I don’t know if it was a recent podcast or one of the snippets on YouTube, but I think Jonathan or Chad said that a rider doing 180w for 1 hour burns 400 calories. For me that’s just below zone 2.
That being the case, having one gel (just using gel because it makes the math easier) every 20 minutes will put me behind by 100 calories per hour. If I use a flask and put 4 gels worth in but consume it in 3 shots (133 cal/28g of carb) I’ll be at brake even and roughly 84g of carb per hour.
In EP 9 of the Science of Getting Faster pod cast Dr. Hearris said that their results indicated that eating once every 20 min was the most efficient. (also that another study indicated rice cakes aren’t as good as gels or liquid carbs for fueling but they were pretty good) Are Gels Really That Bad? w/ Dr. Mark Hearris - The Science of Getting Faster Podcast Ep. 9 - #2 by webdev511
So to avoid deficit at 180w you need 400 calories and roughly 80g of carbs. Oh you’re racing? better turn that up to 11 and your best bet is to still do that every 20 minutes.