The Atkins-type diets aren't for everyone, the way high-carb, low-fat diets aren't for everyone. The Atkins, South Beach, et. al programs are based on the insulin cycle. Basically, neither fat nor protein stimulate the pancreas, which means no insulin is released. Since insulin lowers blood sugar (and is released in a response to elevated blood sugar, usually created by the consumption of carbohydrates), that drop in blood sugar makes people hungry. So if you don't start the vicious cycle of so-called "insulin spikes" in the first place, you eat less because you aren't as hungry. That's why people tend to "pig out" on candy bars as kids, but rarely on, say, steak.

I read some really compelling evidence that one's optimal diet is linked directly to blood type. It's been shown that human blood types evolved over time. First O, then A, then B, then AB, each relating to a point in human evolution. O is a staunchly hunter-gatherer type, based around proteins and vegetables. A is similar, but able to digest a wider variety of vegetables and some grains that have had very little processing. B is somewhat more agricultural, with a balance between protein, vegetables, and some more grain products, while the AB type is semi-vegetarian to vegetarian.

All I know for sure is, it works for me. There's a book called "Eat Right For Your Type" devoted to this idea, which I haven't read.

YMMV.