Yeah. Cyclists in the Tour de France typically eat 5000 calories a day, often more in particularly difficult stages. Obviously none of them have a weight problem.

"Fun" fact: they also shit themselves on the bike. When you eat that much it's inevitable you're gonna have to poop it out, and it's a race -- you can't stop.

The last part isn’t true, at least unless there has been a grave accident. Many pee on themselves during races, but most of the Number 2 is done at port a potties along the way with an assist from the team car or peloton to get back up to speed and get back into place. You might be surprised at how little someone might need #2 when all their calories are from highly digestible into energy food.

It’s a double whammy because every ounce of shit is one more ounce to drag across the finish line.

I think there's also some other physiological action that trigger defecation as a response during long duration high intensity exercise like marathons and bike races.

Edit: here

"It’s related to the fact that during periods of physical stress, the body shunts blood away from organs that are not necessarily critical at that moment,” Michael Dobson, D.O., a colon and rectal surgeon with Novant Health in Charlotte, North Carolina, tells Mental Floss.

https://www.mentalfloss.com/article/648541/why-marathon-runn...

The reduction in mass undoubtedly makes it easier to complete the remainder of the stage.

It might add some propulsion force if it is diarrhea

It's a question of what your baseline is. It seems OP may have had (say) a 3500 calorie diet as a baseline, then started exercising, perhaps burning an extra 500 calories but now consuming 4000 calories to feel normal. In your case, it sounds like you had a lower baseline--let's say 2500 calories. You may have consumed as much as 2000 additional calories, but you ran it all off--your comparatively lower calorie count was what felt normal to you, and what you made a habit of aiming for.

I’ve done it before too but if you get an injury it gets bad quick.