Low carb diets usually produce a high level of weight loss in the first week. A lot of this weight loss is water, but a significant amount is fat. The biggest problem with low carb diets is that your body responds to a prolonged low carb diet by lowering it's metabolism, which makes it harder and harder to lose fat over time, and can result in a lot of rebound weight gain if you stop the diet and start eating whatever you want (which you should never do because you should aim for permanent lifestyle changes, not short-term solutions.)
So what can you do if you need to lose weight? Lots of carbs might keep your metabolism up, but they will make you fat and could cause health problems. Low carb diets can slow your metabolism to a crawl. Seems impossible?
Not really. The key to low carb diets is to do them properly. Never eliminate carbs altogether (unless you are so advised by your doctor) and make sure the carbohydrates you eat are complex carbs which are always ingested with a protein to avoid blood sugar and insulin spikes. Keeping your blood sugar stable over time is the key to avoiding the waking up the "insulin monster" which is determined to make you fat and unhealthy. Remember that there are many starchy vegetables, like carrots, corn, and potatoes, which can get you the carbs your body craves in addition to larger amounts of fiber and vitamins. This helps you avoid eating bread products which can be problematic for many people.
If you notice yourself plateauing on a low carb diet, take one or two days where you increase your carb intake. Keep it healthy--this isn't permission to pig out! Depending on your age, weight, sex, and activity level, extra carbs might mean a whole-wheat bagel or two or it might mean a large portion of whole-wheat pasta as well as the bagels and an extra sandwich. Keep it to no more than two days before dropping back down to your regular carb intake, and you should start to see the scale budge again. Low carb "diets" should really be lifestyle changes--nobody actually needs the level of carbohydrates that the average American considers "normal"!