Under-Fueling is A Man Cycling Thing Too!

According to recent research, RED-S in male athletes, especially cyclists and virtual cyclists, is a significant risk.

Zwift avatar signifying RED-S in male athletes

Low energy availability, or athlete under-fueling, is described as insufficient dietary energy to match energy expended during exercise. Early research focused only on women, and the detrimental physiological effects became known as the female athlete triad—a condition characterized by a lack of menstrual periods, a decline in bone density, and stress fractures from not ingesting enough calories. New evidence suggests RED-S in male athletes is a significant risk.

Early on, the triad was considered a concern restricted to women and only those who didn’t have a menstrual period. Men didn’t have the same hormonal reactions as women and weren’t considered at risk by this definition.

After further research and review of the medical literature, the condition was renamed RED-S in 2014. The definition of RED-S, or Relative Energy Deficiency in Sport, was broadened to include the progressive effects of prolonged low energy availability. The chronic problem of taking in too few calories to offset the energy expended during training and basal metabolic function goes well above the traditional triad. It can affect men just as much as women.

RED-S in male athletes is due to an unhealthy relationship with food
Enjoying a high-fuel meal with cycling friend Doug Mastroianni and his wife in their Ohio home during my cross-country cycling adventure.

Cycling is a weight-sensitive sport, and in many popular virtual cycling platforms, W/KG rule the game. It’s not a mystery to us guys that the lighter we are, the faster we go if our power stays steady. Maintaining the proper balance is highly problematic for many male cyclists, and the isolating and anonymous nature of virtual cycling puts us at greater risk of spiraling out of control. RED-S in male athletes is receiving greater awareness and found to be more widespread than once believed.

Not to mention that virtual cyclists are notorious under-fuelers, with recent research showing that 75% of virtual cyclists and esports competitors consume no carbohydrates during racing and training sessions. RED-S in male athletes isn’t limited to virtual or traditional cyclists. It is a risk in all sports, especially weight-sensitive ones.

The Study of 50 Male Cyclists—RED-S in Male Athletes

Low energy availability and RED-S is not only a female thing, and it isn’t limited to traditional elite cyclists. In a recent study, researchers gave a group of 50 male road cyclists a sport-specific energy availability questionnaire to identify their risk of developing bone health, endocrine, and negative performance due to the consequences of RED-S. 


The questions related to the subject’s cycling history and included:

  • Current cycle racing category 
  • Years of cycling training 
  • Training load: average hours on bike per week 
  • Training load: any strength and conditioning or off-bike exercise? 
  • 60 min Functional Threshold Power: watts 
  • Type cyclist (TT/Climber/Sprinter/All round) 
  • Previous sports to cycling?


The questions also focused on nutrition:

  • Is weight steady?
  • Vegetarian/food intolerances?
  • Supplements?
  • Fasted rides per week?
  • Fuelling during ride> 1 hour?
  • Post-ride fuelling?
  • The average number of portions of dairy per day?
  • Average caffeine per day (coffee/gels etc.)
RED-S in male athletes is a concern
Gas station breakfast pizza is a favorite pre-ride fueling staple in Iowa. Thanks to my gracious hosts, the Rood family of Dubuque.
Group of cyclist fueling before a ride

RED-S in Male Athletes—Are Men Eating Enough?

In addition to questions related to past medical and substance use history. The answers were reviewed by a clinical sports endocrinologist, a sports research scientist, a registered sports performance dietician, competitive male cyclists, and coaches. The research team made a clinical evaluation of Energy Availability according to the following parameters.


Chronic low EA: Disordered eating requiring intervention from a sports performance dietician, a diagnosed eating disorder, or intentional restrictive nutrition to achieve substantial weight loss (>7%) within five weeks and sustained over more than a cycling season (>12 months).


Acute intermittent low EA: Limited fuelling around training (e.g., weekly fasted rides), on a background of non-restrictive nutrition, and minor variations of body weight (<5%) during a cycling season.


Adequate EA: No restrictive nutrition practices and steady weight.


The male cyclists also underwent bone density scans of their lumbar spine and body composition analysis derived from a total-body scan. Blood samples were taken for endocrine and metabolic markers and analyzed for total testosterone, vitamin D, and T3, among others. The results were staggering to this amateur male cyclist.

RED-S in male athletes is avoidable if you follow a sensible nutrition plan

The Jaw-Dropping Results

Scientists identified 14 riders (28%) at risk for low EA and ten cyclists with chronic low EA. The research team diagnosed five athletes with eating disorders or disordered eating. All the athletes questioned expressed strong views that low body weight, especially low body fat, was essential to optimizing performance and watts per kilo.


The cyclists who identified as low EA demonstrated substantially lower lumbar bone density and testosterone compared to adequate EA athletes. The finding is particularly troublesome considering the non-weight-bearing nature of the sport and its predisposition toward osteoporosis. In a recent study of master cyclists, 67% had low BMD at either or both the hip and the spine, 52% were osteopenic, and 15% were osteoporotic.

The most jaw-dropping of the findings for the competitive cycling crowd is that athletes showing signs of low EA demonstrated hindered performance. The cyclists judged to be in low EA didn’t perform as well in a 60-minute time trial when comparing average power output in watts per kilo, which should favor the lighter rider.

Low Energy and availability and RED-S are difficult to detect in men, which is why it was considered a condition affecting only female athletes. It isn’t as simple as menstrual monitoring and usually requires a battery of blood tests and an open mind.

Zwift cycling avatar with large body

Conclusion—RED-S in Male Athletes

The first step is acknowledging the risk and asking yourself difficult questions. We guys aren’t immune to the condition, and amateurs are as much at risk as the pros.


Be honest, realize the tendency to overdo it, and commit to altering your unhealthy behavior. By educating yourself on the warning signs of under-fueling, you can catch it before it develops into something worse. If your training is inconsistent, you have pangs of hunger periodically throughout the day, you experience mood swings and irritability, your sleep quality is poor, and you lack focus, RED-S in male athletes may be the cause.


Be truthful with yourself, identify the signs of RED-S in male athletes, and make the proper nutrition and recovery decisions. Being a cyclist isn’t easy, especially when an amateur athlete with a family and a job. Make it a bit easier by doing the right thing for yourself.

Your Experience?

Are you an amateur who identified the signs of RED-S in male athletes yourself? Comment below! Your fellow virtual cyclists want to know.

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Tony Konvalin
Tony Konvalin
5 months ago

I think this is probably real for those reliant mostly on carbs for energy as it is hard to keep that supply up. However for those of us who have worked to be fat adapted we have access to more fuel than many, sort of like having a hybrid source of energy. Most studies focus on the carb reliant athlete and in that case because one can only store a set amount of carbs they probably can have issues.

I have been OFM fat adapted, this is not the same as KETO, for a number of years and know that having two sources of energy that i can easily access helps greatly. The issue with studies that even appear to deal with this tend to use carb dependent athletes and only give at best a 4 week transition and I saw once three months. But depending on where you are in the carb dependency scale it can take longer to gain the Metabolic Capacity to have true metabolic flexibility..

Fogg Mark
Fogg Mark
5 months ago

This is me to a T all of the symptoms.

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