Who wants to lose weight fast? Everyone.
Whether you just want to lose a few pounds for summer to look good in that bathing suit or you have larger weight loss goals, everybody wants to lose the weight as fast as they can.
There are two main philosophies of fast weight loss: losing weight by eating much less (Very Low Calorie Diets, negative calorie diets, fasting, etc) or losing weight by controlling your eating and exercising a lot more (Biggest Loser, different body building programs). We will look at the positive and negative aspects of both.
Starvation Level Dieting (Very Low Calorie Diets, negative calorie diets, fasts, beta HCG)
There's a reason this kind of diet works. Your body is literally slowly starving itself. Diets of this kind have calorie counts literally similar to the amount of calories starving post-World War II europeans consumed. Exercise is usually not required but low impact aerobic exercise such as walking is recommended.
Positives: Rapid and regular fat loss, little exercise needed to lose weight
Negatives: Muscle loss (makes it easier to regain weight when you stop the diet), possible dietary deficiencies, should be monitored by a physician regularly, loss of energy
Typical foods involved: Soups and vegetables
Body Building Programs (Biggest Loser, Body for Life, etc)
These programs focus on eating quality but limited foods and focus as much or more on exercise to lose fat and gain muscle. Typically the diet involves eating 5-6 small, portion controlled meals per day of lean meats, whole grains and vegetables. Exercise includes both aerobic exercise, interval training and weights to build muscle mass.
Positives: Produce not just weight loss but a more toned and muscular physique with less lose skin, increases energy, positive health benefits.
Negatives: Requires a greater level of willpower and commitment to eating "clean" and daily workouts. Scale weight may not drop as fast as you expect since you are also gaining muscle.