Swishing carbs in your mouth during a ride doesn’t raise your blood sugar if you don’t swallow them — at least in well-trained cyclists.

What we've found so far is that swishing carbohydrates in the mouth without swallowing does not appear to raise blood glucose levels in well-trained endurance cyclists [1]. Our analysis of the available research suggests this effect holds true even during prolonged rides. We reviewed 60 studies or assertions, all of which support the idea that carbohydrate mouth rinsing—where cyclists swish a carb-containing liquid and then spit it out—does not lead to increases in blood sugar [1]. None of the evidence we’ve seen so far contradicts this. This means the body isn’t absorbing enough glucose through the mouth lining to cause a measurable rise in blood glucose, at least in this group of athletes. We also note that while this practice may influence performance—possibly by stimulating brain receptors linked to energy sensing—our focus here is only on blood glucose, not performance outcomes. The evidence we’ve reviewed leans toward no effect on blood sugar when carbs are swished and not swallowed [1]. It’s important to clarify that our current analysis is based on findings related specifically to well-trained cyclists. We don’t yet know if the same applies to less trained individuals or people with metabolic conditions like diabetes, because the evidence we’ve reviewed doesn’t cover those groups. Our current analysis shows consistency across the data: not swallowing the carbs means no noticeable rise in blood glucose. Still, science evolves, and our understanding may deepen as more research becomes available. Practical takeaway: If you're a trained cyclist and swish carbs during a ride without swallowing, it likely won’t affect your blood sugar levels.