Fuelling for Performance and Adaptation

Conrad Goodhew Running

If you’re training for an upcoming multisport race, it is time to focus on your nutrition, the fourth discipline. Nutrition plays an essential role if you want to get the most out of your training and recover effectively. This blog will talk through some signs of undereating and how it can affect you, as well as how to train your gut and reflect and adapt. Read on to optimise your performance.   


How does undereating affect you? 

Meeting your daily energy requirements is essential to make the most out of your training and also for your welling being and daily functions. To ensure you are fueling and recovering optimally it is important to be aware of some of the normal signs of undereating as an athlete: 


Hunger is something that shouldn't be ignored. Your body is designed to tell you when you have not met your correct requirements. This can be signs of irritability (hangry) as well as the common ‘sweet tooth.' 

Three iced donuts in a flatlay with one that has a bite out of it.
Is your sweet tooth a sign of undereating?


Falling asleep mid-afternoon/early evening? Fatigue and tiredness are common signs of undereating, where the ‘caffeine’ boost will be great for an hour, but this will have complications for your sleep that night as it has an 8h half-life, compounding the problem. 


Sleep disturbances are often seen in athletes who are not meeting their needs. Sleep is crucial to any athlete and when there are complications in this area it will impair recovery and increase the risk of injury and illness. 8-10h is the goal for athletes, however, quality sleep is just as important. 


Lady sleeping on a train table
Are you getting enough quality sleep?


Illness will keep you off the track/field a close 2nd behind injury. Our bodies require sufficient fuel to ensure our immune system is functioning correctly, and common signs of under-eating is a frequent illness – supplementation is a band-aid over the bullet hole (not fixing the root cause). 


Poor recovery and injury are common and detrimental for any athlete. Acute undereating may impact recovery initially, but long-term issues can lead to things as severe as stress fractures. 


Adaptive thermogenesis is the phenomenon where, if you don’t eat enough your body adapts to reduce your output. The fitness industry will sell this as starvation mode but it is not as chronic as what people perceive. Yes, when you lose weight, this is often muscle mass and will reduce your calorie outputs (see the significant case of the biggest loser). Put more simply, if we undereat our body slows down, a common sign is tiredness, but also the reduction in step count, less fidgeting, and overall a reduction in accidental movement – NEAT. This means for those that are afraid of eating more and putting on ‘weight,' your body may need those calories to increase your output without you knowing. 

In severe cases, athletes undereat and can develop a clinical diagnosis of relative energy deficiency in sport, also known as Red-S. This is created by long-term undereating and can be intentional as well as by accident. Read the IOC consensus statement on Red-S here. If you have any concerns about this, please seek help from a registered dietitian. 

Train Your Gut  

Your gastrointestinal tract (aka the gut) is your most important organ for performance, which you can in fact train. The gut is the main player when it comes to the availability of fuel and fluid during prolonged exercise. It is important to ‘train the gut’, which can reduce gastrointestinal symptoms and increase the delivery of carbohydrates, both contributing to improved performance. 

GI symptoms such as bloating, cramping, diarrhoea, and vomiting are common symptoms in sports, especially endurance sports. The importance of gut training, however, is often overlooked. 

To prevent dehydration during an endurance race there is an increased fluid requirement, which may lead to increased GI symptoms. Dehydration itself can also lead to GI distress and decreased performance so balance is crucial. To prevent this it has been recommended to train with higher fluid intakes than what you may be planning on doing for race day. This training allows the stomach to be able to hold greater volumes and is better at tolerating being full, which then leads to reduced bloating and lowers your perceived fullness. 

Stay Hydrated Neon Sign

Similar to fluid, training with carbs can reduce bloating and increase your ability to utilize this effective fuel source, which can increase tolerance and performance. For races or training over 1.5h hours, we recommend taking between 30-90g of carbohydrates per hour. Although there has been some recent evidence to suggest that amounts as high as 120g/h may still provide benefit, the type of carbohydrate becomes important with any intake above 60g. To find out more and to plan what is best for you to get in touch with Conrad.  

With these benefits in mind, it might be time to start building a nutrition race day plan and starting to incorporate some of those foods and volumes into your training.  

Reflect and Adapt  

How are you reflecting on what you have done? Are you noting down how you feel? If you are not eating enough to supply your body with enough energy, the symptoms explained above become more prevalent. It’s time to start noticing. Be aware of how you are feeling, whether you are tired or low in mood. What are your symptoms that show you might need some more fuel?  

Planning your week of training along with your non-negotiables (driving the kids around and going to work) is an important way to be able to stay consistent with your training. By understanding your needs and planning your meals and training nutrition, you can help ensure you are getting enough and the right nutrition to support your training and performance. A table similar to below can be a good way to start thinking about what you have on and what you are going to eat to make sure you are getting enough food. You don’t have to eat three meals and three snacks, but at least it will stimulate thought on how much more you are training and how much food you require. Once you start to write it down you may see where your issues lie. 

Also, don’t forget to note down how you feel. 

A Table for you to document your meals


Blog written by Performance Dietitian and friend of Further Faster Conrad Goodhew. To get individualised recommendations (including calorie requirements), get in touch with him here:  https://www.conradgoodhew.com.  

If you enjoyed this blog, here's another one you may find interesting: How to avoid blisters and trench foot when adventure racing.

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