Count what you actually consume
For a runner who already tolerates 60 g/hour, three 20 g gels provide 60 g. Adding a drink containing another 30 g raises that hour to 90 g. That is a different intake, not free hydration; inspect the labels before combining products. These numbers illustrate accounting rather than a prescription.
The gut-training review discusses adaptation and practical rehearsal while identifying limits in the evidence. Use the marathon fueling planner to calculate totals and the fueling practice guide to record the response.