Does a High-fat diet really work for Endurance Athletes?

It has become increasingly common for some endurance athletes to demonize carbohydrates and jump on the high-fat diet, restricting carbohydrates to become ‘fat-burning machines.’ However these diets and ‘gurus’ claims lack substantial scientific evidence, tend to be based on anecdotal evidence or on those suffering from metabolic syndromes. In contrast when looking at scientific evidence for the use of carbohydrates in endurance sport, it’s use and benefits in sport has been widely researched and proven over the past 50 years.

So why exactly are carbohydrates so important for athletes?

ATP synthesis (energy production) is equal to the intensity of exercise you are completing. During exercise fat and carbohydrates are both primary sources of fuel used by the skeletal muscle in the production of ATP. At lower intensity exercise fat is the preferred fuel, however carbohydrates are also being continuously utilized to assist in the conversion of fat to energy. When exercise intensity increases, fat synthesis cannot occur fast enough to meet the rate of ATP synthesis and therefore carbohydrates take over as the major fuel source. Many people falsely believe that when exercising at a lower intensity fat is the only fuel source, when in fact, carbohydrates are always being utilized.

With this in mind, carbohydrate storage within the body (stored in muscle and the liver as glycogen) is limited; therefore carbohydrate feeding during exercise is important to increase carbohydrate availability and to spare liver glycogen. This ‘sparing’ of liver glycogen means that there are still carbohydrates in the liver toward the end of exercise, which could be beneficial if, for whatever reason, carbohydrate intake is not enough. Therefore adequate carbohydrate intake and glycogen ‘sparing’ could then mean the difference between getting the boost you need to smash your competitor at the finish line or only being able to stay at the one pace and placing second. Low glycogen stores have been shown to result in muscle fatigue, reduced force production, inability to complete high intensity exercise and decrease endurance capacity and performance, making carbohydrate intake essential for increased performance.

Adequate carbohydrate intake is also essential for optimal recovery and restoration of glycogen stores (checkout our blog Importance of Carbs in Recovery) Without adequate glycogen stores, subsequent training and racing will be compromised, as your stores will be depleted at a faster rate causing a decrease in performance ability.

In summary carbohydrate intake for athletes and especially endurance athletes is critically important for those trying to compete at their best. With the support of scientific fact we would not recommend a  high-fat diet to an endurance athlete, well maybe only to a competitor who we wanted to beat…

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