I find hunger doesn't kick in until after I've started eating for the day, so that aspect isn't a problem. It's that if I want to cycle for more than a couple of hours, I'm going to need fuel.
40km is easily achievable. 93km would require food or a substantial drop in pace.
If you have not eaten, and you are in a fasted state, your body is going to be burning it's glycogen reserves. As discussed previously (
https://yacf.co.uk/forum/index.php?topic=106640.0), your body has about 2000kcal of glycogen stored. For most cyclists, this is about 80km worth (I work on the basis of 100km == 2500kcal for my food planning). However for most of the population, it is rare that we scrape the barrel of our glycogen stores, and as such we don't react well to depleting them beyond a certain level. Marathon runners and long distance cyclists talk about hitting the wall, and bonking, this is when we have got the glycogen tank down to zero, but if you are not trained, your body gets grumpy when you still have quite a bit left. Fasted training can be very useful for getting your body used to relying on glycogen, and if you really push it, you can get your body to go ketogenic. At which point you've got considerably more resources at your disposal, if you can make your body use it (1kg of body fat ~= 9000kcal).
I realised I'd become "one of those people", when gootube gave me a recommendation of a video titled something like "fuelling for a 100km ride", and my reaction was simply "Any reasonable breakfast and your body's normal reserves are enough to get you round a 100km ride without needing more food. Obviously, getting round 100km at an audax speed, vs your typical roadies' speed can require a slightly different approach, and to those who haven't put their body through it a bit, can't do that. On a 300k Audax in April, I started the day with a brownie, a packet of crisps, and a 500ml bottle of full fat coke. I had a small amount of chocolate at about 40km in. At the first control ~90km, I had a burger, fries, and a bottle of coke. At approx 150km mark, I was cycling along quite happily, singing. My singing was such that one local insect took it upon itself to sacrifice itself to the cause of silencing me, entering my mouth, hitting the back of my throat, and causing me to redecorate the RAVeL I was cycling along with that which I had eaten at the last control. Based on the state of what came up, digestion was still very much are the early stages, and minimal calorific value had been absorbed. Alas, having been put through this, my stomach said enough is enough. No more solids! I managed a 200ml bottle of coke about 10km later at the next control, followed 100km later by ~300ml of fanta, and a with some will power, a mars bar. I finished the 305km in 21:06. Over time, but pretty much running on fumes. I think I ate under 2000kcal of accessible calories (i.e. that which wasn't rejected by the body). For a total energy expenditure of about 7500kcal. With the lack of 'proper' food until noon the day after the ride, and my other training, I lost 1kg over that week, nearly all of it on that one ride.
Human bodies are capable of amazing things if you push them. But like most things, just because you can, doesn't mean you should.
J