I've personally lost that much twice. The second time was due to illness while traveling, but the first time was when returning to serious distance running tra

I've personally lost that much twice. The second time was due to illness while traveling, but the first time was when returning to serious distance running training after a multi-year layoff. Not only did I lost 20lbs in a month, it was a total of 55 lbs over three months. I went from struggling to do an easy one hour run to running over 150km/week. I'm almost positive your math is off on the calorie burning. As an overweight guy, you should be burning over a 100 calories per km, not mile. Also, there's more to it than just what you burn while running. After a certain tipping point (about an hour a day for me), it seems my body just doesn't want to store fat. I'm not sure if it was a factor, but like most successful distance runners, I stuck to a low-protein mostly plant-based diet while training. The other factor to consider is that someone approaching running from being a sedentary programmer (as opposed to a bodybuilder), you'll be building up muscle and even some bone mass as well as losing the fat. This is the case for pretty much any weight-bearing activity (eg, skiing, snowshoeing, etc)