Believe it or not, this has EVERYTHING to do with the rate of loss. Yo-yo dieting slows the metobolism down due to the loss of lean muscle tissue. The aging process also slows down our metobolism. Top it off with a healthy dose of not exercising and bingo.

My two cents for what it is worth to you:
Change your eating habits for life. That is what these low carbohydrate diets are for. To teach us how to eat and what to eat in order for us to maintain our goal weight. Dieting isn't going to do you a bit of good if you don't change the way you eat. You will always bounce back and forth on the scale until one day it won't bounce back, it will stick on the heavy side and nothing you do will get it moving downwards again.

You can rebuild lean muscle tissue by weight training. We can't stop the aging process though.

Eating too little will make the body think it is famine time and it pretty much shuts down fat burning and holds on to water for dear life. Eating a minimum of 10 to 12 times your body weight in calories staves off this starvation switch.