I went on a ride a couple weeks ago (getting a little cold now) after eating primal for a couple of days and was dead tired after like 30 minutes. Usually I don't start feeling tired until approximately 2 hours into a trail ride. For breakfast I had a big shake with some fruit/veggies, and some cereal (figured it would help), and before the ride I had part of a cliff bar. I pushed through the ride, but it was not enjoyable at all. I wasn't riding super hard, and the trail wasn't exceptionally difficult, but I still felt like I was breathing through a straw. Am I not getting enough carbs pre-ride? Is my body still tuned to carb burning? How long does it take to get efficient at burning fats as a primary energy source instead of carbs? Has anybody else had this problem? (I realize I may not be asking the right questions, and I'm open to criticism and advice!)