That’s a great question Orla!

The time to work into another fueling strategy will vary depending on how sensitive your GI system is.

I was similar to you and primarily used gels for the first 3-4 years of running marathons. But then my body started rebelling and I couldn’t take any more gels after mile 16 without feeling like I was going to vomit.

I suffered through a couple marathons like that until I’d had enough. We’d heard about a new fuel called Generation UCAN and in desperation I tried it out at the Tupelo Marathon in Mississippi.

It wasn’t the ideal time to be using a new fuel but I figured the alternative was feeling like I was going to throw up the last 10 miles of the race. I used it during that marathon and haven’t looked back.

I’m not necessarily recommending that strategy (switching so close to a race) but since I was an experience marathoner and didn’t feel like I had much to lose it worked for me.

Typically I’d recommend that you use a new fueling strategy for at least two long runs (of 16 miles or more) before using it for a marathon. That way you know how palatable it is, how often you should take it, and if it will cause any GI distress.

I hope this helps!