I don't think this is universally true.  I am also hypothyroid.  While
I don't use tons of soy protein, I consume some almost every day in
the breakfast cereal I eat and the energy bars I use.  I feel fine,
and when I've experimented with eliminating soy entirely I didn't feel
any different.  Nor has it affected my weight one way or the other.

I asked my endocrinologist about soy, and he just said I should avoid
eating it within a few hours of taking my synthroid.  But since I
don't eat anything within a few hours of taking the synthroid, that's
not a problem.

Chris
262/155/ (holding in 152-165 weight class)

I looked it up today, oddly enough as my protein powder is running low and I
need to decide if I am going to buy it again.

Apparently, the isoflavones in soy act like hormones, estrogen in
particular.  On the thyroid, there are estrogen receptors.  The soy
isoflavone is not exactly identical to estrogen and is much weaker and there
are some reports that soy can cause long term damage to the thyroid.

My take?  Well, people have been eating soy for years.  However, on the
arguments for Soy is that the Japanese and Chinese do not get breast CA or
heart disease with the frequency of those of us in the US and they have a
soy based diet.  However, most of these oriental people do not eat nearly
the amount of Soy recommended.  Also, if you recall, after the big hype
about soy, people started selling soy supplements, etc.  It is the American
way.  We find out something is good and we want more of it.  Also, the fact
that use so much soy means that they have displaced their importance on red
meats.  Does abstention from red meat have anything to do with incidence of
disease?

It is an interesting internet search - wish I had saved the links.  One of
the distressing things was like everything else, there were militant anti
soy people and people who proclaimed soy was the answer to every possible
ailment that is known to man.  I think the answer lies somewhere in the
middle.

j