Even if your body experiences a bit of telogen effluvium as a result of the change in diet, losing hair would be temporary. This post by Michael Eades on the horrendous and, by now, infamous Kimkins Diet and hair loss explains it near the end. Basically, your body may currently be stressed by what you're feeding it. In some cases, this causes your hair to stop growing, but, with nothing to push the hair out, it stays on your head. When your hair follicles realize the stress of the poor diet is passed, they'll start growing again. When your hair starts growing, the new growth pushes the dead hairs out of the follicles. (Read the article, if you can, because I know I flubbed up explaining it!)
I've been primal since March, and my hair is actually thicker and fuller than it has ever been. And it's curly again, oddly enough. (My hair was curly when I was a baby and toddler, then went straight when I was a child.) I lose a lot more of it now, but I'm pretty sure that's because it's so much thicker. Or maybe the curls make it look like it's more.
Motherhood: When changing from pj pants to yoga pants qualifies as 'getting dressed'.