What is RED-S?

Relative Energy Deficiency in Sport (RED-S) is a condition that can affect male and female athletes across various sports disciplines, however it can be particularly prevalent in endurance sports where the weight of the sports person can have a significant impact on performance. For instance, a cyclist may want to lose bodyweight to improve their hill climbing ability, but lose power and strength in the process due to under-fuelling during and round key training sessions. RED-S results from a sustained, long-term imbalance between the amount of calories we consume from food, against the energy we burn for exercise and day to day biological function.

What do we mean by biological function? Well, as humans, our bodies are controlled by regulating hormones, enzymes and neural activity, all of which demand energy to keep the hugely complex operating system of the human body working correctly. In the modern age, we are exposed to more information than ever before, but not all of this information is accurate and trustworthy.

The age of social media has led to an increase in unhealthy body comparisons and this can extend to sportspeople who participate in endurance sports. As we know, lowering our body weight can have a positive impact on health and performance, however weight reduction must be treated with respect and executed gradually. Unfortunately, what we often see is an excessive focus on weight reduction at the expense of power development and the formation of lean muscle tissue, leading to frequent under-fuelling within training sessions. This results in low energy availability and the development of RED-S.

RED-S is not a new concept, but our understanding of it has evolved significantly, especially within the last decade. Science now better recognises the damaging health and performance implications of insufficient energy intake and how it affects long-term performance, health, and well-being.

In the 1980s, Relative Energy Deficiency in Sport was referred to as the Female Athlete Triad. This framework described the interconnected health issues observed in female athletes who consistently burned more calories than they consumed over several months. The term Triad references the link between three negative health conditions.

• Energy Deficiency: Female athletes experiencing an imbalance between calorie intake and expenditure, leading to a negative energy balance.
• Menstrual Disturbances: Irregular or absent menstrual cycles due to energy deficiency affecting hormonal regulation.
• Bone Health Issues: Development of low bone density related conditions such as osteoporosis, increasing the risk of fractures and other bone-related injuries.

Low energy availability was more obvious to identify within physically active females as it became apparent that females who struggled to meet their energy demand, suffered from irregular menstrual cycles and increased bone fracture related injuries. Once the connection had been established between chronic under-fuelling, reproductive activity and injury, research started to pay more attention the impact of under-fuelling in males. It soon became clear that the same consequences are present. Males with low energy availability show a reduction in the sex hormone, testosterone.

However as science on the topic evolved, the International Olympic Committee released a consensus update in 2023, highlighting more information on the topic and the prevalence on low energy availability in male athletes. Thus the broader term RED-S now encompasses male and female athletes and recognises a wider range of health and performance consequences. We will explore some of the symptoms of RED-S in the upcoming sections.

To understand energy balance, we need to understand that our body doesn’t just burn energy when we move. We are constantly burning energy to survive. The energy we need to survive is typically associated with functions which include, but are not limited to; bone growth, reproductive function (menstrual cycle in females), non-exercise activity thermogenesis (energy we use to complete frequent, simple movements which are not classified as exercise) cellular growth & repair, thermoregulation (management of internal body temperature), immunity and brain function.

These biological systems all require certain amounts of energy each day to function correctly. Some of these systems are ranked higher in importance than others, and some of these systems require more energy than others. Collectively, they build a minimum energy requirement known as the Basil Metabolic Rate (BMR).

The gold standard method of accurately identifying your BMR typically requires a visit to a laboratory, however we realise that this is not an option for most people. Alternatively a combination of science and maths has calculated a formula accurate enough to provide a reliable benchmark. If you are interested in calculating your own BMR, you can do so using a BMR Calculator found on the Diabetes.co.uk website.

After determining your BMR, you can further refine your daily calorie baseline using the Harris-Benedict Formula to estimate the total daily calories needed to maintain your current weight. This formula refines your BMR value based on your activity level as follows:

• Little to no exercise: BMR x 1.2 = Survival Calorie Requirement or BMR
• Light exercise: BMR x 1.375 = Survival Calorie Requirement or BMR
• Moderate exercise (3-5 days per week): BMR x 1.55 = Survival Calorie Requirement or BMR
• Very active (6-7 days per week): BMR x 1.725 = Survival Calorie Requirement or BMR
• Extra active (very active with a physical job): BMR x 1.9 = Survival Calorie Requirement or BMR

The diagram above illustrates how you can find yourself in a state of Low Energy Availability (LEA). Starting with Bar 2, this bar represents a physically active person who consumes enough energy from their daily diet whilst also fuelling during exercise to meet their BMR and energy demands of training. We can call this ‘optimal energy availability.’

In the left column (Bar 1), the physically active person has reduced their energy intake while maintaining the same training load, leading to ‘low energy availability.’ This will likely be satisfactory for a few days to a few weeks, however long-term exposure to aggressive energy restriction will likely pose potential health risks such as deep fatigue and impaired recovery.

On the right (Bar 3), the athlete has the same high energy intake as Bar 2 but increases their training load further. This results in low energy availability, potentially causing a decrease in performance, stunted training adaptation and increased risk of injury and illness. The low energy availability negates the efforts of increasing the training load as the energy isn’t available to fuel the training adaptation process post exercise. To prevent this, one of two things must happen – either training load must be reduced, or energy intake must be increased further.

Symptoms of RED-S

The body is a very clever machine and can quite literally sense energy availability. When we find ourselves in a state of low energy availability, the body prioritises energy conservation by slowing down various biological functions. As we identified earlier in this article, low energy availability leads to a reduction of critical reproductive hormones, including oestrogen and progesterone in women and testosterone in men.

Work from the International Olympic Committee in 2018 presented information showcasing additional health and performance related symptoms that could pose as signposts for identifying RED-S. The symptoms can be seen in the table below.

Some of the symptoms listed above may indicate an underlying medical condition so as a first port of call, if you are concerned we highly recommend that you consult with a health care professional.

Preventing RED-S involves considering a few different factors. These factors include nutrition, the volume and intensity of the training being completed, along with the monitoring of recovery between training sessions. Of course, we appreciate that this could be a little daunting, so we will break down each topic in more detail below starting with nutrition.

Protein: Protein contains 4 calories per gram and is essential for constructing our physical body as well as regulating cellular functions. Without proteins, growth, development and overall biological functioning would be impossible. The human body comprises of tens of thousands of different proteins that define our physical makeup. These proteins have specific roles, ranging from forming skin, hair, tendons, and muscle tissue to breaking down food with enzymes and regulating blood glucose levels with hormones like insulin. It’s clear to see that if this nutrient is neglected within the diet, key health and performance factors will almost certainly be compromised.

Whilst protein is hugely important for bodily repair, adaptation from exercise and general bodily function, it does not support the energy needs of exercise. In fact, less than 5% of the energy we burn during exercise comes from protein, so we should aim to consume our protein serves outside of the exercising window. However, exercise acts as a stimulant for the production, but also the breakdown of protein, so it’s important that physically active people aim to consume protein immediately after exercise to provide the body with the nutrients it needs to repair and adapt.

The typical daily recommendations for protein for a physically active person is 1.6g of protein, per kg of body weight per day. For a 75kg person, this would result in a daily protein target of 120g split into 5 evenly dossed serves of 24g – if split into 4 doses per day, each dose should be 30g. Protein can be found in foods such as red and white meat, fish, eggs, cheese, tofu, beans, pulses, nuts and seeds.

To learn more about protein, read our article: Protein, Performance and 20-25g Protein Recipes

Fat: Dietary unsaturated fat aids the absorption of vitamins A, D, E, and K, which are known as fat-soluble vitamins. Fats also play structural roles by supporting cell wall formation, regulating cholesterol, and promote brain development. However, fat is highly calorie-dense, providing 9 kcal per gram, so it’s important that individuals focus on quality over quantity when consuming fats. Saturated fats are generally lower in quality, are found in fatty meats, butter, cream, savory snacks, and processed foods. In contrast, unsaturated fats, especially those rich in Omega 3, 6, and 9 oils, should be consumed in moderation for their health benefits. Foods like oily fish, avocados, nuts, and seeds are excellent sources of these healthy unsaturated fats.

Fats offer a large amount of energy for exercise and do so predominantly at low to moderate exercise intensity. The amount of fat we burn peaks at around 60-65% of a person’s max effort and if the intensity were to continue to progress, we would see a reduction in the amount of fat being burnt in favour of carbohydrate breakdown. Whilst fat can provide a lot of energy, we can also store a lot of it around the body, so we don’t need to hunt for much more than the typical athletic recommendations of around 1-1.5g/kg of fat per day.

Carbohydrate: The main role of carbohydrate is to provide your working muscle and major organs with fuel to function. Carbohydrates are broken down rapidly and at high rates to produce ATP (the energy currency of our cells) during both light and intense exercise. As carbohydrates can be rapidly broken down for fuel, they become the preferred fuel source as exercise intensity progresses. Due to the rapid and high rates of depletion of this fuel, it must be replaced during exercise to prevent poor performance and replenished immediately post exercise to support the adaptation from training as well as refuelling the muscles and liver ready for subsequent training sessions.

Unlike the recommendations of fat and protein which remain stable each day, the demand for carbohydrate will be largely dependent on the amount of exercise being completed, and we will use an acronym known as F.I.T.T to help identify how much carbohydrate we need each day. In the Sports Science world, carbohydrate intakes for athletes and physically active people are often referred to as ‘fuel for the work required’ reflecting this flexible intake approach.

The F.I.T.T principle is an acronym composed of the 4 factors used to manipulate a training programme to ensure progress always occurs. Yet we can also use this tool to help pre-plan our nutritional strategy based on how demanding a training session or race will be. Using these factors we can determine how much carbohydrate we should consider consuming for the day to help meet the energy demand and prevent the development of low energy availability.

The 4 aspects of the F.I.T.T principle include:

• Frequency (how many times per week you complete physical activity)
• Intensity (how intense is the activity)
• Time (how long the session is)
• Type (what sport was completed)

The factors that will impact the amount of carbohydrate needed the most will be Frequency, Intensity & Time. We can then use established carbohydrate recommendations to determine how much carbohydrate we should be aiming to consume per day to help meet the energy demand.

The table below provides an overview of the daily carbohydrate intake recommendations defined by exercise intensity and duration. They can be used to help us define more accurately how much energy in the form of carbohydrate we should be consuming per day to meet the exercise demand. This table has been developed based upon years of sport and exercise nutrition research which helps physically active individuals of all abilities meet their energy needs and prevent issues such as RED-S.

Of course, any fuel that you ingest during your exercise sessions from sources such as Energy Drinks, Bars, Gels or Jellies goes towards this total daily target. Much like the daily carbohydrate recommendations, training session-specific nutritional recommendations have been established to help maximise performance and delay fatigue. These targets differ slightly to the g/kg/day recommendations and are more absolute values such as 30, 60 or 90g of carbohydrate per hour targets. Once again, exercise intensity and duration will determine our hourly carbohydrate recommendations. TORQ have the simplest fuelling strategy of any sports nutrition brand on the market and we have named this the TORQ Fuelling System. To learn more about why fuelling your training sessions is important, you can watch our “Why Fuel” video below.

Prolonged and/or high intensity exercise will deplete your stored carbohydrate supplies. High intensity endurance and sprinting styles of exercise are literally impossible to perform without available carbohydrate. A hard training session today can leave you in no fit state to perform tomorrow, unless you prioritise your recovery strategy. Diligently following the TORQ Fuelling System will provide an alternative external or ‘exogenous’ source of carbohydrate whilst you’re exercising, sparing your endogenous (Internal) stores. This will help to offset some of the energy deficit, making the job of recovery a little easier.  That said, if the training load is high, your endogenous stores will still suffer depletion despite conscientious fuelling. Therefore re-fuelling with a dedicated Recovery Drink presents a major opportunity to deliver much needed carbohydrate immediately after exercise as well as protein for muscular repair. This prevents the development of low energy availability and further supports the process of getting fitter and stronger (training adaptation).

Now we have a better understanding of RED-s, how it develops and how we can recognise the symptoms associated with it, we must provide you with some practical recommendations from a training and nutritional perspective to prevent you from developing RED-s in the first place. Should you feel you are showing signs of REDS-s you can also implement the same steps which should help to either; increase your daily energy intake, reduce your daily energy output, or (most realistically) devise a plan which helps to adjust both.

Adjustments to Training: Reducing the intensity (how hard) and volume (how much) of training is critical if you find yourself showing signs of RED-S. Of course, if you are not currently showing signs of RED-S strategically planning periods of rest and recovery is paramount to the performance development model and should be present within your training cycle as standard. You can learn more about this in our Planning Your Training article.

If you feel you are showing signs of RED-s you should consider temporarily replacing high-intensity sessions with moderate or light activities and reducing the number of training sessions per week. This can help alleviate the energy deficit. It may seem logical to decrease your nutritional energy intake inline with the reduced energy demands however it’s important to remember that we are trying to “fill a gap”. If you were to reduce training volume, but also reduce your nutritional energy intake, the size of the “gap” would remain the same size.

Nutritional Planning: In previous tabs, we learned about the role of each micronutrient (carbohydrate, fat and protein) and how to correctly proportion the amount of each based upon the the frequency, intensity, time and type of our training to help us meet our daily energy balance.

• The type of fuel that we should consume.
• When (timing) we should consume that fuel.

When we consider the Type, Timing and Total, we refer to this as the nutritional 3T’s.

Using the 3T’s help us identify how best to distribute the total amount of energy from the 3 macronutrients in line with the desired performance outcomes for that day. For example, if we were planning a training session that may mimic the demands of a marathon race, or a hilly stage in a cycling road race, its very likely that the total energy requirement for that day will be high.

However in order to perform, we will need to consider what fuel to consume and when to consume that fuel. Breaking this down, we would consider a meal by meal approach, most likely starting the evening or day before the important training session. The plan would be to gradually increase the amount of fuel/energy available for that session in the form of a carbohydrate load. The type of meals consumed would need to be high carbohydrate, but low in fat and fibre to protect you from developing GI distress throughout this important session. Of course, you would not tuck into a bowl of pasta during a marathon, so the type of fuel would likely change to consuming more practical and optimised energy sources from foods such as Energy Drinks, Bars, Gels or Jellies.

Of course, as the start time of the key session creeps ever closer we would move from eating whole meals, consisting of complex carbohydrates, some fat, and protein, to grazing on smaller, high carbohydrate but more easily digestible food sources allowing us to maximally restore carbohydrate but limit gastrointestinal distress throughout the session, foods such as a TORQ Explore Flapjack.

Paying more attention to the nutritional 3T’s may help you to identify more feeding opportunities around your exercise window. This will allow you to meet your total energy requirements, but also provide the correct nutrients at the right time meaning your physical performances during training and recovery after will be improved.

Improving Sleep Hygiene & Stress Management: Sleep is quite possibly the bodies most powerful recovery mechanisms and yet for many physically active people, is the one area that is neglected to simply provide more hours in the day. Whilst poor sleep itself is unlikely to cause a physically active person to develop RED-S, the implications associated with poor sleep can certainly compound over time. These negatively compounding factors can impact how one may respond to general day to day stress, eating habits, recovery time from training and immunity to name a fwe. Sleep has been shown to have an impact on the two hormones that regulate hunger (Gherlin) and fullness (Leptin). Research has concluded that poor sleep can increase concentrations of gherlin, whilst reducing leptin, causing the athlete to feel more hungry. Whilst this could seem like a positive with regards to prevention of RED-s, some physically active people can become obsessive with daily calorie intake (as they attempt to maintain a lean physique which could be desirable to their sport). This feeling of distress triggered by the increase in hunger, driven by poor sleep leads increase hormones associate with stress such as cortisol, which further impacts sleep making the negative cycle even harder to break. We have a dedicated article on Optimising Performance With Better Sleep and we feel that it’s well worth a read to provide more information on this highly important area.

It is clear that understanding and addressing energy requirements of a physically active person is crucial for their long term health and performance. That said it is important to note that understanding RED-s is also a complex area that can affect many different components of a persons heath, making it very difficult to truly identify without access to varying health care professionals and tests.

Overall, Relative Energy Deficiency in Sport (RED-S) highlights the significant consequences of long-term under-fuelling, which affects both males and females across various sports disciplines but is commonly associated with endurance sports or sports which require a low body mass to benefit performance.

Preventing RED-S involves a comprehensive approach which includes proper nutritional planning, appropriate training load planning and the monitoring of associated RED-s identifiers such as injury frequency, menstrual frequency, mood and psychological well-being. The signs of RED-s may not always be obvious, so it is important to familiarise yourself with some of the signs and symptoms found within this article to identify if you are showcasing any of them at any given time.

Utilising the tools such as the BMR Calculator and the Harris-Benedict Formula can help you estimate your daily energy needs more accurately. Additionally, the F.I.T.T and nutritional 3T’s principles can help to guide you in planning your nutritional intakes far more specifically by proving and recognising more obvious fuelling targets and windows of fuelling opportunity.

Ultimately, by prioritising energy input of foods consumed inside and outside of the exercising window and correctly planning your training by providing dedicated recovery periods, you can prevent the development of RED-s and prevent long term health and performance implications.

Mountjoy, M., Sundgot-Borgen, J., Burke, L., Carter, S., Constantini, N., Lebrun, C., Meyer, N., Sherman, R., Steffen, K., Budgett, R. and Ljungqvist, A., 2015. The IOC relative energy deficiency in sport clinical assessment tool (RED-S CAT). British journal of sports medicine.

Mountjoy, M., Sundgot-Borgen, J., Burke, L., Ackerman, K.E., Blauwet, C., Constantini, N., Lebrun, C., Lundy, B., Melin, A., Meyer, N. and Sherman, R., 2018. International Olympic Committee (IOC) consensus statement on relative energy deficiency in sport (RED-S): 2018 update. International journal of sport nutrition and exercise metabolism, 28(4), pp.316-331.

Burke, L.M., Close, G.L., Lundy, B., Mooses, M., Morton, J.P. and Tenforde, A.S., 2018. Relative energy deficiency in sport in male athletes: a commentary on its presentation among selected groups of male athletes. International journal of sport nutrition and exercise metabolism, 28(4), pp.364-374.

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Areta, J.L., Taylor, H.L. and Koehler, K., 2021. Low energy availability: history, definition and evidence of its endocrine, metabolic and physiological effects in prospective studies in females and males. European Journal of Applied Physiology, 121(1), pp.1-21.

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