Thursday, January 29, 2009

Allergy vs. Intolerance...which is which?

This is in response to Eli, who left me a comment asking me to talk a little more about the difference between a food allergy and a food intolerance.

Apologies all around! I forget that while I was a Pecanbread moderator, I answered the same questions over and over...and over and over. LOL. Now that I have my blog, sometimes I am tired of explaining before I even start, so I skip over stuff. Thank you, Eli, for calling me on it.

What's a food allergy, anyway?

A true food allergy generally shows up on a skin test. This is the test that most people are familiar with. It tests for IgE, which is an immediate reaction. This is a true allergy -- generally the anaphylactic kind, but hives can also be a symptom of true allergy. I do not know of anyone who has been healed of a "true" food allergy on SCD.

The skin tests, of course, can be wrong. An acquaintance of mine had a life-threatening allergic reaction to shellfish, went to the emergency room, and tested negative to shellfish allergy right then and there. Do you know what the doctors did? They shrugged and told him to never eat shellfish again.

Here is a page that explains IgE testing. It is the most common because it identifies life-threatening allergies. The other forms of allergy testing are not generally covered by insurance.

In Breaking the Vicious Cycle, Elaine Gottschall urged people to stay away from foods to which they were truly allergic. Do not eat foods that you are allergic to.

So what's an intolerance?

The second type of allergy testing is IgG testing, which tests for antibodies that don't show up as a reaction on a IgE test. These are usually intolerances that can be healed (at least to some degree) while on SCD.

It also helps to mention that almost all of these tests suffer from a fair degree of inaccuracy -- you may show up as allergic to something and have no allergy to it at all, and vice versa.

Here's a page that explains the drawbacks to IgG testing:

Elaine didn't put much stock into allergy testing. She said at one point that some people who were following the diet and getting well decided to get allergy tests. They were horrified at the result. They were getting better, but the tests indicated they should avoid the foods that were making them well.

In the category of hugely important and catastrophic intolerances, I'd like to mention celiac disease. CD is a genetic intolerance to wheat, but it is not an allergy. So, gluten could be ripping your digestive system to shreds while the allergy test calmly insists that you have no problem with gluten at all.

So, I personally will have to define an intolerance as something that YOU have a reaction to -- something YOU can measure, not the lab. Who cares if the allergy test says beef is fine for you, if you get horrible stomach pains after eating it?

But my personal favorite way to distinguish between the two is with this little phrase:

If you're allergic to a food and you eat it, it could kill you. If you're intolerant to a food and you eat it, you'll just WANT to die.

Thank you for writing, Eli. I hope that helps. :)


Eli said...

Yes, it does, thanks.
And I appreciate that it seems some SCD people have moved beyond Elaine's bacteria hypothesis (which is not really supported by data), and recognized that some of what's diagnosed as Chron's/Colitis might actually just be (genetic) intolerances for certain things.
I personally suspect that there are a number of different variants on these disorders since different people can tolerate different things on the SCD [which is kind of a least-common-denominator approach]. If I wasn't busy pursuing other research, in a different field, this might be something interesting to at least try and classify.

The SCD girl said...

It's hard to say for sure. Currently, my rheumatoid arthritis is being treated with antibiotics (more information at

I do believe other things can be and are at work in a variety of other conditions which seem to have no known cure or cause (molecular mimicry comes to mind), but...there are only so many hours in the day for my research as well. :/

I would like to go back through my copy of Breaking the Vicious Cycle soon to see if there's evidence to support your statement about Elaine's bacteria hypothesis.

I know most medical research doesn't support a whole host of possible autism causes, but I doubt they're really invested in anything that can't make the medical industry a fast buck, you know?