This article is from the running Beginners' FAQ, by Ozzie Gontang with numerous contributions by others.
The type of diet that is good for runners is the type of diet doctors
recommend for everyone - high in carbohydrate, low in fat with sufficient
but not excessive protein. Some people find that as they exercise more
their taste changes to prefer this kind of diet anyway. The archetypal Real
Runner eats lots of pasta, rice, potatoes and bread, with little rich food.
It is important to drink sufficient water to make up for that lost in
sweating. You MUST rehydrate yourself properly. Drink water (or fruit
juice, etc) soon after a run, and throughout the day. If you run in hot or
humid conditions, drink before and maybe during the run. Dehydration
interferes with your ability to deal with heat, making your run miserable,
and interferes with your recovery, lessening the effects of training.
Personally I keep a bottle of orange squash and a pint glass on my desk.
Sports drinks such as Gatorade and Isostar are designed to replenish fluid
rapidly and to replace energy rapidly (these two functions conflict), as
well as replacing minerals and vitamins. They have a place in races and
heavy training, but for most purposes water is fine. You should be getting
all the energy, minerals and vitamins you need from your diet.
It has been frequently observed that runners like beer, but it should be
remembered that alcohol is high in calories and has a dehydrating effect,
and may also lower your metabolic rate, so you burn less calories. Caffeine
also has a dehydrating effect.
 
Continue to: