I've been eating low carb Paleo for some time now, but I just recently ate a
cereal product that mostly contained, among other things, wheat bran (don't
ask).  I immediately got sick with a cold-type illness, full of mucus, and
getting chills/sweats.  The only other time this happened was when I ate
some low carb bread that also had wheat/what bran in it.  My guess is that
the wheat bran was extremely irritating to my digestive track, causing my
body to produce mucus in defense and thus giving me something similar to a
cold, but not caused by a virus.

Now, back when I still ate grains, this didn't happen obviously.  It seems
there can be 2 possibilities when eating Paleo:
1.  Paleo diet strengthens your immune system, and thus you are better able
to handle grains on the rare occasion that you do eat them, or
2.  Paleo strenghthens the immune system and still makes you healthier, but
your body is no longer used to grains/grain products and reacts harshly when
you do eat them.  They are recognized as a foreign substance.

For me it seems to be #2, i.e. I'm now extremely more sensitive to bad foods
than before when I was eating them on a regular basis.  Has anyone else
noticed this or experienced something similar?