Anyone Losing Weight Mainly from Fitness?

I did manage what you wish to do a long time ago when I was in my early 20s. It was not my goal to lose weight, it was more of a side effect that kep me at something like 18 BMI and I think now a very low fat percentage for a woman. It involved a routine of something like 3-4 hours exercise per day, at least half of it aerobic, plus walking everywhere. I was at the time a post grad student, so usually I used a combinations of buses and lots of walking to get to uni, then walked really fast for an early lunch break half an hour to the cafeteria and another half to get back, had some more classes, a break of a couple of hours to spend two hours at the gym, a combination of intense dance classes and some weights, then would go back to assist in the lab until evening, and then usually joined a friend who was training for marathons (I was not into races, but would do part of his routine with him, so like an hour interval running). And then I had to use the combination of buses and walking to get back home.
It must have been more than 1000 calories burned per day on exercise alone, but (1) it took me some years to get to that level and (2) it was for fun, doing things I loved, I cannot imagine exercising for hours just to lose weight without dieting.

The thing is, one average sized dessert equals about an hour of walking or half an hour of harder cardio. It is very, very easy to exercise like crazy and still overeat.

I lost 125 lbs, from morbidly obese to normal weight, without ever reducing my calories lower than 1600 daily, and on most days I ate 2000 or more. I aimed for at least 400 calories of exercise daily. That's a lot of work, but it did have great results. I even managed to continue eating in a deficit after a leg injury which restricted my activity, by focusing on what I could still do.

But 400 calories equals the extra part of one slightly too large steak that you didn't weigh, you just eyeballed it. Or half a dessert eating out. Or a few too many fries off your husband's plate because you deserve them for working out every day. For consistent results it really is best to log consistently, so your eating doesn't increase as your exercise does and wipe out your exercise deficit.

Well, I have noticed that the times in my life when I have put on weight have been when my activity level has dropped (getting a sedentary job, or after injury), so adding activity has become an important part of my weight loss.

Being quite short and having a desk job, my recommended intake to lose weight is 1200cal, which doesn't really thrill me - I find it quite useful to supplement that a bit by adding in some exercise.

I spent three hours riding a bike in the sun today. That's three hours I wasn't tempted to snack. It's also fulfilling on a level that makes it easier to say no when people bring doughnuts into work and leave a box in the kitchen for everyone.

I unintentionally did that in high school...but gained it all back when I couldn't keep up with the exercise volume.
Way better to create a deficit with calories, it's more sustainable, but to each their own I guess.

A lot of people here want to say it can't be done.

A friend of a friend just finished hiking the Pacific Crest Trail, and lost 40 pounds in the process. He ate entire jars of peanut butter in a sitting.