The Paleo Diet
The aim of the Paleo diet is to only eat food which was available to our ancestors, and prior to modern farming methods. The thinking behind the diet is that this sort of food is what we are genetically predisposed to find healthy.
The theory behind the paleo diet is that we, as a species, have been eating more or less the same way for over 2 million years. Then, about 10,000 years ago modern agriculture took over our previous hunter and gathering habits which introduced food sources our bodies aren't adapted to use in the best of ways.
The argument is that our genetics haven't changed in the last 10,000 years to be able to cope with the multitude of new food sources available to us.
What can't I eat?
By eating Paleo you remove starchy carbs (bread, pasta etc), refined sugar and dairy from your diet. Basically if you can't pick it or kill it you don't eat it. Also no potatoes or legumes (as these have only been bred to be consumed by humans and are very starchy)
What can I eat?
Meat, fish, Veg, seeds, fruit & nuts.