Relative Energy Deficiency in Sport (RED-S) in Female Athletes: Let’s Talk About Our Energy Levels, Performance, and Periods!

Photo Credit: Presca Sportswear

“No excuses!” As athletes, that’s what we hear repeatedly. Push yourself. Push your body. Push your mind. Going to our limits is often recognised as good thing, an attribute to be praised and celebrated. But where is the line drawn? This mindset, alongside the increasing number of metrics available to all athletes (e.g., activity and sleep data from sports watches, or body fat and muscle mass from smart scales), can lead to fixation on performance and body composition, leading us to focus on the here and now rather than considering our long-term mental and physical health. It’s therefore no surprise that endurance sports such as ultra running aren’t necessarily always seen as healthy. In fact, very large training volumes and/or sudden spikes in training loads can predispose endurance athletes to an overall lack of energy that compromises various biological processes. Related to this, you might have heard of the “female athlete triad”, which is characterised by loss of menstrual cycles (“amenorrhoea”), low bone mineral density, and disordered eating. As we now know that some men experience similar problems, the triad has now largely been replaced by “Relative Energy Deficiency in Sport” (RED-S), which is the subject of today’s blog. As part of our International Women’s Day series, we’ll focus on RED-S in female athletes.

So, what is RED-S?

Simply put, RED-S is not eating enough to support normal bodily functions alongside the stress of exercise, and it can affect athletes of any level. To enable biological processes such as reproduction and immune function, your body needs sufficient “energy availability” (EA). This is calculated by subtracting the energy required to exercise (above the energy you’d expend at rest) from the energy you consume, and this number is then divided by your fat-free mass (i.e., your bodyweight minus the weight of your fat):

EA = energy intake − energy expenditure during exercise / fat-free mass

While scientists give guidance about what constitutes sufficient EA, I’m hesitant to share these numbers because I frankly don’t want to give you numbers to compare yourself to. Also, it might be that the number that corresponds to adequate EA varies substantially between individuals, depending on factors such as age.

Despite how serious RED-S can be, it’s still not widely discussed within many sports, and further education is still required. For example, a study from 2015 found that only 7% of female ultramarathon competitors knew about RED-S, despite 44% being at high risk! Education and screening will be key in preventing RED-S. 

If so impactful, how does RED-S go so unnoticed?

Due to the current cultures in some sports, RED-S is easily missed until it’s already had serious consequences. RED-S manifests as a number of psychological and physiological symptoms, and I’ve summarised some of these in the table below.

Effects of RED-S

Psychological effects

Physiological effects

Increased irritability

Decreased muscle strength


Lowered endurance performance

Impaired judgement

Hampered training response

Worsened concentration

Impaired co-ordination


Diminished immune function


Increased injury risk


Disturbed gastrointestinal function


In females specifically, a key sign of RED-S is the absence of menstruation.

Wait, no periods?! No cramps?! No headaches?! Sounds convenient, right?

Train harder with no inconvenience, my coach praised my training this week, best not mention anything… you can easily see how this major health indicator can be overlooked if an athlete is too focused on performance. Lack of menstruation can also be masked by contraceptive methods, so the athlete may not even realise they aren’t menstruating anymore. This, alongside what seems to be cultural inability to discuss menstruation, means this key symptom is easily disregarded. And the dangers of RED-S are not just its consequences, but our failure to recognise them. 

What other signs of RED-S are there?

As well as loss of menstruation, other signs of RED-S include reduced bone mineral density (which can contribute to injuries such as stress fractures) and disordered eating - or even frank eating disorders. In relation to the latter, a key dimension of disordered eating behaviour is often secrecy and denial, which can also make RED-S hard to identify. Other behavioural warning signs include pre-occupation with food (e.g., constantly talking about it), strict control of diet, poor sleep (e.g., shortened sleep and/or frequent awakenings from sleep), reluctance to take rest days, and eventually overtraining.

Take-home messages

  • Listen to your body. Performance should not be at a cost of health. EVER.
  • If you think that you or someone you know might have RED-S, start a conversation. Raise awareness of this condition. The first step in helping those with RED-S is educating them about it.
  • Be wary of messages such as “eat less, move more”, and avoid diets that divide foods into “good” and “bad” items.
  • If you want to perform well, you need to fuel your body correctly. For more on this, check out our free e-book. Shameless plug: If you’re looking for a delicious performance-enhancing fuel, we think you’ll love Long Range Fuel.
  • If you’re a female athlete, consider tracking your menstrual cycle. Tech can be useful here. For example, Garmin Connect now has a menstrual cycle tracking function, and there are specific apps for this purpose, such as Fitrwoman.
  • Last but not least, seek professional help if you think you might have RED-S. There is some helpful guidance on this at Athletes in Balance.