When Arnold Schwarzenegger was asked if he drinks milk, he famously answered that «milk is for babies», implying that it’s not good for adults to consume this white liquid. To most people, this statement probably seems highly controversial, and based on their knowledge, incorrect. They may have been consuming cow’s milk their whole life and have been led to believe that milk is a very healthy food; a belief that has likely been imprinted in them by the dairy industry – which has done a remarkably “good” job of convincing the public that milk is the perfect food, for adults and children alike – and government nutritional agencies – which typically recommend that everyone should consume low-fat dairy products.
Not everyone is on board the ship that holds these beliefs though. Some people, myself included, are a lot more skeptical when it comes to the healthfulness of milk. I actually think Arnold hits the nail on the head with his statement. He may have been half-joking, but the fact is that milk is indeed for babies. There’s no doubt that milk is the perfect food for a growing child. It’s not the perfect food for an adult though.
What role does milk play in the mammalian diet?
The milk of each mammalian species here on Earth was designed by evolutionary forces (e.g., natural selection) to support the growth and development of the young of that species. It was obviously not designed to promote health or longevity in members of another species.
This basic fact is often left out in discussions about milk. Instead of taking a step back and asking what role milk plays in our diet, dietitians typically jump straight into the specifics and examine what types of nutrients and other compounds that are present in the white liquid we call milk.
This approach is very common in nutrition, regardless of what type of food that’s being investigated. This is unfortunate, because this approach doesn’t really give us a good answer as to whether or not it’s healthy to consume the food in question.
The fact that a specific food is high in certain vitamins or minerals or low in certain nutrients that are believed to cause us harm doesn’t necessarily mean that it’s a healthy food. It’s important to see the forest for the trees. If we stand too close to the object under investigation, we’ll be able to closely inspect its composition and details; however, we may be unable to see the big picture of things.
Milk, regardless of what animal species it’s derived from, contains an impressive repertoire of nutrients, growth factors, hormones, and bacteria. These compounds are there for a reason; they didn’t just happen to be there by chance, which seems to be what some people think.
Here’s what a recent review paper had to say about the role milk plays in the mammalian diet:
Milk plays an exceptional role in the beginning of mammalian life and performs its biological function by delivering its amino acid hardware and exosomal microRNA software. These messengers of milk have only one primary mission: to activate and maintain mTORC1-dependent translation and other mTORC1-mediated anabolic effects during the period of postnatal growth and postnatal metabolic programming.
Mammary gland-derived exosomes transmit a sophisticated array of microRNAs that function as a “Trojan horse”, like a retrovirus infection, to “transfect“ the newborn infant with maternal microRNAs that modify infant’s gene expression at the level of posttranscriptional regulation [9,293,294]. In this context, milk is best viewed as each mammalian mother’s nutrigenomic doping system, accelerating postnatal anabolism, cell growth, and cell proliferation of the offspring. (1)
The unique properties of milk
Milk is a very special food. It is produced with the exact purpose of nourishing a growing child. Over evolutionary time, the milk of each species here on Earth has evolved, changing in its composition and nutritional characteristics. These changes have occurred as a result of selective forces acting upon the natural world.
Milk is also an extraordinarily dynamic food: it can change a lot in a very short time. These short-term changes are shaped by mother-child interactions. You may find it surprising to hear, but research has shown that a lactating mother can respond to her child’s needs by altering the production of antibodies and other compounds found in her breast milk (2). This is obviously not something she does consciously, but rather something that occurs naturally as a result of signaling between the mother and child.
This process clearly highlights that milk is a food that’s specifically produced for babies. It is tailored to provide babies with all the nutrients, microbes, and immune-enhancing substances they need to grow into healthy, strong adults that are able to reproduce themselves one day. Because that’s of course the fundamental reason why evolution “bothered” to design a white liquid that provides “everything” that young, fragile infants need to grow and survive in the big, scary world we find ourselves in; it helps them pass on their genes.
“But… I’ve heard that we’ve adapted to drink milk. If I’m not lactose intolerant, why shouldn’t I drink milk?”
I often come across people who make the case that we have adapted to drink milk. In support of this statement, they present evidence showing that a large proportion of the population in many European countries is able to digest lactose without experiencing gastrointestinal distress. In other words, they have a lactose-persistence phenotype.
What a lot of these people fail to recognize is that natural selection doesn’t select for health, but rather for reproductive success. The fact that you’re able to digest and make use of the nutrients in milk without experiencing any acute health problems doesn’t necessarily mean that it’s healthy for you to drink milk.
Lactase-persistence alleles didn’t spread in European populations because those people who were able to digest lactose lived longer, healthier lives than those who weren’t capable of breaking down this milk sugar, but rather because the former had a higher reproductive success than the latter. I.e., they got more surviving offspring.
This isn’t surprising, given that milk is a very nutritious food. Particularly during times of scarcity, it would have been a significant evolutionary advantage to be able to digest milk.
Often, health and reproductive success are linked; but not always. For example, some chronic diseases develop primarily late in life and have little impact on reproductive success. It’s therefore important that we don’t confuse evolutionary fitness with physical fitness. If a trait confers increased reproductive success, it will spread, regardless of how it affects the health of the organism. As we’ll see in the next section, milk consumption has been associated with a range of adverse health effects. Since most of these health effects have little impact on evolutionary fitness, natural selection doesn’t pay them much attention.
Some of the problems with milk
I’ve talked quite a bit about the problems with milk here on the blog in the past. Let’s briefly summarize the core points…
- Milk has been implicated in the pathogenesis of many chronic diseases and health disorders
Milk seems to play a role in the pathogenesis of several chronic diseases and health disorders, including heart disease, insulin resistance, acne vulgaris, and Parkinson’s disease (1, 3, 4, 5).
- Milk is packed with substances that are not a natural part of the adult human diet
Milk contains a wide range of hormones, bioactive peptides, and other similar compounds, some of which breach the gut barrier and induce adverse health effects (3).
- Pasteurization and homogenization may change the structure of some of the nutrients found in milk
Pasteurization and homogenization can force milk casein and fats into new configurations that make the proteins stackable into fibers/amyloids (6). These milk protein fibers may play an important role in diseases such as type I diabetes and Alzheimer’s disease (6).
- Milk is extremely high in calcium
Contrary to what dairy lobbyists want you to believe, the fact that milk is very high in calcium could actually be a bad thing, as an abnormally high intake (from an evolutionary perspective) of calcium may cause mineral imbalances and increase the risk of heart attacks, among other things (3). Moreover, several large meta-analyses have shown that calcium intake is not significantly associated with hip fracture risk in women or men (7, 8, 9). One of these analyses even found that calcium supplementation may increase hip fracture risk (8). Yes, calcium is important, but maybe we’re better off getting it from green vegetables?
- Cow’s milk consumption may adversely affect bone health
Recent research suggests that regular consumption of milk and other dairy foods may increase the risk of osteoporosis (10). In other words, milk may actually weaken our bones, as opposed to strengthening them.
- The macronutrient characteristics of milk differ markedly from that of other foods
Milk (e.g., cow’s milk) is unique in that it contains whey protein, casein, and the disaccharide lactose, as well as many other special nutrients. It’s undoubtedly beneficial for a growing mammal (e.g., a calf) to take in these compounds; however, the scientific research indicates that it’s not beneficial for an adult human, which is not surprising, given that these nutrients are a novel component of the adult human diet. A low intake of these nutrients is unlikely to do much harm; however, a high intake may certainly do. Casein has been shown to trigger opioid-like effects in the brain (one of the main reasons cheese is so addictive) (11, 12); whey is very insulinogenic, may destabilize the gut microbiota, and promote the development of acne vulgaris, among other things; and lactose has been linked with premature cataract formation (3). If that wasn’t enough, milk also contains high concentrations of saturated fat (About 60% of the fat in milk is of the saturated kind).
Milk is a growth stimulant
Another problem with milk that I haven’t talked much about here on the blog in the past has to do with the impact it has on growth and development. Given that milk’s role in the mammalian diet is to support and promote the development of the young, it shouldn’t come as a surprise that milk has been shown to stimulate growth. In children, there’s a strong association between cow’s milk consumption and linear growth. Children who drink a lot of cow’s milk as they grow up tend to become taller than those who don’t (13, 14, 15).
It’s often assumed that this effect is beneficial. After all, we all want strong and tall children. There’s only one (big problem): Cow’s milk wasn’t “designed” to be a health food for the young members of the species Homo sapiens, it was designed to nurture and strengthen calves. I very much question the conventional idea that it’s good for children to drink milk because milk makes them taller.
Unlike what some people think, milk’s effect on growth can’t solely be attributed to its high nutritional value. Milk is capable of activating evolutionary developmental genes, such as FTO and MTOR, which are very important for perinatal programming. This signaling cascade is a natural part of the developmental phase of mammals and helps promote proper growth and development. However, it’s certainly not a natural part of adult life.
Here’s what the review paper mentioned earlier had to say about this issue.
Daily consumption of cooled pasteurized milk thus allows excessive intake of milk’s amino acid hardware and milk’s gene-regulatory software, which in a synergistic fashion upregulate mTORC1 signaling enhancing mTORC1-dependent anabolism and mTORC1-dependent mRNA translation. It is becoming apparent that this unnoticed modification of epigenetics by milk consumption has had an enormous impact on modern human nutrigenomics 10,000 years since the Neolithic revolution.
… Permanent overactivation of mTORC1 signaling is the key mechanism driving mTORC1-mediated age-related diseases of civilization [16,17,18,19,67,89,287,293]. … Persistent milk signaling leads to alterations in cell homeostasis, ER stress, cellular malfunctions, organ damage and thus early onset of age-related diseases. (1)
The bottom line
I’d like to finish off with the quote below, which I feel nicely summarizes the main problems with cow’s milk consumption.
Persistent abuse of a developmental nutrient and programming system of another mammal such as Bos taurus, a species whose initial growth rate is four times that of humans, is thus a major pathogenic factor promoting the epidemic diseases of civilization . Wiley was right when she pointed out that persistent cow’s milk consumption is a novel human behavior potentially exerting long-term adverse effects on human health . Taken together: “No milk today, that’s what this message means, the end of obese and Western disease!”. (1)