Why eat Paleo – Isn’t it really restrictive?  I get this question all the time.  My best answer...

Peanuts aren’t paleo, what is the deal with that? Peanuts are not considered paleo because they are a legume. Legumes are removed from the paleo diet because they contain a large amount of phytates that make it difficult to get nutrition from them. They are also a dense carbohydrate food compared to the amount of nutrition that you can get. Legumes contain lectins that can wreck havoc on your gut causing inflammation and damage to our small intestine cell wall. Specifically, peanuts are prone to a mold that produces aflatoxin that can have damaging effects on the liver.

... You follow these diets until you lose the weight or you lose interest. They are not sustainable and usually the whole time you are on them you are thinking about what you will eat once you are off. 

I have been a dietitian since 1999 and worshiped the Food Guide Pyramid up until August of last year (2013).  It was what we were taught in school and so the burden of proof was on any other way of eating.  I never had any real research to back up my love of the Food Guide Pyramid but a lot of time and money was put into that guide and it was widely accepted as true so why should I question it?