Milk is often treated as the essential source of calcium, but the evidence for that special status is less clear than advertising suggests. Plant foods contain calcium too, and a diet built more around them may support bone health with less calcium overall.
Calcium Beyond Dairy
Grass contains calcium—and so do fruits, vegetables, grains, beans, and nuts. While many plant foods contain smaller amounts of calcium than dairy products, those amounts add up over a day of normal eating.
Plant foods may also have an advantage: they generally contain fewer substances that promote calcium losses. The high calcium recommendations often promoted in the United States may be necessary largely because typical diets are high in protein and sodium, both of which can accompany dairy consumption and increase calcium loss. People who eat a greater proportion of plant foods may do just as well—or better—with less calcium from any source.
Dairy and Chronic Disease
Research on dairy and broader health outcomes remains inconsistent. Dairy foods contain fat and saturated fat, which raises the possibility that they could increase the risk of heart disease or cancers of the colon, prostate, ovary, or breast.
Yet the published research is confusing. Studies often fail to separate high-fat from low-fat dairy, or to distinguish the effects of fat from those of calcium, lactose, growth hormones, or other milk components. Heart-disease studies are somewhat clearer, but even they sometimes associate dairy with higher risk and sometimes with lower risk; the differences tend to be small.
The safest conclusion is that dairy foods have no special role in heart disease beyond their contribution to overall saturated-fat intake.
What Is Lactose?
Lactose is the sugar in milk. An 8-ounce glass contains about a tablespoon. It is a “double” sugar made of glucose and galactose linked together.
Because double sugars are too large to be absorbed directly, the body must split lactose into its two single sugars using the enzyme lactase. Babies produce lactase from birth; the sweetness of lactose in breast milk helps encourage nursing. But after weaning—often by around age five—most children stop producing much lactase, since from an evolutionary standpoint the enzyme is no longer needed.
Lactose Intolerance
When the body does not make enough lactase, undigested lactose travels through the digestive tract intact. Intestinal bacteria then digest it, producing gas and small molecules that draw water into the intestines. The result can be significant discomfort.
People who suspect lactose intolerance can ask a doctor for a breath test, which measures gas produced by bacterial digestion of undigested lactose. Those who want to keep eating dairy can experiment carefully:
Start with hard cheeses and yogurt, whose bacteria have already digested much of the lactose.
Try small amounts of dairy foods one at a time.
Use lactase-treated products such as Lactaid, or take lactase supplements with dairy foods.
Lactose-free products can help lactose-sensitive people enjoy dairy without symptoms. But “lactose-free” does not necessarily mean low-calorie or fat-free. These products also create a premium-priced, value-added market for the dairy industry—so their purpose is not only health, but sales.
Milk Allergies and Infant Feeding
Breast milk is the ideal food for human babies; cow’s milk is ideal for calves. Cow’s milk is too concentrated for human infants and must be diluted and otherwise processed to become infant formula. Formulas can trigger allergic reactions in some babies.
Milk allergies are caused by proteins. Cow’s milk contains at least five proteins capable of causing allergic reactions in sensitive children and adults. For infants who are not breast-fed and react to cow’s-milk proteins, soy or other formulas may be an alternative.
Adults with milk-protein allergies must avoid not only milk, cheese, and yogurt, but also processed foods containing dairy ingredients. That requires careful label reading and detailed questions for restaurant staff.
Autoimmunity and Diabetes: A Theory, Not a Conclusion
Some researchers have proposed that milk proteins might cause “cross-reactivity”—an immune response to milk proteins that could, in theory, also react with the body’s own proteins and contribute to autoimmune disease.
This idea arose partly because longer breast-feeding in infancy has been associated with lower later risk of autoimmune conditions. Some children with type 1 diabetes have antibodies to cow’s-milk proteins, leading to speculation that these antibodies might cross-react with insulin-producing cells in the pancreas.
But the evidence remains circumstantial. People commonly develop antibodies to many food proteins, and many children with antibodies to cow’s-milk proteins never develop diabetes. The research does not clearly show that milk-protein antibodies cause autoimmune disease or childhood diabetes rather than antibodies to other food proteins. Breast-feeding may help avoid very early exposure to cow’s-milk proteins, but many studies still call for more research—partly because advising children to avoid cow’s milk would have serious economic and infant-feeding consequences.
Hormones in Milk
Lactating cows secrete estrogens and other hormones into their milk, just as lactating human mothers do. The amounts are small and do not appear to affect infants, older children, or adults who drink cow’s milk.
However, dairy farmers have strong incentives to increase milk production. Cows can produce 10 to 20 percent more milk when injected every two weeks with cow growth hormone. The most commonly used version is genetically engineered and known as recombinant bovine somatotropin, or rbST.
The Bottom Line
Dairy can be part of a diet, but it is not the only—or necessarily the best—route to adequate calcium. Plant foods provide calcium with potentially fewer calcium-loss-promoting factors, while the health effects of dairy remain difficult to interpret because studies often fail to separate fat, lactose, proteins, hormones, and other components.
For people who enjoy dairy and tolerate it, moderation and informed choices matter. For those who are lactose intolerant or allergic, avoiding dairy is entirely feasible: calcium can come from plant foods, fortified foods, or supplements when needed.
Source : What to Eat by Marion Nestle
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