If I understand South Beach correctly,
it is how I normally eat and have for years. I'm a bit rabid about avoiding processed anything, eat only whole grain products, etc. For a long time I had an inexplicable non-issue with weight (this was before it had a name lol). In the last ten years, however, I have a bunch of weight that will NOT come off no matter how little I eat. In my particular case, a modified Atkins (under 30 carbs a day) worked wonders: stripped weight off while at the same time I had much, much more energy and felt overall better.
I don't know why I stopped, but after the baby is born I plan to resume soon. Provided, of course, that my research convinces me that it is safe while nursing...