I think onions are without a doubt the main cause of bad underarm body odor. I made this discovery years ago when working in an office. Every few days, the receptionist would start reeking by mid-day. It was so bad you didn't want to stand anywhere near her. I decided I had to say something (no one dared too). She was completely mortified, but identified the onions on hamburgers that she ate as the culprit. She stopped eating onions and never had a problem again. I also start to reek if I eat onions 2 days in a row. I think this is the issue for people with bad BO... get rid of the onions!