Gatorade is actually really good for you. I recently worked as an intern for a pro football team, and all they drink is gatorade as you can tell by on TV. it helps to replenish the fluids lost during exercising. Even though during practice they had the choice of drinking gatorade, most drank water. But gatorade is filled with a lot of sodium, so when your on long rides (practices in there case) don't pass out from de-hydration. My guess is you drank so much that you replenished your fluids in your body, and then gain 3 pounds in water weight. Its really easy to lose and gain water weight. So my suggestion for next time, is drink water, but when you get back from your ride/run, drink a gatorade to regain the sodium you burnt off.