Question: Why can we not eat onions, garlic, mushrooms etc?
Answer by Romapada Swami: These foods are known to influence us with the modes of passion and ignorance. Bhagavad Gita describes how different types of foodstuffs affect our consciousness with different qualities of nature. (Bhagavad Gita 17.8-10) Based on this principle, different types of food are analyzed to belong to any one of the three modes of nature. Those who are on the spiritual path are recommended to accept only foods in the mode of goodness which are fit to be made as an offering to Lord Krishna. Onions, garlic and mushrooms which increase the influence of lower modes are avoided in offerings to Krishna and therefore we avoid eating them too.