We're talking about milk on this week's program with Andrea Wiley, professor of anthropology and human biology at Indiana University. Her books include Re-imagining Milk and Cultures of Milk: The Biology and Culture of Dairy Consumption in India and the United States.
To set up the conversation, I wanted to see what recommendations MyPlate has for our daily dairy consumption:
- 2-3 years old -- 2 cups
- 4-8 years old -- 2 1/2 cups
- 9 years old and continuing throughout life -- 3 cups
When Andrea Wiley was growing up, drinking a couple cups of cow's milk every day was encouraged. Her mom was a school nutritionist who drove around with a "Got Milk?" bumper sticker on her car. Then Wiley started studying biological anthropology in college, and she learned that not everyone can drink cow's milk into adulthood.
"When I started to learn about population variation and the ability to digest milk, it kind of raised a lot of questions for me about what I had grown up assuming about milk," she says.
For more on this, I want to hand it off to Leigh Bush and Maddie Chera from the Indiana University Food Institute.
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Bush: We wanted to start with Andrea Wiley's research because she really enlightened us as to how milk became such an integral part of the American diet.
Chera: Yet, there are some of us who just can't or would rather not drink dairy milk. In fact, Andrea's own son is allergic to milk.
Bush: There are a lot of conversations happening around food and diets right now, and we're seeing it in both research and popular media. We're starting to understand more and more how the foods we eat interact not just with our physical bodies. With Andrea's research, she's also interested in finding connections with culture, history and our food lives.
Wiley: So, it's pretty well-established at this point that the mutation that underlies the ability to digest the lactose in milk could spread only in populations that have histories of dairying. We have now worked out the underlying genetics of that, what specific mutations are there. There are different ones in Europe than exist in sub-Saharan African pastoralist populations, but they all have the same effect of basically keeping this enzyme, called lactase, on throughout life. In most mammals and most humans, that gene actually has a regulatory area next to it that turns it off early in childhood. For most mammals, it's some time around the time of weaning, which makes good sense, because mammals are never going to see milk again. It's an unusual feature of some human populations that that gene does not get turned off. It persists. This is what we call lactase persistence.
Chera: We have lingo here, Annie, that we need to define. Lactase persistence means you have the genetic mutation that allows you to digest the lactose in milk throughout your life. The flip side of that is lactase impersistence, which should not to be confused with lactose intolerance.
Bush: Right. Lactose intolerance is a biomedical diagnostic term for what happens if you drink milk and then develop... uncomfortable gastrointestinal symptoms.
Chera: Okay, so that's the biology of it. Andrea also looks at the cultural side of things. In the case of milk, many many generations ago, certain pockets of humans decided to domesticate other mammals and drink their milk.
Wiley: How did that set up a new kind of evolutionary scenario that led to basically natural selection favoring the spread of lactase persistence in populations that did develop dairying? So, you have a cultural change that leads to a biological change. And what I am fascinated in as well is how we understand biology in a cultural context. When you have a population where most people have the mutation that allows them to drink milk, how does that then get elaborated in cultural institutions that, for example, promote milk as an ideal food or this perfect food for humans?
Bush: This hit especially close to home when her first son was born.
Wiley: For example, when I would take my son to the pediatrician, and one of the questions they asked was, ‘What kind of milk is your child drinking?' I thought that was an interesting way of asking that question. Why aren't you asking me, ‘What does your child drink?' or ‘Does your child drink milk?' Instead, it was assumed your child drank milk and the question was simply, ‘What kind?'
Bush: And the assumption is that not only do all kids drink dairy milk, but that milk is essential to helping them grow into healthy adults.
Wiley: I think many of us heard that phrase growing up, that you have to drink your milk in order to grow. I was surprised when I started working on this about ten years ago to find that there was actually very little written on this topic. It was a cultural assumption that didn't seem to have a strong scientific body of evidence supporting it. I will say that there's absolutely no evidence at this point that calcium itself is what is making children grow. There are a number of calcium supplementation studies that don't show any impact on growth.
Chera: This idea that milk helps kids grow taller is part of what she's currently studying in India, where, like the U.S,, dairy is an important part of the culture.
Wiley: Milk has a complex cultural status there as well, and certainly in the Indian context where you have a majority Hindu population, the cow is a sacred animal. At the same time, most of the milk in India actually comes from buffalo, who do not have sacred status.
Chers: She's been following a group of kids for six years to try to understand how milk relates to children's growth. We'll have to talk to her again when that project is published.
Bush: We asked her for a takeaway about milk's place in our culture, and she said despite its importance to some of us, it's not essential for a nutritious diet.
Chera: Right. We have to look at the evidence and also consider the influences. She made a point of saying that the dairy industry has been very successful in overseeing child nutrition programs. But, milk remains a fixture in our food culture, and Andrea's work explores why. Bottom line, milk is an especially interesting food, biologically and culturally.
Wiley: As an anthropologist, I think a close and holistic examination of particular foods actually tells us a great deal about ourselves. Milk just happens to be this phenomenal example, I think, because there's such a strong biological component to it that maps onto human biological variation and there's an interesting evolutionary story around it.
Bush: Which brings to mind, Annie, that Andrea has a project in the works on another rather "special" food at the intersection of biology and culture -- gluten.
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