The reason is clear if you are of sound mind. The consumption of milk meat and eggs is vital.

Protein intake and intake of individual amino acids can affect brain functioning and mental health. Many of the neurotransmitters in the brain are made from amino acids. If the needed amino acid is not available, levels of that particular neurotransmitter in the brain will fall, and brain functioning and mood will be affected.

http://www.minddisorders.com/Kau-Nu/Nutrition-and-mental-health.html