Yoga and Nutrition
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Thursday
Oct302014

On milk, bodies, and bones

Raise your hand if you were taught to drink milk “for strong bones” when you were growing up.

Me, too.

Remember images like this?

And a decade or so later, this?


Since then, Gen Xers, skateboarders, and nutritionists alike have questioned that advice. A study published earlier this week in the British Medical Journal supports an idea that many plant-based eaters already believe: Milk might not, after all, do a body good.

In two large Swedish cohorts, higher milk consumption was associated with poorer health outcomes. Women who drank 3 or more cups of milk daily were 16% more likely to experience any bone fracture and 60% more likely to suffer a hip fracture compared with women who drank less than a cup a day. Drinking more milk also was associated with significantly higher risks of cancer and heart disease in women, and higher all-cause mortality in both women and men.

I hear vegans shouting vindication, while the National Dairy Council is unavailable for comment. But what have we really learned here?

One explanation for the study’s results is that D-galactose, a product of the milk sugar lactose, increases oxidative stress, inflammation, and bone loss. These effects have been demonstrated in mice. Of note, yogurt and cheese intake were not associated with higher morbidity or mortality in the BMJ study. They were also not associated with elevated urine and serum markers of oxidative stress and inflammation (8-iso-PGF2 alpha and interleukin 6, respectively), whereas milk intake was. Other studies suggest a lower likelihood of heart attack and insulin resistance (which is increasingly implicated in cancer and other diseases), as well as more favorable short-term biomarkers, with yogurt- and cheese-containing diets. Quite the opposite with diets high in milk. We know that other fermented and cultured foods offer health benefits. Perhaps this is so with dairy, too.

Of course, there are myriad other possibilities. Maybe people who drink the most milk also eat more red meat and fewer vegetables, or exercise less. Maybe they’re more likely to be of a certain ancestry or ethnic group. They probably aren’t lactose-intolerant; this might be due to genetic differences compared with people whose bodies are unable to digest milk. Any of these factors could be the link with worse outcomes in the heavy milk drinkers, rather than just the milk itself.

It’s important to remember this study was observational, not the gold-standard prospective, double-blind, randomized controlled trial. The study authors explain that “no randomised trial has examined the effect of milk intake on incidence of mortality and fracture,” and “long-term experimental evidence is needed to confirm a causal association.” Point taken. But practically speaking, how do we conduct a sizeable, replicable study in which one group drinks milk, another doesn’t, but neither participants nor researchers can know who’s drinking what, and participants actually adhere to strict diet protocols in the real world, for years upon years? Furthermore, who’s going to fund it? Sometimes, in nutrition research, the “gold standard” really isn’t. No, we can’t draw a cause-and-effect conclusion from the current information. But do we always need perfect causal evidence in order to make practical and sensible whole-foods diet choices?

Now would also be the time to bring up two of what I call my broken-record words: moderation and variety. Eat excessive amounts of any given food, or eat it day after day after day, and your body needs to process a whole lot of whatever is in there, for better or for worse. Choose a balanced diet with a broad array of foods and you’ll promote greater benefits, fewer risks. More isn’t always better. Diversify and practice portion control. Why not have some aged Parmesan on your salad today, but garbanzos tomorrow? A little milk in your morning coffee, but not a 16-ounce glass with every breakfast? Soy milk in this week’s grocery shop, almond milk in the next?

The U.S. Dietary Guidelines recommend three servings of dairy foods every day to help reduce the risk of heart disease, hypertension, and type 2 diabetes, as well as promote good bone health. To me, that’s unacceptable. It may be a boon to the powerful dairy industry lobby, but it’s not supported by the literature, doesn’t distinguish among types of dairy foods or account for production methods, and makes a sweeping assumption about what’s best for all persons and bodies. Ridiculous. The most healthful diets are personalized, adaptable, and sustainable over time. They’re not about taking sides, catching trends, or getting someone re-elected.

They also probably don’t include upwards of three glasses of milk per day.

 

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