REDs Explained: How Low Energy Availability Impacts Health and Performance

Written By CarliRunNutrition .

Maybe this sounds familiar: a runner deep in training, pushing peak mileage, eating “clean,” and chasing that next PR. But sleep is shot. Mood’s off. Recovery feels slower by the day. Their last menstrual cycle? Can’t remember. But they brush it off—not a priority right now, they tell themselves. The focus is on winning, getting stronger, grinding it out—because surely the body will adapt…

Or so they thought.


A lot of athletes and runners may tilt their head when relative energy deficiency in sport (REDs) is brought up. This is no fault of their own, as awareness has only recently increased. Studies show less than half of coaches and physicians surveyed were able to identify the three components of the female athlete triad and other studies reported similar knowledge gaps with physiotherapists and athletic trainers. So what IS REDs? Let’s break it down starting with the history. 

The Female Athlete Triad is a medical condition seen in physically active females and involves one or more of the three components which include: low energy availability (LEA) with or without disordered eating (DE), menstrual dysfunction, and low bone mineral density (BMD). In 2014, the International Olympic Committee (IOC) published a consensus statement expanding on this condition naming it Relative Energy Deficiency in Sport (REDs) to bring to light the additional consequences of LEA on health and performance in both sexes. 

Since then the consensus statement has been updated a couple times with further research uncovering and solidifying the different health and performance detriments REDs can cause. The latest statement published in 2023 can be found here.

REDs is defined as “A syndrome of impaired physiologic and/or psychological functioning experienced by female and male athletes that is caused by exposure to problematic (prolonged and/or severe) low energy availability. The detrimental outcomes include, but are not limited to, decreases in energy metabolism, reproductive function, musculoskeletal health, immunity, glycogen synthesis, and cardiovascular and hematological health, which can all individually and synergistically lead to impaired well-being, increased injury risk, and decreased sports performance.” 

LEA is a mismatch between dietary intake and energy expended in exercise that leaves the body’s total energy needs unmet. EA is the dietary energy left over and available for optimal function of body systems after accounting for the energy used in exercise and can be further explained in this formula: 

EA (Energy availability) = EI (energy intake (kcal)) - EEE (Exercise energy expenditure (Kcal)) /

FFM (Fat free mass (kg) /day)  

Now that you have an overview of some of the terminology and how they are connected, let's dive into more of the science and different scenarios that stem from this LEA. This way you can be more aware of some of the possible signs and symptoms. Of note, REDs is a diagnosis of exclusion so it is important to ensure you are looping in your health care providers so you have a multidisciplinary approach to help exclude other causes before confirming a diagnosis of REDs. For other healthcare providers, the examples of differential diagnoses are listed in table 2 here.


Potential Health Outcomes 

Impaired Reproductive Function & Heart Health

Male and female athletes can experience impaired reproductive functions. Females with LEA can start to have irregular menstrual cycles and/or have this go missing (eg, primary amenorrhea, oligomenorrhea, secondary amenorrhea, luteal phase defects/deficiency, and anovulatory cycles). This occurs from poor EA and causes a decrease in luteinizing hormone (LH) concentrations or pulsatility, reduced estrogen and progesterone levels, and decreased testosterone. Males who are under LEA can experience lowered testosterone, sperm abnormalities, and erectile dysfunction. This can lead to decreased libido in both male and female athletes alike.

Female athletes may want to brush off a missed period or irregular cycle, but I encourage you not to do this. We have come too far to prove that an irregular period due to LEA is only putting your health at a greater risk such as early signs of atherosclerosis (aka heart disease). Dysfunction in arteries and unfavorable cholesterol levels have been reported in amenorrheic athletes. When we can get that period back, improvements in vascular endothelial function can return. In more severe cases of LEA seen in eating disorders (ED), significant cardiovascular changes can occur, including valve abnormalities, pericardial effusion, severe bradycardia, hypotension, and arrhythmias. 

Bone Health

 Short term LEA has been shown to negatively affect bone turnover markers in women and men. Women who have missing or infrequent menstrual cycles, or measured LEA, have been found with decreased bone mineral density (BMD), altered bone microarchitecture and bone turnover markers, decreased estimates of bone strength, and increased risk for bone stress injuries compared to women who have adequate EA. A more recent finding has shown the additive impact of low carbohydrate availability (LCA) in the development of REDs. In a study including male endurance athletes that looked at 3 different types of intakes (i.e., high energy and high carbohydrate availability, high energy with LCA but high fat diets, or low energy with low to moderate carbohydrate availability) on bone, immunity, and iron biomarkers. The results showed increased bone resorption biomarkers (i.e., breakdown) and impairments in biomarkers of bone formation. They also found increased post-exercise inflammation markers such as interleukin-6 (IL-6) and hepcidin after LCA. Hepcidin is a hormone produced by the liver that helps regulate iron absorption and when elevated, decreases iron absorption. Thus, suggesting damaging effects on bone, immunity, and iron biomarkers as a result of LCA even if energy needs were met. Studies have shown just 3.5 weeks of a low-carbohydrate, high-fat (LCHF) diet  in elite endurance athletes resulted in impaired markers of bone remodeling both at rest and around exercise (up to 3 hours post exercise), and elevated IL-6 concentrations compared to the same calorie intakes with higher carb intakes.  Six other studies since 2019 have shown this negative LCA impact on the development of REDs in the body. While meeting protein and fat intakes to support health and performance are also important, this highlights the importance of meeting carbohydrate goals while also meeting energy needs to protect bone health and prevent other REDs outcomes. 

Iron & Red Blood Cells

Iron is essential for red blood cell production which helps carry oxygen throughout the body. Iron deficiency, often seen in female athletes, can directly and indirectly lead to LEA. This occurs due to the potential for a decrease in appetite, decreased metabolic fuel availability, and impaired metabolic efficiency, leading to an increase in energy expenditure during exercise and rest. Iron deficiency may also interact with bone health via dysregulation of the growth hormone (GH)/ insulin growth factor-1 (IGF-1) axis, hypoxia, and hypothyroidism, along with playing an important role in thyroid function, fertility, and psychological well-being. Hepcidin has been shown to be elevated by 264% with a low energy, low carb diet compared to only 69% increases seen in those who adhered to the same energy intakes with higher carbohydrate intakes. This shows the importance of adequate carbohydrate availability to also support iron stores. Beyond bone and blood, metabolism also takes a hit when energy is lacking.

Metabolism

Increasing training loads while not adjusting intakes to match the demands training puts on the body, has been shown to significantly reduce the body’s resting metabolic rate. Women who have severe energy deficiency from increased exercise and lowered intakes have revealed significant decreases in the hunger satiety hormone leptin, thyroid marker T3, IGF-1, and an increase in the hunger hormone, ghrelin. If this energy deficit continues, overall hunger cues can become muted due to an increase in stress response from the body, and overall metabolism slows. This is why even at an energy deficit we may see someone's weight stay the same or increase. If we are not getting enough fuel in the tank, the body is smart enough to prioritize slowing down metabolism to keep vital functions operating to keep you alive. This is where that survival hormone, cortisol, kicks into higher gear and will increase in order to keep you going. That energy you get clearly isn’t coming from skipping your pre-workout fuel or breakfast, it's coming from your adrenal glands being placed on high gear. This is where lab testing can be so helpful, because REDs does not discriminate based on body size. Anyone can be dealing with this and it can look different depending on the person’s situation. 

Psychological 

Adolescent females with FHA have had higher incidences of mild depressive traits, psychosomatic disorders, and a decreased ability to manage stress. There is overlap seen in adolescents with EDs and those with FHA showing both increased depression, social insecurity and introversion, and hyperfixation around weight gain compared with healthy controls. These psychological problems can precede or be caused by LEA. Overly restrictive patterns in male athletes have also shown negative psychological effects leading to mood disturbances, endocrine dysfunction, and a reduction in muscle mass with loss of strength. Other impaired neurocognitive functions resulting from problematic LEA include reduced/impaired: sleep disturbances, memory, decision-making, spatial awareness, poor planning/cognitive flexibility, and reduced executive function. If an athlete is starting to have a change in character such as becoming more socially isolated, overfixating on a drive for thinness or becomes more rigid/restrictive in their intakes, it may be good to check-in with them on why and consider addressing any potential need for guidance on nutrition to best support their whole being.

GI Function

Inadequate nutrition can negatively influence the whole gastrointestinal tract. Reports of altered sphincter function, delayed gastric emptying, constipation, and increased intestinal transit time have been seen in those with LEA compared to those with adequate EA. Other symptoms include abdominal pain, cramps, and bloating. This can cause a vicious cycle as many athletes may end up cutting out certain food groups thinking there is an intolerance that was never there before their activity increased. But before we continue adding to the list of foods they can’t tolerate, it’s important to first rule out if we are dealing with an underfueled gut. Your GI tract needs fuel to function as well. When we are underfueled, this puts stress on the gut and we are unable to digest and absorb nutrients as we were before. Add that to increased training where less blood flow and more stress is placed on the gut which means we can definitely be adding to the fire. This is why it’s important to ensure there is optimal guidance on nutrition by a trained professional who can distinguish between the “chicken or the egg” theory and what came first. There is always a place for testing to rule out actual food allergies. However, it is not uncommon for those pesky GI complaints and intolerances to improve once we have a nourished gut.  

Immunity 

Studies have shown increased rates of illness involving the upper respiratory tract and GI tract, bodily aches, and head-related symptoms associated with LEA states. There are also symptoms of a decreased immune response, such as lower immunoglobulin A secretion rates, reported in athletes with amenorrhea versus those with a healthy menstrual cycle. If we are not maintaining adequate EA throughout training, there is an increased infection/illness susceptibility. Sure there are seasons where we might be at risk for the common cold or flu, but if there is an athlete who continues to get sick during training it may be due to a lack of adequate fuel to help support a robust immune system. After all, about 70% of our immune system can be found in the gut, which shows you how that underfueled gut can also be connected to your immune response. 

Growth and Development

In both male and female athletes with severe LEA as seen in anorexia nervosa, impaired linear growth has been reported in studies demonstrating partial, but not always complete, catch-up growth after recovery. These findings are consistently noted with decreases in IGF-1, increases in GH and increased GH resistance. Young athletes need to fuel not just to perform in sport, but to support their growth, development, and long-term health.

Impaired Glucose Metabolism

Low energy availability can cause decreases in insulin and IGF-1 and elevations in cortisol. When there is a lot of demand on the body, but little fuel to support it, the body has a stress response and blood sugar is made via the liver by a process called gluconeogenesis to further increase blood sugar levels to support important bodily functions. So while some may harp that carbohydrates are “inflammatory”, having a lack of carbohydrates to support an active individual can actually be the cause of higher stress on the body, and elevated fasting blood sugar levels. This can be why we sometimes see underfueled athletes have elevated hemoglobin A1c lab values (a measure that looks at one's average blood sugar level for the past 3 months).

Performance Outcomes

When problematic LEA occurs, we start to see decreased power and endurance in performance as well as decreases in: 

  • muscle strength

  • motivation

  • cognitive performance/skill (reduced reaction time, impaired judgement and decreased coordination and concentration)

  • recovery

  • training response, and 

  • decreased athlete availability due to illness or injury.  

Those At Risk

Any very active person, whether you call yourself an “athlete” or not, can be at risk for this. This also does not discriminate on someone’s body size. This can happen intentionally or unintentionally. If you are a recreational athlete or any type of athlete for that matter, and you also work a full time job, have a family, and have other expectations on your plate, it can be easy to miss important energy and nutrient needs to support your sport and your day-to-day life.


Steps to Address and Prevent RED-S

  • Prioritize fueling: Adequate carbs, protein, fats, and micronutrients throughout the day to support the demands you are placing on your body. We need to account for not only your physical activity, but what your day to day looks like. A good portion of one's total energy needs is required to just support their body to stay alive (Breathing, digestion, other vital organ functions).

  • Avoid long periods without eating, especially after workouts. Plan your meals and snacks accordingly. Some may need to be eating every 2-4 hours to reach their goals.

  • Include recovery nutrition within 30–60 minutes post-exercise. This includes pairing your protein with a carbohydrate. If you plan to have a well balanced meal within the hour, great! But definitely plan on your recovery nutrition snack or shake to buffer any prolonged time between your workout and a meal to get you out of that breakdown state, and into recovery mode.

  • Listen to body signals: fatigue, mood, menstrual cycle changes.

  • Seek professional support from a sports RD for personalized nutrition to support training load, performance, and overall health and wellbeing.

REDs can feel overwhelming when you read through all of its possible effects—but here’s the truth: your body isn’t failing you. It’s communicating with you. Low energy availability is not a sign of weakness—it’s a sign that you’ve been asking your body to do more than you’ve been giving it.

The good news? With the right fuel, the right rhythm, and the right support, your body can come back into balance. Cycles can return. Energy can rebound. Performance can thrive again.






Resources: 

Mountjoy, M., Ackerman, K. E., Bailey, D. M., Burke, L. M., Constantini, N., Hackney, A. C., Heikura, I. A., Melin, A., Pensgaard, A. M., Stellingwerff, T., Sundgot-Borgen, J. K., Torstveit, M. K., Jacobsen, A. U., Verhagen, E., Budgett, R., Engebretsen, L., & Erdener, U. (2023). 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British journal of sports medicine, 57(17), 1073–1097. https://doi.org/10.1136/bjsports-2023-106994

Mountjoy, M., Sundgot-Borgen, J., Burke, L., Ackerman, K. E., Blauwet, C., Constantini, N., Lebrun, C., Lundy, B., Melin, A., Meyer, N., Sherman, R., Tenforde, A. S., Torstveit, M. K., & Budgett, R. (2018). International Olympic Committee (IOC) Consensus Statement on Relative Energy Deficiency in Sport (RED-S): 2018 Update. International journal of sport nutrition and exercise metabolism, 28(4), 316–331. https://doi.org/10.1123/ijsnem.2018-0136

De Souza, M. J., Nattiv, A., Joy, E., Misra, M., Williams, N. I., Mallinson, R. J., Gibbs, J. C., Olmsted, M., Goolsby, M., Matheson, G., & Expert Panel (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. https://doi.org/10.1136/bjsports-2013-093218

CarliRunNutrition .