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 African-Americans–lack enough of a particular enzyme to easily digest the sugar in milk and many of its derivatives.
A dairy tradition
But a milk-free diet goes against years of European and American tradition, in which milk has been portrayed as essential to the well-being of the young and has become the basis for a large dairy industry. Who hasn’t seen the milk moustache ads featuring famous faces from Spike Lee to Rudy Giuliani produced by the National Fluid Milk Processors Promotion Board?
That kind of advertising probably is vital for an industry that has seen consumption of its main product decline radically over the last three decades while the consumption of sugar-laden soft drinks has risen. Statistics indicate that the move away from milk is even more pronounced in young women.
Those kinds of figures worry Dr. Robert Heaney, a research professor at Creighton University in Omaha and a specialist in bone biology. He long has argued that this country’s epidemic of osteoporosis in older people is a result of them not getting enough dietary calcium and other bone-building nutrients in their youth. He is fond of saying that osteoporosis is disease of teenagers that strikes after 60.
“Of course, it is not absolutely necessary that anybody drink milk,” Heaney says. “It’s quite possible to get calcium from other sources, and people in some countries, such as China, do. But milk is such a nutrient-dense package, especially fat-free milk, that it is difficult for Americans to get those nutrients without it.”
A decline in calcium
So serious is the calcium crisis in this country, Heaney believes, that he has proposed adding the mineral to popular products for young people.
That already has happened, but in a typically twisted marketing fashion. In “Food Politics,” Marion Nestle, chairman of the Department of Nutrition at New York University, writes that just between January and August of 1998, manufacturers introduced 31 calcium-fortified products, many of them candy, snacks or sweetened drinks “of otherwise questionable nutritional value.”
Willet sees no “calcium emergency,” though. His book states that population studies around the world show “huge variation” in the correlation between calcium intake and fractures. Countries with the largest calcium intake also have higher hip fracture rates. Even the large Nurses Health Study in the U.S. showed that participants who drank two or more glasses of milk per day were at least as likely to have fractures as those who drank one glass or less a week, he writes.
Heaney, who says he works with data from more tightly controlled studies, disagrees. Large population studies are complicated by unknowns such as sunlight exposure, exercise, other nutrients and the calcium sources, he says. The data drawn from the nurses study were secondary, statistically insignificant and different from the researchers’ main focus, he says.
Although Heaney respects Willet as a scientist, he says that implications drawn from the nurses study are “not supported by clinical trials and not supported by later, updated observational studies.” (Such large studies often show a variety of data, some of it even contradictory. For instance, that same nurses study recently was used to show that even a modest increase in calcium appeared to lower the risk of some types of colon cancer.)
Meanwhile, there have been dozens of studies linking calcium, along with other nutrients, to increases in bone density and thus prevention of osteoporosis, Heaney says.
One such study is reported in a recently published paper by Bess Dawson-Hughes, chief scientist of the Calcium and Bone Metabolism Laboratory at Tufts University in Boston and president-elect of the National Osteoporosis Foundation. It shows that both protein, especially animal protein, and extra calcium are necessary for optimal bone growth.
Though calcium gets most of the attention, bone is more than 50 percent protein and about 20 percent calcium.
Researchers have long known that an increase in protein in the diet tends to increase the amount of calcium lost in the urine. This leads some to reason that milk, with its high protein content, is a poor way to deliver calcium.
But Dawson-Hughes’ study (published in the March Journal of Clinical Nutrition) found that the protein-related calcium loss was easily countered by calcium supplementation and vitamin D: Extra calcium along with protein promoted bone growth. Protein does cause calcium loss up to a point, Dawson-Hughes says, but it also stimulates bone formation, so if you have enough calcium to offset an increase in excretion, the net effect is bone growth.
The study also showed that lowering protein intake lowered calcium absorption. “Other studies suggest that calcium intake may influence the effect of dietary protein on the skeleton,” she says. Doesn’t that also suggest that milk is the perfect vehicle for delivering protein, calcium, vitamin D, magnesium and phosphorus to build bones?
“That is a reasonable conclusion,” Dawson-Hughes says.
“Getting calcium from milk is also a cheaper alternative to synthetic supplements, such as those used in the Dawson-Hughes study,” Heaney says. “You save at the checkout counter as well as at the emergency room.”
Nestle, whose book examines the close relationship between the dairy industry and the USDA and goes to great lengths to show how food processors market their wares, acknowledges that the question of milk “is really a mess.”
How about some vegetables?
“The American diet is too high in calories and not high enough in fruits and vegetables,” she says. Milk is better than soft drinks, but she cautions that it has the baggage of bovine growth hormones, saturated fats and lactose.
What about people who don’t tolerate lactose? If dairy is such a great calcium/protein/vitamin D delivery system, aren’t they left out?
Not necessarily, says Christina Economos, assistant professor of nutrition and an osteoporosis researcher at the Department of Agriculture’s Human Nutrition Research Center on Aging at Tufts.
“Some people lack enough of a particular enzyme to digest the lactose sugar,” she says. “But it’s inconsistent and not always related to the amount of the enzyme a person has.
“Many can adapt to small amounts, especially in products such as hard cheeses and yogurt.” Even so, people with a low tolerance for lactose need to know about other sources of calcium, such as fortified juices and certain green vegetables, she says.
“The problem is not lactose intolerance; it’s osteoporosis,” Economos says.
It all is complicated by the fact that intolerance often is self-diagnosed.
If people want to substitute soy products and supplements, that can work, Heaney says. But dairy products are convenient and relatively inexpensive.
