A Milky Way

In the mammalian family to which we belong, there is one time-honored way to develop from infancy—drink milk. An infant calf, for example, gains over a pound of body weight a day. Supporting the transformation of meek boniness into bovine bulk is the warm nectar of protein, calcium, and fat known as mother's milk. But beyond infancy, it's no longer needed.

So it appears to be with humans. Mother's milk is specific for each species and human milk is especially rich in fats that build our beefy brains. A staggering proportion of the earth's population—92 percent in China, close to 70 percent in Mediterranean countries—do not retain the ability to digest milk beyond infancy. They lack the enzyme lactase, which breaks down the sugar lactose abundant in milk products. Only in northern Europe and Russia—where the domestication of cattle occurred some 10,000 years ago—and in cattle-herding America and Australia, are adults significant milk drinkers.

Even the belief—not to mention the ad campaigns—that milk is necessary for building strong bones may be more myth than reality. "Calcium increases bone density," says Teresa Fung, professor of nutrition at Simmons College, "but that doesn't necessarily prevent fractures." And studies tracking the health of menopausal women have found that milk consumption either has no effect on the frequency of bone or hip fractures or actually increases the rate of fractures.

"If you look without bias at all the scientific studies of dairy, you're left, really, with more questions than answers," says preventive medicine specialist David Katz, founder of the True Health Initiative and the author of The Truth About Food. Does dairy have significant benefit for nourishing the adult brain or body? The reality about dairy, as with many other foods, says Katz, is: "It depends."

To a considerable extent, it depends on whether it's fermented. Fermentation, accomplished by the addition of bacterial cultures to milk, renders dairy products largely digestible by converting lactose into lactic acid. Cheese, yogurt, kefir, quark—all fermented, all linked with health.

A recent long-term study of more than 2,000 men in Finland—where milk and a sour (fermented) milk called piimä are popular—found that those who regularly consume fermented dairy products, including cheese, have a significantly lower risk of heart disease than those who don't. Those who consumed the most fermented dairy products with under 3.5 percent fat—typically piimä—had a 26 percent lower risk of coronary incidents than those who consumed the least dairy, researchers report in the British Journal of Nutrition. Eating high-fat fermented dairy products such as cheese had no effect on risk.

Consumption of nonfermented dairy did raise the risk of heart disease—but only when intake was "very high," nearly a liter of milk a day.

Researchers believe that the probiotic bacteria intrinsic to fermentation favorably influence the composition of the microbiome. Fermentation also yields vitamin K2, which protects blood vessels by blocking calcification processes that harden arteries.

But the effects of dairy products—fermented and nonfermented—extend beyond traditional concerns about heart disease to other aspects of health, including metabolism, obesity, and markers of inflammation, all of which directly and indirectly affect mental health, cognitive functioning, and the long-term risk of neurodegeneration.

In a recent meta-analysis reported in the British Journal of Nutrition, total dairy consumption was associated with lowered risk of metabolic syndrome, the cluster of conditions (high blood pressure, high blood sugar, excess abdominal fat, and high cholesterol or triglyceride levels) that co-occur and raise the risk of heart disease, stroke, and diabetes.

Every daily glass of milk reduced the risk of abdominal obesity by 12 percent, and each daily serving of yogurt diminished the risk of hyperglycemia by 16 percent. "Specific types of dairy food consumption such as milk and yogurt, as well as total dairy food consumption," the researchers conclude, "were inversely related to risk of metabolic syndrome and its components." Other studies show that the protective metabolic effects of milk are most pronounced for obese children. Insulin and blood sugar are better regulated in children who consume at least two glasses of whole milk a day.

Another study, reported in the American Journal of Clinical Nutrition, found that eight servings of high-fat dairy per day decreased diabetes risk in adults. And yet another found that a high-dairy diet correlated with greater working memory, and a low-dairy diet with poor working memory. Dairy contains the antioxidant glutathione, which may specifically protect against neurodegenerative disorders.

Among the nutrients in cheese is the monounsaturated fatty acid palmitoleate. It clears excess sugars and lipids from blood. It also has anti-inflammatory effects. On the other hand, the saturated fat found in cheese and other creamy dairy products is pro-inflammatory.

Kefir, lighter than yogurt but thicker than milk, involves fermentation with multiple microorganisms. Like yogurt, it benefits the biome while minimizing saturated fat.

The value of dairy varies not only with fermented and nonfermented products but with what else is in the diet. "If you're eating cheese in the place of cheese doodles," Katz says, "you're probably trading up." A high-quality, nonprocessed cheese is always better than junk food. Still, he sees "no convincing case in the overall scientific literature to add cheese to your diet for the sake of a health benefit." Saturated fats clog arteries. Cheese is high in sodium. It's dense in calories—although there are benefits to the microbiome, and "linking decisive harm to cheese is hard to do."

Katz sees consumption of cheese much like that of alcohol: A glass of wine a day has some cardiovascular benefits; a dollop of cheese has positive effects on the microflora of the gut. "The place for dairy in the modern diet needs to be small," he argues, citing the so-called blue zones—areas of the world where an unusually large proportion of the population lives to be more than 100. Sardinia, for example, boasts the highest concentration of male centenarians in the world.

In the blue zones, dairy is usually from sheep and goats. And it's embedded in the Mediterranean way of eating. A small amount of cheese is balanced with a large amount of fruits, vegetables, nuts, and grains. The whole package is linked to long life-span, low rates of depression, and a low risk of neurodegeneration.

Islands of Eternal Health

There are five blue zones in the world, areas researchers have identified as having unusually long-living populations. Most have distinct lifestyle and dietary patterns—dairy from sheep or goats, for example—conferred by geography. Loma Linda, on the other hand, is home to many Seventh Day Adventists, who favor a vegetarian diet and consume no alcohol.

1. Ikaria, Greece
2. Okinawa, Japan
3. Ogliastra Region, Sardinia
4. Loma Linda, California
5. Nicoya Peninsula, Costa Rica