As some of you know, I subscribe to Runner's World magazine. This magazine has a lot of really great articles about training, diet, and anything else that relates to running. I read in March's issue about how your body burns sugar vs fat. It suddenly made my training make more sense. I don't have the issue in front of me, but the gist of the article was that in the first 20-25 minutes of your run you're using quick energy (sugar). Once your quick energy is used up, your body switches over to long-term energy (fat). Getting the fat to start burning can take a little bit, but once it starts burning you have your "second wind". I really identify with that. It's always around the 25 minute mark that I start to feel a bit fatigued.
Why do I bring this up? Well, I noticed a more significant weight loss when I was training for the Peachtree last year, when I was running 50-60 minute runs. I wasn't eating less. In fact, I was eating more because I was hungry all the time. I wasn't trying to lose weight, but it happened. So it seems like to maintain this weight loss I should have been running at least once a week for 30+ minutes. I guess it's one more incentive to keep training!