Aside from the fact it probably wouldn't be beneficial, most commissions only allow you to drink water and gatorade (and whatever other drinks are equivalent).
Not to mention no amount of food intake will stop you from being arm weary. That takes hours if not a day to recover from. These guys are putting their bodies to the limits of the extreme, no way some simple sugars are going to undo that in a matter of minutes.
Actually I play tennis and I sometimes use the energy gel when it gets really hot. I prefer it to gatorade etc. because drinking that much liquid makes me feel bloated, slow, and upsets my stomach when I start running. The stuff that I use says to take 15 minutes before every 45 minutes of workout. I usually consume one after the first set and another if the match goes 3 sets. Most of them come caffeinated and I can feel it start to take effect within a minute or two. It's much more effective than anything else available.
They should be given bumps of coke or meth between fights. Then we would see some REAL action from all fighters
A top up with water is really all a fighter needs. Plus there are rules regarding what you can and can't have.
The main reason is, that you don't burn so much energies in twelve rounds to make it necessary, otherwise ifghters would do it and rules would be changed. You have just 36 minutes of action, and not even that. If you have eaten enough before the fight you will never need to refuel. Not even close. Just go running or cycling for 36 minutes, you won't need to eat after that. You may want to, but you don't need to. Otherwise heavy workers would be constantly eating, once every half hour. Yet they eat 3-4 times at day. there are a lot of sports with way more continuative action than that, and they too don't drink or eat much. In football you need to run for one hour and a half, 90 minutes of action, and they don't eat too. They drink a lot, but that's it. Eating becomes helpful in longer competitions, such as tennis and maraton runners. Some tennis matches have lasted 3-4 hours, there you burn so much calories you need to eat something.