Our body relies on glucose (or sugar) as one of its main energy sources — but when our body runs out of glucose, it turns to an alternative source of energy: fat. At this point, fat is broken down in the liver and converted to ketones, which are then released into the bloodstream to provide energy. This process is called ketosis.
However, instead of waiting for the natural process of ketosis to occur, ingesting ketone supplements — ketones created externally — has gained attention in diet culture (e.g., the keto diet) and among athletes. For athletes, it was hypothesized that ingesting both ketone supplements and a typical high-glucose diet would deliver more energy to the body, potentially leading to greater endurance and enhanced performance. But studies have shown mixed results regarding the impact of ketone supplements on athletic performance.
To shed further light on this topic, a recent study published in the International Journal of Sport Nutrition and Exercise Metabolism and conducted by researchers at McMaster University and Maastricht University aimed to determine the effect of acute ketone supplementation on endurance exercise performance in trained individuals. The study specifically recruited participants who were trained cyclists between the ages of 18 and 60 years old who did not follow a keto diet and who cycled at least three times a week for five hours or more.
In the end, 23 participants with a mean age of 31 years were included in the study. All of the participants took part in two experimental visits to the lab where they were given either a placebo or a ketone drink, with the opposite being administered during the subsequent trial. For both trials, the athletes were asked to complete a 20-minute cycle (similar to a 40 km race performance).
The results of the study demonstrated that mean performance during the 20-minute cycle was lower when participants ingested the ketone supplement compared to the ketone-free placebo drink.
The researchers suggested that the ketone drink may have increased the participants’ cardiorespiratory stress as they were exercising, indicating that the heart may not have received enough blood or oxygen during the 20-minute cycle, thus potentially hindering their performance. These findings suggest that acute ketone supplementation may not benefit the performance of all endurance activities uniformly.
Nonetheless, previous research has demonstrated that ketone supplements can be beneficial for longer endurance activities, such as running a marathon or cycling for an hour or more. This makes sense, as our bodies first rely on glucose as an energy source, followed by ketones. This may explain why the current research study did not find a beneficial effect of ketone supplementation during the shorter endurance activity.
Based on this current study, ketone supplements do not hold promise for enhancing endurance performance of shorter-length activities — but based on previous research, they may be useful for longer (specifically aerobic) activities.
However, further research is required to fully understand the mechanisms and limitations of ketone supplementation, which the researchers at McMaster University have hinted are already underway.