The price of success: At the start of the Tour de France Femmes, French cyclist Océane Mahé, riding for the small Ma Petite Entreprise team, was delighted to have won the polka-dot jersey for the best climber and was cheered on by the fans. At the end of the Tour de France Femmes, she admitted to suffering from RED-S and confessed: “I haven’t had a period for three years.” The fact that she is by no means an exception in women’s cycling had already been highlighted by the German professional cyclist Clara Koppenburg in a much-talked-about interview described. At the height of her success as a road cyclist, she stood 1.70 metres tall and weighed only around 47 kilograms; looking back, she said: “I would call it a classic case of RED-S.”
Anyone who dismisses this, thinking that such health problems are only found in elite sport, is mistaken. Sport as a means to a healthy lifestyle and weight loss – that is the hope of many people. However, anyone who exercises very regularly and intensively whilst also following a diet can end up in this dead end. This is because, in the worst-case scenario, a consistently low energy intake leads to a chronic problem that has often been – and continues to be – misunderstood: RED-S, short for ‘relative energy deficit in sport’, i.e. a relative energy deficit in athletes.
Too much training, too little rest
Dr Christine Kopp, a senior consultant in sports medicine at Tübingen University Hospital, is seeing an increasing number of women and men who overdo it in their leisure time: “The problem in recreational sport is, first and foremost, too much training without recovery,” says Kopp, “these people are training themselves into a state of exhaustion without anyone to guide them.” Her clinic offers a consultation service specifically for RED-S. She often has several appointments a day dedicated solely to this issue.
Having a bout of hunger – at first glance, that doesn’t sound too bad. But RED-S refers to a chronic condition: people who systematically build up this deficit. And who suffer physically and mentally as a result. Dr Alena Schmelz, a specialist in general practice and sports medicine from Schwerte, is also seeing more and more people who want to lose weight or eat healthily alongside their exercise regime. “But they combine a calorie deficit with high training volumes, without realising that the body cannot compensate for both at the same time,” says Schmelz.
RED-S is often only noticed at a late stage. Dr Andrea Jeschke, a cycling coach and expert on the Apotheken Umschau coaching team, has observed this time and again in her work. Nutrition expert Katja Mangold has also drawn attention to the risks associated with training on an empty stomach.
But: anyone who identifies with others, emulates celebrities or internalises Instagram images can sometimes find themselves caught in a vicious circle. “If people uncritically copy what they read online or see on social media, it can be unhealthy for their bodies in the long run,” says Christine Kopp. Alena Schmelz from Schwerte describes it like this: a full-time job, family, constant comparison with social media and wearables – a never-ending quest for self-optimisation. Meanwhile, those affected don’t even realise what is happening inside them and to them.
What is RED-S?
RED-S is a condition that arises when energy intake consistently fails to keep pace with energy expenditure. People who exercise burn more energy. If they do not replenish this energy, they develop an energy deficit. Therefore, as a general rule, exercise should only be undertaken when there are sufficient calories available in the body.
Anyone who burns 1,200 calories in two hours of exercise should eat or drink that amount before, during and after their workout. The key point here is that these 1,200 calories are in addition to your normal daily requirement – that is, on top of your basal metabolic rate. You can find estimates of your calorie requirements during exercise in many tables – though, of course, these are only accurate if you know your personal figures or performance data. This is often underestimated, and the actual gap between what you consume and what your body needs is often wider than you might think.
Let’s take the author of this article as an example: I recently spent 2 h 30 mins cycling on a road bike in low mountain ranges and, weighing well over 90 kilograms, burnt around 1,800 kilocalories in the process. Nutrition expert Katja Mangold comments: “It often makes a crucial difference to actually do the maths and track the calories consumed on individual training days. People’s estimates are often far off the actual calorie target required.” She also advises treating your everyday diet and your training nutrition as separate matters to a certain extent, and consistently adapting your training nutrition to your training workload.
If the body does not receive an adequate supply, its energy levels drop. In the long term, this leads to biological mechanisms being scaled back. Dr Schmelz describes this mechanism from a clinical perspective: “At some point, the body switches gears: it reduces its basal metabolic rate, lowers hormone levels and curtails everything that consumes energy and is not immediately necessary for survival.”
Not losing weight despite a calorie deficit
This is a key misconception that Dr Andrea Jeschke encounters time and again in her work as a trainer: despite an energy deficit, RED-S does not necessarily lead to weight loss. That is what makes this situation so treacherous and dangerous. Jeschke explains the principle as follows: exercise is a bit like ‘running away from a sabre-toothed tiger’. The body first channels all its energy into the task at hand, diverting it away from basic nutritional needs or basal metabolic rate. The result can then be a starvation metabolism.
This is important information for anyone who exercises specifically to lose weight: anyone who tries to create a calorie deficit through exercise rather than through their daily diet risks precisely this effect – and, on top of that, all the health consequences of RED-S. In other words: I can easily cut down on the calories I would normally consume – but I should make sure to replenish the calories I need for exercise before, during and shortly after my workout!
Warning signs for RED-S
The symptoms are varied and are often masked by everyday ailments. This is one of the reasons why diagnosis is so difficult and can sometimes take months or even years. The problem is more evident in women than in men. A missed period is a commonly reported symptom. This occurs because the body’s hormonal balance is downregulated as a result of energy deficiency. Exercise-induced oestrogen deficiency before the age of 35 leads to a significantly higher risk of osteoporosis – for the rest of a woman’s life. “Many female athletes accept this as normal, sometimes even as confirmation that they are training hard enough. But every missed period counts. The longer this condition persists, the more difficult it is to reverse some of the damage,” says Dr Schmelz.
In elite sport, this condition is known as the ‘athletic triad’ (the prolonged absence of the menstrual cycle (amenorrhoea), osteoporosis and, frequently, eating disorders) and was in fact often described in the past as simply part of the game. However, Kopp clearly disagrees: “I know plenty of female elite athletes who have perfectly normal periods whilst performing at the very highest level.”
In men, physical exhaustion, erectile dysfunction and a general loss of libido may be signs of RED-S. According to Katja Mangold, the lack of energy often gives earlier warning signs: “Even before the classic symptoms appear, you often notice it in the form of poor sleep and a reduced ability to recover.”
Stress fractures – bone fractures caused by strain – are also a very clear physical warning sign. And certain things may also become apparent in a person’s social circle: those affected train an immense amount, but do not become fitter; they simply become more exhausted. “This doesn’t necessarily have anything to do with control or restriction. It may simply be that someone doesn’t know how much energy their body actually needs at the moment,” emphasises Dr Schmelz.
RED-S and its consequences
From a sporting perspective, the opposite of what is desired occurs. Dr Andrea Jeschke describes a ‘plateau’ that her clients reach: despite all their efforts, they can no longer make progress; their performance may even decline. Endurance and strength may decrease, whilst the likelihood of injury increases. Training loses its effectiveness when RED-S is severe. Dr Schmelz describes the short-term mechanism: ‘You become slower or weaker and take longer to recover. Many people affected respond by training even more – which drives the body even further into energy-saving mode.’
Katja Mangold emphasises that women are more sensitive to low energy intake than men. Research into RED-S shows that even brief periods of insufficient energy intake in female athletes can trigger hormonal cascades: elevated cortisol levels, impaired thyroid function and menstrual cycle disturbances.
Anyone who follows methods such as ‘One Meal a Day’, training on an empty stomach or strictly avoiding fats should be aware of the risks involved – and under no circumstances should they blindly adopt them from the internet.
The first step is to recognise the signs. Have your training volume and eating habits become out of sync? Am I ignoring warning signs such as infections or menstrual irregularities? If so, I should seek professional help: if you suspect a problem, your GP or a specialist sports medicine clinic – such as those in Tübingen, at Ruhr Medizin in Schwerte or at Olympic training centres – is the right place to go. Experts such as Dr Christine Kopp and Dr Alena Schmelz provide their patients with comprehensive advice; this requires laboratory tests, consultations and time.
What helps combat RED-S?
First and foremost, people should look into their so-called basal metabolic rate, either in general terms or on a personalised basis. There are average figures available for this, but these are calculated statistically and are not based on individual measurements. Katja Mangold also recommends having your actual resting metabolic rate measured, as rules of thumb only provide approximate results. Sometimes, the amount of exercise needs to be reduced temporarily to give the endocrine system and the bones time to recover.
Dr Schmelz highlights another point: “For active people, I recommend at least 1.6 grams of protein per kilogram of body weight per day; for those with a high training workload, the amount should be higher. Protein protects muscle mass, supports recovery and has a direct influence on hormone metabolism.” Furthermore, patience is key: whilst energy levels can rise quickly, the endocrine system takes months and bone density may take years to stabilise.
“Sport should give the body something, not take anything away,” summarises Dr Schmelz. “But that is exactly what happens when exercise and diet are consistently out of balance.” Many people underestimate just how much their energy requirements increase during periods of peak exertion – and how quickly a seemingly small deficit can turn into a real problem over the course of weeks.
RED-S and its potential consequences
• Bone density Anyone who develops a deficiency before the age of 35 may no longer be able to fully compensate for it – bone density usually peaks at around the age of 30. Any bone mass not built up by then cannot be achieved afterwards. The risk of injury remains elevated, and the risk of osteoporosis increases over the course of a person’s life.
• Hormonal balance and fertility A disruption to the hormonal balance can prevent fertility. In women, secondary amenorrhoea is a serious long-term problem with direct consequences for bone health, blood vessels and general well-being. It is reversible if action is taken early enough.
• Immune system A lack of energy can weaken the immune system; those affected are more susceptible to infections. Weight loss fails to materialise: anyone who wants to lose weight through exercise but finds themselves in a state of RED-S may put their body into such a severe ‘energy-saving mode’ that they simply can no longer achieve the desired weight loss.
• Cardiovascular system In extreme cases, there may be adverse effects on the heart: cardiac arrhythmias, electrolyte imbalances and, in severe cases, bradycardia. Dr Schmelz: “The body of research on this is only just beginning to grow, but the findings are clear enough to warrant taking this seriously.”
• Mental health issues A lack of energy is described as being linked to increased irritability, anxiety and possible depressive moods.
>> Cycling nutrition: What are the benefits of calorie tracking?
>> Cycling nutrition: Tips from the World Tour kitchen
>> Cycling Nutrition: Everything You Need to Know About Protein
Tim Farin
Editor