hi, nutritionist in training right here 4laugh
i personally do not follow it as i do like my legumes and grains (i just soak em)... but my opinion on paleo is that it's a great lifestyle to adopt... note lifestyle, not diet. there's more to paleo than not eating grains and going heavy on the meat and veg. (here's a little spiel!)
So basically Paleo comes from the idea that modern day diseases such as heart disease, obesity, diabetes, and allergies (to name a few) were brought about due to the introduction of agriculture. So dating back to the time of about 2.6 million years ago, our diets consisted largely of meat, fish, insects, fruit, vegetables, and nuts. During the Paleo era, there were no grains.
Now, our modern paleo diet is basically everything except no grains, dairy, or refined sugars. The focus is on cooked and natural foods. (note, not a lot of people follow this strictly) There is also emphasis on quality which is that produce should be organic, local, and pasture raised. (again a lot of people ignore this, and this is where problems for people who loosely follow paleo pop up)
Yeah the big thing with grains and legumes is that there's a theory of it having toxicity and GI distress. There's anti-nutrients found in them (ex: phytic acid, oxalic acid) and they are thought to interfere with the absorption of nutrients. I could write paragraphs on that, but that's just the basic idea of why people avoid the grains and legumes smile
lifestyle wise, the idea is that there's intermittent fasting, functional fitness (like caveman movement, vibrams), sleep cycles, cold thermogenesis, and grounding mats/earthing which they try their best to follow. this added with the diet = paleo lifestyle!
some pros: there's lots of flexibility, it is quality based if you choose it to be, it cuts out refined/packaged foods, no calorie counting/restrictions, and cuts out major allergens (your gut may just love you!)
some cons: quite high in meat (often treated like atkins), it may be low in fibre, quite expensive, and can potentially increase inflammation.
if you're interested in some cool resources i'd recommend:
The Paleo Diet - Loren Cordain
The Paleo Solution - Robb Wolf
Primal Blueprint - Mark Sisson
Bulletproof Executive - Dave Asprey
I'd give these things a quick google if you're ever curious to learn more about it smile
oooookay that's my huge little text post, i hope at least some of it helped or enlightened you!