I know this post might be controversial but I hope people will be reasonable.
I have very low caloric needs. I am convinced that my RMR may be about 1100 to 1000. ( I weight at 157) but even when I was 220 I think it was low, about 1300. I even suspect that I do not burn calories off like I am supposed to. Working out for me doesn't seem to do what it says it does. When I was a teen I would skate every single day for hours... and I never seemed to get the bang for my buck that I should have.
For my entire 20's I searched and searched for a physical cause. But my thyroid is normal. I don't have PCOS and, metabolism testing came back normal. I have normal blood sugar and excellent insulin. How I wished there was some physical cause but none could be found. My doctor insists that it is extremely hard to move metabolism substantially either way.
I believe I take after my mother. My mother told me stories of how she had to eat very little to lose weight when she was about 30 and had been slightly over weight her entire life. Here is the thing that got me though... my mom died of stomach cancer... and for about 6 months prior to her death she was hiding what was going on. She wasn't eating at all... and was throwing up. They put in a feeding tube when she was discovered and I will never forget her doctor being amazed that she only lost 10 lbs. TEN! Now she was 83.. but ... she couldn't physically eat...and only lost a small amount of weight.
After 20+ years of failure last year I lost weight on a very low calorie diet that was medically supervised. So I had proper nutrition. But it took about 600 - 800 cals per day to get results.
Now I know you may think that I :messed: the metabolism up, but I think that isn't true. I think I have been this way my entire life. I gained my weight when I went to college and tried to eat like normal people. At that point it was impossible to lose because it was hard to get regular food that had low enough calories.
Since there were plenty of people in my diet program I am going to have to presume there are people like this. I felt like last year I embraced and accepted the reality of the situation and finally did what I needed to do.