If you're a hobbyist runner, this equation very quickly gets flipped on its head. It's very difficult to make up the calorie deficit from a 20 mile long run every week. Throw two big races a year into the mix, and maintaining weight and muscle mass is the challenge. When I trained for ultramarathons, I sometimes ran two mountain long runs back to back. That put me 5000 calories in the hole every single weekend. I used to eat an entire large pizza by myself (2000 calories) and still be hungry 30 minutes later. There is an upper limit to how fast you can digest food, and that quickly becomes the limiting factor. I was not a professional. I ran as a hobby, rarely exceeding 50 miles a week. There are thousands of others who run at this level.
If you’re a hobbyist runner who finds it challenging to eat an extra 5000 calories in a weekend, you’re in the socio-physiological upper 0.1%. It’s great for you, but not a very relevant anecdote to the majority of people seeking help with weight management.
It's interesting, though, even if it doesn't apply to you. It's something to think about, and something I do think about with some regularity -- how I'm going to schedule all the additional eating I'm going to have to do if I start a real exercise regimen at my height and weight.
