I actually do think it's pretty much as simple, for most people, as counting calories and determining approximate usage. Is it exact? No...but it's close. There's some fluctuation as far as water weight.
I use this...works great...
https://www.precisionnutrition.com/w...oss-calculator
My non-expert opinion is that people aren't honest with themselves over activity level, or caloric intake. They forget that 32 oz soda and then complain that calorie counting doesn't work. Garbage in/garbage out. I also think a whole lot of pseudo-experts make a lot of money by over complicating it.
How'd I get big? Well, I've been heavy to some extent for most of my life. My family tends to be heavy...my parents were both over eaters, and poor eaters, and neither were active at all. I learned poor habits, just like they did, and I really like food. I was nonathletic, and that discouraged me from athletic endeavors.
I was mostly able to keep my weight somewhat under control through cycling. Sometimes I rode more, and I'd be less heavy, sometimes less, but i ALWAYS rode. About 6 years ago, I was hit by a car and it broke my knee. It was a rough year...there was the injury, we were robbed, my brother in law died...i fell into a depression and got complacent. A year or so later, I was laid off from work and began a new path to be a CPA...which meant lots of work going back to school. Then I had tax season.
Classes were tough...the CPA exams were tough...and I was having marriage issues, though I didn't realize it. My wife was also inactive, and prone to complaining about our inactivity without being willing to do anything about it. We both like heavy, rich foods, and she was a great cook. So she'd complain about our diet while baking cookies. I was depressed, I was inactive and the inactivity and weight gain led to back issues, which made me less active. Life has inertia, in both directions.
Last year I was gasping for breath, and in pain, walking a quarter of a mile.
My wife separated in December, and it was a serious wake up call. I had gotten to 330 lbs...could barely ride at all, could barely walk...was depressed...
I started just walking around the block...but I did it REGULARLY...and I started counting calories. Within a month I could walk a mile. Two months...3 miles. I started riding again, and it kept getting easier the more weight I lost...and more enjoyable.
I'm down to 210...almost totally out of obesity range. Went from 3x to L. I ride 30-40 miles at a brisk pace (average about 13-14mph) every other day. I walk 5 miles on ride days and 10+ on non-ride days. I've slacked slightly on food intake, but I still count...and I keep it REASONABLE. I'm still losing, just not as quickly, which is perfectly fine. My back still bugs me at times, but no where NEAR as badly, and I can fight through it more easily. I feel 100% better.