What it is: inositol hexakisphosphate, a molecule that plants use to store phosphorus. It's not digestible by humans, so it has no effect on you directly.
Why it's bad if you're trying to remineralize teeth: phytic acid binds to minerals and prevents them from being absorbed. Among the minerals that it binds to: iron, zinc, and calcium. So if you eat a lot of foods that contain phytic acid, you absorb less calcium, which slows down or stops the remineralization process.
Foods that contain phytic acid: grains, nuts, beans, seeds, and anything made out of them.
Does phytic acid have any benefits? Many people have called it an "anti-nutrient", but there are some benefits to having phytic acid in your diet. First of all, it will bind to certain toxic metals and prevent your body from absorbing them. This decreases your risk for cancer and heavy metal poisoning.
So is it still OK to eat grains, nuts, etc? In moderation, yes. Just make sure you've got a lot of calcium in your system, too. If you have a peanut butter and jelly sandwich once a week, you will not completely destroy your teeth (as some people would lead you to believe).
But it's definitely a big contributor to tooth decay. I only had one tiny cavity until the age of 21. Then I started eating a lot of oatmeal at work (without much calcium in my diet). Within a few months, I had at least 7 cavities. Oatmeal has a high phytic acid content, so those results aren't surprising.
That's why my system for <a href="http://www.cureforcavities.com/p/blog-page.html">tooth remineralization</a> (and pretty much everyone else's system) basically excludes grains, nuts, and seeds for the most part. IF you eat them, do it in small amounts and make sure you have a lot of calcium in your system.
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