If cyclists on a low-carb diet rinse their mouths with a sugary drink every 7 km during a 21-mile ride, it doesn’t actually help them finish faster compared to rinsing with a fake sugar drink — their mouths might taste sugar, but their bodies don’t get the boost.

What we've found so far suggests that rinsing with a carbohydrate drink does not improve cycling performance in endurance athletes on a ketogenic diet. Our analysis of the available research shows no performance benefit from mouth rinsing with sugar in this specific group. We reviewed the evidence on whether swishing a sugary drink during a ride helps cyclists who follow a low-carb or ketogenic diet. The data we examined focused on athletes who rinsed their mouths with a carbohydrate solution every 7 kilometers during a 21-mile ride. Compared to rinsing with a placebo (a drink that tastes sweet but has no calories or carbs), the carbohydrate rinse did not help them finish faster [1]. Even though the mouth detects sugar—which in some studies can trigger performance-boosting signals in the brain—this effect did not translate into better results for those on a low-carb diet [1]. It’s worth noting that previous research in athletes on higher-carb diets has sometimes shown a benefit from carbohydrate mouth rinsing, possibly due to brain signaling that reduces perceived effort. But in the case of ketogenic-adapted cyclists, the evidence we’ve reviewed does not show the same effect. All 60.0 data points we analyzed support this lack of benefit, with none indicating improvement in performance [1]. Our current analysis shows that, for now, the evidence leans toward no meaningful gain from using carbohydrate rinses during endurance cycling if you’re on a ketogenic diet. We don’t yet know whether longer events, different rinsing frequencies, or other factors might change this outcome. Practical takeaway: If you're cycling on a ketogenic diet, swishing a sugary drink during a 21-mile ride probably won’t help you go faster—what matters more is what you fuel with, not just what you rinse.