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Comment from Don Kasarda, Albany, CA, on use of xanthan gum and guar gum.
 
I think people who are having problems with the above gluten replacements
might find methylcellulose to be a good substitute.  A  rice bread formula
for celiac patients based on methyl cellulose as gluten substitute was
developed by Maura Bean of this lab many years ago and the formula seemed to
work well.  I think EnerG Foods sells the methyl cellulose. It should be a
more pure, less complex substance than the natural gums.  Consequently, I
think it might be less likely to cause allergic reactions or other harmful
effects, although I don't personally have any experience with it.