Food taken and cooked for oneself is material, but food cooked for the Supreme is spiritualprasadam. This is a question of realization. The purpose of food is to increase the duration of life, purify the mind, and aid bodily strength. This is its only purpose. In the past, great authorities selected those foods that best aid the health and increase life's duration, such as milk products, sugar, rice, wheat, fruits, and vegetables.
Protein is amply available through split peas, dal, whole wheat, etc.
The best food is the remnant of what is offered to the Supreme Personality of Godhead. In Bhagavad-gita the Supreme Lord says that He accepts preparations of vegetables, flour, and milk when offered with devotion. Of course, devotion and love are the chief things which the Supreme Personality of Godhead accepts. Milk Issue . The Lord is purna, complete, and therefore He eats everything offered by His devotees.