I lost a lot of weight, which was such a pain I wouldn't bother again (Yes gradually a lot has gone back on)
I saw a dietician who told me 2500 is a myth, there's a wide range. My Base Metabolic Rate was right at the low end of the curve, around 1300 cal/day. To lose weight I needed to go under 900, which meant recording everything I ate and keeping a diary. Reducing intake reduces the MBR. I got more tired, etc etc etc. I read up loads of stuff... Complicated.
The Minnesota Starvation Experiment has been re-examined more than once, fascinating stuff. REALLY showed how different we all are. Worth looking at the outcomes.
I went to a gym every other day for 2 months - it helped, but not much. Glad to give that up! Switching between low fat and low carb did help, the keto diet worked. I remember the weight had plateaued for about 2 months, then on keto it dropped off a cliff. Another time I'd been doing very low cal "balanced" and it stuck, until I went to a wedding. I overdid the carbs, and it dropped suddenly - common apparently.
Maybe I'll try Atkins (keto) again. After the first few days you feel a "flu" feeling then you feel fine. Exercise is limited now my joints hurt.