For most people, milk, yogurt, and cheese are important sources of calcium, protein, potassium, and (in some cases) vitamin D. But to others, they’re “white poison” that hurts humans (abdominal discomfort, broken bones, prostate cancer), dairy cows (inhumane living conditions), and the environment (greenhouse gas emissions, waste buildup).

Is dairy as good for you as its proponents claim? Or as bad as its critics charge?When it comes to human health, the answer lies somewhere in the middle. Here’s some of what researchers are finding.

Bones

“Milk is Bad for You and Your Bones,” warns saveourbones.com. The Web site, which offers a “revolutionary program that reverses osteoporosis in three easy steps” (yours for just $67), recommends mushrooms, onions, walnuts, apples, and other foods, but not dairy products, because “milk depletes the calcium from your bones.”

“That makes no sense if you look at the scientific evidence,” counters bone researcher Katherine Tucker, chair of the department of Health Sciences at Northeastern University in Boston. “Contrary to what some people believe, animal protein does not appear to be harmful to bones.”

Tucker and her colleagues are looking at how diet affects bone and fracture risk in the residents of Framingham, Massachusetts.“What we’re fi nding there—and it has also been found in several other studies—is that bone mineral density is actually higher in those eating more protein and lowest in those eating the least protein,” she notes.

Milk critics have long insisted that eating animal protein, including dairy protein, creates an acidic environment in the kidneys, which our bodies neutralize by leaching calcium from the bones. “So even though milk contains calcium, it ends up sapping your bones of that crucial mineral,” claims saveourbones.com.

Not so, says Jay Cao of the U.S. Department of Agriculture’s Grand Forks Human Nutrition Research Center in North Dakota. “Urinary calcium excretion does increase after consuming animal protein, but that calcium comes from increased absorption from food, not from bones.”

Cao and his colleagues showed that when they traced radioisotope-labeled calcium in meals eaten by postmenopausal women.1 Researchers at the University of Connecticut found the same.2 “Women lose calcium as they age, but eating dairy foods does not make this worse,” says Tucker.

The Bottom Line: Eating dairy foods does not appear to harm bones.

Colon Cancer

“Milk probably protects against colorectal cancer,” concluded a recent panel of experts convened by the World Cancer Research Fund and the American Institute for Cancer Research.3 (The finding didn’t apply to yogurt or cheese.)

When researchers at the Harvard School of Public Health pooled the results of 10 studies that tracked the diets and diseases of more than half a million people in five countries for six to 16 years, they concluded that those who consumed at least one cup of milk a day had a 15 percent lower risk of being diagnosed with colorectal cancer than those who drank less than two cups a week.4

“We don’t know whether it’s the calcium or something else in milk that may be lowering the risk,” says researcher John Baron of the University of North Carolina.

Most researchers would probably bet on calcium, which is “the only nutrient that has been shown in randomized clinical trials to prevent the development of neoplasms, or tumors, in the colon,” Baron notes.

He and his colleagues studied more than 800 people who had precancerous lesions removed from their colons. Those who were randomly assigned to take 1,200 milligrams of calcium from a supplement every day for four years had a 15 percent lower risk of lesions’ coming back than those who were given a placebo.5

But that was only true among people whose vitamin D levels were above average.(Baron is currently testing whether 1,000 IU a day of vitamin D by itself prevents lesions from recurring.)

Would milk also help keep colon polyps from returning? “I think it probably would,” says Baron. “But that hasn’t been tested so we don’t know for sure.”

The combination of calcium and vitamin D protects against colon cancer in animals.

When researchers at Rutgers University in New Jersey fed laboratory mice a Western-style high-fat, low-fiber diet that was low in calcium, vitamin D, and folicacid, a quarter of them developed colon tumors. But when mice fed the same diet also got calcium and vitamin D beginning early in life, none got tumors.6

Scientists don’t know how calcium Protects the colon. Among the theories: It may bind bile acids that are made in the liver to digest the fats in foods, preventing the acids from inflaming the mucosal lining. Or calcium-sensing receptors in the colon may keep precancerous lesions from proliferating.

The Bottom Line: Milk probably protects against colon cancer.

Prostate Cancer

“There is limited evidence suggesting that milk and dairy products are a cause of prostate cancer,” a panel of experts from the World Cancer Research Fund and the American Institute for Cancer Research concluded recently.3 “Limited” means that the evidence falls short of “probable” or “convincing.”

“The evidence is inconsistent, and that makes it difficult to make recommendations to men about what to do,” says epidemiologist June Chan of the University of California at San Francisco.

How might dairy affect the prostate?

Milk increases the levels of insulin-like growth factor-1 in the body, and higher levels of IGF-1 may raise prostate cancer risk.7 (IGF-1 also promotes bone and muscle growth.)

Or it could be the calcium.The panel of cancer experts concluded that diets high in calcium (around 1,500 mg a day or more) are a “probable cause of prostate cancer.”3

However, it’s reassuring that calcium didn’t promote tumors in a clinical trial.

Men who were randomly assigned to take 1,200 mg of calcium every day (in addition to the 900 mg they got from their food) for four years had no greater risk of prostate cancer over a 10-year period than placebo takers.8

What should men do? To play it safe,Shoot for no more than the Recommended Dietary Allowance (RDA) for calcium, which is 1,000 mg a day—from food and supplements combined—for men up to age 70 and 1,200 mg a day after 70.

Typical daily calcium intakes from food alone are about 1,000 mg for men up to age 70 and 800 mg for men over 70.9

The Bottom Line: High intakes of dairy foods are linked to a higher risk of prostate cancer in some studies, but not in others. There are too few studies to draw firm conclusions.

Blood Pressure

“Dairy products have a consistent, modest blood-pressure-lowering effect,” says Penny Kris-Etherton of Pennsylvania State University. Kris-Etherton served on the 2005 Dietary Guidelines committee that raised the government’s recommendation from two servings of dairy products a day to three.

“The effect is seen especially in people with prehypertension and in African- Americans,” she says. About a third of adults in the United States have prehypertension, which is blood pressure between 120 over 80 and 139 over 89.

What’s the evidence for dairy?

The fruit-and-vegetable-rich DASH (Dietary Approaches to Stop Hypertension) diet reduced systolic blood pressure (the higher of the two numbers) by an average of 7 points in people with hypertension.

However, adding two servings a day of low-fat dairy foods (and cutting saturated fat) lowered blood pressure by an extra 4 points. And the DASH-plus-dairy diet trimmed blood pressure in those with prehypertension by an average of 4 points.10

“This modest effect of dairy foods might be valuable in preventing people from progressing from prehypertension to fullblown hypertension,” says Kris-Etherton.

And, in fact, in the Women’s Health Study, which followed more than 28,000 middle-aged and older women for 10 years, those who averaged at least two servings of low-fat dairy foods a day had about a 10 percent lower risk of developing high blood pressure than those who averaged two or fewer servings a week.Women who ate high-fat dairy foods or who got their calcium from supplements had no lower risk.11

The Bott om Line: A diet rich in fruits and vegetables and low-fat dairy and low in saturated fat lowers blood pressure in people with hypertension or prehypertension.

Weight Loss

“Milk-cheese-yogurt. Burn more fat, lose weight,” the dairy industry’s TV and magazine ads used to say. That was before 2007, when the government pulled the plug on the campaign after critics charged that the evidence was inconclusive. Still, the question lingers: If you include dairy foods in a weight-loss diet, will you lose more pounds or fat than if you just cut calories? No, concludes a new trial funded by industry but conducted by government scientists.

“It was not what industry was expecting,” says Marta Van Loan, who led the study with her fellow researchers at the U. S. Department of Agriculture’s Western Nutrition Research Center at the University of California at Davis.

Van Loan’s team fed 71 overweight or obese men and women diets that contained 500 fewer calories a day than they needed to maintain their current weight. Roughly half were assigned diets that included three or four servings a day of dairy foods, while the other half got diets with less than one serving a day of dairy.

After 12 weeks of dieting, the high-dairy group had lost the same amount of weight (14 pounds), the same amount of fat (11 pounds), and the same amount of belly fat as the low-dairy group.

“So it was all about cutting calories, not whether they ate dairy foods,” Van Loan concludes. The results have been presented at scientifi c conferences but haven’t yet been published.

Still, the dairy eaters did benefit. “In the low-dairy group, we saw a loss of bone mineral in the hip as well as Markers of increased bone turnover and bone loss,” says Van Loan. “We didn’t see that in the high-dairy group.”

What’s more, when all of the dieters were offered two buffet dinners near the end of the study where they could eat all they wanted, the high-dairy group ate about 100 fewer calories at each meal than the low-dairy group.

“So, while dairy foods may not help you lose weight, they might have a slight satiating effect that can help you eat less to keep lost weight off,” says Van Loan.

Of course, it would take more research to know if dairy curbs appetite over the long haul.

The Bottom Line: Eating more dairy foods while you’re cutting calories won’t help you lose more weight or more fat.

Lactose Intolerance

“Fifty million Americans experience intestinal discomfort after consuming milk, cheese, or ice cream,” claims Robert Cohen, who runs the anti-dairy Web site notmilk.com. “Symptoms include stomach pain, gas, and diarrhea.”

That number is likely an exaggeration, counters Purdue University’s Dennis Savaiano, who has been studying lactose intolerance for 30 years. (Some of his work has been funded by the dairy industry.)

“Among those who think they’re lactose intolerant, the research shows that a signifi cant portion—anywhere between a third and three-fourths depending on the group being studied—are really not,” says Savaiano.

“When you give them lactose disguised in a beverage so they don’t know what they’re getting, they don’t show the signs of lactose intolerance.12 For whatever reason, they’ve come to believe that they can’t eat dairy foods, but in fact they can.”

Lactose intolerance is the inability to adequately digest lactose, the sugar in milk. Infants and children have lactase enzymes in their small intestine that break lactose down into the simple sugars glucose and galactose, which are then absorbed into the bloodstream.

If lactose isn’t digested in the small intestine, it passes into the large intestine, where it can draw fluid and produce gas, causing bloating and other discomfort.

But even if you’re an adult without lactase enzymes, the bacteria in your large intestine may still be able to digest lactose for you, says Savaiano.

“If you consume lactose regularly for a few weeks, a different metabolic capacity will develop in your colon as the microflora bacteria there adapt to digesting lactose,” he notes.13

People who are truly lactose intolerant may be able to include dairy foods in their diet without symptoms, according to Savaiano, if they follow a few simple rules:

Limit lactose to no more than 12 grams (the amount in 8 oz. Of milk) at a time.

Consume lactose with other foods to slow down the transit of the sugar through your intestines and give it more time to be digested.

Eat dairy foods regularly so that your intestinal bacteria remain adapted to digesting lactose.

Yogurt has about 10 grams of lactose per cup (the yogurt’s bacteria help digest the lactose). A serving of hard cheese or cream cheese has a gram or less, while a half cup of cottage cheese or ice cream has 4 to 5 grams.

Why try To work dairy into your diet?“People who avoid dairy foods usually don’t compensate by consuming other sources of dietary calcium,” says Savaiano.

The Bottom Line: Many people who believe they are lactose intolerant can adjust to consuming dairy foods without digestive discomfort.

No Milk? No Problem.

Don’t drink cow’s milk? Most soy, rice, and almond milks are fortifi ed with at least as much calcium and vitamin D as cow’s milk, and none of them contain lactose. Some also have as much vitamin A, vitamin B-12, and potassium as cow’s milk.

Our advice: stick to soy milk because it has almost as much protein (6 to 9 grams in an 8 oz. Glass) as cow’s milk (8 to 11 grams).

Almond and rice milk have only 1 gram.Just avoid chocolate-flavored soy milk, which contains around 20 grams (5 teaspoons) of added sugar.

Milking Dairy

In several of the studies below, dairy foods were linked to an increased or reduced risk of disease. But the studies couldn’t say whether dairy—or something else about dairy eaters—was responsible.

Diabetes. In four studies that followed more than 200,000 middle-aged U.S. men and women for up to 20 years, those who consumed an average of three to five servings of dairy foods a day had a 14 percent lower risk of being diagnosed with type 2 diabetes than those who consumed an average of fewer than 1½ servings a day.1

Breast cancer. In eight studies that tracked more than 350,000 women in the United States, Canada, Sweden, and the Netherlands during the 1980s and 1990s, those who consumed the most dairy foods were no more or less likely to be diagnosed with pre- or postmenopausal breast cancer than those who consumed the least.2

Ovarian cancer. Among more than half a million North American and European women who were followed for 7 to 22 years, consumption of milk, cheese, yogurt, and ice cream wasn’t linked to the risk of ovarian cancer.3 The researchers found an increased risk only when they looked at women who consumed at least 30 grams of lactose a day from all sources. (That’s the amount in 2½ cups of milk.) However, the link was “weak” and “marginally significant.” There was insufficient data for the World Cancer Research Foundation and the American Institute for Cancer Research to reach any conclusion.