5 Things Every Cyclist Needs to Know About Fat As A Fuel

As a cyclist, you’ve undoubtedly heard of the importance of fat as a fuel for your cycling. 

In this article, we will look at some of the key things you need to know about fat as a fuel source. 

1.     It’s a huge energy reserve – As cyclists, we have a very limited capacity to store carbohydrates. For example, a highly-trained endurance athlete will have <740g of carbohydrate (equivalent to <3000kcals of energy) stored in the body as liver and muscle glycogen when rested and well fuelled; most of us will have significantly less. 

This is only enough energy for as little as 90-120 minutes of moderate to high-intensity exercise before it depletes and we fatigue.

In contrast, Fat is an almost limitless reserve of energy. Even lean individuals with 70 kg and 10% body fat would have in the region of ∼68,250 kcal (7,000 g) of energy stored as fat within the body, enough for literally days’ worth of riding.  

Fat is a very dense (and therefore efficient) store of energy. 1 gram of fat contains ~9.75 kcal of energy. In contrast, 1 gram of carbohydrates contains only 4 kcals. However, carbohydrate also requires ~3 grams of water to store, so to store the equivalent energy of 7kg of fat as glycogen (carbohydrate), the combined weight of fluid and glycogen would weigh over 68kg! 

2.     Fats are the predominant fuel source at low to moderate exercise intensities – When we ride, we predominantly rely on fat and carbohydrates. From rest, as exercise intensity increases, we see an increase in the use of fat as a fuel before it peaks and then its use starts to drop off. This peak is referred to as the maximal rate of fat oxidation (reported in grams of fat used per minute) or Fat Max, which refers to the power output/exercise intensity at which the maximal rate of fat oxidation occurs. This peak typically occurs around 50-75% of an athlete’s VO₂ Max. The use of fat as a fuel then drops off to very low levels as exercise intensity increases above this. Partly because they’re a less efficient fuel than carbohydrates, requiring more oxygen to produce the same amount of energy.

3.      The highest-ever fat-burning rate recorded in an athlete was 1.8 grams of fat per minute; this is equivalent to 972 kcal an hour. The amount of energy required to hold roughly 280 watts for an hour, which is by no means a world-class performance. This was an extreme outlier in a group of world-class athletes endurance athletes who had just completed two weeks on a strictly controlled ketogenic diet (Study here). In contrast, a study measuring maximal fat oxidation in over 1100 male and female athletes from a range of different sports at Loughborough University found a range between 0.17 to 1.27 g·min with a mean value of 0.59 grams of fat per minute. In effect, fat is not able to fuel high-intensity efforts. 

4.     The rate at which we use fat during exercise is influenced by an array of different factors. The key factors include our training status; athletes of a higher level/high level of fitness tend to have a higher rate of fat utilisation during exercise, and generally, if we improve our fitness, we’ll also improve our fat max. Our gender, females tend to be better at utilising fat than males. Finally, our Short and long-term nutritional intake, our habitual diets and what we eat immediately around training can influence the rate at which we burn fat. For example, having a high carbohydrate intake around training can reduce fat use, particularly whilst glycogen stores are still high. In contrast, having a habitual diet that is low in carbohydrates can increase our use of fat during exercise. 

5.     High rates of fat oxidation don’t immediately = high performance. Yes, we generally see that higher-level athletes have a better ability to utilise fat as a fuel source, but they are also generally better at storing and using carbs and, most importantly overall, have a higher level of fitness. 

Whilst having the ability to utilise more fat can be useful from an endurance perspective by preserving precious glycogen stores, increasing fat use does not directly relate to performance. In many cases, athletes’ attempts to improve fat use through things like low carbohydrate diets can impair performance by reducing the body's ability to utilise carbs and reducing high-intensity exercise performance. 

For amateur athletes undertaking ultra-endurance events such as ultra-endurance bike rides where the goal is to complete the event rather than be competitive, a low-carb diet to maximise fat use may not negatively impact performance. However, for any event where intensity is key, an ability to use both carbs and fat will be important for performance. 

-       Coach Ben