Have any ex fat guys/girls lost any weight without a diet change when you started?

Just exercising? I know it won't work forever but there still must be a significant amount you can lose going from dormant to exercising. Especially if you're like 300lbs.

I'm just wondering for the start mostly. Not the entire time I know it will have to change eventually to maintain a healthier body.
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The reason I ask this is I'm not ready to change my diet. It's hard enough for me to do the exercise so I wanna start with that and then do diet later. I'm not the one that buys the food at my house either so I can't really do it until I have money.
Have any ex fat guys/girls lost any weight without a diet change when you started?
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