Until the dawn of agriculture 10,000 years ago and the subsequent domestication of dairy animals, milk, butter, cheese, and yogurt were never part of our ancestors’ menu.
Although 10,000 years ago seems unimaginably distant compared to a single human lifespan, it is very, very recent on an evolutionary time scale. Only 333 human generations have come and gone since we first domesticated animals (cows, sheep, and goats) and began to consume their milk. Consequently, as a species we have had scant evolutionary experience to adapt to a food that now comprises about 10 percent of the calories in the American diet. As such, milk and dairy products have an enormous potential to disrupt our health and wellbeing.
The bottom line is this: We are the only species on the planet to consume another animal’s milk throughout our adult lives. Humans don’t have a nutritional requirement for the milk of another species, nor do any other mammals. And an increasing body of scientific evidence supports the evolutionary caution that this dietary practice may be harmful.
As much as 70 percent of the world’s adults are lactose intolerant. This means they cannot drink milk without digestive discomfort because they lack the enzyme (lactase-phlorizin hydrolase) necessary to digest the sugar (lactose) in milk. This indicates that milk and dairy products could not have been a component of the original adult diet that shaped the human genome until very recent times.
Some people do have the gene for lactase persistence (LCT), which allows them to digest milk sugars into adulthood. Unfortunately, that doesn’t protect them from the many physiological consequences of drinking fresh cow milk, which contains the full complement of enzymes and hormones that are present in cow blood.
It was once assumed that these bioactive compounds in cow’s milk were degraded in the human gastrointestinal tract and that our immune systems ultimately prevented their entry into our bloodstreams. In reality, cow’s milk appears to elevate a key human hormone (IFG) known to affect insulin and glucose metabolism and promote various cancers. Other elements in cow’s milk are implicated in human cancer and disease, including miRNAs and the stimulation of the mTORC1-signaling. Recent studies have tied dairy intake to prediabetes and type-2 diabetes in adults and children.
Dairy products are not part of a Paleo Diet.
