When you lose weight, it's normal for your metabolic rate to slow down. The reason being when your body weighs less, it has less work to do and the less work your body does the less calories you burn.
For example. if you weighted eleven stone before you completed your diet, and now you weigh nine stone you need too eat less so you can maintain your correct weight.
This can be very difficult to maintain, normally when people complete diets successfully they feel great, two years later often people end up gaining more weight that when they started the diet two years before.
When the metabolic rate slows down within the body, you'll have to reduce your overall food intake forever, this is a very though challenge.
Exercise and healthy eating is the best way to help weight loss. People whom take up physical activity as regular practise can help change the metabolic rate. Aerobic exercise will burn calories during training also will increases your metabolic rate, for up to several hours post workout. Crash diets tend to affect your muscle tissue.
This form of dieting in the long run can be harmful as it focuses on the muscle tissue loss. The more muscle you have the more fat you will lose, best to not diet at all! all you need to do is eat less carbs more fresh proteins then exercise regular.