If you're new to the concept of eating Paleo, here is the abridged version. The Paleo Diet, by Dr. Loren Cordain, refers to the way our paleolithic ancestors ate before we turned agrarian roughly 10,000 years ago. The premise is that 10,000 years is too short in evolutionary terms for our digestive system to have adapted from hunter-gatherer to a diet higher in grains, nuts, seeds and seed oils, legumes, tubers and dairy. In order to be healthy, we need to eat true to our evolutionary profile.
You may have heard the Paleo Diet referred also as the Primal or New Evolution diet. They have slight variances in what foods they allow and disallow. The guiding principle, however, is to look at what our paleolithic ancestors ate and use that as a template (within reason) for today's diet. If you can 'gather' it and eat it directly, chances are it would be Paleo-approved. However, any food requiring grinding, fermenting, processing - you get the picture - to make it palatable would not be on the menu for our paleolithic ancestors.
Grains in particular, which are high in lectins, have been implicated as being one of the primary culprits in causing a leaky gut. Dr. Cordain believes that the development of a leaky gut is what triggers most - if not all - autoimmune diseases. Many of these diseases are on the rise, such as Ulcerative Colitis, Crohn's, Celiac, Multiple Sclerosis, and Type 1 Diabetes. By removing grains completely from the diet, the intestines have a chance to heal, which may prevent the onset of or minimize the symptoms of existing auto-immune diseases.
The other area that the Paleo diet is said to help is with Metabolic Syndrome, a catch-all term that includes Obesity, Heart Disease, and Type 2 Diabetes. By removing foods high on the Glycemic Index (such as potatoes), blood sugar and insulin levels are normalized and risk factors are reduced.
I strongly believe that by eating the right food, we can heal ourselves. The difficulty is in figuring out which food that is. A lot of different diets argue convincingly that their diet is the best, but I really don't think you can argue with evolution.
The Paleo Diet, Dr. Loren Cordain
The Evolution Diet, Arthur De Vany