I don't know about studies on cardio or what not, but I'll say that as a D1 runner, I have never seen an overweight person who runs more than 50 miles per week (and I have met thousands of runners in my life).
"This is joke, right? I almost stopped at the first sentence."
"Derp"
"Most basketball players are tall. I guess basketball makes you taller."
If you know some counterexamples personally, I'd be very interested in hearing about them -- it would be an unusual situation.
They also run a slow 50. But, they still run around 50 a week and they are overweight.
The point being there is nothing magical about running long distances and being lean, IMO. Someone could (and like I said, I know several) run that and be overweight). I know plenty of people who ride bikes 150-200+ miles a week and are overweight.
What I suspect you mean when you say 50mpw is that someone running 50mpw at 5 min/mile pace (or less) is not going to be overweight. And that is probably true. But you are factoring in intensity then, which changes the equation entirely.
For instance, I know someone that lifts weights 4 times a week for 1 hour a day and is fat. He's been doing it for years.
I also know someone who lifts weights 4 times a week for 1 hour a day and just won a local bodybuilding contest.
There are so many things I didn't say in the above it isn't worth talking about them? What are they eating? What does their workout look like? Are they both lifting the same weights? How intense are they working out? Adequate sleep in both cases? Any sprinting?
Like I said, I suspect what you meant in the 50mpw case was also something about intensity, not just distance.