There is a large body of evidence that up until 9,000 years ago in the Middle East1 and 7,000 years ago in Northern Europe2, no human being on the planet consumed non human milk or dairy products. So on an evolutionary time scale, non-human milk is a relatively newcomer into human diet. By using the evolutionary template, and knowing that that milk is species specific, we would expect this new habit to have unintended consequences, which go way beyond lactose intolerance (which is actually very common), since only a minor percentage of the world’s population continues to produce lactase into adulthood3.
Indeed there are several lines of evidence raising concerns with milk and dairy intake, such as:
1) Milk and fermented milk (yoghurt, for instance), despite having a low glycemic index and load, elicit a very high insulin response and this has been shown repeatedly in intervention studies 4-9.
As you may be aware, constantly increasing insulinemia may downregulate the insulin receptor, and hence lead to insulin resistance10-12, which in turn is the primary metabolic defect underlying The Metabolic Syndrome13, and may be a driving force in obesity14, 15. It should also be mentioned that a chronic state of Hyperinsulinemia may set a hormonal cascade that ultimately results in cancer, acne and juvenile myopia, among other diseases13.
Indeed, a high bovine milk diet has been shown to cause insulin resistance in boys9. Moreover, dairy intake is strongly associated with a higher incidence of Acne16-18 and moderately associated with Prostate Cancer19-23.
2) Cow’s milk appears to be involved in certain autoimmune diseases (AD):
3) Hormones in Milk:
In addition to proteins, fats, lactose, vitamins and minerals, milk contains various growth-stimulating steroid and peptide hormone and also catalysts, transporters and stabilizers that ensure their maximum bioactivity45.
Here’s a short list of some hormones present in cow’s milk that could be problematic for humans:
Cow’s Milk, as well as human milk (and presumably milk from all mammals) contains insulin46-49, and we know that bovine insulin - BI (which differs from human insulin by three amino acids50) survives pasteurization, because immunity to this hormone is common in children who consume cow’s milk or who have been exposed to infant formulas containing cow’s milk51-54.
This not only confirms that BI is present in commercial pasteurized milk, but also in infant formulas and perhaps other dairy products (although direct evidence is lacking). Moreover, these studies provide evidence that BI survives the human digestive processes and crosses the gut barrier intact, although this could be related to the fact that infants have higher intestinal permeability than older children and adults50. Nevertheless, various factors may cause the so called "leaky gut" in virtually everyone, so we shouldn’t dismiss bovine insulin altogether.
Cow’s milk contains active IGF-155, but this has been largely dismissed as relevant, since pasteurization (time and temperature are crucial factors) and fermentation appears to reduce its content56, 57. Yet cow’s milk consumption, compared to various foods, is associated with a higher plasma IGF-1 concentrations in humans (both children58-61 and adults62-66), which could be due to calcium in milk (which has been shown to increase IGF-1 in boys and girls67), the effect of milk upon insulinemia (the high elevation of plasma insulin caused by milk drinking 4-9 could lead to a higher plasma IGF-113) or indeed residual IGF-1 in casein68 (the major protein in milk).
Betacellulin (BTC) belongs to the Epidermal Growth Factor family of hormones69, and is found not only in cow’s milk70 and whey70, but also in cheese70. Therefore, it survives pasteurization and processing. Although no direct evidence yet exists, bovine milk does contain peptidase inhibitors which prevent human gut enzymes from degrading EGF5 (and most likely BTC), and a low ph such as that found in the gut, it does not impair or prevent BTC from binding its receptor71. Finally, there is a luminally expressed EGF receptor in the gut, through which BTC may enter circulation69.
The major sources of animal-derived estrogens in the human diet are believed to be milk and dairy products, which presumably account for 70–80% of the total estrogens consumed72, 73. Furthermore, it has been pointed out that most milk for human consumption is obtained from cows in the latter half of pregnancy when estrogen metabolites levels are greatly elevated72-74. Confirming this, US researchers have measured estrogen metabolites in various milks and shown that buttermilk contains the highest total amount of estrogen metabolites, followed by skim milk, 2% milk and whole milk72. Therefore, estrogen metabolites appear to survive pasteurization, and estrone sulphate, which comprises 45% of the conjugated estrogens in Premarin and Prempro (the most frequently prescribed hormone replacement therapy for menopausal women73) has high oral bioactivity73, and is the most prevalent form of estrogen in cow’s milk72, 73.
There are also other steroid hormones in commercial pasteurized cow’s milk, such as progesterone, 5α-androstanedione and 5α-pregnanedione, which are dihydrotestosterone (DHT) precursors75.
As expected from the evidence presented, dairy intake is strongly associated with a higher incidence of acne16-18, moderately associated with prostate cancer19-23, and mildly associated with ovarian cancer76, 77.
Dairy consumption was also associated with an increased incidence of testicular78, 79, kidney80, and head and neck cancer81, but very few studies have been conducted to draw more significant conclusions.
Although epidemiological evidence can’t show a clear cause and effect, and clearly much more studies need to be conducted, the current evidence strongly suggests that cow’s milk may be implicated in a variety of autoimmune diseases, certain cancers, as well as acne.
4) Milk has a very high calcium/magnesium ratio and may contribute to some micronutrient imbalances.
5) There is evidence of higher fracture incidence rates in countries with higher milk and calcium intake82, some long term prospective studies have failed to show a benefit from drinking milk or taking calcium supplements83-85, and a recent meta-analysis, which analyzed seven prospective cohort studies (170,991 women), five prospective cohort studies (68,606 men), five clinical trials, (5,666 women, and 1,074 men), and four clinical trials with separate results for hip fracture (6,504 subjects), concluded that calcium intake doesn’t decrease the risk for fractures86. Calcium intake is only part of the story; we need to consider GI absorption and renal excretion. In these regards, vegetables from the brassica family have a clear advantage over milk87.
I know this may sound overly alarming, and possibly exaggerated, but given what I know about milk, I have a hard time recommending it - even though it has some positive effects, such as being a cheap source of high quality protein and various micronutrients.
For those who are fortunate and have access to good (real) food, supplements such as Vitamin D, (which by the way, may be needed in much higher doses than the ones provided by three or four servings of dairy a day), and adopt a diet that has a low glycemic load, is moderate in fructose, is net base yielding and provides sufficient protein, soluble fiber, essential fatty acids, especially EPA, DHA, GLA and AA (with a w6/w3 ratio < 4/1) and all the micronutrients, I believe milk is not necessary.
I hope this helps.
Pedro Carrera Bastos
- Various epidemiological studies have associated it with Type 1 Diabetes24-31, especially when the initial exposure begins in the first months of life.
- Epidemiological studies have repeatedly shown a strong correlation between Multiple Sclerosis and cow’s milk consumption32-36.
- There is molecular mimicry between Bovine Serum Albumin and Human Collagen Type 1, which has implications for Rheumatoid Arthritis37. Indeed, case studies have shown that elimination of milk and dairy products from the diets of patients with RA improved symptoms, and the disease was markedly exacerbated on re-challenge37.
- Bovine milk is also implicated (or appears to have adverse effects) in other auto-immune diseases, such as Crohn's disease38, Sjögren's syndrome39, IgA nephropathy40-42, Behçet's disease43, and even Celiac disease40.
Nutrition Researcher, Lisbon, Portugal
Stabbing conventional wisdom in its face.
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