Consuming milk post weaning
As a food substance, milk has its own special place. Milk is meant specifically for the very rapid body and organ growth that is required in the very initial stages of childhood. Since milk has its own specific rapid growth purpose, it is available for the baby only till it is required. Post that, milk simply stops existing naturally in nature, since no animal that has been weaned away any longer requires the very rapid growth characteristics of this food substance.
Lactose forms the majority of the carbohydrate in milk. The presence of the enzyme lactase is essential to be able to break down lactose to deliver energy present in milk. The body is genetically programmed to consume milk only until weaning is over, and therefore the body of most animals (including the majority of humans) stop producing lactase after weaning. An adult animal therefore, does not have the essential lactase enzyme to be able to break down lactose and gains it nutrients, and naturally stops consuming it.
Humans are the only animal species on the planet that continue to consume milk, as adults. The exception is of domesticated animals such as cats & dogs, where we choose what they eat despite vets indicating the harmful effects of milk on the kidneys of dogs & cats.
There is nothing in our physical and biological structures, that requires us to have a food substance meant in nature exclusively for babies. Man did not even start consuming milk until the recent domestication of farm animals, and even then there are large cultures (including most of Asia) which do not consume any milk.
Consuming the milk of another animal
There is simply no dispute that a mother's milk is what nature has unequivocally planned for growth of babies across all species. The mother's milk of any particular species is unique, based on the essential nutrients, fats, proteins, vitamins, hormones and enzymes that are required for the development of that particular animal.
Not only are humans the only animal species to consume milk into maturity, but we are also the only animal species that consumes the milk of another animal. What is even more remarkable is that we have chosen the milk of an animal (cows and buffalo milk is the most common) that has very little in similarity to us.
Cows and buffalo's weigh anywhere between 8 – 20 x an average humans weight and have a significantly lesser developed brain. A baby calf will grow from 60 pounds to over 600 pounds in less than 8 months – cows milk has been designed for the purpose of this kind of rapid growth.
Given that the milk of every animal is specifically composed to provide the growth required by that particular animal baby, is it likely that the combination of nutrients, fats, proteins, vitamins and hormones that are meant for the rapid growth of a baby calf, are similar to what is required for nutrition for a human (baby, child or adult).
To understand the same, it is essential to look at the composition of cows milk, and how this differs to the composition of breast milk from a human mother.
Nutrient composition of cow vs human milk
Saturated Fats: A calf doubles in size in 45 days, while humans take 180 days for the same relative (not absolute) growth. To aid this rapid growth, cows milk have significantly higher levels of saturated fats and animal proteins than human breast milk. Cows milk contains high levels of saturated fats – 'bad' fats which lead to adverse health effects on humans.
Polyunsaturated fatty acids (PUFA): Humans have the most advanced brains of all species on earth, and human breast milk has evolved accordingly having high levels of PUFAs which is responsible for rapid brain development in humans. The brain of a cow is significantly less developed than that of humans, and cows milk accordingly has significantly lower levels of PUFA.
Proteins: Not only are there higher absolute levels of protein in cows milk, but there are also major differences in the composition of this protein. There are 2 important proteins: casein and whey. Caseins can be very difficult to digest, often causing allergies and has been linked to Type 1 diabetes. Caseins are so tough that are even used as a base for some glues.
The amount of protein in cows' whole milk is around 3.3 g/100g (3.4g in semi-skimmed milk) while it is only 1.3g/100g in human milk. Moreover, the ratio of caseins to whey proteins is 40:60 in human milk but it is 80:20 in cows' milk. Both the absolute levels and high caseins levels of fat & proteins in cows milk are unsuitable for human bodies. This leads to a number of adverse health benefits including cardiovascular risk, diabetes and cancers.
Beta-lacto globulin: Cow's milk has beta-lacto globulin, an offending protein to a range of humans, and one of the prime causes of milk allergies. Human breast milk has no beta-lacto globulin.
Nutrient Composition: Cow's milk has very little iron, retinol, Vitamin E, Vitamin C, Vitamin D and unsaturated fats that are considered essential for human babies and are accordingly present in abundance in human milk. On, the other hand cows milk contains too much sodium, potassium, phosphorous and chlorides all of which add strain to human kidneys.
Hormones: Cow's milk contains a cocktail of 35 hormones and 11 growth factors – perfectly suited for the growth and development needs of a baby calf. However, these hormones / growth factors can accelerate cancer growth in an adult human body – simply because there is nothing left to grow except for malignant cells. Estrogen and Insulin like growth factor 1 (IGF-1) are possibly two of the most harmful of these hormones, having been linked to increased breast and prostate cancer risk in humans.
Infectious particles and somatic cells: Dairy cows are prone to disease and the modern intensive way of farming cows leads to diseases spread fast. Cows suffer from a range of infectious diseases including brucellosis, bovine tuberculosis, foot and mouth disease, mastitis, viral pneumonia and Johne's disease. As a result various contaminants can occur in milk. Mastitis (inflammation of the mammary gland) is very common. It is caused by bacteria and leads to the whole udder or a part of it being inflamed, swollen and very painful. The cow's body responds to the infection by producing white blood cells (somatic cells) that combat the infection in the udder. These cells, together with dead cells and waste products of the inflammation are components of pus and are inevitably excreted into the milk. Every country has a defined limit on the amount of pus in milk which is considered acceptable.