A fad diet is a diet that promises you to lose weight fast and keep it off, but it's not a way of living that one can stick with for the rest of their life. A fad diet can be anything from LCHF (low carb high fat) to shakeology, these days fad diets are mostly low carb diets.
Most people these days know that fad diets do not work, but there will always be teenagers and desperate people who wants to lose weight and don't know where to start, and those infomercials are pretty convincing.
Some people may lose weight from a fad diet, but it won't stay off. The weight that you lose is not fat, it is water. And since your body is made up of about 60% water, you got a lot of water to lose. If you stay on that fad diet you will be losing your own muscle mass along with the water, still not fat. The way that works in short is that the body will still need to get energy from somewhere and if it cant get it from carbs, it will take it from your muscles (that are pure energy) and if you do not get carbs into your system after a workout for recovery, the muscles will try to survive by taking energy from themselves. The scale will go down for you because you will lose fat free mass, but the fat will stay. Losing muscle mass will lead to a slower metabolism and that will definitely not burn stored calories/fat. The reason why you gain all that water back is because the body needs to restore the balance, you need to have a lot of water in the body to be healthy and survive. The reason why you'll now store even more calories than before has to do with the fact that now you have a slower metabolism because you've lost muscle mass.
To get rid of stored calories you need to eat, and eat often. You need to eat protein, carbs and fat every 3 hours. Healthy food is your best friend in losing the stored calories that you so desperately want gone, drinking liquid will never be as healthy as eating real food. And your body knows this, it can tell quality from quantity and the results comes from what you eat. Any information that you read about neglecting carbs, fat or protein to lose weight is wrong. Without all macronutrients, your body will not function properly. It may take a week for you to notice, it might take years before you see the consequences of your lack of a certain macronutrient. Another problem that I see with restricting a certain macronutrient, for example carbs, is that you increase another macronutrient which is not a good thing either. Too much protein for example, will drive even more water and also calcium out of your body. Lack of calcium will take time to notice and will have devastating consequences especially for women and the lack of water will decrease your performance and make you retain water and sodium.
You will need to exercise. Fad diets rarely put any effort into pointing out that you need to workout. To burn stored calories, keeping active is one of your best weapons. If you do not workout right now, any kind of movement will increase your metabolism and reduce stored calories/fat, take a walk or a bike ride for half an hour a day for example. You will want your weight loss to take time, to make sure that you are losing stored calories/fat and not water or muscle mass and also to make sure that you wont get sick or hurt.