This is why people cannot maintain their weight loss once it has occurs. Diets teach deprivation or require eating special diet foods, and because of this, we cannot possibly stay on it. How realistic is it to believe that we can stay on grapefruit or cabbage soup for the rest of our lives? When we deprive ourselves of the foods that we like, we crave them even more! This often leads to bingeing on the foods that we have been trying to avoid.
Dieting and depriving our bodies of proper nutrition will affect our metabolism. After all, our bodies will not let us starve. Eating too little food can actually make it more difficult to lose weight. Our bodies try to hold on to the weight to survive. The metabolic rate slows down, and our bodies try to store any portion of the incoming calories in our fat cells to make sure there is a reserve for the next time you go on a starvation diet.
The moral: the problem of gaining weight gets worse with every diet that you go on, and you will probably weigh much more than before you started the diet.