The problem with diets is that they invariably restrict the intake of certain food types (e.g. Carbohydrates). This leaves your body starved of energy and so it starts to break down your fat reserves to make up for the shortfall in your diet. This sounds great in principle and achieves the desired weight loss.
To stay on these diets for long periods of time can leave you feeling tired all the time and be detrimental to your health.
Moreover when you come off the diet your body says to itself “hello, carbohydrate… I haven’t had that for a while…I’d better store this as FAT because I don’t know when I might get any more.”
You may find that not only do you quickly put the weight back on but very often end up fatter then when you started.
And so you start the whole process again sending you into a never ending cycle of Yoyo dieting, never achieving your goal for very long, always hungry and miserable.
The key to weight loss is portion control at meal times and regular exercise.