Warning: this article contains discussion of eating disorders

"If you keep this up, you will be in a wheelchair at 30."

That warning came from physicians to British long-distance runner Jake Smith four years earlier.

Outwardly his professional path appeared successful.

At age 23 he secured a Nike sponsorship deal and competed for Great Britain internationally.

Yet internally his physique was breaking down through repeated bouts of racing then illness then injury.

Combining heavy training loads with irregular eating left the 28-year-old returning from a Uganda camp at just eight stone (51kg) while standing 5ft 5in (1.7m) tall. His bones had become fragile enough that doctors warned his running days might end.

Following two stress fractures within four months Smith sought specialist support and received a REDs diagnosis - relative energy deficiency in sport.

The syndrome can strike any athlete and when missed or ignored it harms results while triggering lasting medical complications.

Effects receive more attention among women. Tennis player Emma Navarro recently disclosed her own case and a break from events until 2027.

Men face equal risks yet stigma plus fewer visible signals allow the issue to persist unnoticed so many endure it alone like Smith.

BBC Sport outlines the condition its influence on both sexes and the reasons it stays under-recognised despite its frequency and seriousness.

REDs produces bone stress reactions sleep disturbance tiredness and depressed mood. Without treatment it risks osteoporosis heart disease and reproductive problems.

Dr Nicky Keay a hormone specialist notes many effects trace to hormone imbalance from low energy supply.

"Hormones reach every part of the body. When they function poorly the effects appear across multiple systems" she explains.

"Healthy hormones require regular fuel. An energy shortfall often slows or halts certain hormone pathways."

Women gain a monthly indicator through their cycle which Keay calls a free medical check.

In simple terms REDs turns periods off she states.

Men experience quieter changes as testosterone falls leading to lower drive and tiredness.

The menstrual link led to the original label female athlete triad in the 1990s.

The International Olympic Committee renamed it in 2014 to cover wider energy-shortage effects and male athletes too.

"We had overlooked half the population" Keay observes.

"Usually women's health receives less focus yet here men lacked recognition."

Twelve years on research confirms high rates among men.

A meta-analysis in Sports Medicine last year reviewed thousands of elite and recreational athletes worldwide and found low energy availability in 44.2 percent of females and 49.4 percent of males.

Why does REDs occur so often?

Part of the answer rests in the belief that lighter means faster.

Endurance running cycling climbing dance and aesthetic events long accepted this idea.

Smith traces his difficulties to that mindset.

"I accepted it for years and saw it as the route ahead" he recalls.

"I wondered whether dropping weight would shave 10 seconds off my half marathon. Then my thinking spiralled."

At first the approach may succeed.

The body evolved to favour movement over storage when energy runs low so athletes can lose weight yet still train and post strong times.

Eventually reserves deplete.

Keay labels this fool's gold because performance then falls and injury risk rises sharply.

Olympic and world champion triathlete Jonny Brownlee admits under-fuelling contributed to major injuries in his career.

"I failed to grasp its importance. Training came first and education on fuelling was lacking" he tells BBC Sport.

"Culturally you looked weak if you ate on the bike. The result was injuries slower recovery stress responses and stress fractures plus reduced race performance."

Brownlee who recently retired says the culture around on-bike nutrition has improved yet stigma around REDs persists especially the view it is mainly a female concern.

"Women show clearer signs but in men it can stay hidden until a serious injury appears" he notes.

"Stigma delays recognition and men hesitate to discuss under-fuelling because they feel they should manage it themselves."

Those attitudes led Keay to run a 2019 study on 50 male competitive cyclists.

Initial checks showed nearly half had weak bones and a quarter had REDs.

She split them into groups. One continued unchanged while the other received nutrition and training guidance over six months.

"The unchanged group lost more bone density like astronauts in space and underperformed relative to expectations" she reports.

"The guided group gained bone health and posted strong race results."

She concludes REDs exists widely among male cyclists and insufficient fuelling leads to poorer outcomes. Recovery is possible but inaction brings decline.

Because awareness remains low many struggle to locate support.

Former GB runner Pippa Woolven founded Project REDs after her own experience offering guidance for athletes coaches parents and clinicians.

Keay assists competitors at every level. While most clients are women increasing numbers of men contact her often already in poor condition.

"Men may hesitate more or fail to recognise the signs. Some call it burnout" she says.

"A psychological element exists. Why avoid carbohydrates?"

Sometimes under-fuelling happens unintentionally through misjudged needs or failure to increase intake with heavier training.

For others like former British cycling champion Brian Smith the cause is deliberate.

His 1996 Olympic road race appearance masked an eating disorder and bulimia rooted in cycling's weight focus.

"I always felt too heavy. Pressure existed yet discussion was absent" he remembers.

At nearly six foot he raced at 68kg and dropped to 66kg feeling weak.

Now 59 Smith learned of his REDs only after taking up running eight years ago and suffering three severe stress fractures including one in his femur.

The cumulative damage leads him to advise against professional cycling careers.

"It harms long-term health. Teams prioritise performance over future wellbeing. I suffer now and wish I had known more."

British Cycling reports progress via education from academy level and regular screenings.

"We frame it as performance-related: under-fuelling prevents peak results rather than simply demanding lower weight" says chief medical officer Dr Nigel Jones.

"Prevalence should fall with continued work."

World Climbing introduced mandatory health checks two years ago.

Questionnaires plus random and targeted screenings at events monitor low energy availability. Athletes may be barred if unhealthy.

Professor Naama Constantini who helped shape the policy says the goal is education and prevention not punishment.

"We want athletes healthy. Prevention is key. Focus on strength performance and proper fuelling rather than unsafe weight loss."

Greater awareness offers hope of reversing REDs trends.

Many still suffer unaware and silent. Jake Smith continues sharing his recovery online receiving messages from hundreds seeking advice.

He has overcome the condition and recently set a personal best of two hours nine minutes 24 seconds at the Berlin marathon.