Hi nzkoobi- I run races of 50 miles and up. I am going to run my first 100 miler within the next year. I know this goes against Mark's beliefs on fitness but I have built up my body to where 50 miles doesn't phase me. This is from a combination of moving at a slow speed for an extended period of time, which would have been required by primal man if he had to relocate due to the absence of food in the surrounding area. My body seems to be built for it as I have never been injured when running 12+ hours. I do take walking breaks just to switch muscle use, and my running muscles are able to recover while I'm walking. This fast recover rate has taken years to acquire. I never run myself into the ground. I have switched over to a primal diet for several months now and so have tampered with incorporating PB with my training. I have found that I run best when I have not eaten breakfast prior to a run, I have found that this causes my digestive system to do too much work in addition to increasing blood sugar levels. The main idea is to make sure your body is in fat burning mode before running, and to keep it in fat burning mode. When this is accomplished, you have a nice slow steady burn of fuel because your body is burning fat rather than sugar. If you enter sugar burning mode, you will have cravings for sugary things, which will make it hard to stay primal, in addition to causing your body to tear apart your muscles for fuel rather than using fat. I always eat a hearty meal the night before a race, or long run of a lot of meat very dense in saturated fat (I prefer red meat the night before), I have found that the fattier the meat the night before the better run I have, then I throw in a lot of green veggies, and usually some cheese or sourcream (which I admit may or may not be the best but the general idea is to get lots of fat and protein). I am usually stuffed at this point, and not in the mood for more food, so I let my stomach settle for a few hours then that is when I get in some primal sugar to top off my sugar stores, which is usually berries. However, I don't eat them alone, I always throw in some sort of fat source, just to make sure that I don't spike my blood sugar before my run. Usually I douse my berries in yogurt, but you can do it any way you want but I would recommend some sort of fat with it. I would also recommend running barefoot or in vibram fivefingers at least once a week, this teaches you good posture, which will also help you avoid injuries.