Animal fat is available in the form of milk, which is the most wonderful of all foods. Milk, butter, cheese and similar products give animal fat in a form which rules out any need for the killing of innocent creatures. It is only through brute mentality that this killing goes on. The civilized method of obtaining needed fat is by milk. Slaughter is the way of subhumans.
Protein is amply available through split peas, daal, whole wheat, etc.
For example, for an impersonalist, the Lord, or the Absolute, being impersonal, cannot eat. Whereas an impersonalist tries to avoid good eatables, a devotee knows that Krsna is the supreme enjoyer and that He eats all that is offered to Him in devotion. So, after offering good eatables to the Lord, the devotee takes the remnants, called prasadam. Thus everything becomes spiritualized, and there is no danger of a downfall. The devotee takes prasodam in Krsna consciousness, whereas the non- devotee rejects it as material.