Most people who report a quinoa allergy report similar symptoms: cramps, intense stomach pains, gastrointestinal problems and the like.
While such symptoms could be caused by allergies, I would expect such allergic reactions to be rare. Also, there is a remarkable consistency in the symptoms, which is rare for a food allergy since allergy symptoms typically vary from person to person rather than from food to food.
One theory is that the quinoa was not washed properly. It is possible that toxins made by the plant to protect itself from insects could make you sick if not properly removed. Many people reporting symptoms had properly washed the quinoa. Also, you would expect the producer to take care of such issues since people don’t always follow instructions and the producers will likely do everything they can to prevent people from getting sick, otherwise their food won’t be very popular and they won’t sell much.
Another theory is that quinoa can have mold grow on it in certain weather conditions, which produce mycotoxin, which is as the name suggests toxic.
I don’t yet have a clear answer.
Please feel free to share your experiences, good or bad, with quinoa. Also, if you have further insight into why quinoa makes some people sick, feel free to share.