Xanthan gum vs. Guar gum

"Did you know that xanthan gum is fermented with corn;
the amount is very small but some corn-allergic people may
not be able to tolerate xanthan for this reason. Guar gum
and xanthan gum are interchangeable in gluten-free baking.
Some cookbook authors suggest using 1 1/2 teaspoons guar
gum for every 1 teaspoon xanthan gum. But replacing xanthan
with an equal amount of guar gum works just fine."

-Living Without Magazine December/January 2011