Not a pro, nor do I play one on tv. However, I have restricted carbs and paid the price with wonderful bonks. One while hiking that had my legs shaking so badly that I could barely walk, and numerous other times on the bike. Problem is, sometimes you don't really know what's happening at the time. You're just slower than anyone else and just can't ride as fast as you think you should. As others have suggested, low-carb is fine for sedentary folks. Moderately active, or cyclists, who tend to workout for periods longer than most one-hour aerobic classes, need to be on a smart-carb diet. No refined sugars, but brown rice (no, fried rice with soy sauce is NOT the same thing!) whole grains, high-fiber, fruit and veggie carbs are the way to fuel your active lifestyle.