Barry Sears's Zone Diet is - by default if nothing else - the official diet of CrossFit.  It is what they taught me at my certification, and it is by far the most popular eating plan of the most performance-oriented CrossFit athletes. Within that population, however, there exists an even more hardcore dietary philosophy, espoused by CrossFit gurus at the highest level and followed by the most dedicated of athletes.

While Zone may be the official diet plan of CrossFit, it only deals with proportions. There is in fact a higher commandment, handed down by Coach himself in one of his earliest Journal articles and posted at CrossFit.com - so ancient that he suggests you use "alta vista" for more information about it.  The commandment is this:

"Eat meat and vegetables, nuts and seeds,
some fruit, little starch and no sugar."

And that's it. As it happens, this is a perfect synopsis of the paleo diet.

What is Paleo?

It goes by many names.  Mark Sisson brands his version "The Primal Blueprint."  Art Devany calls it "Evolutionary Fitness."  But the source of paleo is usually attributed to one man:  Dr. Loren Cordain.  Regardless of the source, however, the core philosophy is the same:  humans evolved over millions of years to thrive on a specific diet of things that could be hunted and gathered.  Then, about 10,000 years ago - an evolutionary eyeblink - the invention of agriculture changed everything.  And as agriculture was refined and industrialized, it became an ever-increasing part of our diet, bringing with it an ever-increasing list of ever-increasing ailments: everything from heart disease, diabetes, cancer, all the way to bad teeth.

The paleo response to this is simple:  don't eat anything that paleolithic man would not have eaten.  You wind up with a menu essentially like the one quoted above.  It sounds pretty great, actually, until you get into the details of what you can't eat:  No grains, sure, but also no beans, potatoes, dairy, alcohol, caffeine, sugar... or salt?!

It's not that simple, really

A couple points that I feel need to be made here, right up front.  While I agree with the fundamental argument of paleo, in common practice I find it to be both naive and drastically oversimplified.  First of all, evolution didn't stop 10,000 years ago.  Yes, it's a tiny fraction of time compared to 2 or 7 million years, but we haven't exactly been sitting on our evolutionary asses all this time.  We've gotten much better at digesting and processing foods that would likely have killed our ancestors outright.  Secondly, as far as I can tell, all the dietary restrictions of paleo are built around a series of intolerances that are not consistently represented across the population - that is, foods that are a problem for some folks, but not others.

A more nuanced take on paleo, therefore, would suggest finding those things that YOU are intolerant of, and cutting back on just those things.  Much better, right?  So, what are the candidates?

The Intolerables

Grains
This is the big one, so lets start here.  You see, the trouble with grains is that they pack a double wallop of dietary disaster.  First of all, they provoke a much larger insulin response than they really should.  This is true of whole grains as well as processed ones, though the processed ones are definitely worse.  Second, grains contain a group of antinutrients called phytates and lectins (most specifically gluten) that, in some cases, cause a severe autoimmune response called Celiac Sprue.  Not everyone has a severe response, but everyone shows some degree of inflammation from consuming gluten.  And the hyperinsulinism and toxicity feed off each other, compounding the damage wreaked by each.  Personally, I find the evidence persuasive enough that I eat very little grains.

Sugar
We've covered this one.

Beans/Legumes
The argument here is that these require some degree of processing/cooking/blanching in order to become edible, and many of the toxins present in the raw plant remain.  It's basically the grain argument again, with the same cast of characters:  beans are high in phytates and lectins, antinutrients that can cause some folks a lot of damage.  The biggest bummer?  Peanuts and Cashews are legumes.

Dairy
I remember some authoritative and self-righteous vegan once telling me that humans are the only species that continues to consume milk after weaning, and the only one that consumes the milk of another species.  I don't know if that's actually true, but I can't think of any counterexamples off the top of my head.  Dairy and all of its many delicious, creamy byproducts are a result of animal domestication and agriculture, and therefore off the menu.  Plus:  lactose intolerance is a real thing, and not uncommon.

Nightshades
This one is so hardcore that it's controversial even within paleo.  Nightshades are a particular class of plant that includes potatoes, eggplants, tomatoes, and peppers.  They contain a high concentration of alkaloids, which can impact nerve function and digestion.  Those who abstain say that they cause a kind of soreness/lethargy throughout the whole body.

Yipes!

Yeah, no kidding.  Cutting all that out would, in a word, suck.  Sure, you'd be safe from just about every autoimmune disease out there, but you'd also be a serious pain in the ass at dinner parties.  Better, in my opinion, to figure out which things really affect you and just limit those.  You don't even need to eliminate them completely - we're not talking anaphylactic shock as a consequence, here.  But at least you would know what digging into that ratatouille really means, so when you wake up aching the next day, you'll know why.  I hope it was worth it.

So how do you know?  Well, there's really only one way:  pick a thing, and stop eating it for a while.  See how you feel.  Measure your performance - does it go up or down noticeably after 2-3 weeks of rigorous abstention?  Reintroduce it, and see what happens.  If it's nothing, then yay!  You're all clear.  If you feel like a racehorse without it and a pile of horse crap after eating it, well:  sorry.  Now you have a story to tell at dinner parties when you have to explain why you're not eating whatever dish the hosts have lovingly prepared for you.  Jerk.

You see, if you've lived your whole life with a mild intolerance to a type of food, you likely don't even know it's there.  If you lived your whole life with a mild allergy to something in your environment, the constant mild aggravation to your system would just be background noise.  You'd be used to it.  Until you went on vacation somewhere else, and got a taste of life without those allergies - you'd suddenly feel phenomenal in comparison!  Same thing.*

Here we go...

So, in the interest of this personal experimentation, Rebecca and I have embarked on a journey of ridiculous difficulty:  30 days without dairy.  This was actually her idea - I swear!  At the end of which time, we shall down some cold, refreshing, achingly delicious organic milk, and pray that we don't feel a thing.

I am not a dietician.  CrossKitchen articles come from my personal experience, observations and research, and should not be construed as professional medical advice.

*Props to Byers for the metaphor.