Can Ketogenic Diet Enhance Endurance Performance?

The Keto diet has been taking over for the past few years. According to research, it creates significant cellular changes resulting in increased mobilisation, transport, uptake and oxidation of fat during exercise, even in elite athletes who purposely train to optimise fat oxidative pathways. These research findings ignited curiosity amongst endurance athletes, coaches and scientist and raised few questions.

• Is it possible to replace carbohydrate loading with ‘fat loading’ and can fuelling on predominantly fat lead to improvements in endurance performance?
• How long does it take to become ‘keto-adapted’?
• Could periodising ketogenic diet with high carb availability provide alternative strategy to enhance endurance performance?

Several trials conducted between 1983 and 2020 compared Ketogenic- Low Carb High Fat Diet (LCHF, we will call it just keto in this article), to high carbohydrate diets, non-ketogenic low carb diets as well as hybrid diets such as keto with extra carbohydrates added on heavy training days or before and during an endurance event as well as carbohydrate cycling (periods of keto and high carb). They used various methods, diet strategies and sporting events (cycling, running and race walking) and ended up with more or less same results. 

• None of the studies found a performance advantage with keto. Although most trials reported that the ketogenic diet was not detrimental to endurance performance, studies testing 5km treadmill run and 10km race-walk experienced notable performance impairment.
• Nearly all studies found a significant increase in fat oxidation and loss of body mass and/or fat mass with keto.
• Most trials had issues with subjects adhering to the diet for the whole duration which was four weeks minimum
• The time we need to become keto-adapted depends on how fit we are, it seems. Although most studies stated that the full adaptation requires 3-4 weeks, a recent study from 2020 found that elite athletes took only 5-10 days to achieve high rates of fat oxidation on a keto diet as well as on very low carb non-ketogenic diets.
• Before we get adapted, we experience the so-called ‘keto-flu’, which presents itself as a reduction in well‐being (e.g. fatigue, irritability, loss of concentration) and increase in perception of effort during exercise. The muscles and brain simply suffer from the lack of carbohydrate and it takes time to switch to using fat and ketones. Electrolyte and fluid imbalances resulting from the initial renal response to the keto diet are another reason why we feel unwell in the first week or so.

The verdict - can ketogenic diet enhance endurance performance?

Being a top athlete takes a toll on the body and it’s not necessarily the healthiest way to live. Unless you are an elite endurance athlete trying for the Olympic games, you don’t need to carb load and can totally race and thrive on keto. It will not make much difference to your performance plus you might lose more fat if that’s your goal.

The carb-appropriate diet

However, in our opinion, a ‘carb-appropriate diet’ is the way to go if your goal is optimal health, antiaging and injury-free life. Carb-appropriate diet means that you eat more carbohydrates on your heavy training days and race days and low carb or keto when you sit at your desk all day. This way of eating also allows you to cover all your micronutrients (vitamins, minerals, phytonutrients) and fibre, which can be difficult on a strict keto. We’ve covered this in our previous article on ketogenic diet.