Sports Medicine.

[12] https://bjsm.bmj.com/content/bjsports/49/7/421.full.pdf




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