TL;DR incoming. Sorry but context is relevant. I'll try to summarise.
When I was 20, I exercised vigorously everyday- aerobics and weights. I was 5'3" and I weighed 200lbs but I looked oddly fit (well, I mean for a fat person) because I exercised so much. Every day I ate exactly 300cal salad, a 250 cal soy bar, a normal meal of around 350cal, and two small snacks. My total calorie intake was under 1200cal. I did fasting days as well. I was BMing regularly everyday, had normal monthly periods, felt good, but I was not losing weight.
Went to an endo. She ran some tests and was baffled. My bloodwork was very nearly perfect.
BP: 100/69 Heart rate: 60-65bpm. HGA1C: 4.6 Fasting blood sugar: 85 Triglycerides: 60 I don't remember what my HDL and LDL were but they were both well within range of normal. So were my T3s, T4s, and TSHs. I was metabolically very healthy.
The ONLY spot on my health record was PCOS. Everything else was perfect and yet there I stood, a fat little shit. She made me run on a treadmill for an hour which I did without any problems. She made me monitor what I was eating. She sent me to counseling. She made me fill out a comprehensive history of my entire life (the main points of interest were extremely unhealthy eating habits as a child and antidepressants from the age of seven).
She told me that I have hyperplastic obesity. Because my eating was so out of control in my childhood and teenage years and also because of all the medications I was on, my body made more fat cells than it was supposed to. Fat cells only shrink and expand. They can't disappear out of your body. She told me I would never be able to get below 200lbs.
I was in shock. I didn't believe her so I went to someone else. She did something called a "body comp test (?) and told me my lowest healthy possible weight, at 5'3", was 190lbs. (Long story short, I refused to believe her too. Found another doc who nearly killed me with dangerous meds that accomplished nothing.)
I wanted to die. As far as I was concerned, I had been condemned being a disgusting amorphous blob. So I went home and tried to kill myself. My mother saved my life so I waited a week and tried again but she saved me again. I realized that would destroy her so I figured I'd wait till she died then kill myself. Until then, I figured I'd just eat whatever I wanted because it doesn't matter. I'm going to be a fat disgusting monster no matter what I do. 200lbs, 300lbs... what's the difference? Fat is fat. So I ate whatever I wanted. I didn't really eat a lot of food, just bad things. I stopped eating soy bars and salads and switched to ice cream and cookies.
It was not long after that I decided to go off the meds. They had never worked anyway. Lo and behold, nothing changed. I realized that if I was going to find happiness, I was going to have to work for it. No pill would solve my problems. I learned how to be happy. It wasn't easy and it took me years but I experienced real, genuine happiness for the first time at the age of 25.
Unfortunately, by then, the damage had already been done. I fucked up. I had a chance and I blew it. I'm pretty much screwed. I handicapped myself so badly that I'm beyond fucked.