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Takeaway: We humans have a long history with milk and with good reason in many places, but many people may be intolerant of the sugars in milk.
Have you ever heard the quote attributed to Jonathan Swift, ““He was a brave man who first dared eat oysters”? I think of the same when I wonder about which Stone Age ancestor first decided to try animal milk. Not as much of a leap as eating an oyster, but still a brave person to put themselves so close to the kicking bits of another animal.
Archaeologists think we’ve been consuming milk since about the time we started domesticating animals 10,000 years ago, give or take a few millennia. And despite what you may have heard about northern Europeans having the lock on lactose tolerance later in life, other groups also possess the genes for processing lactose, one of the naturally occurring sugars found in milk. Interestingly, the genes developed independently, at least in some parts of East Africa.
Figure 1 Source: Nature, 31 July 2013 from an paper by Leonardi, M., Gerbault, P., Thomas, M. G. & Burger, J. Int. Dairy J. 22, 88–97 (2012).
But what is milk, anyway, and why is it good (or bad) for us? Scientifically speaking, it’s an emulsion of water and butterfat (think of oil and vinegar salad dressing, two things that are normally immiscible, or “unblendable”).
Altogether, milk has fats, carbohydrates (lactose, a sugar), proteins and minerals, which each vary by the source of the milk, but regardless of source water comprises over 80% of milk by volume. Many trace vitamins and minerals are found in milk, but the most prominent are B vitamins like B12, and minerals like calcium, phosphorous, iodine, magnesium, calcium, and zinc. Considering the composition, it’s no wonder why many see it as one of the more perfect foods, especially in places where milk products provide nutrients otherwise difficult or expensive to obtain.
And what about the bad? Milk is relatively high in saturated fats, many people are intolerant, there’s the link between phlegm, and possible links to prostate cancer and Parkinson’s (you can find that all in the Wikipedia entry, with references). If you’re just not into milk, there’s no conclusive reason to start drinking it, but there might be a reason to experiment with taking a break, considering the numbers of people with undiagnosed intolerance.
(As far as the phlegm/mucus connection, in some people, particularly those with asthma, there does seem to be some sort of allergic reaction, but scientists don’t seem to be totally sure how it works. Check it out journal articles here and here.)
More information about the kinds of milk (raw, whole, skimmed, etc.) can be found here: http://www.milk.co.uk/page.aspx?intPageID=43
This blog post has some interesting information about milk trends and what the different labels mean (grassfed, raw, organic, etc.):