Once again, it was on day four or five of mapping out microorganisms on a giant flowchart that I was struck by an idea that zoomed me out to the scale of human history.
On our bodies live bacteria and viruses that we refer to as “normal flora” and with whom we happily coexist. In an oversimplified model, when humans interact with a new organism for the first time, either our immune systems kill it, or it kills us. Neither of these situations benefits an organism, because by killing its host it’s lost its place to live. Over time, microorganisms have evolved alongside humans so that they can reproduce in and spread from human-to-human, and so that they can live in their hosts for a long time. Thus, our normal flora are creatures that don’t harm us.
Except: some pathogens are normal flora organisms that have escaped from where they are supposed to live on our bodies (the surface of our skin, the inside of our gut, etc.) and found residence in tissues where they do harm us.
So it occurred to me that these normal flora with pathogenic capacity are probably at an evolutionary disadvantage to their normal flora compatriots without pathogenic capacity. They are slowly killing off their hosts faster and thus wiping themselves out relative to other bacteria and viruses. That means that we are studying a set of pathogenic normal flora that exist at a unique moment in history: there may have been others before that wiped themselves out; this set we have now would eventually wipe itself out if left to its own devices.
Like yogurt, buttermilk derives is characteristic sour taste from lactose-fermenting bacteria. Paired with chocolate, this makes a tangy and refreshing snack or dessert. One cup of buttermilk has 100 calories and eight grams of protein–on par with yogurt.
Chocolate Buttermilk Shake
- 1 cup half-frozen buttermilk
- 1 tsp vanilla extract
- 1.5 tsp cocoa powder
- 1.5 tsp brown sugar (or maple syrup or honey or white sugar)
- chia or other seeds for fun (totally optional)
- (I’m sure this would be delicious with a banana or frozen berries — I happened to be out.)
The Med School Cookbook offers a weekly account of the challenges and wonders of med school as seen through the eyes of a student. Each post includes a healthy and easy recipe designed for busy people on a budget. Read the daily blog here.