Subject: Oils & Indigestion: What's proper handling of frying oils?

Prior to hearing the TV warnings, I unknowingly ate about 1/3oz of 
Olean-fried corn chips and had a very violent reaction: nearly 3days of 
violent cramping diarrhea and anal leakage.  I swore off the stuff FOREVER! 
  (that was 2yrs ago)  Earlier this week, I had a similar reaction to my 
own cooking.  I began to suspect the oil I used for frying.  I'd reused it 
two or three times, filtering it and adding some fresh oil each time.  It 
ended up a mixture of corn, canola, and safflower oils.  I presume that the 
high heat of frying killed any biological agents; but did the shelf time 
and reheating create some nasty by-product which brought back the violent 
symptoms?  If so, are vegetable oils more susceptible than animal fats to 
such time&heat distortions?  How to commercial fryers, KFC, McD's et.al 
deal with frying oils?

Re: Oils & Indigestion: What's proper handling of frying oils?