I did the Fast 800 programme and went down to 9st 7lb (am 5.6) and STILL didn't like the way I looked.
I was quite surprised actually as I thought I would. I couldn't understand why I didn't look good.
Then discovered the gym and got a personal trainer.
What I learned from own reading is that its all about loss of muscle mass.
When you lose weight, you may think you are only losing fat (I certainly did think that when I yo yo dieted in my late 20s) but actually the body makes no distinction between types of weight.
Weight is actually made up of fat and muscle mass.
So while you are losing weight you are losing fat. But you are also losing a proportion of muscle mass.
This is inevitable for two reasons.
First if you aren't lifting weights I.e. applying progressive over load then your brain thinks....uh oh we have less calories coming in...am I going to ditch body fat or muscle mass....well we aren't using the muscles so let's ditch some of that and keep a bit more of the fat for a rainy day.
Alternately you might be exercising, in which case the proportion switches up a bit, you might lose more body fat and less muscle mass, but you will still lose some muscle mass. Unless you are lifting heavy weights, at the sort of level you would lift if you were really trying to grow your muscles i.e. training to failure on a set of reps in the gym.
So all this means we lose weight but look less toned.
It's actually quite a challenge to build muscle mass once it's been lost as it requires progressive overload, AND eating in a calorie surplus to actually build it from something.
But you can recomposition body fat into muscle to some degree, if you are lifting weights and eating at your TDEE level.