Milk is an important part of a child's diet, because it helps to deliver calcium and nutrients that promote lifelong health. Young children -- those between the ages of 1 and 2 -- typically drink whole milk and may continue to do so throughout childhood. Most adults, however, shy away from whole milk because it is high in calories and saturated fat.

Some of the qualities that make whole milk a good drink for young children make it less desirable for adults. Whole milk is high in saturated fat and, as a result, in calories. A glass of whole milk has nearly twice as many calories as a glass of skim milk, half again as many as a glass of 1 percent milk, and a quarter again as many as a glass of 2 percent milk. Three glasses of whole milk a day would exceed an adult's recommend intake of saturated fat, without even taking into account other foods eaten that day.

More than 70 percent of the calcium Americans consume comes from milk products, including whole milk, according to "Dietary Guidelines for Americans," jointly published by the Department of Agriculture and the Department of Health and Human Services. Because of the health risks of saturated fat, which is linked to heart disease, obesity and other health problems, the Dietary Guidelines recommend that adults drink lower-fat milk as a way to reduce saturated fat intake.

In addition to concerns about fat and calories, some adults simply can't digest whole milk -- or any kind of milk -- effectively. In fact, the mutation that allows adults to digest the lactose found in milk is a relatively recent introduction into the human genome. It is only common in populations with a long history of drinking milk products. As a result, approximately 65 percent of the world's adults have some degree of difficulty digesting milk.

The health risks associated with high levels of saturated fat don't mean that adults, or at least adults with the right genes, can't enjoy the taste of whole milk. Keep an eye on the level of unhealthy foods in your diet overall. This is a much more productive strategy than simply avoiding certain foods as "bad." Adults who enjoy whole milk and are able to digest it can drink it occasionally as long as they make it part of a balanced diet, keeping a careful eye on their overall intake of saturated fats.