It’s perhaps the most widely advocated nutrition recommendation of the last half-century: For strong bones and overall health, consume three servings of reduced-fat milk a day.
The USDA’s “ChooseMyPlate” dedicates a corner of their icon for milk and equivalent dairy products (Figure 1).
Schools must offer fat-free or 1% low-fat milk at lunch and other meals. To get kids to drink it, the government allows chocolate and other sugary varieties — but not plain whole milk!
And celebrities from Jennifer Aniston to Taylor Swift have donned the milk mustache, assuring us that milk does a body good.
To comply with this recommendation, Americans would need to double their intake (now averaging one and a half glasses a day), which would amount to billions of extra gallons a year. However, my colleague Walter Willet at Harvard and I examined over 100 studies and we conclude, in a new article in New England Journal of Medicine, that the evidence in support of this long-standing recommendation is surprisingly thin.
The most common health reason for drinking milk is to strengthen bones, to create a “bank” for calcium throughout life and prevent fractures. None of this seems to be true.
The purpose of animal milk
Because the natural purpose of cow, goat, or sheep milk is to help young animals grow quickly and avoid predators, it contains all essential nutrients, including protein and calcium. For this reason, milk can provide a nutritionally balanced alternative to the sugary drinks, chips, and other low-quality, processed foods that have flooded our diets.
Milk also contains a variety of growth-promoting factors. But today, the milk supply has increased levels of hormones like estrogen and progestins, because industrial dairy cows are pregnant for most of the time they are milked. In fact, children who drink a lot of milk, even those with good overall nutrition, tend to grow an inch or two taller. As we’ll consider below, this can be a mixed blessing.
Is milk really good for bone health and preventing fractures?
The most common health reason for drinking milk is to strengthen bones, to create a “bank” for calcium throughout life and prevent fractures.
None of this seems to be true — at least for the general population.
Above age three, the suggested intake of calcium in the United States varies from 1,000 to 1,300 milligrams a day — amounts that for all practical purposes require daily dairy consumption (or a regular dietary supplement). However, the World Health Organization (WHO) suggests barely half that amount, 500 milligrams a day. So, who’s right?
Systematic reviews of all studies done on the topic show no relationship between the hip fracture rates for calcium intakes ranging from about 500 milligrams to more than 1000 milligrams a day. Similarly, milk intake ranging from virtually none to more than four servings a day was unrelated to hip fracture in men or women.
Remarkably, countries with the highest milk consumption, like Sweden, tend to have a higher risk for hip fracture than those with the lowest consumption, like China (Figure 2). While international comparisons such as these can be “confounded” (meaning influenced by other factors including genetics and physical activity level), they show that high intakes of dairy products are not required to keep our bones from crumbling.
Even among the young, there is no evidence that milk protects against fractures later in life, and if anything, the opposite may be true. Among almost 100,000 adults studied in middle age or older, each additional glass of milk a day consumed in adolescence was associated with a 9% higher risk of hip fracture in men — a relationship apparently explained by height (there was no relationship in women). That is, milk may not strengthen bones, but children who drink lots of it tend to be taller. And as the proverb aptly states, “the bigger they are, the harder they fall.”
What about milk and obesity?
Despite widely advertised claims to the contrary, clinical trials show no overall effect of dairy products on body weight or the success of obesity treatment.
The amount of fat in dairy products does seem to influence weight over the long-term… just not in the way experts had thought. In studies involving young children, adolescents, or adults, consumption of full-fat milk was associated with less weight gain or a lower risk for obesity compared to the same amount of reduced-fat milk.
Remember the first Food Guide Pyramid? During the low-fat diet craze of the late 20th century, Americans were told that eating fat makes you fat, and that carbohydrates were the healthiest nutrient. Of course, things didn’t turn out well, with skyrocketing obesity rates over the last 40 years.
We now know that many high-fat foods are not only healthy, but also highly “satiating” — helping us to feel full after eating. Consider a child in the 1960s who, for an after-school snack, had a glass of whole milk and two cookies. Today that typical child might have fat-free milk and, because she felt less satisfied, four or five cookies — a bad trade-off for metabolism, weight, and general health.
The link between milk and heart disease
In addition to the (mistaken) belief that it would promote weight loss, reduced-fat milk was recommended out of concern for the high saturated fat content in whole milk. Saturated fat is known to raise LDL (“bad”) cholesterol and, in population studies, is associated with heart disease.
However, saturated fat also increases HDL (“good” cholesterol) and lowers triglycerides in comparison to carbohydrates. In addition, all saturated fats are not alike, with those in dairy having some potentially beneficial effects.
As with weight, a critical and often overlooked question is how dairy foods fit into an overall diet. Specifically, what other foods might be eaten in place of dairy products, or dairy fat? If the replacement is sugar and other processed carbohydrates, the impact on your waist and heart will probably not be good.
What about milk and cancer risk?
Since dairy products contain growth-stimulating factors, could high levels of consumption increase risk for cancer, a disease of uncontrolled cellular growth? Despite extensive study, the answer remains… maybe.
Milk consumption is linked to prostate cancer in men and endometrial cancer (but probably not breast cancer) in women. In contrast, milk consumption may protect against colorectal cancer. However, as with other studies of associations involving cancer, it can be difficult to prove cause and effect. Furthermore, most studies focus on adults in middle age or later, whereas risk factors for cancer may extend back to childhood.
Other issues to consider: allergies and environmental risks
Many populations around the world have lactose intolerance, limiting the amount of milk that can be consumed. For some people without symptoms of intolerance, regular consumption may predispose to allergies and allergic conditions, such as eczema and asthma.
Beyond the direct health effects, dairy consumption also impacts the environment in which we all live. In contrast to traditional integrated farming methods — with grass-fed animals that may help recycle carbon into the soil — high-intensity industrial milk production produces large amounts of greenhouse gasses, water pollution, soil degradation, antibiotic resistance, and other environmental disruptions.
In the end…
There is no human requirement to drink the milk of other animals. All the nutrients in milk can be obtained in the necessary amounts from other dietary sources. For calcium, alternative sources include kale, broccoli, nuts, seeds, beans, sardines, and other whole foods.
Milk and other dairy products may provide health benefits for those with poor diet quality, especially children. For people following a healthy diet, high intakes of dairy might cause harm. Furthermore, there is no evidence for health benefits of reduced-fat over whole milk.
Here are our take-home messages:
1. The currently recommended three servings a day of milk is excessive. Consider zero to two servings a day as a reasonable range.
2. Avoid sugar-sweetened milk and dairy products.
3. If you consume dairy, enjoy the full-fat versions!