>> If I consume 1500 calories per day and burn 2500 I think the key insight is that the body is a complex, dynamic system. So the exercise required to burn 250

>> If I consume 1500 calories per day and burn 2500 I think the key insight is that the body is a complex, dynamic system. So the exercise required to burn 2500 calories will vary between individuals, and even for a single individual based on any number of factors. I won't profess to have all the answers here, but I don't think it's as simple as X calories per mile x Y miles = 2500 calories, where X comes from a table on the Internet. I think it's more of f(X) calories per mile, where f is a compound function that includes the composition & fluctuations of your gut biome and its effect on your metabolic rate. My foggy memories of the research are that in practice, solving f in the real world is quite difficult. So while your calorie deficit theory works, in practice unless you're precisely measuring your compound (i.e. you plus your gut flora) metabolic rate in a lab, you don't actually have a way to know how many calories you're burning.