Originally Posted by chasm54

How much to eat and drink is not about how much energy you burn, it is about how much you can absorb. Most of us can absorb only about 60 grams - 240kcal - of carbohydrate per hour, so eating more than that simply means you won't finish digesting it until after the ride has ended. So my advice would be to make sure you are well fed before the start, then start eating at the end of the first hour and consume c.250kcal per hour thereafter. What you eat depends on taste, but something easily digestible that you like and know agrees with you.

Drinking is more controversial, because most people will tell you to drink more than you feel you need. In fact, the latest evidence appears to be that it is fine to drink when you are thirsty, and that over-hydrating can be worse than mild dehydration. Once again, there's a limit to how much water your system can process. If I recall correctly it's around a litre per hour, more in hot conditions. But drink a great deal more than that and you tend to bloat. Drink far too much and you risk hyponatremia, which screws up your sodium levels and can be dangerous.

Someone on here linked recently to the guidance on the Hammer nutrition website, which spells a lot of this stuff out. I'm not advocating that you buy their products - I don't - but the analysis of nutritiona and hydration needs is useful.

Edit-hammer guidance