Re: Sacred Cow is in India only, not overseas.
For desis, traditionally, food is medicine. You take certain food items/ avoid certain others when inflicted with specific diseases. I don't think this is something that many would disagree with.
The implication is that the food we eat has an affect on us - physically, physiologically and emotionally. In tropical countries at least, some of the food that is eaten, tends to 'heat' up the body resulting in disorders. Hence we eat/ drink something else to 'cool' down the body, particularly during summers.
Ancient Indian medicine classifies various food items into specific categories. One is encouraged / discouraged to consume them depending on one's constitution. Certain food items are reputed to make you 'hot of blood' - angry, emotional and quick to pick up a slight. Certain others do the opposite.
Depending on one's profession, again, one was encouraged/ discouraged to consume specific food stuffs.
Contrary to perceptions in some quarters, very few Indians - less than 10-15% are vegetarian. Brahmins were expected to be sober, not get physical and be tolerant to extremely touch situations. Hence they were required to avoid non-vegetarian food.
The society was primarily agrarian. Hence the importance to cows. In ancient times, the only way to protect organisms key to the agrarian way of life was to deify them - cows, snakes, trees and even rivers. This could have spawned theories and ideas associated with sacredness and "it is said in the holy books" and "it is beneath your status" etc.