Milk: How much should you drink?

In 2005, the agency in charge of the food pyramid started recommending three cups of dairy products a day for anyone over 8, a full cup more than before. By the USDA's standards, one cup of yogurt, one and a half ounces of hard cheese, one-third cup of shredded cheese or two cups of cottage cheese counts as a cup of dairy. So, of course, does a cup of milk.

The USDA actively promotes dairy products — it administers the National Milk Processor Board that gave us the ubiquitous "Got milk?" media campaign — but the change in guidelines wasn't simply an attempt to sell more milk, says Dr. Theresa Nicklas, a dairy researcher and professor of pediatrics with the Children's Nutrition Research Center at the Baylor College of Medicine in Houston. According to Nicklas, the push for more dairy was driven by fears that Americans weren't getting enough calcium, potassium and magnesium, nutrients that are relatively plentiful in milk.

"Low-fat dairy is a way to meet these nutrient needs without a lot of fat and calories," she says. "It's a unique nutritional package." Like many milk researchers, Nicklas receives substantial research funding from the National Dairy Council.

The recommended daily allowance for calcium is 1,000 milligrams for young adults and 1,200 for adults 50 and over. A cup of milk has about 300 milligrams, making it an obvious shortcut. The RDA for potassium is a whopping 4,700 milligrams (4.7 grams), a level that fewer than 5% of Americans actually meet. A cup of milk has more than 360 milligrams of potassium.

Dairy products could obviously help people meet those goals, but Dr. Walter Willett, chairman of nutrition at the Harvard School of Public Health, feels the targets may be overly ambitious. He points out that much of the world doesn't drink much milk or get anywhere close to 1,000 milligrams of calcium, "and their bones aren't crumbling and falling apart all around us."

The RDA for potassium is based on a small study measuring how much of the mineral it took to lower the blood pressure of hypertensive African American men.

In Willett's mind, that's a flimsy foundation for an RDA. On a break during a recent 150-mile bike ride, he paused to look at the label for the orange juice (another so-called good source of potassium). He calculated that he would need to get just about his entire day's calories from juice to reach the 4,700-milligram mark. He decided he would just have to fall short.

Likewise, Willett says, one or two cups of milk might not be enough to help people reach guidelines for calcium and potassium. But he believes it's enough for good health.