I think it really depends on what works for you and what type of rides you're doing. I've found that when I ride in the morning, about 200 calories is usually enough to keep me going for a 1.5 hour, pretty hilly ride. I've noticed that if I eat anything heavy directly before riding, I feel sluggish. I would be curious to know whether the idea of a large meal directing blood flow to the GI tract really just has to do with the type of meal you eat. Are they comparing what your body does while riding when it's trying to digest a meal of whole grains and veggies that you ate before the ride vs. what it does when it's trying to digest gels, bars, and other easily digestible foods that you ate on the bike?

I have a feeling that this idea is related to bonk training. Bonk training is a good idea in theory but I don't know, glycogen is also fuel for your brain, which is a good thing to have fully functioning when you're going fast on a bike...