In the Manu-saṁhitā there is a list of different kinds of men eating different kinds of flesh, and in the Āyurveda there is a list of dravya-guṇa.
Dravya-guṇa means medical effect of certain type of things. So that is a very big book, and all kinds of vegetables, all kinds of flesh, all kinds of fish and everything is detailed there, and there is description what is the effect of eating such-and-such things.
So it is not that the Vedic civilization does not know what is the effect of eating flesh. They have got very broad analytical knowledge, and in the recent years Mr. George Bernard Shaw, he also said that, "You are what you eat." So if you eat a certain type of food, then your constitution of the body, mentality, status—everything—becomes according to that food. That is a fact.
So there is a class of men who are called śvapaca. Śvapaca means dog-eaters. So the dog-eater is called caṇḍāla, pañcama. The human society is divided into four: first class, second class, third class, fourth class, and pañcama means fifth class. So these dog-eaters, they are considered as the fifth class.