I have a few friends that have been using the Atkins diet. There is little disputing that it can work, but the only info I have turned up on it is pretty negative. Something about really depleting the body of calcium, by being in a state of ketosis you dramatically increase the acidity level in your body which can quite quickly impact on bone density etc. I am not an expert by any means but it was enough to give me cause for concern. I wouldn't do the diet.
I wouldn't however rule out First Contact