Fat Adaptation and Endurance Performance

Is this the perfect way to train for longer and lose weight?

There is a vast amount of nutrition advice for athletes and one area of current interest is the use of low carbohydrate, high fat diets to improve performance.  The idea is that if you can train your body to become ‘fat adapted’ you will be able to better utilize fat as a fuel source when training or competing. 

Fat provides more than twice the energy, per gram, than carbohydrate and even the most lean athletes have an unlimited supply of fat – no matter how far you go. In contrast, the body can only store a limited amount of glycogen – the stored form of carbohydrate.  The muscles will store about 500g, the liver about 100g, which together provides about 2400kcal of energy.  If we estimate that we burn 100kcal per mile when running – our body’s store is not enough to fuel a marathon.  Therefore the ability to utilise our abundant fat stores is clearly beneficial for endurance sport. 

If an athlete could train themselves using a low carb, high fat diet, to be ‘fat adapted’ would they be able to better utilise fat, saving the glycogen stores for later in a long training session or for that vital sprint finish? 

The body needs more oxygen to enable it to metabolise fat, so running aerobically – at a low intensity, would mean that your body would choose the limitless store of fat to supply fuel rather than the glycogen stores.  So far, so good! However, when you work harder up a hill, for a sprint finish or to overtake a fellow competitor your body will need to utilise glycogen.  Therefore, if training in a low glycogen state, you will be unable to produce the same results and benefit from the same training stimulus than when starting training with fully stocked glycogen stores.  An athlete will just be unable to improve their overall endurance performance through this dietary manipulation strategy.  In fact, research showed that the muscle’s ability to utilise glycogen may actually be impaired following a low carb, high fat diet. So, whilst a low carb diet will stimulate fat metabolism, it may hinder your performance…being unable to sprint finish, run up that hill or overtake on the bike. In fact, there is no evidence that a low carb diet has enhanced elite performance1.

But it is not all negative.  There are health benefits to low carb diets such as improving insulin sensitivity, which is important for those individuals with/susceptible to diabetes. There could be some good news for athletes that benefit from a positive power to weight ratio.  A low carb diet can help an athlete to obtain a better body composition which may decrease weight, and therefore have a positive impact on climbing hills on the bike.

Changes to a diet should be done with the support and advice of a specialist.  At Tri & Run we have a sports nutritionist in training….ready to gain experience and help you achieve your nutritional goals.

1 Burke, L.M. (2020). Ketogenic low‐CHO, high‐fat diet: the future of elite endurance sport? J.Physiol. 599 (3) 819-843 [online]. Available at: https://doi.org/10.1113/JP278928 (Accessed 20 Feb 2021) 

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.