Nancy, in your Sports Nutrition Guidebook, you mention that athletes can eat within 5 to 30 minutes of exercise and get results. It has always been my understanding that it takes quite a bit of time before food can be digested. I have been taught that food doesn't leave the stomach for about 2 hours. I also was under the impression that physical activity, such as running, drew blood away from the stomach thusly slowing down the digestion. Thanks for helping me better understand how to eat pre-exercise.
Yes, believe it or not, 100 to 200 calories of carbs eaten even 5 minutes pre-exercise can enhance your performance (assuming you can tolerate the light snack). If you were to eat a heavy high protein/high fat meal such as a cheese omelet or cheeseburger, the protein and fat would linger in the stomach and possibly talk back to you. But carbs are readily available, as witnessed when a person with diabetes has low blood sugar and is given some orange juice or cola. That sugar gets into the system within three minutes. The same goes for athletes.
As for blood flow, if you are exercising at a pace you can maintain for more than 30 minutes, you can both digest the food and use it to enhance performance. The trick is to practice pre-exercise fueling, so you learn what foods, and how much of them, will contribute to better performance for your body.