Why Avoid Onion & Garlic?

Q. I would appreciate if you can elaborate on why we should not consume or eat either onion or garlic. Is it stated in any Sastra? Please help me this question will be helpful for my preaching purpose.

A. In Bhagavad Gita (17.9) Krishna states that ‘Foods that are too bitter, too sour, salty, hot, pungent, dry and burning are dear to those in the mode of passion. Such foods cause distress, misery and disease.’ Onion and garlic fall in this category. They excite the baser instincts and make it difficult for one to control the senses. The prohibition on onion, garlic etc. is implicit, by virtue of their characteristics.