(This is a posting Melissa did a while back. I've added a few things in here that might be of interest).
One of the toughest concepts to swallow when it comes to Paleo eating is the No Grains rule. How in the world could bread, the manna from heaven be bad for you? I had the same reservations as the rest of you. I just couldn't wrap my brain around it. Grains provide Fiber, B-vitamins, whole carbohydrates, FIBER, right? Well, that is true but grains also provide: phytates, gluten, and lectins. What is wrong with that group you ask? 
Well, phytates bind to iron, zinc, calcium and magnesium making them nonabsorbable in the human gut.
Gluten destroys/damages the intestinal microvilli causing a host of problems. Think you don't have an issue with gluten? Think again. A recent study showed 29% of asymptomatic (non-Celiac) folks tested positive for a reaction to gluten. I have seen other studies showing a 90% reaction when looking at another marker. Take home message: even if you do not have gut irritability, you still have a reaction to gluten. That "reaction" may not rear its head now, but more and more studies are linking gluten issues to autoimmune diseases such as rheumatoid arthritis, Type I diabetes, Lupus, and a medley of other maladies like migraines, acid reflux, reproductive problems, arthritis and asthma. If you would like science to back this up, hop over here.
Per the British Medical Journal, Lectins are toxic, inflammatory, bind to the human GI tract and are indigestible in humans. More on lectins here.
FIBER: non-starchy vegetables can have up to EIGHT times the fiber of grains. That's eight.
Dr. William Davis, New York Times best-selling author of Wheat Belly, has a slightly different perspective on grains. His 30 second elevator speech: "You have been part of a grand deception. The wheat you are being sold is not the wheat of 50 years ago. The genetics changes introduced by geneticists that made it to your store shelves in the 1980s has been largely responsible for the increased calorie consumption, weight gain, and epidemic of diabetes experienced by Americans. Incredibly, we are blamed for these problems, accused by our own government agencies of being gluttonous and lazy. No, I say it is the fault of our own agencies, either through ignorance or turning a blind eye to the incredible changes introduced into this plant. Saying goodbye to modern wheat is reclaiming control over weight, impulse, and health. And it works."
Now you have a bit of an expanded explanation on why grains might not be the best choice. But how do you handle friends and family that are skeptical of your new approach to food? Here is my (Melissa's) elevator speech:
Believe me, I was skeptical too. I thought grains were really good for me. However, I did a little research because I knew eating grains was making me sick with: x.....issue. For me it was IBS. Turns out grains have anti-nutrients which bind to all the great minerals we think we are getting out of bread and pasta. It also has the kind of fiber that kind of scratches the inside of our intestines making them inflamed just like the redness we get around the area when we skin our knee. That inflammation keeps our immune system busy so it might miss a real bacteria that it might need to squish. That bacteria gets through and we get sick. Once I quit grains (and beans for that matter), I really don't get sick. Maybe once a year! The best thing about removing grains and adding more vegetables is that you are getting tons more vitamins and minerals than ever before because your body can actually absorb and use them now!
So, my speech was a little longer than I wanted, but you get the idea. When I get tired of discussing I always give them a challenge: why don't you just try it for a couple of weeks and see if you see a difference! Most folks see or feel an immediate change and your work is done!
What is your elevator speech when it comes to grains? (Beans have similar issues, I lump them into one when emplaining).
(Jules here. I like to put it simply as this: "What do huge factory farms feed cows to quickly fatten them up for slaughter? Instead of grasses, they are fed a diet of grains, soy and corn. This enables the farms to fatten those cows up really quickly. If you're wanting to lean out, might it make sense to try to avoid the very things that enable cows to put on a couple hundred pounds in just a few months?")
So here's one other anecdote: this weekend I was around an awesome, intelligent, handsome 3-year-old who does not eat grains. When he was - once - accidentally exposed to grains, it caused some serious vomiting. Now, I know some people say "well that's because he's not had grains as part of his life! He needs to build up "tolerance" to them!" Of course that makes absolutely no sense. It's like saying we should be making sure our kids drink alcohol to "build up their tolerance" so that in case they drink some by accident, they're okay.
I know there are some blog readers here who have done our BTB45 challenges before, and then introduced grains/gluten/soy/dairy back into their lives afterwards. How did it feel?