Manipulation of diets and its effect on endurance exercise

Dietary Manipulation and its effect on endurance exercise

How do Low carbohydrate high fat diets (LCHF) effect endurance exercise performance?

Elite point of view

Low carbohydrate high fat diets (LCHF) have received increasing attention among athletes and physically active individuals, especially endurance athletes and are a highly debatable topic in nutrition today. The effect of LCHF diets have been explored within numerous areas of nutrition in the recent years. Many studies have explored the physiological responses towards a LCHF diet and how physiological factors can be altered and affected through the consumption of LCHF diets. Research shows that LCHF diets improve cardiovascular risk factors such as; lowering elevated blood glucose, insulin and saturated fat concentrations, as well as reducing blood pressure and body weight. Since the carbohydrate (CHO) content of this diet is significantly reduced, the relative proportion of energy derived from protein and fat will increase. This therefore leads to an individual’s overall calorie consumption decreasing which leads to weight loss.

Findings show that LCHF diets can enhance endurance capacity, increase recovery from fatigue and prevent muscle and organ damage induced by exhaustive exercise. Endurance is typically defined as a resistance to fatigue. Endurance sports are classified as continuous events of >30 minutes duration, with activities lasting >4-5h being considered as ultra-endurance. Studies dating back to the 1960’s established that one of main factors of fatigue during exercise was substrate depletion, for that reason understanding how nutritional supplements can enhance endurance performance is extremely important. It is often assumed that by increasing fat oxidation we may reduce glycogen breakdown and in turn enhance endurance performance. By consuming high fat diets it increases fatty acid availability which can be used as the main energy source, meaning our bodies will have spare muscle glycogen stores. After the body adapts to a high fat diet, the bodies ability to use fatty acids instead of carbohydrates increases because of an adaptation in the muscle cell.

There is no agreement in the current literature on what classifies as a LCHF diet. However we can assume that when an individual consumes 130g CHO/day and above this is classed as a moderate CHO diet as it accounts for 26%-45% of daily kcal intake, therefore anything below this will count as a low CHO diet. Within studies exploring LCHF diets, LCHF diets are classed as “those that restrict CHO intake to 130g/day or less”. This is the same as <26% of total energy intake (TEI). Other examples of LCHF diets are the ketogenic diet and the Atkins diet.

The ketogenic diet (KD) is a very low CHO diet that may induce ketosis in some individuals. Ketosis is a process that happens when your body doesn’t have enough carbohydrates to burn for energy so instead it’ll burn fat and produce things called ketones which it’ll then use for fuel. A ketogenic diet is typically said to be a consumption of 20-50g CHO/day or less than 10% of daily kcal. Overtime when an athlete consumes a LCHF or KD diet their body will adjust to using ketone bodies as their main fuel, therefore consuming a LCHF diet brings about ketosis. This is important as fat and ketone bodies can quickly provide energy making ketones the most efficient energy source. As ketone bodies have the potential to provide a fast energy supply that is consistent they have the ability to increase exercise performance and capacity . The ketogenic diet is seen as favourable within the endurance exercise community as it brings about metabolic changes that enhance performance levels in ultra-endurance sport such as marathons and triathlons.

Coaches who are contemplating recommending LCHF diets to their endurance athletes should make sure their athletes review their personal experiences to evaluate how important carbohydrates  are in relation to their goals before switching their diets, as findings show that one diet does not suit the individual metabolic profiles of everyone. However, the findings show that practitioners can be reassured that LCHF diets are safe in terms of weight loss in athletes and still provide adequate nutrition.

Sports practitioners may find the results of this research valuable as the findings show us that when practitioners recommend exercise prescriptions and dietary recommendations there are many factors that need to be considered. This includes the athletes specific exercise goals such as; duration and intensity, to facilitate a training plan that will obtain the ultimate substrate oxidation adaptations relevant to enhance endurance exercise performance.

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Summary of Study – “Ketogenic low‐CHO, high‐fat diet: the future of elite endurance sport?

The ability of ketogenic low‐carbohydrate (CHO) high‐fat (K‐LCHF) diets to enhance muscle fat oxidation has led to claim that it is the ‘future of elite endurance sport’. Therefore the aim of this study was to review previous literature with the focus on three issues: 1. Do maximal rates of fat oxidation achieved by K-LCHF transfer to performance benefits in endurance sport?; 2. What is the apparent time course of ‘keto-adaptation’? and 3. Could strategies that periodise K-LCHF with high CHO availability provide alternative models for performance benefits? The review focuses on applications to the metabolism and performance of elite endurance athletes. This study shows that LCHF diets induce certain adaptations within the body that can be beneficial for endurance exercise performance.


If you would like to read the full article click the link below:

Burke, L.M., 2021.

Ketogenic low‐CHO, high‐fat diet: the future of elite endurance sport?. The Journal of physiology599(3), pp.819-843.

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