Split milk: Though everyone agrees that calcium saves bones, researchers clash over dairy.(Chicago Tribune)

Long America's nutritional icon, the milk bottle recently has come under some intense scrutiny.

A few scientists and researchers are questioning whether dairy products are even necessary in the modern diet, let alone essential.

Milk is probably not "the world's most perfect food," as the dairy industry used to proclaim: Milk and milk products often are high in saturated fat. They also have lactose sugars that some people have difficulty digesting and a significant amount of animal protein, which others find objectionable.

But if we discard dairy as a key wedge in the food pyramid _ as Harvard professor Dr. Walter Willet recommends in his book "Eat, Drink and Be Healthy" _ what are the risks? Aren't there ingredients in dairy products that are vital to the American diet, such as calcium, potassium and magnesium, ingredients not easily available elsewhere?

(We are talking about cows' milk, not mother's milk, which experts agree still is the best nourishment for infants.)

Some researchers, including Cornell University biochemist T. Colin Campbell and Dr. Neal Barnard of the vegetarian- and animal-rights-oriented Physicians Committee for Responsible Medicine, ask why it is that humans are the only mammals that feed their young the milk of another species.

Much of the world seems to get along very well without eating a lot of dairy products. And a percentage of this country's population _ mostly Asians, Hispanics and blacks _ lack enough of a particular enzyme to easily digest the sugar in milk and many of its derivatives.