I have no idea but wonder if it has to do with set point theory. A person who always weighed 140 has a metabolism that maintains that weight for her at 1800c, but if she dieted to lose that weight, she had to fight her higher established set point to get there. One theory holds that one can change one's set point through cardio activity over a period of time, which changes the metabolism.
This also reminds me of a similar sad fact. After 50, women just can't maintain their weight eating the number of calories that the math or SP ranges would prescribe. We know that, sadly, we have to consume at the low end of our range to lose or maintain.
"Awareness is all."
"Letting go is much harder than fighting."
"Everything is exactly the way it's supposed to be."
“Life is about not knowing, having to change, taking the moment and making the best of it, without knowing what’s going to happen next.” —Gilda Radner
"God grant me the serenity to accept the things I cannot change;
the courage to change the things I can; and the wisdom to know the difference." --Reinhold Niebuhr
| current weight: 3.4 over