Nutrition and Fat Adaptation


By Rebecca Dent, Uphill Athlete High Performance Dietitian

This is the first of a series on the role of diet on endurance performance. Be sure to read the second article, Nutrition Strategies to Maximize Fat Adaptation, which explains what to eat before, during and after endurance training sessions. And the third article, High Fat Diets and Ultra Endurance Performance which explores diet’s role during endurance training and looks at the overall affect of a high fat diet on performance.

In this article we will explain why the endurance training itself is ultimately more important than your diet’s macro-nutrient distribution of fat, carbohydrate and protein. We will also explore what training at a low carbohydrate availability means in practice and we will provide dietary strategies for training low.

The Benefits of Fat Adaptation to the Endurance Athlete

Carbohydrate and fat are the primary fuel sources used by the muscles during endurance exercise. However, intensity and duration of the exercise, fuel availability and training status (your level of training/fitness) will dictate the contribution of each energy source used. Endurance exercise lasting longer than 90 minutes results in depleted muscle glycogen (carbohydrate) stores and the need to eat carbohydrate during exercise in order to prolong performance and reduce the time it takes to reach fatigue (1, 2, 3) as well as speed recovery.

Nutrition strategies have traditionally focused on optimizing carbohydrate storage in the muscles and liver to enhance endurance performance. However, we are only able to store a limited amount of carbohydrate in the body.  Even in the leanest of athletes there is an abundance of fat that can be used to provide a steady supply of energy. Recently there has been a resurgence of interest in fat adaptation training and high fat, low carbohydrate (LCHF) diets, in an attempt to optimize the usage of this fat reserve, helping you go further for longer.

To try and keep it simple: when training endurance, ultimately it is the actual endurance training that will cause the physiological adaptations that result in being able to perform at higher intensities for longer durations. That includes the body increasing its ability to use fat as a fuel source regardless of carbohydrate intake. The number one driver for fat adaptation is training!  However, fat adaptation training (e.g. training with low carbohydrate availability such as when in a fasted state) has shown to further increase these physiological adaptations, including the body’s ability to use fat as a fuel source when training at low to moderate intensities (4) as is the case when in zones 1 and 2.

As highlighted above, because carbohydrate ingestion before and during endurance exercise of low to moderate intensity (zone 1 and 2) reduces the body’s ability to utilize fat as a fuel source (5), the goal of every endurance athlete should be to train the body to use a greater contribution of fat as a source of energy (i.e. training in a fasted state). This also has the added benefit of reducing the body’s reliance of eating carbohydrates during the endurance exercise, thus sparing muscle glycogen levels. This enables you to tap into your carbohydrate store when you need it the most, during those higher intensity moments (i.e. the steep climbs, picking up a faster pace to get you down before dark, strength moves/cruxes during a long alpine route). This is known as fat adaptation.

When preparing for your event, whether an expedition, alpine rock trip, summit attempt or ultra distance race the aim is to optimize availability of BOTH fat and carbohydrate as fuel sources. Research has shown that when you eat a high fat diet and carry out fat adaptation strategies on all exercise types this has a ‘switching off effect’ of your body being able to use carbohydrate as a fuel source (6).

The greater the intensity of exercise, the greater reliance your muscles have on carbohydrates to fuel the movement (7), therefore it is important to eat carbohydrate around your high intensity sessions (zone 3 and 4 –  eg, strength training, intervals etc) to get the most out of the training.


  1. Enhances physiological adaptations to endurance training (go further, faster, for longer).
  2. Enhances the body’s ability to use fat as a fuel source during endurance exercise (your endurance training) reducing the reliance on the need for carbohydrate during endurance performance (that summit attempt, ultra-race, alpine expedition).

We advocate a lot of fasted training, but on the days you want to go fast by tapping into your maximal intensities, your goal climb or race, you definitely want to eat a high-carbohydrate diet.


As our resident High Performance Dietitian Rebecca Dent is available for both phone consultations about diet and she can create a Custom Performance Nutrition Plan for you.


Be sure to read the rest of the articles in this series:



  1. Cermak and Loon 2013 The Use of Carbohydrates During Exercise as an Ergogenic Aid. Sports Med. Nov;43(11):1139-55.
  2. Wee Kian Yeo, Andrew L. Carey, Louise Burke, Lawrence L. Spriet, and John A. Hawley (2011). Fat adaptation in well-trained athletes: effects on cell metabolism. Physiol. Nutr. Metab. 36: 12–22.
  3. Louise M. Burke, John A. Hawley, Stephen H. S. Wong & Asker E. Jeukendrup (2011): Carbohydrates for training and competition, Journal of Sports Sciences, 29:sup1, S17-S27
  4. Hawley, J, A and Morton, J, P (2013). Ramping up the signal: Promoting endurance training adaptation in skeletal muscle by nutritional manipulation. Proceedings of the Australian Physiological Society 44:109-115.
  5. Spriet, L, A (2014) New Insights into the Interaction of Carbohydrate and Fat Metabolism During Exercise. Sports Med 44 (Suppl 1):S87–S96.
  6. Louise M. Burke (2015) Re-Examining High-Fat Diets for Sports Performance: Did We Call the ‘Nail in the Coffin’ Too Soon? Sports Med (2015) 45 (Suppl 1):S33–S49.
  7. Jeukendrup, A, E., Saris, W.H.M., Wagenmakers, A.J.M (1998). Fat metabolism during exercise: a review–part II: regulation of metabolism and the effects of training. Int J Sports Med. 1998 Jul;19(5):293-302

About Author

Comments are closed.