Under-Fuelled, Not Undertrained: Low Energy Availability in Age-Group Triathletes (Including Men)

You are doing the sessions. The consistency is there, week after week, and yet the fitness is not showing up the way it should - recovery feels harder than it used to, small niggles keep flaring, and races that should be within reach feel just out of grip. The usual response is to assume a discipline problem: train harder, sleep more, grind through it. For a meaningful number of age-group triathletes, the actual explanation is close to the opposite. The body is not getting enough fuel to support both the training load and normal physiological function, a state sports science calls low energy availability (LEA), and its downstream effects are known as Relative Energy Deficiency in Sport (REDs).

This article is not about weight, calories, or body composition. It will not give you a number to hit or a target to chase. It is about recognising a pattern - performance and health warning signs that show up when training output has outpaced fuelling input for long enough - and knowing when that pattern warrants a conversation with a professional rather than another block of harder training. It also matters for a group frequently left out of this conversation entirely: men. LEA and REDs are not female-only issues, and treating them that way leaves a meaningful share of affected athletes without a reason to look further.

What low energy availability and REDs actually are

Energy availability is the energy left over for normal body functions - hormonal regulation, bone maintenance, immune function, reproductive function - after the energy cost of exercise is subtracted from what you eat. When that leftover amount is too low for too long, the body starts deprioritising "non-essential" functions to protect basic survival, and REDs is the resulting collection of health and performance consequences.

The 2023 International Olympic Committee consensus statement on REDs describes exactly the conditions that make endurance sport a high-risk setting: training volumes that can exceed 30 hours a week in some endurance disciplines, and exercise energy expenditure that can outpace the gut's capacity to absorb and use energy even when an athlete is trying to eat enough (BJSM, 2023). Add in a sport culture that often equates lighter with faster, and age-group triathlon - with its long training hours squeezed around work and family life, and its three-discipline energy demands - sits squarely inside that risk profile.

What the evidence actually says

The scale of the problem in real endurance athletes

A 2025 cross-sectional study of 55 UK endurance athletes - just over half of them triathletes, roughly evenly split between national age-group standard and recreational level - found that 77% of the female athletes screened at risk of low energy availability using the LEAF-Q screening tool. Strikingly, the same study found that 31% of the male athletes had low lumbar bone mineral density, a finding that undercuts the assumption that this is purely a female health issue (JISSN, 2025).

A separate 2025 study looked specifically at 20 top-performing female amateur triathletes training around 11 hours a week and found that 30% scored at or above the at-risk threshold on the LEAF-Q, 50% reported at least one symptom associated with low energy availability, and 80% were assessed to be in an energy deficit at the time of testing (Nutrients, 2025). These are small samples, and they cannot tell us the true population prevalence among all age-group triathletes - but the direction and consistency of the numbers, across different athlete groups and different studies, is hard to dismiss as noise.

Low awareness compounds the problem

A 2025 review of REDs in ultra-endurance sport documents high rates of menstrual irregularity, bone stress injury and disordered-eating risk across endurance cohorts, alongside strikingly low awareness of the condition itself: in one cited sample of 306 female ultrarunners, 92.5% had never heard of the Female Athlete Triad, an earlier framework closely related to REDs (PMC, 2025). If elite-adjacent, highly engaged endurance athletes are largely unaware this condition exists, it is reasonable to assume most recreational triathletes are too - which matters because it means symptoms often get reframed as "just needing to train smarter" or "just getting older" rather than investigated as a fuelling problem.

Screening tools are useful for awareness, not diagnosis

Tools like the LEAF-Q (Low Energy Availability in Females Questionnaire) and its male-oriented counterpart, LEAM-Q, are screening instruments, not diagnostic tests. A 2026 review on rethinking energy availability points out that prevalence estimates vary enormously depending on the screening instrument and population used, that key triathlon-specific studies are small and cross-sectional and cannot establish cause and effect, and - importantly for this article's inclusion of men - that male thresholds for these tools are far less well established than female ones (PMC, 2026). A broader 2020 review of LEA in athletes reports prevalence estimates ranging from roughly 22% to 58% depending on the sport and screening method used (PMC, 2020), underscoring just how much these numbers move around by methodology. The honest summary: the direction of the evidence is consistent and concerning, the precise scale of the problem in age-group triathlon specifically is not settled, and no questionnaire result should be treated as a diagnosis.

Why this is not a women-only issue

REDs has historically been framed, researched and discussed almost entirely around female athletes, largely because menstrual cycle disruption is one of its most visible markers. That framing has left male athletes under-screened and under-recognised. The 31% low bone mineral density figure among male athletes in the UK endurance cohort above is a direct data point against the female-only assumption (JISSN, 2025), and the broader REDs literature increasingly recognises that men can experience reduced testosterone, impaired bone health, poor recovery and performance stagnation from chronic under-fuelling, even without the menstrual signal that often prompts female athletes (or their coaches) to ask questions (Triathlon Magazine Canada). Practically, this means male age-groupers experiencing unexplained performance decline, recurrent stress fractures or persistent fatigue deserve the same consideration of under-fuelling as female athletes with the same symptoms - not a default assumption that it "can't be that" because they are men.

Why this shows up as a performance problem, not just a health one

It is easy to file this under "health topic" and assume it does not apply if you feel broadly fine and are still finishing races. The IOC consensus statement frames REDs explicitly as a performance issue as well as a health one: the same energy shortfall that affects bone, hormonal and immune function also impairs training adaptation, glycogen replenishment, and recovery between sessions (BJSM, 2023). That is precisely why the practical hook for age-groupers is not a health checklist read in isolation, but the training-log pattern of doing the work and not getting the expected return - because impaired adaptation is one of the first things to happen, often well before more obvious health markers change.

This is also why the standard age-group response to a plateau - add more sessions, add more intensity, sleep more, and otherwise just try harder - so often fails to fix the problem and can make it worse. If the limiting factor is fuel available for adaptation and repair rather than training stimulus, additional stimulus without additional fuel simply widens the shortfall.

Practical application: the pattern to watch for

None of this article is asking you to track calories, weigh food, or judge your body composition. The useful, evidence-aligned approach is pattern recognition across your training and how you feel, sustained over weeks and months rather than a single bad session. The core reframe worth carrying into your own training log is this: if training isn't producing the gains you would expect given consistent effort, chronic under-fuelling - not a lack of discipline or toughness - may be a meaningful part of the reason.

Warning signs worth taking seriously, especially in combination rather than isolation, include persistent fatigue that does not improve with normal recovery, recurrent illness or a string of minor infections, stress fractures or bone stress injuries, changes to the menstrual cycle (including missed or irregular periods, which should never be dismissed as simply "training hard"), reduced libido, disturbed sleep, mood changes, and - the one most likely to actually get an age-grouper's attention - a training response that has plateaued or reversed despite training volume and consistency staying the same or increasing.

• Persistent fatigue that does not resolve with a normal rest day or easy week.
• Frequent minor illness or infections that keep interrupting training blocks.
• Stress fractures or other bone stress injuries, especially recurrent ones.
• Menstrual cycle changes, including missed or irregular periods - never a sign to normalise as just training hard.
• Poor recovery between sessions despite what looks like adequate sleep.
• Reduced libido, low mood, or disturbed sleep alongside training fatigue.
• A stalled or declining training or race performance despite consistent, sustained effort.

Common mistakes

The most common mistake is assuming this only applies to female athletes, or only to elite and highly lean athletes. The evidence above directly contradicts both assumptions - a meaningful share of male athletes showed low bone mineral density in the same study where female athletes screened at risk of low energy availability (JISSN, 2025), and the studied triathletes were amateurs training roughly 11 hours a week, not full-time professionals (Nutrients, 2025).

The second common mistake is responding to a training plateau by adding more volume or intensity, on the assumption that stalled progress means insufficient stimulus. If under-fuelling is the actual driver, more training load only widens the gap between energy expenditure and intake, and can make symptoms worse rather than better.

The third, and most important to state plainly: pursuing "race weight" through extreme dietary restriction is not a safe workaround, and it is one of the more common pathways into low energy availability in the first place. Deliberately under-fuelling to hit a body weight or leanness target - even short-term, even close to a big race - runs directly counter to everything the evidence above describes, and should not be treated as a legitimate performance strategy.

A fourth mistake is treating a LEAF-Q or similar questionnaire score as a diagnosis rather than a prompt to seek professional input. These tools are useful for raising awareness, but their accuracy varies by sport, sex and individual characteristics, and they are explicitly not designed to replace clinical assessment (PMC, 2026).

How to apply this week

This week, rather than adjusting anything about what or how much you eat, simply take stock. Look honestly at the last two to three months: has training output matched training input? Have you had more minor illnesses than usual? Any bone pain, stress reactions, or a menstrual cycle that has changed? Is recovery between hard sessions taking noticeably longer than it used to, even with what looks like enough sleep?

If two or more of the warning signs above have been present for several weeks or longer, the useful next step is a conversation - with a GP or sports physician, and ideally a registered sports dietitian - rather than a change of training plan alone. Bring your training log and an honest account of your symptoms; you do not need to arrive with a self-diagnosis or a calorie count. If nothing on the list above resonates, this article is simply a reference point to keep in mind if things change, not a signal to start scrutinising your eating.

It is also worth being clear about what a useful conversation with a professional looks like, since the idea of "seeking help" can feel vague. A sports physician can assess for the physical markers associated with REDs - bone health, hormonal signs, blood markers of iron and thyroid function - and rule out other explanations for the same symptoms. A registered sports dietitian can look at the balance between your training demands and your actual eating pattern over a typical week, without you needing to arrive with your own analysis or a calorie count already worked out. Neither conversation requires you to have already decided what is wrong; describing the pattern of symptoms and training response is enough to start.

References

• 2023 International Olympic Committee's consensus statement on Relative Energy Deficiency in Sport (REDs) (BJSM)
• Assessing the risk of low energy availability, bone mineral density and body composition in endurance athletes (Journal of the International Society of Sports Nutrition, 2025)
• A Preliminary Study of Nutrients Related to the Risk of RED-S in Top-Performing Female Amateur Triathletes (Nutrients, 2025)
• Exploring the presentation of REDs in ultra-endurance sport (PMC, 2025)
• Rethinking Energy Availability: from conceptual models to screening limitations (PMC, 2026)
• Low Energy Availability in Athletes 2020: prevalence estimates (PMC)
• RED-S: What's That? (Triathlon Magazine Canada)