Reincarnation is one basic tenet of Buddhism, and this includes rebirth of humans as other animals, and vice-versa. As a result, many Buddhists do not kill animals and many also do not eat meat. Other common reasons cited are that killing animals and/or eating their meat are a violation of the Five Precepts, bad for one's own karma, and because of a compassion for other animals. Many vegetarian Buddhists are not vegan, but for those who are vegan, such beliefs are often due to objections about the circumstances in which the animals producing products such as milk and eggs are raised.
Some Mahayana Buddhists in China and Vietnam also avoid eating strong-smelling plants such as onion, garlic, chives, shallot, and leek, and refer to these as wu hun (五葷, 'Five Spices'). One theory behind this Buddhist dietary restriction is that these vegetables have strong flavours which are supposed to excite the senses and, thus, represent a burden to Buddhists seeking to control their desires. Another theory is that these are all root crops, and harvesting them requires killing organisms in the soil. The latter explanation is accepted in the Jain religion that sprung up in India at the same time as Buddhism, and quite possibly influenced its practices. It is unclear, historically, what the original reason was for this restriction.
Alcohol and/or other drugs are also avoided by many Buddhists.
