I would eventually like to consider a marathon once dd starts nursery and I've time to train but am clueless about the fuelling part.
[gets on podium, adjusts mic]. IMO, one of the errors runners make when working up to longer distances is that they fuel their training runs far too heavily - I see this a LOT on a FB forum I'm on where people are recommending gels for 6 mile runs- craziness. These runners don't then improve their ability to burn fat to fuel longer distances (because they're drip feeding glucose in) which is not ideal because fat (your own) has to be your primary fuel source to attain any sort of endurance, and that has to be learned via the long slow run. Then, at the other end of the spectrum you have the " carbs are the devil" people who fuel races by eating neat peanut butter with only 2 hrs to run, which is pointless because it takes your body 3 hrs to turn the fat in peanut butter into energy. It's great for ultra runners (I use it in races over 6 hrs) but not really for anything under a marathon, especially as it requires energy to digest. Even worse, I've seen protein bars recommended- protein is only used as fuel of last resort. You really don't want to be eating them as race fuel.
In races you want to go as close to glucose as you can as this is the fastest and most energy efficient way of delivering fuel to your muscles, but this is GI dependent as not everyone can tolerate chugging down sugar for hours on end. I use a caffeinated energy/electrolyte powder called Tailwind (diluted a bit more than recommended) and then top up with gel cubes/ sweets as I go. Therefore, as people have said, there's a lot of trial and error involved. I often have a Mcmuffin/ cheeseburger before races of 6 hrs plus which I'm sure is in no running book ever, but really seems to do the trick. It stops me getting the gnawing hunger around the 4 hr mark. Most critically though is starting with topped up glycogen levels and a good level of hydration.
In training I would recommend just going for a good quality diet with a reasonably high percentage of favourable carbs (e.g rice, jkt potato, not Haribo) and good protein intake (but no need to go crazy on that).
The marketing of gels/ protein/ electrolyte powders etc has increased massively and to grow the market they are persuading people who don't really need them to use them. I think they have their place, but they're overused.
5 to add from me to make 937.36. Ankle is tolerable but not great. Really hoping it miraculously fixes itself for my 70k race next Saturday.