Recently, Mark Bittman, minimalist chef-turned-novice-food-advocate published an opinion piece in the New York Times regarding his personal challenges digesting milk. In his article he attempted to dissuade Americans from consuming milk, because according to him it’s not so good for us and we haven’t evolved to drink it. For all his citations and quotes, it turns out that his reasoning isn’t exactly based in peer-reviewed literature (aka Science!).
Rather interestingly, milk isn’t tragically bad for us (1) and the ability to digest the milk sugar lactose is one of the cooler examples of convergent evolution (2). (For a fuller response, see my sweetie Will Fertman’s article Mark Bittman: Don’t be a weasel).
Most disappointingly though, in all of Mr. Bittman’s griping, he gave very short shrift to a better reason to reduce milk intake. It’s not our own poor digestion we should be concerned about when drinking milk, but rather the poor little cow’s digestion when they are making it, as this digestion is a significant contributor to climate change (3, 4).
So I know you all saw an Inconvenient Truth, but it’s been a couple years so here is a quick refresher: People/animals release greenhouse gases (carbon dioxide, methane etc.) into the atmosphere, these gases trap heat, the heat warms the planet, the more gases there are the more heat gets trapped. Gases have different heat trapping potential and methane is particularly good at this (go methane!).
The flatus and eructation (aka farts and burps, well really mostly the burps) coming from ruminants (sheep, cows…camels) are one of the largest sources of anthropogenic methane emissions (ie what doesn’t come from a wetland comes from cow burps). It turns out though, that we may have more control over these “end pipe emissions” than we ever would like to think in polite society (oh my!).
Ruminants have specialized stomachs that allow them to eat grass and other cellulose rich foods. This stomach is filled with bacteria which actually ferment the grass in the cow bellies and it’s this fermentation process that releases methane. In fact, if you work on a farm then you know if a sheep really likes you, she will complement you by sidling up next to you and giving out an enormous smelly burp (uh, thanks sicko sheep).
Aside from smelly sheep burps, this is actually when it gets sort of cool, because you can control the amount of methane being produced by controlling the diet being fed to the ruminant (or really the ruminant’s bacteria).
Since cows are big money makers (and big burpers too), a lot of research has gone into studying this ruminant and its bacterial family. So what do the cows (I mean bacteria) like? Well the bacteria in the cow’s belly tend to emit less methane with a higher quality diet. For example, fancy bourgeoisie cows/bacteria grazing on mixed-alfalfa emit less methane than those proletariat cows/bacteria grazing on grass (snobs) (5). Though not yet cited, I imagine it would be the same for your burpy sheep friend as well.
Bacteria also are pretty picky about the pH they live in. This may seem like a strange thing to consider, but would you be happier bathing in orange juice (acidic), water (neutral) or lye (basic)? Reducing the pH of this pre-stomach environment can slow down the methane creating bacteria and/or alter the bacterial community to favor other types of bacteria, reducing the amount of methane being produced in the end (ha!) (6).
As a result, it has been suggested that if we could manipulate the wee creatures living in the cow rumen than we could reduce methane emissions (7). Many different ideas have been floated, from vaccines or probiotics that alter the microbial community to killing off the community altogether (which could kill the cow….which would sort of take care of the problem). Or you could, you know, consume fewer cow products (am I agreeing with Mark Bittman? Gasp!) (8).
If you are a farmer though, your bottom line (pun intended) usually has more to do with liquid cow emissions (milk, you pervert) than the gaseous stuff. Until stronger policy measures or consumer pressure pushes farmers to consider how cow diets affect greenhouse gases, I may have to agree with Mr. Bittman about reducing my milk intake even though I doubt we could ever agree on the reason why – burp!
Minda Berbeco has a PhD in Biology from Tufts University and is a science blogger in the Bay area. She was delighted to learn while researching this article the many scatological words people use in polite society to refer to farting and burping. These include flatulence, belching, eructation, expulsion, projection, flatus, emissions, end of pipe (Ha! Ha!!!), passing gas, and breaking wind. Thank you.
Further Reading:
(1) The Consumption of Milk and Dairy Foods and the Incidenceof Vascular Disease and Diabetes: An Overview of the Evidence
(2) Convergent adaptation of human lactase persistence in Africa and Europe
(3) EPA: Methane
(4) Climate Change 2007: Working Group I: The Physical Science Basis: Methane
(5) Enteric fermentation and ruminant eructation: the role (and control?) of methane in the climate change debate
(6) The role of pH in regulating ruminal methane and ammonia production
(7) Methane production by ruminants: its contribution to global warming
(8) Climate benefits of changing diet
I remember once reading that humans are the only species that consume the breast milk of another species. I also remember that this substance was intended to turn a 60 lb calf into a 600 lb steer in one year!
Cow’s dung is also an alternative source of energy (methane).