'95% of dieters fail to maintain their weight loss within a five year period.' (Anita Bean, Sports Nutrition, 2013). Rather, changing your lifestyle is what has long-term effects on maintaining a healthy weight.
Rapid weight loss is damaging to the body and doesn't work long-term. You should think about how your lifestyle needs to change otherwise all your hard work at losing weight short-term, will be pointless because it will creep back on.
Combine a MANAGEABLE and MAINTAINABLE nutrition and exercise programme.
To achieve weight loss, you do need a modest decrease in calories, but only by around 10-20% of what your body's calorie intake should be. For example, if I currently have 2,200 calories per day and decrease this by 15% to give me 1,870 calories per day, I can begin losing weight without dropping too many calories.
By modestly reducing your calories by only 10-20%, it will not slow your metabolism down like reducing yor calories drastically does. This is because the body will recognise that it is only a small reduction in calories and so will react by burning more fat. Whereas, if you drastically reduce your caloric intake, your body won't burn fat. Instead it will slow down your metabolism in an attempt to preserve its energy, not knowing when it will next get fuel. It will also cause your body to use up what's left of the glycogen (carbs) in your body and begin using protein as fuel (needed for muscle). The end result being loss of lean muscle, low energy (not good if you enjoy training), hunger, mood swings oh and smelly breath.
For fat loss, stick to 10-20% of what your daily calorie intake should be, which is your Basal Metabolic Rate + the calories you use for exercise (You can work out your BMR by following this link- http://www.myfitnesspal.com/tools/bmr-calculator). By reducing your daily calorie needs by only 10-20% you will have slower fat loss i.e. 1lb every 10 days, but surely this is better because it is more realistic and sustainable. Not to mention kinder to your poor insides!