I think it depends on your training volume. It's interesting; I see so many sources that claim that exercise is not helpful for weight loss, but it's so different from my personal experience. I personally lost 25 pounds without decreasing calorie intake while preparing for and doing marathon training. I experimented with a vegetarian diet, but I lost little to no weight during that 2 or 3 month phase.
Admittedly, I saw no changes in weight until I hit about 20 miles per week when preparing for starting an actual training schedule. After around a 25 pound decrease, or ~30 to ~27 BMI, I think I'm closing in on my personal limit for weight loss without dietary changes or sacrificing more than I'd like to before the marathon, although I'm eating much more to sustain 40-50 miles per week.
At an estimate of 100 calories per mile [0], 20 miles per week is about 2,000 calories burned, and 50 miles per week adds up to 5,000. I find it difficult now to improve substantially without increasing calorie intake, but the weight loss just happens whenever I ignore nighttime hunger for 2 or 3 days a week during training. I ate the same amount or less without experiencing this hunger when I was heavier.
I wish I could offer some sort of source other than my anecdote. I can think of a few possible reasons why I'm not finding any data on this:
1. It's hard not to increase calorie intake while increasing exercise enough for weight loss to be noticeable. Based on my note above about only experiencing weight loss when I experienced mild hunger, it seems as though the same traditional calories in, calories out principle and the difficulties that come with that apply.
2. At the slower pace I've been running and that many who start off obese may run, it takes a lot of time to build up to the training volume necessary to experience weight loss. This may be difficult to replicate with a large enough number of individuals willing to participate in a study due to individual time constraints or job inflexibility.
3. This only works up to a certain point. I have not been successful in getting down to <25 BMI. BMI's an imperfect measure, but it aligns with my goals. I will be making dietary changes to decrease weight further, but intense exercise has been great for getting me started.
4. Not all calories are equal. I've learned a lot about nutrition since starting training and try to eat more foods that are high in iron. My diet is quite high in carbs, though, which most plans that don't require sacrificing calories do not recommend for weight loss.
5. It's possible that I've actually decreased my calorie intake without realizing it. I really doubt this. On Saturday to load up for a Sunday long run, I ate an entire small pizza, french fries, and tacos for dinner.
Does anyone else have similar experience with weight loss or have any sources that would advocate for high volume endurance exercise for weight loss?
[0] https://www.healthline.com/health/fitness-exercise/running-b...
Edited for grammar.