When working with active individuals and athletes, one of the common themes we see is gastrointestinal symptoms during or after exercise. Symptoms can include nausea, vomiting, diarrhoea, abdominal pain, reflux and bloating. Exercise-induced gut symptoms can be common, particularly in relation to endurance exercise such as running and cycling. There are various mechanisms which can explain gut symptoms around exercise such as blood flowing away from the stomach. There has been recent interest in adopting a ketogenic diet for exercise performance, with the view it may help to improve fat oxidation so that fat can be used as fuel during performance, instead of relying on carbohydrate.
Let’s look at what a ketogenic diet is and a recent study that examined it’s impact on gut symptoms.
What is a ketogenic diet?
A ketogenic diet is a low carb, high fat diet. There are a few variations of the diet but typically it consists of 70-80% fat, 10-20% protein, 5-10% carbs. For a 2000 calorie diet this would be approximately 165g fat, 40g carb, and 75g protein. One of the biggest issues with a ketogenic diet is the negative impact it may have on gut health. We know from an abundance of research that plant foods such as wholegrains, legumes, fruits and vegetables are what our gut bacteria thrive off. As well as impacting the diversity of our gut microbiome, a ketogenic diet can trigger gut symptoms such as diarrhoea, constipation, nausea and bloating. Why? We’re cutting out majority of our fibre sources. Fat is a common gut irritant as well, and can trigger gut symptoms as a result when intake is too high.
Impact on exercise-induced gut symptoms
A recent study looked at the impact of a short-term ketogenic diet on exercise-induced gut symptoms. 28 male race walkers were included in the study. All athletes were given a high carb, high calorie diet for 6 days to ensure adequate energy available at the start and completed a base line 25km race walk. They were then divided into 3 groups – a low-carb high-fat (LCHF) group, a high-carb high-calorie group, and a low calorie group. All groups then repeated the 25km race walk.
What did they find? The LCHF diet resulted in greater biomarkers of intestinal epithelial integrity and gastrointestinal symptoms. So, a ketogenic diet may lead to a greater prevalence of exercise-associated gut symptoms compared to a diet containing carbohydrate.
The take-home message
The findings are concerning with regards to the impact a ketogenic diet may have on exercise-induced gut symptoms and therefore performance. More research is required to determine whether the changes in biomarkers are due to restriction of carbohydrate or high levels of fat. However, it highlights the importance of ensuring adequate carbohydrate to fuel performance, particularly for endurance athletes and active individuals!