Why do we need to avoid onion and garlic?
We do not recommend onion and garlic. Let's understand why.
Both are very powerful medicines, but it’s one thing to consume something as a medicine and an entirely different thing to consume it as a daily food substance. These are very strong nervous stimulants. However, such stimulants should not become a part of our daily food, as they can be very violent for our body.
On an energetic level, onion and garlic prevent a person from experiencing mental clarity, focus & higher states of consciousness, that is the reason why practitioners of yoga & meditation are advised to stay away from onion & garlic before their practice. It increases desires & leads to discontentment & lack of self-control. Taking advantage of this character, restaurants or dhabas always serve you diced onion before your meal so that by consuming it you desire to eat more food.
This is also confirmed in the Bhagavad Gita. In chapter 17, Lord Krishna says that foods that are very strong & pungent in Nature fall in the Tamasik category & promote disease, pain & distress. Onion and garlic are extremely pungent in nature.