Sports nutrition guidelines have moved away from giving universal and one-sided nutrition advice regarding macronutrient intake for optimal performance. Rather, a more individualised and periodised approach is promoted, guided by the level of athlete, type of sports, training and racing intensity that is undertaken.
In terms of carbohydrate intake during exercise, science tells us:
- for exercise that requires higher intensity workloads, high carbohydrate availability is recommended to support workout quality and promote recovery;
- for exercise that is completed at low-to-moderate intensity it might not be necessary to support exercise with high carbohydrate intake;
There is a growing body of evidence suggesting that intentionally undertaking prolonged training sessions with low carbohydrate availability can lead to favourable muscle adaptations.
During endurance exercise our bodies are using a mix of fat and carbohydrate based fuels. How much of each energy source that is being burnt at a given exercise intensity is determined by multiple factors, some of which are individual.
Exercise intensity is the main “switch” that shifts the mix of carbohydrate and fat burning. High intensity efforts are almost primarily fuelled by carbohydrate-based fuels, mainly coming from the breakdown of muscle glycogen, and immediate consumption of carb-based supplements (such as energy gels).
At lower exercise intensities, more calories are provided from fat-based stores (such as muscle triglycerides and plasma free fatty acids). Carbohydrate load, therefore, could be reduced during prolonged but lighter intensity training days. Our body’s fat stores are practically unlimited compared to glycogen (carbohydrate) stores.
For that reason, some athletes choose to maximise their body’s ability to use fat as a fuel during exercise by modifying their diet or energy intake during training. In addition, completing selected training sessions with reduced carbohydrate consumption or availability (i.e. low muscle glycogen) has been shown to promote adaptations to training.
There are multiple scenarios when low-carbohydrate intake could be beneficial and/or practical:
- During prolonged exercise at low-to-moderate intensity physical efforts, without a need to engage in high-intensity exercise.
- When your endurance mission is long and it’s important to consume a range of foods (and avoid taste fatigue).
- For people that are more sensitive to sugar intake during exercise and experience unpleasant symptoms, such as gastrointestinal upset.
- As part of a specific diet, such as a low-carbohydrate high-fat (LCHF) or a ketogenic diet as mentioned above. Some athletes consume low carbohydrate foods during long sessions at low-intensity as part of a LCHF or ketogenic diet, to promote muscle retooling and enhance fat utilisation. It is known that chronic exposure to low-carbohydrate high-fat diets can boost an athlete’s fat burning capacity as much as four-fold.