There are so many diets that it's hard to separate which work and which don't. You can choose to go low carb, low fat, only fruits, only lemonade, detox and the list goes on for a long time. All diets work off of the same principle: if the calories you burn are greater than the calories you eat, you will lose weight (calorie calculator). If the diet is based on this principle, you will lose weight. Whether it's healthy or not will be determined by what rules the diet has, therefore there are some diets you should avoid.
You should be weary of detox diets that force you to drink a special juice for a few days. When you take in such a small amount of calories, toxins actually start to build up in your body, they don't magically get flushed out by the juice.
These diets are unhealthy because you won't get 100% of the vitamins and minerals you need and the only reason you lose a significant amount of weight is because you're not eating anything. As soon as you start eating normally, the weight will come back and you'll probably gain more weight than you lost.
Single Food Diets
You should also be skeptical of diets that force you to eat only one food: grapefruit, lemonade, cabbage soup. These diets are unhealthy because they also restrict calories too much and prevent you from getting all the nutrients you need. Diets that dip your calorie intake below 1,200 are also not healthy or practical.
When you go under 1,200 calories per day for an extended period of time, your metabolism slows down to conserve energy. This means that your body will burn fewer calories and you won't lose as much weight as you planned.
When you cut calories that much, it is also hard to get all the nutrients you need. These starvation diets will cause you to lose weight but it will most likely be in the form of muscle instead of fat. When you lose muscle, your basal metabolic rate will decrease even further.
Low Carb Diets
Diets that cut out an entire macronutrient (macronutrients are fats, carbohydrates and proteins) would lead you to believe that there is something special about that food group that is causing you to gain weight.
The reason that these diets work is because you're reducing calories. Instead of cutting out an entire food group, concentrate on reducing calories from all unhealthy foods, not just those high in carbs or fat.
The Bottom Line
The saying goes, "if it's too good to be true, it is" and evaluating claims made by a diet is no different. The healthiest rate of weight loss is 1-2 pounds per week. While you may want to lose weight at a faster pace, doing so is unhealthy and increases the risk that you'll gain the weight back once you're done with the diet. It isn't worth the cost to your health to lose a few extra pounds.