In his Stages of Meditation [Bhavanakrama] Kamalashila says:

When yogis meditate, they should always refrain from eating meat, fish, and so forth. For such foods are at variance with their meditation. They should be moderate in their eating habits.

(Source: FD. p. 72 and Teachings of H.H. Dali Lama on The Middle Stages of Mediation in PDF, page13)