Have to disagree with the last one. There's a lot of solid biochemical and nutritional research behind the Caveman (aka, paleo, aka, primal) diet. See, e.g.,
PaNu or
Mark's Daily Apple for any number of posts -- some technical, some not so technical -- about the science behind the diet. With links to peer-reviewed medical research, esp on PaNu.
In practice, the paleo diet is much *less* extreme than Atkins or other popular low-carb diets. The latter ask you to keep carbs <50g/day (or, in some cases even lower) in order to be in ketosis. In practice, achieving this means that you not only have to eliminate grains and sugar, but also curtail the amount and types of veggies, nuts, and fruits you eat. Oh, and count carbs assiduously.
The paleo diet isn't about counting carbs, but most people who follow it eat about 100-150g carbs/day. Less than the SAD (300-600g carbs per day, mostly from refined sugars and grains), but it still allows you to load up on veggies and nuts and eat fruit in moderation.
The basic argument behind the paleo diet is just that humans transitioned from a hunter-gatherer to an agricultural society only about 10,000 years ago. This isn't long enough for our physiology to evolve to the point where we can process grains. We didn't become cows with the advent of agriculture. Well, except in the pejorative sense.
Buy it or not, it's not even close to the level of ridiculousness as the other diets in the list! (Which I agree are really, really silly.)