The history of milk
Evolutionarily speaking, mammals aren't meant to drink milk beyond infancy. During infancy, mothers milk provides many benefits including the transfer of protective antibodies from mother to child, helping to build the infant's gut microbiota, and provides hormones and other nutrients to the baby. However, after a certain amount of time the mother stops lactating and the infant moves on to a "normal" diet.
Humans probably started drinking milk as a necessity. Nomads in central Europe kept herds of animals and likely drank the milk when other food was scarce, or possibly as a necessity to provide vitamin D to the diet in more Northern regions where there is not enough sunlight during winter months. Normally lactase, the protein that breaks down lactose, is no longer produced after infancy. However, in European populations a mutation in the promoter gave expression into adult-hood. This makes sense as looking at a global map of lactose intolerance (below) the most lactose tolerant populations are descendant from Europeans.
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| Photo credit: http://bit.ly/1f5hLd7 |
Humans were not meant to drink cow's milk
Evolutionarily speaking humans were not meant to drink milk. The majority of the worlds population does not produce lactase beyond infancy and ingestion of milk can cause reactions such as constipation, irritable bowel syndrome, bloating, gas, diarrhea, allergies, eczema, and acne
Not to mention "The biochemical make-up of cow's milk is perfectly suited to turn a 65-pound newborn calf into a 400-pound cow in one year. It contains, for example, three times more protein and seven times more mineral content while human milk has 10 times as much essential fatty acids, three times as much selenium, and half the calcium." Cows milk was made for cows, not humans.
So evolutionarily speaking humans were not meant to drink milk.
But milk has all sorts of other benefits right? It is high in protein, calcium, it's good for your bones. It contains 18 of 22 essential nutrients including phosphorous and vitamin D! How could we look past something that obviously deserves superfood status??
Milk is good for your bones
Oh boy did they feed you a lie on this one. Studies suggest that not only is milk not good for your bones, it actually contributes to osteoporosis; incidents of hip fracture were actually increased with milk consumption. One explanation suggested by the study was the effects of galactose. In digesting milk, lactose is digested to glucose and galactose. Galactose induces changes that resemble aging, providing galactose through injections or diet is an established animal model for aging. Galactose increases oxidative stress, chronic inflammation, neurodegeneration, decreased immune response, and broad changes in gene expression levels. Chronic low grade inflammation is also associated with heart disease, cancer, age related bone loss, and sarcopenia. These effects are seen at a dose of 100 mg/kg which amounts to 1-2 glasses of milk. Conversely, in cheeses and yogurts, bacteria have already broken down lactose; fermented dairy products contain less lactose and galactose than milk. Intake of fermented dairy products such as yogurt and cheese are associated with lower rates of osteoporosis and does not contribute to inflammation or oxidative stress. While milk consumption was associated with lower levels of HDL cholesterol, higher blood pressure, and higher levels of insulin resistance, consumption of fermented dairy products was associated with the exact opposite. So while dairy producers are asking "Got Milk?", scientists find themselves asking more and more "Got Proof?" (and I find myself saying "No, but I have some yogurt over here!").
One other suggestion that I came across is that milk proteins specifically acidify your blood due to "Protein Renal Acidification Load" or PRAL. In response to increased blood acidity, your bones release calcium to act as a base and buffer your blood. This may or may not be true (I didn't take the time to look), however, cheese has a much higher PRAL than milk does but none of the effects of milk; yogurt has a higher PRAL as well. This would seem to contradict this argument so I have a hard time accepting it at this time, and an easier time blaming galactose for all of milk's troubles.
A healthy microbiota is a happy microbiota
Increasingly the gut microbiome is associated with more and more diseases and conditions. Gut microbiome has been linked to Irritable Bowel Syndrome (IBS), Crohn's, colitis, obesity, diabetes, and even (tentatively) to autism. The impact that the composition of microbial populations have in our health is becoming more and more known, and the implications are staggering; altering the lung microbiome of cystic fibrosis patients can have drastic impacts on outcome. Needless to say that unhealthy gut microbiota, or a microbiome that is out of equilibrium can cause vast health effects.
Here I have no proof. I have no papers to refer to, they may exist but I didn't look that hard, however, a certain level of logical abstraction should do. By consuming milk we are providing different nutrients to our gut microbiota; different proteins and fats than are found in meats, vegetables etc... With different nutrients we can expect that different microbes will react differently, some may grow better, some may grow worse, but overall the microbiota composition will change as compared to a diet with less or no milk. Given the implications of an altered microbiome above, it is not a far leap to expect that drinking milk could contribute to some of the problems.
Bottom line, drink milk, don't drink milk, I don't care. I'll stick with my yogurt which has all the same great nutrients, none of the osteoporosis.
What do you think? Is milk the superfood our parents told us it was? Share your thoughts!
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