29 June 2009
The Milk Myth: What a Body Really Needs
Young adults are not drinking enough milk, according to a study published in the July/August issue of the Journal of Nutrition Education and Behavior by researchers from the University of Minnesota, Minneapolis.
Well, at least that's according to the press release about the study, along with a few press reports on the matter. But according to lead author Nicole Larson, the focus on the study was on calcium.
Once again, we see the words "milk" and "calcium" used interchangeably in the popular press. Milk is a calcium source, but by no standard other than that of the National Dairy Council is it the best calcium source.
Hard to swallow
This study, an important one, found that during the transition from middle adolescence to young adulthood, females and males reduced daily calcium intakes by an average of 153 milligrams and 194 milligrams, respectively.
This is indeed troublesome because peak bone mass isn't reached until the early 20s. Like a retirement fund, you have to start banking your calcium early because you will lose it slowly later in life.
How much calcium we need is an open-ended question. The recommended level is 1,300 milligrams for ages 9 through 18; 1,000 milligrams for ages 19 through 50; and 1,200 milligrams for ages over 51.
Yes, older kids stop drinking milk. That's to be expected. As delicious as dairy products can be, to suggest that we need to drink three glasses of the secretion of a cow's mammary glands in order to be healthy is a bit outrageous and doesn't fit our evolutionary profile. If fact, most of the world, aside from a group of minorities called white people, cannot easily digest cow milk.
We do need calcium, though, and there are plenty of ways to get enough.
The recommended level of over 1,000 milligrams is a U.S. standard based largely on how lazy we are and how much meat we eat. Weight-bearing movements such as walking strengthen bones by increasing calcium uptake and by signaling bone cells to maintain calcium stores. Too much protein might be associated with calcium leaching and higher fracture rates. This is according to the Harvard-led Nurses' Health Study and other studies, although the results do remain controversial.
Numerous studies have found no association between high calcium intake and lower fracture risk. Regardless, a milk-free diet won't leave you deprived of calcium. Yogurt has more calcium than milk and is easier to digest. Collards and other greens also have about as much or more calcium than milk by the cup. Greens, unlike milk, have the added benefit of vitamin K, also necessary for strong bones. Tofu and sesame are also very high in calcium.
When you measure calcium by cup of food product, milk is high on the list. When you view it by calorie, though, milk is at the bottom. A hundred calories of turnip greens have over three times as much calcium as 100 calories of whole milk, for example.
What non-milk calcium sources lack, usually, is the saturated fat. Recommendations to drink more milk concern the low-fat variety, which few of us like.
Who to trust
Studies on milk's usefulness vary by advocacy group. A study published in 2005 in Pediatrics by the pro-vegetarian Physicians Committee for Responsible Medicine concluded that "scant evidence supports nutrition guidelines focused specifically on increasing milk... for promoting child and adolescent bone mineralization." A study published in 2006 in the Journal of Dairy Science by the National Dairy Council reports how milk builds strong bones, lowers blood pressure, contributes to weight loss and body fat reduction and protects against several kinds of cancer.
Who can you believe? Likely not the latter. But the other extreme is off the mark, too.
For example, some vegans state that milk causes osteoporosis, or weak bones. They point out how the Inuit eat protein-heavy diets and have the highest rate of osteoporosis in the world. If this is true, it would more likely be due to the Inuit's minimal exposure to sunlight (missing half of the year) and dark skin, which blocks ultraviolet light. UV is needed to manufacture vitamin D in the skin, crucial for strong bones and more.