I think there is a level of calorie intake for women that constitutes something not quite at famine or anorexic levels but is still a deficit and if you spend a long period of time at this level the body adapts to it very well. The body slows whatever processes down that it can to preserve fat. You probably also slow yourself down, doing less activity, doing whatever activities you do do at a reduced or less effective level, choose activities that your body has adapted so well to that they aren't even exercise anymore. Your body probably also refuses to grow any new muscle so you'll just spin your wheels at anything you do try to do to improve your body composition.
You can decrease calories to anorexic levels (remember, anorexics don't eat 1000 calories a day, they eat more like 500 or less) or you can increase it a little so that the body will stop slowing things down. It's like a sweet spot. You have to have the energy to be active or your only other choice is actual starvation.
Anyway, for anybody trying to lose weight, it's a good idea to ask yourself once in a while if what you are doing is working for you. Catrin had to ask herself that and so she tried something that seemed radical and it worked. Just because it doesn't make sense doesn't mean it didn't work.
Female, 5'3", 49, Starting weight: 163lbs. Current weight: 135 (more or less).
Starting squat: 45lbs. Current squat: 157.5 x 2