Some religions that forbid meat also forbid these. When I did my cooking courses at the local Buddhist temple they taught vegan cooking with no onion, garlic or chilli. Apparently they inflame the mind and body, make one quicker to anger, and they stop you from mediating as well. Or, that was their theory anyway. I love onion and garlic. They used asafoetida powder instead of garlic, which is a horrible spice that looks and smells liked dried cat urine rather than garlic. So some strands of Buddhism avoid it, and Jains avoid onion and garlic too, as well potatoes (you have to pull them out of the ground thus killing the plant). Some people also avoid the garlic/onion group along with the nightshades (eggplant, potatoes, tobacco, tomatoes etc).
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