How Long Should You Wait to Exercise after Eating?

from ACE's Essentials of Exercise Science:

"It is generally recommended that exercisers wait about three hours after eating a full meal to engage in a strenuous exercise program.  That is about how long it takes for a balanced meal including some carbohydrate, protein, and fat to move from the stomach into the small intestines, where nutrients are absorbed and energy becomes available.  Exercising before food has had time to empty from the stomach can cause cramps and abdominal discomfort.  But people respond differently and there is no set amount of time to wait.  If an individual exercises in the morning, a quick carbohydrate--dense snack might help to provide some energy during the workout without a lot of discomfort.  Generally, carbohydrates are digested in about an hour, while protein takes about two hours and fat about four hours.  But remember, most foods are a combination of the three types of macronutrients."