You don’t have to eat ‘regular food’ or ‘solid food’ during a 24 hour time trial. You can if you want but you don’t have to.
And maybe it’s individual. Maybe some riders really do have to take down some regular food for mental reasons. That might be true. Also, maybe if it’s a cold race? I’ve only ever done a 12hr that was just right at freezing & I was OK to drink mostly surgar water through that ride but who knows what a cold 24 would be like.
But if somebody tells you it’s not possible to drink all your nutrition over a 24 hour period of bike riding…well, that’s either just outright ignorance or willful misinformation. It’s no prob during a 24 hour race. In fact, much to the detriment of the field at this race. I’ve never been so whooped by one of the ladies at an ultra event & she drank all her nutrition the whole race. Yikes. Go back to gummy worms, please.