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

Ladies and gentlemen,

Please note, first of all: I'm a biophysicist, not a nutritionist. Take 
this with a few parts per million of salt, for now, and if I get any 
authoritative responses from other scientist types I'll send out a 
summary. PPM has been beaten to death on here and most of it I've only 
skimmed. Thus, please accept my apologies if I'm repeating something 
someone else has said.

Do not think of a certain quantity in PPM as a value that is "safe" for you.

For example: if a manufacturer tests a food for wheat gluten and says it 
contains *less than* 100 PPM, this does not mean that the food contains 
even 1 single protein molecule of gluten. It means that the test is 
sensitive to amounts of gluten *greater* than 100 PPM.

The reason they use PPM is that it's impossible for them to test every 
single particle in a food to see if it's gluten (thus, to say something 
is tested 100% free of gluten is impossible to confirm). Imagine that 
you've got a huge stack of cards and have to turn each one over and read 
the number. If you've got a billion cards, you're not going to want to 
check every one of them--you're just going to look at a decent sample.

So. 100 PPM tests are accurate to that amount. If they say something 
contains 100 or 1000 PPM gluten, first of all, be skeptical. That's 
almost as difficult of a claim to make as tested 100% gluten free. 
Secondly, if they say something contains 100 or 1000 PPM gluten, then 
that means it failed a GF test accurate to 100 PPM but passed one 
accurate to, say, 1000 PPM. They're establishing upper and lower limits 
for the amount of gluten in something.

As far as what's safe for you: well, say you've got a carrot and it 
brushed up against some bread. Say that carrot's got a single molecule 
of gluten on it, now, and you eat it. There's a good chance that the 
single molecule of gluten will not encounter any of your body's immune 
defenses on its way through you, and thus will not cause a reaction. 
However, there's also a finite but small possibility that it will, even 
if it's the only molecule of gluten you eat.

Now, this is just hypothetical. I'm not an expert on immune systems, but 
I imagine it takes more than one encounter with the immune system to 
trigger a gluten reaction. However, this will vary significantly for 
everyone and be based on a lot of different factors. So, if someone says 
something can safely have 100 PPM gluten, well, that's probably not 
accurate (unless they're a biophysicist studying the immune system).

--however, with that said, if something is 100% gluten free but not 
*tested* gluten free, well, that just means it wasn't made anywhere near 
wheat and on equipment that has never touched it. Provided you can trust 
whoever made it, and whatnot.

Feel free to direct questions or assaults toward me.

Cheers,
John
Blacksburg, Virginia

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