Low energy availability and REDs in combat sports

What REDs is

The consensus gives two formulations. The first is the summary:

REDs is a clinically diagnosed, multifactorial syndrome characterised by the accumulation of the deleterious health and performance outcomes resulting from exposure to problematic LEA.

The second is the formal 2023 definition:

a syndrome of impaired physiological 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 haematological health, which can all individually and synergistically lead to impaired well-being, increased injury risk and decreased sports performance.

Several things in that definition deserve to be read rather than skimmed.

"Clinically diagnosed." This is not something an athlete determines from a calculator. The consensus develops a clinical assessment tool for physicians, and the diagnosis depends on indicators measured rather than symptoms recognised.

"Female and male athletes." The 2014 framework grew out of research on the female athlete triad and the acronym changed from RED-S to REDs partly to move away from a female-specific framing. The consensus is explicit that males are affected and that the research covering them is thin.

"Problematic (prolonged and/or severe)." Two dimensions, not one. A brief, moderate energy deficit is not the same exposure as a sustained one, and the definition builds that in.

"Accumulation." REDs is what happens after exposure, not during a single week. It is a chronic condition, which is exactly why a sport organised around repeated fight camps is a plausible setting for it.

The formula, and its denominator

Energy availability is the energy left for everything other than exercise:

EA = (EI [Energy Intake, kcal] − EEE [Exercise Energy Expenditure, kcal]) ÷ FFM [Fat-Free Mass, kg] per day

Take what you ate, subtract what the training cost, divide by your fat-free mass. The result is the energy per kilogram of metabolically active tissue available to run everything else: immune function, bone remodelling, hormone production, digestion, thinking, healing.

The denominator being fat-free mass rather than body weight is deliberate and consequential. Fat-free mass is what is doing the metabolic work; adipose tissue is largely a store. Two athletes at the same body weight with different body composition have different denominators, and the same intake and training produce different energy availability figures.

That also means the calculation requires a body-composition measurement to be meaningful — one of several reasons the consensus is cautious about the number's use in the field.

The consensus offers a set of descriptive ranges: high energy availability for mass gain and growth at 45 kcal/kg FFM/day or above; approximately 45 kcal/kg FFM/day for body function; reduced energy availability for body mass and fat loss in the range of 30–45 kcal/kg FFM/day; and energy availability causing health implications at or below 30 kcal/kg FFM/day.

Those are useful orientation. What follows is why they should not be treated as diagnostic boundaries.

The number everyone quotes

Here is the passage that should accompany the 30 kcal/kg figure every time it is repeated, and almost never does:

The concept of the LEA threshold (30 kcal/kg FFM/day), below which health problems occurred, was based on elegant but short-term laboratory studies that investigated stepwise changes in EA, perturbations of sex hormones and changes in markers of bone turnover in a small sample of sedentary females. Although this concept was intended as a guide, rather than a diagnostic end-point, more recent information gleaned from real-life clinical observations, as well as short-term studies, theoretical constructs and methodological challenges in assessment, around the frailty of a single, universal threshold, have identified large differences in the EA level associated with health and performance concerns between individuals, the sexes, and among different body systems.

And the conclusion it draws:

Therefore, although EA calculations may inform research interventions or observations, there are risks in setting a definitive clinical threshold of EA due to many moderating factors.

Read what that is conceding. The threshold came from short-term studies in a small sample of sedentary females. It was intended as a guide. Real-world observation has found large differences between individuals, between the sexes, and — importantly — between body systems, meaning that the level at which bone health suffers may not be the level at which reproductive function or immunity does.

This is what intellectual honesty looks like in a consensus document, and it is the single most useful thing in the paper. A number carried into popular usage as a diagnostic line is described by its own custodians as a research heuristic with known frailty.

The situation where this stops being academic is an injury mid-camp, because the requirement rises exactly as the training that justified the intake disappears. That collision is worked through in what an injury does to a weight cut.

The practical consequence for a fighter is not that the figure is useless. It is that "I calculated 28 and I am fine" and "I calculated 32 so I am safe" are both misuses of it. The threshold is a prompt to ask a question, not an answer to one.

Males, and the size of the gap

The consensus does not soften the state of the evidence on male athletes:

While a universal cut-off of 30 kcal/kg FFM/day as a threshold of LEA leading to some REDs outcomes in females is debated, such a cut-off or range at which males experience REDs-related symptoms is even less understood, but appears to be lower (eg, ~9 to 25 kcal/kg FFM/day). Indeed, there is evidence that most males can sustain a lower EA before physiological [disruption].

And on the literature itself: although the research community has emphasised the need for studies in men, only about 20% of original studies from 2018 to 2022 include male athletes as subjects. Of the roughly 178 REDs and low-energy-availability publications since 2018, covering approximately 23,822 participants, around 80% of participants were female, and about 62% of the studies used a cross-sectional design.

Three consequences for combat sports, where the professional population skews male.

The threshold most likely to be quoted at a male fighter is one derived in females. The range that may actually apply to him — roughly 9 to 25 kcal/kg FFM/day — is both lower and described by the consensus as much less well understood. And a research base that is 80% female and 62% cross-sectional is not in a position to give a male athlete a precise personal figure at all.

None of that means male fighters are not affected. The consensus's whole point in raising it is that they are and that the evidence has not caught up. It means the honest answer to "what is my number" is currently "there is not one that has been established for you."

Why combat sports are the high-risk category

The consensus identifies body composition management as particularly important — and particularly fraught — in "weight-sensitive and leanness-demanding sports", noting that athletes may experience internal or external pressure to attain an athletic look, potentially leading to body dissatisfaction, low energy availability, and then to REDs symptoms, disordered eating behaviours or eating disorders. It flags this as of particular concern for young athletes because of potentially long-lasting physical and psychological outcomes.

Combat sports sit in that category, and they arrive at it by a route that deserves distinguishing from the aesthetic sports.

In gymnastics or dance the pressure is largely about appearance. In combat sports it is about a rule. A division is a hard boundary with a legal consequence, and the competitive logic of being at the bottom of one is explicit rather than implied. Nobody has to tell a fighter they should be lean. The weigh-in tells them.

Four features of the sport compound it:

Repeated camps. An athlete fighting three or four times a year spends much of the year in a descent, with the recovery periods between them shorter than the deficits.

Enormous exercise energy expenditure. Combat training combines high-volume conditioning with technical work and sparring. A large EEE term makes the numerator of the energy availability equation smaller for any given intake.

Descents that treat food as the lever. Because the rules set the target and the training is not negotiable, intake is the variable that moves. That is the direct route to a low numerator.

And a culture that reads under-fuelling as professionalism. Being hungry in fight week is normalised to the point of not being counted as a symptom, which is precisely the condition under which a chronic problem stays invisible.

The relationship between camp structure and fuelling is the whole subject of fight camp nutrition, week by week, and the macronutrient floors in the combat-sport position stand exist because descents routinely go below them.

Adaptable versus problematic

One of the 2023 update's substantive changes is the insistence that low energy availability is not uniformly harmful.

The consensus's models distinguish adaptable from problematic exposure, and describe LEA as existing on a spectrum. Short, moderate reductions in energy availability are a normal part of periodised body-composition management and produce adaptations rather than pathology. Prolonged or severe exposure is what accumulates into the syndrome.

That framing is genuinely useful for a sport in which every athlete is periodically in a deficit. It means the question is not "am I ever in low energy availability" — most competitive fighters will be, deliberately, in the run-up to a weigh-in. It is whether the exposure is bounded in time and magnitude, and whether it is followed by genuine restoration.

Which turns the practical concern into a calendar question. An eight-week camp with a controlled deficit and a real off-season is a different exposure from four camps a year with three weeks between them and a walking-around weight that never recovers. The consensus's own emphasis on off-camp weight has a parallel in the combat-sport nutrition literature, which puts habitual weight at 12–15% above the division for exactly this reason — a fighter living close to their division has no room to descend without going somewhere they should not.

A worked scenario, and what the arithmetic exposes

Take a hypothetical 77 kg fighter at approximately 12% body fat, so about 67.8 kg of fat-free mass, six weeks out from a bout and training twice most days.

Suppose the training costs 900 kcal on an average day — a figure chosen for illustration, since exercise energy expenditure is one of the hardest terms in this equation to establish, and one an athlete's watch is not measuring accurately.

To sit at approximately 45 kcal/kg fat-free mass per day, the level the consensus associates with body function, this athlete needs energy availability of about 3,050 kcal, and therefore an intake of about 3,950 kcal. To sit at 30 kcal/kg FFM/day — the bottom of the reduced-availability band the consensus associates with body mass and fat loss — they need availability of about 2,034 kcal and an intake of about 2,934 kcal.

Two things fall out of that arithmetic, and both are more useful than the numbers themselves.

The intake required to stay out of the low band is larger than most fighters assume. Nearly three thousand kilocalories, in this scenario, is the floor of the band the consensus describes as reduced availability for body-composition change. An athlete eating 2,200 kcal through a hard camp — an intake that would strike many people in this sport as disciplined rather than alarming — would be at roughly 19 kcal/kg FFM/day.

And every term in it is uncertain. The exercise expenditure figure is an estimate. Self-reported intake reliably runs low. Body composition needs measuring. The consensus's caution about the burden of measuring energy availability in free-living athletes is not academic modesty; it is a description of why an athlete cannot resolve this with arithmetic alone.

This is a worked example on published ranges for a hypothetical athlete, not a prescription, and none of your variables are in it.

How it is diagnosed

The 2023 statement introduces the REDs Clinical Assessment Tool version 2 (CAT2), a severity and risk stratification with four categories rather than the three-colour system used previously: healthy (green), mild (yellow), moderate (orange) and severe (red).

The tool works on accumulated indicators rather than a single measure. Primary indicators are counted, with severe primary indicators counting as two, and the resulting stratification carries associated training and competition recommendations. The consensus notes that the earlier yellow zone had an extensive clinical severity/risk range, which the four-category system is intended to resolve.

The indicators span the body systems named in the definition, and include measures such as reduced or low resting metabolic rate — the document lists an RMR below 30 kcal/kg FFM/day or an RMR ratio below 0.90 among them.

Two things follow. This is a clinician's instrument, applied by a physician-led team of REDs health and performance experts, and it is not something to self-administer. And the categorisation drives real decisions about training and competition participation, in the context of decision modifiers such as the athlete's performance level.

If you recognise yourself in this article, the correct next step is a physician and a registered dietitian, not a spreadsheet.

It is worth noting how the consensus was built, because it tells you what kind of document it is. The panel put 135 evidence statements to a first round of confidential voting, reaching full agreement on 76 of them, then a second round of 44 statements, of which 24 were revotes on items that had produced disagreement. The final document rests on 144 statements, and 27 of those retained a minority disagreement — meaning at least 80% agreement was reached but one or more of the seventeen authors still dissented. A consensus statement that publishes its own dissent rate is telling you which of its claims are settled and which are the field's current best judgement, and that is worth more than a document that reads as though everything in it were equally certain.

Measuring energy availability is hard, and what to watch instead

The consensus is direct about the practical obstacle:

Unfortunately, the measurement of EA in free-living athletes is challenged by a high level of burden (eg, time, effort)…

Getting a real number requires accurately measured energy intake — which self-report reliably underestimates — accurately quantified exercise energy expenditure, and a body-composition measurement for the denominator. Each of those carries error, and the errors compound.

The consensus calls for standardised methodologies to improve this. In the meantime, a fighter is better served by watching the things that are actually measurable and that change when energy availability has been low for too long:

Body mass trend across months, not days. A walking-around weight that keeps drifting down between camps is information.

Training quality that no longer responds to rest. Performance decrement is one of the named outcomes and it is the one athletes notice first.

Injuries that recur, and bone injuries in particular. Musculoskeletal health is in the definition. What repeated camps do to a skeleton over years — and the awkward fact that nobody has ever counted cuts against bone in any combat sport — is taken up in bone health in combat athletes.

Sleep and mood. Psychological functioning is explicitly part of the syndrome, not a side-effect of it.

And in female athletes, menstrual function. Reproductive function is among the named outcomes and disruption is a clinical sign, not an inconvenience or a normal consequence of hard training. The link runs through chronic energy availability rather than any single fight-week cut, a distinction covered in more depth in menstrual cycle and weight cutting.

None of these diagnose anything. They are reasons to have the conversation with someone who can.

Where this sits alongside the weight cut

The two problems are related and they are not the same problem, and conflating them muddles both.

Acute weight loss is a fight-week fluid manipulation with its own literature, its own supervision requirement and its own risks. It is measured in hours and percentages of body mass.

Low energy availability is a chronic energy state measured in weeks and months. An athlete can execute a disciplined acute cut while chronically well-fuelled, and an athlete can be in a serious energy deficit for a year without ever doing anything dramatic in a sauna.

What links them is that the same competitive pressure produces both, and that the first is much harder to do safely when the second is present. A fighter arriving at fight week already depleted has less to give and less capacity to recover — which is one more reason the graded figures in how much weight you can cut before a fight assume an athlete who has been eating.

What we could not verify

• Any prevalence figure for REDs in combat sports specifically. We did not locate one, and we will not estimate. The consensus notes REDs is common in male and female athletes across many sports and that awareness remains low; that is not a prevalence rate for fighters.
• A threshold applicable to a male combat athlete. The consensus gives ~9–25 kcal/kg FFM/day as the region where males appear to experience symptoms and describes it as much less well understood. That is a range from a thin literature, not a figure to plan against.
• The complete REDs CAT2 indicator set. We describe the tool's structure — four severity categories, primary indicators, severe indicators counting double, physician-led application — from the consensus text. The full scoring tables belong in the paper and in a clinician's hands.
• The 30 kcal/kg threshold's underlying studies. We report the consensus's own characterisation of them: short-term, laboratory-based, a small sample of sedentary females. We did not read those primary studies.
• Nothing here is specific to you. REDs is a clinical diagnosis made by a physician-led team using measured indicators. This article is a description of a framework, not an assessment of anyone.

Sources

Sourced to

1. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs) — Mountjoy M, Ackerman KE, Bailey DM, Burke LM, Constantini N, Hackney AC, Heikura IA, Melin A, Pensgaard AM, Stellingwerff T, Sundgot-Borgen JK, Torstveit MK, Jacobsen AU, Verhagen E, Budgett R, Engebretsen L, Erdener U, British Journal of Sports Medicine, 2023;57(17):1073–1097. DOI 10.1136/bjsports-2023-106994
2. 2023 IOC consensus statement on REDs (full PDF) — International Olympic Committee, hosted copy of the British Journal of Sports Medicine consensus statement
3. IOC publishes new Consensus Statement on Relative Energy Deficiency in Sport (REDs) to protect athlete health — International Olympic Committee, announcement of the 2023 statement
4. International society of sports nutrition position stand: nutrition and weight cut strategies for mixed martial arts and other combat sports — Ricci AA et al., Journal of the International Society of Sports Nutrition, 2025;22(1):2467909. DOI 10.1080/15502783.2025.2467909, PMID 40059405
5. International Society of Sports Nutrition Position Stand: protein and exercise — Jäger R, Kerksick CM, Campbell BI et al., Journal of the International Society of Sports Nutrition, 2017;14:20. DOI 10.1186/s12970-017-0177-8, PMID 28642676
6. A Systematic Review of Dietary Protein During Caloric Restriction in Resistance Trained Lean Athletes: A Case for Higher Intakes — Helms ER, Zinn C, Rowlands DS, Brown SR, International Journal of Sport Nutrition and Exercise Metabolism, 2014;24(2):127–138
7. Does Relative Energy Deficiency in Sport (REDs) Syndrome Exist? — a published critical examination of the REDs construct, included because the framework is contested in parts of the literature
8. How to minimise the health risks to athletes who compete in weight-sensitive sports: review and position statement on behalf of the ad hoc research working group on body composition, health and performance, under the auspices of the IOC Medical Commission — Sundgot-Borgen J, Meyer NL, Lohman TG et al., British Journal of Sports Medicine, 2013;47:1012–1022
9. An alternative structured weight management protocol to rapid weight loss in mixed martial arts: a prospective interventional study — Maurício CA et al., Frontiers in Nutrition, 8 October 2025;12:1581698. DOI 10.3389/fnut.2025.1581698, PMID 41132567
10. Effect of Dietary Protein on Fat-Free Mass in Energy Restricted, Resistance-Trained Individuals: An Updated Systematic Review With Meta-Regression — Refalo MC, Trexler ET, Helms ER, Strength and Conditioning Journal, January 2025. DOI 10.1519/SSC.0000000000000888

Read next