lactose intolerance
"I lived in pain from most foods, until a new Gastroenterology doctor (Mayo Clinic) tested me for lactose intolerance. I proved to be VERY lactose intolerant. He recommended that I avoid milk, yogurt, and ice cream but try Lactaid with every meal, particularly canned foods and restaurant foods.  Trace amounts of lactose can be present in canned products. When dining out, there are no guarantees of what is put in the food. Even foods that seem relatively safe, could contain lactose. 
Lactaid has worked GREAT! I no longer get sick after canned tuna fish or eating out. I continue to avoid milk and ice cream, but I can eat cheese within moderation. 
I hope the product works for those who need it. For me, it's been a lifeline to normalcy."