Authors:Brandon L. Lee¹

¹The Department of Exercise, Health, and Sport Sciences, Pennsylvania Western University

Corresponding Author:

Brandon L. Lee, MS, RD, CCRP
10263 4th Armored Division Dr.
Fort Drum, NY 13603
[email protected]
315-772-0689

Brandon L. Lee, MS, RD, CCRP is a Holistic Health and Fitness (H2F) Dietitian for the U.S. Army Forces Command and a Doctor of Health Science (DHSc) student at Pennsylvania Western University. Brandon’s research interests include energy systems and metabolism, energy availability, andragogical methods for adult learning, and reflective practice to enhance learning in formal education..

ABSTRACT

Purpose: Low energy availability (LEA) is a physiological state when there is inadequate energy to meet the demands placed on the body, often through physical activity, exercise, or sports. LEA can impact any athlete engaged in a sport with low energy intake or excessive energy expenditure. LEA is a precursor to the onset of The Male Athlete Triad (MAT) and Relative Energy Deficiency in Sport (RED-S). There is no defined low energy availability threshold specific to male athletes engaged in high-energy expenditure sports leading to MAT and RED-S. This literature review evaluates the literature on the relationship between LEA and signs or symptoms of MAT and RED-S to establish a low energy availability threshold specific to male athletes engaged in high-energy expenditure sports.

Methods: The Pennsylvania Western University library electronic database was used for the literature search. Search terms included “male athletes”, “low energy availability”, “male athlete triad”, “relative energy deficiency in sport”, and “energy deficiency”. Research studies included cross-sectional, experimental, systematic reviews, meta-analyses, case studies, and some narrative and literature reviews. Studies must have been peer-reviewed and published within five years of the literature search (12/2018- 12/2023).

Results: A review of the literature shows that it is difficult to determine a LEA threshold due to present research gaps and inconsistent findings related to health and performance consequences. Based on the results of experimental studies, practitioners can expect an LEA threshold of 20-25kcal per kilogram (kg) of fat-free mass (FFM) per day in male athletes engaged in high energy-expenditure sports.

Conclusions: Athletes engaged in sports that lead to inadequate energy intake or high energy expenditure are at risk for LEA, MAT, and RED-S. Experimental research on the LEA threshold in athletes engaged in physiologically demanding sports is the greatest research gap. Based on present findings, male athletes may have an LEA threshold of <30kcal/kg of FFM/day.

Applications in Sport: Healthy nutritional practices are essential to sports performance. Interdisciplinary sports performance teams must collaborate with nutrition professionals to develop effective LEA prevention, screening, and intervention protocols.

Keywords: energy intake, energy deficiency, energy expenditure of exercise, male athlete triad, relative energy deficiency in sport, sports nutrition

Low Energy Availability (LEA) in Male Athletes: A Review of the Literature

Energy availability (EA) is the energy dedicated to body system functions. In sports nutrition, energy availability is defined as the amount of energy remaining to support an athlete’s bodily functions after energy expenditure of exercise (EEE) is deducted from energy intake (EI) (2). Health and athletic performance issues arise when athletes have inadequate energy intake or excessive energy expenditure, depleting their EA. The designated term for this is low energy availability (LEA). LEA is defined as a physiological state when there is inadequate energy to meet the demands placed on the body, often through physical activity, exercise, or sports (23). Causes of LEA include obsessive causes (disordered eating or eating disorders), intentional causes (attempts to modify body mass or composition), and inadvertent causes (byproduct of high EEE) (1).
LEA can impact any athlete engaged in a sport with low energy intake or excessive energy expenditure. LEA is most common in sports of high intensity, duration, volume, or frequency and in sports that emphasize low body weight/fat, aesthetics, or thinness, including distance cycling and running, triathlons, tactical (i.e., military), swimming, gymnastics, wrestling, bodybuilding, martial arts, boxing, soccer, tennis, rowing, horse racing, and volleyball. LEA is a precursor to the onset of both The Male Athlete Triad (MAT) and Relative Energy Deficiency in Sport (RED-S), two conditions that result in weakened physiological functions, with the former focused on reproductive and bone health decline (22). The problem is the prevalence of LEA among male athletes participating in high-energy expenditure sports, leading to potential health and performance issues. Additionally, there is no defined low energy availability threshold specific to male athletes engaged in high-energy expenditure sports leading to MAT and RED-S (3, 4, 5, 9, 11, 14, 17, 22, 26).
This literature review aims to evaluate the literature on the relationship between LEA and signs or symptoms of MAT and RED-S to establish a defined low energy availability threshold specific to male athletes engaged in high-energy expenditure sports. This literature review will report on LEA’s impact on health, body composition, athletic performance; establish LEA thresholds, and address research gaps.

RELATIVE ENERGY DEFICIENCY IN SPORT (RED-S)
LEA is a common precursor to many health and athletic performance issues. In 2014, the International Olympic Committee (IOC) developed a consensus statement titled “Beyond the Female Athlete Triad: Relative Energy Deficiency in Sport (RED-S)” and established RED-S as a new condition that refers to diminished physiological processes due to relative energy deficiency. The most current IOC RED-S models show that RED-S can impact the following systems: immunological, menstrual/reproductive function and bone health (related to athlete triad), endocrine, metabolic, hematological, growth and development, psychological, cardiovascular, and gastrointestinal. Moreover, another IOC RED-S model shows the potential performance effects of RED-S, including decreased endurance performance, increased injury risk, decreased training response, impaired judgment, decreased coordination, decreased concentration, irritability, depression, decreased glycogen stores, and decreased muscle strength (19). Much of the research on the impact of LEA and the cascade of events that lead to RED-S has primarily been conducted on female athletes, and the findings are extrapolated to their male counterparts; however, this is changing.

MALE ATHLETE TRIAD
The Male Athlete Triad (MAT) was first introduced in the 64th Annual Meeting of the American College of Sports Medicine (ACSM) in 2017 (6). MAT has comprised three essential components: LEA (sometimes referred to as energy deficiency), impaired bone health, and suppression of the hypothalamic-pituitary-gonadal (HPG) axis (22).
Prevention and treatment methods of MAT hinge on the EA or energetic status of the athlete at risk. Nattiv et al. (2021) explain that energy deficiency or LEA is confirmed when one of the following metabolic adaptations is presented: reduced RMR compared to body size or fat-free mass (FFM), unintentional weight loss resulting in a new low set point, underweight body mass index (BMI), and reduced metabolic hormones such as triiodothyronine (T3), leptin, and several more. Hypogonadotropic hypogonadism can manifest as oligospermia (deficiency of sperm in the semen) or decreased libido (reduced sexual drive). Lastly, poor bone health can manifest as osteopenia, osteoporosis, or bone stress injury (22).
The energetic status of the athlete can vary greatly depending on frequency, intensity, duration, type of sport, volume, and progression. Nattiv et al. (2021) have surmised that male athletes engaged in leanness sports typically have low energy intake compared to recommended amounts from the Institute of Medicine Daily Recommended Intakes or Food and Agriculture Organization of the United Nations/World Health Organization. Unfortunately, male leanness sports or weight-class athletes potentially consume up to 1000kcal/day less than required to support their exercise demands (22). Athletes consistently at risk for MAT include runners and cyclists, primarily if they compete in long-distance competitions.

Cardiovascular Health
Cardiovascular health (CVH) is essential to every athlete engaged in any sport. A healthy cardiovascular system effectively moves blood from one location to another to transport oxygen-containing blood cells for muscular activity. Langan-Evans et al. (2021) studied the impact of incorporating daily fluctuations in LEA on cardiorespiratory capacity via treadmill test in one combat athlete preparing to make weight for competition. The athlete experienced microcycle EA fluctuations ranging from 7 to 31 kcal per kilogram (kg) of FFM/day (mean EA of 20kcal/kg of FFM/day) for seven days and did not experience any significant changes in resting heart rate, cardio output, or overall CVH (14). Theoretically, LEA would have significant structural, conduction, repolarization, and peripheral vascular effects on CVH (17). However, a scant amount of research establishes any correlation between CVH and LEA, and primary research studies conducted within the past five years have yet to establish causation between the two.
On the other hand, Fagerberg (2018) has found that EA <25kcal/kg FFM over six months in bodybuilders preparing for a competition can impact CVH by reducing heart rate. According to Fagerberg (2018), low body fat percentages in bodybuilders worsen CVH risk (4). This heart rate reduction, paired with low body fat, is likely a physiological adaptation to conserve energy and sustain life. There needs to be more consistency in the literature regarding the impact of LEA on CVH.

Physiological Health
LEA and RED-S are both physiological and psychological health risks. Sports that emphasize leanness (e.g., cycling) or have weight divisions (e.g., combat sports) often place additional mental stress on athletes to perform well and possess a specific physique. For example, Schofield et al. (2021) found that male cyclists are at risk for LEA and RED-S due to rigid weight management practices, desire for leanness, disordered eating and eating disorders, and body dissatisfaction (26).
Elevating psychological health is commonly conducted via a questionnaire or interview. Langbein et al. (2021) explored the subjective experience of RED-S in endurance athletes through semi-structured, open-ended interviews. The first male participant commented on hitting “rock bottom” and the body’s sensitivity to energy intake changes. In addition, the other male athlete appeared to have a transactional relationship with food and exercise, void of any joy or performance goals. Both male athletes reported negative psychological consequences regarding RED-S; these consequences included increased rates of irritability because they were obsessed with food and exercise and feelings of helplessness and despair (15).
Perelman et al. (2022) also examined the male athlete’s psychological state by evaluating and intervening on body dissatisfaction, drive for muscularity, body-ideal internalization, and muscle dysmorphia. Male athlete participants (n=79) were from various sports, including baseball, golf, soccer, swimming, track and field, volleyball, and wrestling. The results showed that group sessions focused on reframing ideal body perception, the consequences of RED-S, encouraging positive self-talk, and reviewing strategies to modify energy balance healthfully can significantly reduce body dissatisfaction, body-ideal internalization, and drive for muscularity (p < .05) (24). The results demonstrate the value of understanding, supporting, and guiding an athlete’s psychological state toward personal health and satisfaction.

Reproductive Health
Functional hypogonadotropic hypogonadism is one of the three primary pillars of the MAT. LEA can induce disruptions to the hypothalamic-pituitary-gonadal (HPG) axis, resulting in functional hypogonadotropic hypogonadism. Signs of hypogonadotropic hypogonadism include (1) reductions of testosterone (T) and luteinizing hormone (LH), (2) decreased T and responsiveness of gonadotropins to gonadotropin-releasing hormone (GnRH) stimulation after training, (3) alterations in spermatogenesis, and (4) self-reported data on decreased libido and sexual desire (22). Most current research studies examine free and total T as an indicator of HPG axis suppression. Lundy et al. (2022) categorize low total T (<16nmol/L) and low free T (<333 pmol/L) as primary indicators for LEA (16).
A significant contribution to this area comes from the work by Jurov et al. (2021) who conducted a non-randomized experimental study with a crossover design to investigate the reproductive health impacts of progressively reducing EA by 50% for 14 days in well-trained and elite endurance male athletes. The results demonstrated a positive correlation between T levels and measured EA; as EA declined, so did T (9).
The empirical evidence on the causal relationship between LEA and T has been growing over recent years, with studies such as one conducted by Dr. Iva Jurov and colleagues. In three progressive steps, their quasi-experimental study reduced EA (via increasing EEE and controlling EI) in well-trained and elite male endurance athletes. Participants had statistically significant T changes starting at the 50% EA reduction phase with a mean EA of 17.3 ± 5.0kcal/kg of FFM/day for 14 days (p < 0.037). Furthermore, T levels continued to significantly decline at 75% EA reduction phase with a mean EA of 8.83 ± 3.33 for ten days (p < 0.095) (10). Conversely, in another quasi-experimental study by Jurov et al. (2022b), endurance male athletes had their EA reduced by 25% by increasing EEE and controlling EI for 14 days. The mean EA was 22.4 ± 6.3kcal/kg of FFM/day. The results show no significant changes to T levels, potentially indicating that a greater EA reduction was required to induce change (11).
Stenqvist et al. (2020) conducted four weeks of intensified endurance training designed to increase aerobic performance and determine the impact of T and T: cortisol ratio on well-trained male athletes. After the four weeks of intensified endurance training, the results showed that total T significantly increased by 8.1% (p=0.011) while free T (+4.1%, p=0.326), total T: cortisol ratio (+1.6%, p=0.789), and free T: cortisol ratio (-3.2%, p=0.556) did not have significant changes when compared to baseline (27). It is complex to determine the EA threshold defined by HPG axis suppression. Research on LEA and suppression of the HPG axis (i.e., T reduction) have demonstrated varied results based on athlete EA study design features (e.g., high EEE intensity or low EI duration); however, endurance athletes remain at the highest risk (18, 22, 26).

Bone Health
The last pillar of the MAT is osteoporosis with or without bone stress injury (BSI). Impaired bone health is most common in athletes in sports that have low-impact loading patterns, such as cycling, swimming, or distance running. Bone mineral density (BMD) is the primary measurement method to evaluate overall bone health and risk for osteoporosis. Dual-energy x-ray absorptiometry (DXA) is the gold standard for assessing bone density, but quantitative computed tomography (QCT) is also emerging as an equally acceptable alternative. In outpatient or rehabilitation settings, frequency of DXA scans is recommended no sooner than every ten months to allow for detectable changes in bone mineral density (17).
Risk factors for low BMD include LEA, low body weight (<85% of ideal body weight), hypogonadism, running mileage >30/week, and a history of stress fractures (22). In addition to BMD, other indicators of bone health include bone mineral content (BMC), markers of bone formation including β-carboxyl-terminal cross-linked telopeptide of type I collagen (β-CTX), bone alkaline phosphatase, and osteocalcin, and markers of bone resorption including amino-terminal propeptide of type-1 procollagen (P1NP), tartrate-resistant acid phosphatase, and carboxy-terminal collagen cross-links (4, 17). Studies will occasionally implement biomarkers such as Vitamin D and calcium to evaluate dietary intake and risk of BSI or osteoporosis.
What is the prevalence of low BMD in athletes? Tam et al. (2018) evaluated the bone health and body composition of elite male Kenyan runners (n=15) compared to healthy individuals. The results showed that 40% of Kenyan runners have Z-scores indicating low bone mineral density in their lumbar spine for their respective age (z-score <−2.0). This study did not measure energy availability with bone mineral density (29). However, based on previous research, low bone mineral density may have LEA origins.
Heikura et al. (2018) studied the BMD of middle- and long-distance runners and race walkers and found that athletes had an LEA (21kcal/kg of FFM/day) (7). Athletes with a moderate EA generally had better z-scores than the LEA athletes; however, the differences were not statistically significant. Similarly, Õnnik et al. (2022) found that high-level Kenyan male distance runners had an average EI of 1581kcal, and male controls had an average EI of 1454kcal per day. The male athletes did not show a statistically significant difference in BMD (p = 0.293) compared to the male control group, with only one runner (out of 20) at risk for osteoporosis (lumbar spine z-score <1.0) (23).
Cyclists are at the highest risk for poor bone health due to chronic LEA, reduced osteogenic simulation, and low levels of impact or resistance (26). Keay et al. (2018) assessed the efficacy of a sport-specific EA questionnaire and clinical interview (SEAQ-I) in British professional cyclists at risk of developing RED-S. Based on the results of the SEAQ-I, 28% (n=14) were identified with LEA, and 44% of the cyclists had low lumbar spine BMD (z-score <-1.0) (p< 0.001). Also, cyclists with a history of lack of load-bearing sports or activities had the lowest BMD (p= 0.013) (13). This study demonstrates a clear association between LEA and reduced lumbar spine BMD in professional cyclists.
In a randomized controlled trial, Keay et al. (2019) investigated the efficacy of an educational intervention with British competitive cyclists to improve energy availability and bone health. The researchers induced LEA by 25% (mean EA of 22.4 ± 6.3kcal/kg of FFM/day) for 14 days. Athletes who implemented nutritional strategies (provided by nutrition professionals) to improve EA and strength training strategies to improve skeletal loading saw lumbar spine BMD improvements. Mean vitamin D levels significantly improved from pre-season (90.6 ± 23.8 nmol/L) to post-season (103.6nmol/L; p=0.0001). Calcium, correct calcium, and alkaline phosphatase had no statistically significant changes between pre-season and post-season (12). Keay et al. have established the prevalence of LEA and poor bone health in cyclists and demonstrated nutrition education efficacy for BMD improvements. Noteworthy findings such as these help to raise awareness in the cycling community and can inform preventative or rehabilitative strategies.

BODY COMPOSITION
Body composition is the distinction between fat mass and fat-free mass. Fat-free mass includes water, tissue, organs, bones, and muscle (e.g., skeletal muscle). Body composition control and maintenance are essential for an athlete’s health, performance, and mindset. Research measurements of body composition include weight, body mass index, body fat percentage, lean mass, and water content. According to Lundy et al. (2022), a body mass index <18.5 kg/m2 is a primary indicator of LEA; this suggests body composition changes in response to LEA (16).
What is the impact of LEA on body composition? Stenqvist et al. (2020) implemented a four-week intensified endurance training designed to increase aerobic performance and elevate body composition’s impact on well-trained cyclists. The results did not show statistically significant changes in energy intake, body weight, fat mass, or fat-free mass. Body weight loss was potentially averted due to reduced resting metabolic rate as a protective mechanism (27). Whereas Stenqvist et al. (2020) focused on increasing EEE, Jurov et al. (2021) attempted to induce LEA via EI manipulation. Jurov et al. (2021) progressively reduced EA by 50% for 14 days in well-trained and elite endurance male athletes; the results showed no significant changes in body mass and fat-free mass (9).
Regarding resistance training and LEA, Murphy and Koehler (2022) conducted a meta-analysis to quantify the discrepancy in lean mass accretion between interventions providing resistance training in an energy deficit and those without an energy deficit. The literature findings demonstrated lean mass gains impairment in athletes resistance training in an energy deficit compared to those training without an energy deficit (significantly, p = 0.02). The results also surmised that an energy deficit of as much as 500kcal/day could impede lean mass gains (21).
Roth et al. (2023) evaluated the impact of a relatively high- versus moderate volume resistance training program on alterations in lean mass during caloric restriction in male weightlifters. The results showed that whole-body lean mass significantly declined in both groups (high and moderate volume groups) following six weeks of energy restriction. The high-volume group had an EA of 31.7 ± 2.8kcal/kg of FFM/day, and the moderate-volume group had an EA of 29.3 ± 4.2kcal/kg of FFM/day (25). Both studies demonstrate that muscle hypertrophy is unattainable in the presence of LEA.
Furthermore, Murphy and Koehler (2020) found that three days of caloric restriction at an EA of 15kcal/kg of FFM/day in recreational weightlifters resulted in significant reductions in weight (p<0.01), fat mass (p<0.01), and lean mass (p<0.001). Also, the total mass loss was significant (p<0.01) when compared to a control group (EA of 40kcal/kg of FFM/day) (20). The results of studies focused on resistance training and caloric restriction hold applicability for athletes in sports that rely on lean mass gains while manipulating EI, such as bodybuilding (4).

CARDIORESPIRATORY ENDURANCE
Cardiorespiratory endurance (CRE) is the ability of the lungs, heart, and blood vessels to deliver sufficient oxygen to cells to meet the physiological demands of exercise and physical activity (8). Evaluating maximal oxygen uptake or VO2max is a standard CRE measure. A VO2 max of 67.9 ± 7.4 mL/kg/min is categorized as a high fitness level (28).
What is the impact of induced LEA on CRE performance outcomes? Jurov et al. (2021) investigated the endurance performance impact of progressively reducing energy availability by 50% for 14 days in well-trained and elite endurance male athletes. The researchers increased EEE to achieve a mean energy availability of 17.3 ± 5 kcal/kg of FFM/day. The results showed lowered EA reduced endurance performance, as indicated by respiratory compensation point (RC) and VO2max. Jurov et al. (2022b) reduced EA by 25% (by increasing EEE and controlling EI) in trained endurance male athletes and monitored for aerobic performance changes. The results showed that inducing LEA by 25% (mean EA of 22.4 ± 6.3kcal/kg of FFM/day) for 14 days reduced hemoglobin levels, indirectly impacting VO2max and aerobic performance (11). Beyond research conducted by Dr. Iva Jurov and colleagues, there is insufficient experimental research on LEA and CRE.

MUSCULAR STRENGTH AND ENDURANCE
In recent years, few experimental studies have evaluated the impact of LEA on muscular strength, endurance, and athletic performance. Research on athletic performance and LEA has shown that endurance athletes with an EA of 17.3 ± 5 kcal/kg of FFM/day show no reductions in agility t-tests, power output, or countermovement jump results, indicating no association with EA (9). Also, Jurov et al. (2022b) found that a mean EA of 22.4 +/- 6.3kcal/kg of FFM/day in endurance male athletes for 14 days results in significant changes to explosive power (countermovement jump) but not agility t-tests (11).
Furthermore, Jurov et al. (2022a) also reduced EA (via increasing exercise energy expenditure and controlling energy intake) in male endurance athletes to evaluate performance and muscular power impact. The results showed significant reductions in explosive power (measured via vertical jump height test) at a mean EA of 22.4, 17.3, and 8.82 kcal/kg of FFM/day. Based on these findings, athletes reach the LEA threshold after a long time in an energy-deficient state, such as ten to 14 days (10).
However, Stenqvist et al. (2020) aimed to measure peak power in male cyclists after four weeks of intensified endurance training. The results showed that the cyclists significantly improved their peak power output (4.8%, p < 0.001) and functional threshold power (6.5%, p < 0.001) measured via stationary bike. Possibly, the EEE of the intervention was insufficient to induce LEA but instead induced the Specific Adaptation to Imposed Demands (SAID) principle in the athletes (27).
Regarding weightlifters, Murphy and Koehler (2022) studied whether energy deficiency impairs strength gains in response to resistance training. This research study was a meta-analysis of randomized controlled trials. The study findings showed that strength gains were comparable between resistance training groups in either an energy deficit or a balance state. These results demonstrated that low energy availability for prolonged periods (i.e., RED-S) did not impede strength output (21). There are a few studies that report bodybuilders with strength declines with estimations of EA <20 kcal/kg of FFM/day (4). The theory remains that inadequate energy intake will inevitably reduce muscular strength and output.

LOW ENERGY AVAILABILITY THRESHOLD
To date, optimal EA levels and the threshold for LEA in male athletes are under investigation. However, many research studies are cross-sectional, only demonstrating a correlation between athletes and energy availability (e.g., LEA commonly found in endurance athletes). The scant number of current experimental studies often fail to induce LEA and thereby fail to establish clear LEA thresholds.
To prevent LEA and subsequent conditions such as RED-S and MAT, athletes need to maintain their energy availability. Primarily, athletes need to ensure adequate EI and carefully manage their EEE. Current EA “zones” for female athletes are also applied to male athletes until experimental research can demonstrate a need for separate guidelines. EA >45kcal/kg of FFM/day supports body mass gain and maintains healthy physiological functions; 45kcal/kg of FFM/day is optimal for weight maintenance and healthy physiological functions; 30-45kcal/kg of FFM/day is considered suboptimal and at-risk for reduced physiological functions; and ≤30kcal/kg of FFM/day is considered low energy availability (1, 3, 4, 9, 10, 14, 17, 26).
Research by Jurov and colleagues has demonstrated mixed results regarding performance outcomes, body composition, and bone health (9, 10, 11). Mean energy availability in those studies ranged between 17-22 kcal/kg of FFM/day (9, 11). Based on their research findings, Jurov and colleagues have proposed a range of 9-25kcal/kg of FFM/day (mean value of 17kcal/kg of FFM/day) for an LEA threshold (10).
Regarding performance and body composition outcomes, Murphy and Koehler (2020) conducted a randomized, single-blind, repeated-measures crossover trial that showed three days of caloric restriction at an EA of 15kcal/kg of FFM/day induced considerable anabolic resistance to a heavy resistance training bout (20).
In a case study by Langan-Evans et al. (2021), an EA of 20kcal/kg per FFM/day led to weight loss and fat loss without signs of MAT and RED-S. However, an EA of <10kcal/kg of FFM/day did result in signs and symptoms of MAT and RED-S, including disruptions to the hypothalamic-pituitary-gonadal axis, resting metabolic rate (measured), and resting metabolic rate (ratio) (14). Additionally, some LEA thresholds may need to be sport-specific. For instance, Fagerberg et al. (2018) suggest an LEA threshold of 20-25kcal/kg of FFM/day for male bodybuilders with a lower body fat percentage (4). Research to establish EA zones and an LEA threshold for male athletes continues, and guidelines primarily still consider ≤30kcal/kg of FFM/day appropriate for male athletes. However, some researchers have also contested that male athletes can go lower before exhibiting signs and symptoms of MAT and RED-S.

RESEARCH GAPS
There are sizable research gaps regarding LEA and RED-S. First, this literature was unable to address the impact of LEA on endocrine, metabolic, hematological, and gastrointestinal health due to insufficient research published in the past five years. Mountjoy et al. (2018) identified the following research gaps: (1) lack of practical tools to measure and detect LEA and RED-S, (2) lack of validated prevention interventions for RED-S, (3) RED-s in male athlete research, (4) health and performance consequences of RED-S research, and (5) lack of evidence-based guidelines for treatment and return-to-play for athletes with RED-S. Research gaps focused on male athletes with MAT are even more prominent (19).

Moreover, Fredericson et al. (2021) listed several research gaps that need scientific attention, including screening protocols to detect MAT in adolescent and young males, identification of MAT energetic and metabolic impact factors, prevalence of DEED in male athletes with MAT, evaluating the efficacy and effectiveness of clearance and return-to-play protocols, risk assessment for BSI and poor bone health, prevalence of MAT in military recruits, health interventions on the prevention and treatment of MAT, and lastly, cutoff values (or threshold) for LEA (5). Addressing these research gaps would enable sports and health practitioners to effectively prevent and treat LEA, RED-S, and MAT, ensuring athlete health and sports performance.

SUMMARY
LEA is defined as a physiological state when there is inadequate energy to meet the demands placed on the body, often through physical activity, exercise, or sports (23). LEA can impact any athlete engaged in a sport with low energy intake or excessive energy expenditure. LEA is a precursor to the onset of both The Male Athlete Triad (MAT) and Relative Energy Deficiency in Sport (RED-S), two conditions that result in weakened physiological functions, with the former focused on reproductive and bone health decline (22).

Recent literature has shown mixed results on LEA’s impact on immunological health, metabolic markers, bone health, body composition, cardiorespiratory endurance, and muscular strength and endurance. There has been little evidence to connect LEA and endocrine, metabolic, hematological, and gastrointestinal health. However, a notable causal relationship exists between LEA and psychological health and reproductive health. Currently, there is still no defined low energy availability threshold specific to male athletes, however, EA zones from 15-25kcal/kg of FFM/day may be appropriate based on current literature (4, 20, 10, 18, 22, 26).

APPLICATION TO SPORT
Healthy nutritional practices are essential to sports performance. Interdisciplinary sports performance teams must collaborate with nutrition professionals such as Registered Dietitians accredited by the Commission on Dietetic Registration to develop effective LEA prevention, screening, and intervention protocols. Preventative measures must prioritize energy availability, modify sporting culture to encourage energy intake, and mitigate barriers to calorie- and nutrient-dense foods in male athletes. Screening protocols must include EA evaluations based on dietary intake, exercise energy expenditure, and fat-free mass measured via DXA or bioelectrical impedance analysis. Male athletes with an EA ≤20-25kcal/kg of FFM/day must receive nutritional guidance to reduce health and performance impairments. Intervention protocols must be enacted when LEA is confirmed and should primarily focus on increasing energy intake, decreasing energy expenditure, and addressing other associated aspects such as psychological health. Athletes, coaches, and practitioners must raise LEA awareness, dispel energy consumption stigmas, and foster an environment where food and nutrition fuel peak performance.

ACKNOWLEDGEMENTS
This work was supported by the Pennsylvania Western University Department of Exercise, Health, and Sport Sciences. The author would like to thank Dr. Marc Federico and Dr. Brian Oddi for their guidance and feedback on the manuscript

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