When you're younger your metabolism is faster. I weighted 8.5 st most of my life...until i hit 40. Then your body does a weird thing...it worries that if you fall over you might break a bone, since they're getting more brittle with age... So what does it do? It bulks you out so if you fall over you just bounce instead of break.
In 4 yrs i went up from 8.5 to 12 st and i WASN'T pigging (well not all the time...) Tried eating healthily, took PLENTY of exercise (paintball, gym 2-3 times pw, 2-3 boxercise type classes pw, dancing for 3 hours twice pw and my job is relatively active).
But the soup diet works - trust me if you need to shed some kg - i lost 16lb in 10 days and wasn't hungry once. After, when i ate normally the weight stayed off- for 4 months my weight has been stable. The trick is only to do this for short periods. No it's probably not healthy but if healthy eating and exercise doesn't work and you want to see your feet/tackle again from an upright position, try it