Just think about this logically for a moment.
Diets like the ones marketed -yes marketed, because each of these diets is a brand, a product that you are being asked to buy - by Atkins, the South Beach product-makers, and others emphasizing low or almost no carbohydrates, are asking you to believe the impossible.
The claim that "a diet rich in fats without carbohydrates will lead to stunning weight loss" sounds too good to be true, because it is - at least in the long run.
Sure, as your body goes into shock without the critical addition of carbs you will lose some weight, but this diet is not sustainable - it is very, very difficult to adhere to in the long-run.
That short-term weight- and fat-loss is the only dramatic effect you will experience.
This type of diet, scientifically dubbed "ketogenic", forces the body to turn to fat stores to burn in the absence of energy from carbs.
It should be noted that the word ketogenic is also related to the serious illness ketosis, which is the buildup of harmful acids in the bloodstream, something that can occur with long-term adherence to a diet of this sort.
You may be losing weight at first, but a great deal of it is water.
Furthermore, your body catches on to the changes that are happening and slows your metabolism accordingly - not a good thing.
You are now stuck with a lowered metabolism and a diet that is designed to fail without the strictest adherence for the long haul.
And honestly, who can really adhere to these diets for several years?