I once weighed nearly 300 lbs and am now in the high 180s (”normal” weight for a man my height) so I know both sides of the coin.
I do strengh training or cardio nearly every day and my friends remark at how little I eat. I determined my caloric needs to be no more than 1200-1500 calories depending on the foods. I never feel full and often times eat less than women do. Sometimes, I won't feel hungry all day if I'm stuck behind a desk.
If I eat any more than that, I gain fat instantly. My friends normally eat double that, don't work out regularly and have always been thinner. When I ate like my friends, I became 300 lbs.
I like to hike, and have been surprised to see people who are outright obese climbing mountains. I have also seen really old people making it to the top. However, I am reminded of the saying that there are "old pilots, and bold pilots, but no old bold pilots." I have yet to see any old obese hikers!