A low-carb diet did not work for me. A couple of years ago, I went on the Atkins Diet. The first two weeks where carbs are severely limted (like 20 grams per day), I felt just horrible all day and it got worse when I exercised. I would try to mtn bike or hike and I thought I would collapse. My whole body felt like it was suddenly made out of lead.
I tried this plan because some people have reported losing like 11 pounds in the first two weeks. I lost 3. Eleven pounds would have been worth feeling miserable, but 3 was not.
Low-carb diets may work for some active people, but maybe you need to work into it slowly. Also, if I were to try it again, I would do something less restrictive like Carbohydrate Addicts or Sugar Busters.