Episode 86 – Nutrition For Endurance Athletes

Key Topics Covered

  • Carbs vs fats for performance 
  • Intra-race carbs and carb loading 
  • Body composition and performance 
  • Hydration, electrolytes and easy wins/supplements for performance 

Carbs vs Fat for Performance 

  • The consensus from our current body of research is that high carb approaches are superior to low carb approaches for performance in endurance athletes.  
  • While people can make arguments for low carb approaches, the research hasn’t actually found it to outperform high carb approaches in most circumstances.  
  • Which makes sense when you think about the fact that carbohydrate utilization in endurance sports is quite high – so having higher carb availability seems like the intuitive choice for these sports  
  • There are also multiple types of lower carb approaches used by endurance athletes including the concept of train low, compete high and carbohydrate periodization which is not an overall low carb approach but focuses on sometimes training with lower carb availability for enhanced training adaptations. 
  • OVERALL In most cases a high carb approach makes sense. Although, lower carb approaches don’t seem to underperform as much as you think they would and there is some arguments to be made about potentially having some sessions with low carb availability.  

Intra-Race/Training Carbs 

  • We know that glucose is the most effective fuel source for endurance activity above a certain level of intensity 
  • We have a finite supply of it though. We have a small amount in our blood and we have stores in our muscles and liver called glycogen. 
  • Even if you maximize glycogen stores, if you are exercising intensely, it is borderline impossible to have >90 minutes’ worth of glycogen. When it starts to get low, performance declines.  
  • One way to preserve that for longer is to consume carbs while exercising. 
  • Since glucose seems to be capped at being able to be absorbed at a max of about 60g per hour, using multiple carb sources such as glucose and fructose can help you absorb higher. Theoretically the limit is around 90g per hour, but a lot of top athletes consume >100g per hour. 
  • Most sports drinks/gels contain multiple carb sources in the ideal 2:1 ratio 
  • Very few people can consume anywhere near that high without GI symptoms unless they practice it and “train” their gut to tolerate it. This is part of why it is necessary to do in training too.  

Carb Loading 

  • Carb loading is a tool that can be used in the lead-up to events that basically allows us to maximize glycogen stores 
  • We can get about 60-90 minutes worth of glycogen with maximised stores so we definitely want to be carb-loading appropriately before endurance events  
  • Although, most athletes who carb load without a specific plan usually get around 5-6g/kg of carbs. 
  • Whereas the gold standard for carb loading is 10-12g/kg of carbs for 1-3 days before the event 
  • To do this you likely need to choose low fat and low fibre foods for a large portion of your intake – so that you can get it all in  

Body Composition 

  • Obviously body composition matters for endurance athletes 
  • In most cases, getting leaner helps improve performance. We have talked a lot about fat loss elsewhere, so won’t focus on it much here. One added challenge for endurance athletes though is they often need to consume a lot of calories to fuel their performance + are quite hungry usually, so this makes it a more difficult balance.  
  • Leaner isn’t always better though. At some point, trying to get leaner comes with downsides such as low energy availability and results in getting sick more frequently, more injuries and worsened performance. 
  • Another aspect is that if you are trying to get leaner, you are also consuming a sub-optimal amount of calories and carbs for fueling your training and performance, by definition. Because of this, you should only have planned phases of aiming to get leaner and it should not be an indefinite type of approach.  


  • Hydration is surprisingly simple in most cases – drink when thirsty and stop when you are not thirsty. 
  • This is often better than a specific plan. Sweat rates change based on variables such as the weather. If you have a plan that doesn’t factor that in, you can unintentionally over or underhydrate. 
  • Research shows that losing >2% of body weight through dehydration leads to loss of performance. So if you want to double check that you are drinking enough in training, weigh yourself before and after training. 
  • A caveat to that though is that the majority of elite athletes who are winning races actually are losing slightly more than 2% – so perhaps it doesn’t matter as much as we think, and the logistics around consuming fluids may lead to overall slower times in some cases  


  • Electrolytes are more of a “do no harm” situation than a “nailing this will improve your performance” 
  • We want to avoid going exceptionally low in anything, which can happen if you solely consume water and then sweat a LOT 
  • The main guideline is to consume 300-600mg of sodium per hour during an event. For long events, it makes sense to consume other electrolytes too. But most sports drinks contain enough of these things to optimise them without even thinking about it. 


  • Having at least 1-3mg/kg of caffeine has been shown to reduce the rate of perceived effort and improve race times. 
  • Going slightly higher at 3-6mg/kg of caffeine can improve times a bit more as this dose seems to have more of an effect on performance
    • The mechanism involves interactions with adenosine receptors and the nervous system.  
  • For long events, it makes sense to consume caffeine throughout the event too, not just prior – using caffeinated gels can be a simple way to do this, although you may want to be mindful of potential gut issues from consuming too much caffeine (very individual)  

Beetroot Juice 

  • Nitrates, which are in beetroot and other vegetables, can improve vasodilation, which improves blood flow and endurance performance. 
  • Most research on the topic has found that beetroot juice improves race times. 
  • The dosage is quite high, usually at 500ml or higher, so arguably it is easier to use concentrated beetroot juice. 
  • This can be consumed 1-3 hours before the race. But consuming it for a few days leading up to the race helps even more. 

Elite-level athletes seem to get a bit less benefit out of beetroot juice, but using an even higher dosage looks like a promising solution to this.

beetroot juice sys review summary

Relevant Links/ Resources

Studies Mentioned:

Low Carb and Performance Study

Low Carb and Performance Study 2

Dehydration and Performance

Nutrition Strategies for Distance Runners/Walkers (+ caffeine)

Beetroot Juice

Related Blog Posts:

120g Carbs Per Hour Mountain Marathon Runners

Nutrition for Endurance Athletes

Carbohydrate Loading

Beetroot Juice

Carbohydrate Periodisation