<<Disclaimer: Verify this information before applying it to your situation.>>

Thanks for all the responses to my question as to whether guam gum was
interchangeable with xanthum gum.

26 said that it was.  Many of them mentioned that because of its high
fiber content it tends to have a laxative effect.  One said it also
causes a lot of gas.  Many use it regularly and have no problem.   One
said it should be avoided.  One indicated a gluten-like reaction.

One said that xanthum seems to make smoother bread. Others claimed great
results with guar.  One said to use only 1/2 tsp. per recipe, two said to
use the same amount of xanthan the recipe calls for.   Another uses up to
3 tbsp. per loaf without significant laxative effect.  One said not to
use it in yeasted recipes.  Guar gum is used in many gf bread mixes and
in some gf bakery products..  I used it in the last loat of bread I made
(yeasted); the bread was good and I experienced no problems.

One wanted to know where I found it - at a health food store.

Below are two longer posts with more information.

1.  Guar & xanthan are not as interchangeable as we are led to believe.  If
you mix a half tsp of each w/ a cup of water you will see what I mean.  After
a while, the guar will set up/gel kind of like Metamucil.  The xanthan on the
other hand will stay a thick pourable liquid--"slime factor" as my kids call
it--making it great for fat free salad dressings.  You need this softness if
you are going to are going to replicate the gluten in really chewy moist
yeast bread.  My son makes lots of pizza crusts w/ white rice flour, & has
experimented to find that half xanthan & half guar gives a chewy crust that
is less moist/slimey in the center.

The cost is xanthan is high, but it lasts a long time.  Guar is much cheaper
and also has a place in the g.f.  kitchen--it probably a better choice for
cakes & muffins.  I resisted using guar for years, but it does work
differently & now my cupboard always has both.  I have also blended 1/4 tsp
xanthan w/ 1/2 c.  water & used it to replace 1/2 c.  oil (out of 1 cup) in a
favorite salad dressing recipe--nothing to do w/ baking.

2.  You can always subsitute the two, but after using Xanthum and Guam for
the last 16 years (not quite that for Xanthum) I prefer Xanthum Gum.  It
makes it possible to use almost any standard recipe sustituting Rice flour
for wheat and adding one teaspoon of Xanthum for each cup of flour used.
This is of course IMHO.

Thanks again for your help.

Pat