A vegetarian diet helps cultivate meditative concentration (samādhi)

The Buddha said in the Śūraṅgama Sūtra that when sentient beings consume meat and pungent foods, there are various harms, which greatly obstruct cultivation of the Path. Therefore, if one wishes to cultivate Chan and meditative concentration (samādhi) well, one must eliminate meat and pungent foods. "Pungent" refers to foods that, once eaten, leave an unpleasant odor in the body, such as chives, scallions, garlic, garlic scapes, garlic sprouts, onions, and so on; "meat" refers to the flesh of sentient beings as food. 

When these meat and pungent foods are eaten into the body, they make the mind impure, easily give rise to desire and anger, and also easily attract the approach of ghosts and spirits. Ghosts and spirits are fond of meat and pungent foods; they will lick your lips and sniff the odor. This is unfavorable for cultivation and can also easily invite calamity. It is also a disguised form of killing, and in the future one must repay the debt a thousand- or hundredfold. According to the Buddha's teaching in the Śūraṅgama Sūtra, one should eliminate a diet of meat and pungent foods as soon as possible and enter the Path without delay.