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Milk proteins

Milk is a rich source of protein — providing approximately 1 gram of this nutrient in each fluid ounce (30 mL), or 8.14 grams in each cup (249 grams) (1). Proteins in milk can be divided into two groups based on their solubility in water: •Insoluble milk proteins are called casein. •Soluble milk proteins are known as whey proteins.

Milk fat

Whole milk straight from the cow is around 4% fat. In many countries, marketing of milk is mainly based on fat content. In the United States, whole milk is 3.25% fat, reduced fat milk 2%, and low fat milk 1%. Milk fat is one of the most complex of all natural fats, containing about 400 different types of fatty acids (7). Whole milk is very high in saturated fats, which make up about 70% of its fatty acid content. Polyunsaturated fats are present in minimal amounts, making up around 2.3% of the total fat content. Monounsaturated fats make up the rest — about 28% of the total fat content. In addition, trans fats are naturally found in dairy products. In contrast to trans fats in processed foods, dairy trans fats — also called ruminant trans fats — are considered beneficial for health. Milk contains small amounts of trans fats, such as vaccenic acid and conjugated linoleic acid (CLA) (7). CLA has attracted considerable attention due to its various possible health benefits — though evidence is still limited (8, 9, 10). Some research suggests that CLA supplements may harm metabolism (11, 12).

Carbs

Carbs in milk are mainly in the form of the simple sugar lactose, which makes up around 5% of milk (13). In your digestive system, lactose breaks down into glucose and galactose. These are absorbed into your bloodstream, at which point your liver converts galactose into glucose. Some people lack the enzyme required to break down lactose. This condition is called lactose intolerance — which is discussed later on.

Milk contains all the vitamins and minerals necessary to sustain growth and development in a young calf during its first months of life.

It also provides almost every single nutrient needed by humans — making it one of the most nutritious foods available.

The following vitamins and minerals are found in particularly large amounts in milk:

•Vitamin B12. Foods of animal origin are the only rich sources of this essential vitamin. Milk is very high in B12 (1, 14).

•Calcium. Milk is not only one of the best dietary sources of calcium, but the calcium found in milk is also easily absorbed (15).

•Riboflavin. Dairy products are the biggest source of riboflavin — also known as vitamin B2 — in the Western diet (16).

More than 50 different hormones are naturally present in cow’s milk, which are important for the development of a newborn calf (20).

With the exception of insulin-like growth factor-1 (IGF-1), cow milk hormones have no known effects in humans.

IGF-1 is also found in human breast milk and the only hormone known to be absorbed from cow’s milk. It’s involved in growth and regeneration (21).

Bovine growth hormone is another hormone naturally present in milk in small quantities. It’s only biologically active in cows and has no effect in people.

Bone health and osteoporosis

Osteoporosis — a condition characterized by a decrease in bone density — is the main risk factor for bone fractures among older adults (22). One of the functions of cow’s milk is to promote bone growth and development in the young calf. Cow’s milk seems to have similar effects in people and has been associated with higher bone density (15). The high calcium and protein content of milk are the two main factors believed responsible for this effect (23, 24). However, more recent evidence is conflicting. Some studies have failed to show a connection between dairy intake and osteoporosis (25, 26, 27).

Blood pressure

Abnormally high blood pressure is a major risk factor for heart disease. Dairy products have been linked to a reduced risk of high blood pressure (28, 29). It’s thought that the unique combination of calcium, potassium, and magnesium in milk are responsible for this effect (30, 31). Other factors may also play a part, such as peptides formed during the digestion of casein (3, 4).

Lactose intolerance

Lactose, or milk sugar, is the main carbohydrate found in milk. It’s broken down into its subunits — glucose and galactose — in your digestive system. However, some people lose the ability to fully digest lactose after childhood — a condition known as lactose intolerance. An estimated 75% of the world’s population has lactose intolerance, though the proportion of lactose intolerant people varies greatly depending on genetic makeup (32). Lactose intolerance is most prominent in parts of Asia, Africa, and South America, where its estimated to affect 65–95% of the population (33). In Europe, the estimated prevalence is 5–15%, with people in Northern Europe being the least affected (33). In people with lactose intolerance, lactose is not fully absorbed, and some or most of it passes down to the colon, where the residing bacteria start fermenting it. This fermentation process leads to the formation of short-chain fatty acids (SCFAs) and gas, such as methane and carbon dioxide. Lactose intolerance is associated with many unpleasant symptoms, including gas, bloating, abdominal cramps, diarrhea, nausea, and vomiting.

Milk allergy

Milk allergy is rare in adults but more frequent in young children (34). Most often, allergic symptoms are caused by whey proteins called alpha-lactoglobulin and beta-lactoglobulin, but they can also be due to caseins (35). The main symptoms of milk allergy are skin rash, swelling, breathing problems, vomiting, diarrhea, and blood in stools (34, 36).

Acne

Milk consumption has been associated with acne — a common skin condition characterized by pimples, especially on the face, chest, and back (37, 38, 39). High milk consumption is known to increase levels of insulin-like growth factor-1 (IGF-1), a hormone thought to be involved in the appearance of acne (39, 40, 41).

Pasteurization

Pasteurization is the process of heating milk to destroy potentially harmful bacteria that are occasionally found in raw milk (47). The heat eliminates beneficial as well as harmful bacteria, yeasts, and molds. However, pasteurization does not make milk sterile. Therefore, it needs to be quickly cooled down after heating to keep any surviving bacteria from multiplying. Pasteurization results in a slight loss of vitamins due to their sensitivity to heat but doesn’t have a substantial effect on milk’s nutritional value (48).

Homogenization

Milk fat is made up of countless particles, or globules, of different sizes. In raw milk, these fat globules have a tendency to stick together and float to the surface. Homogenization is the process of breaking these fat globules into smaller units. This is done by heating the milk and pumping it through narrow pipes at high pressure. The purpose of homogenization is to increase the shelf life of milk and to give it a richer taste and whiter color. Most milk products are produced from homogenized milk. An exception is cheese, which is usually produced from unhomogenized milk. Homogenization does not have any adverse effects on nutritional quality (49).

Raw milk is a term used for milk that has not been pasteurized or homogenized.

Pasteurization is the process of heating milk to increase shelf life and minimize the risk of illness from harmful microorganisms that may be present in raw milk.

Heating results in a slight decrease in several vitamins, but this loss is not significant from a health perspective (50, 51, 52).

Homogenization — the process of breaking the fat globules in milk into smaller units — has no known adverse health effects (49).

Drinking raw milk is associated with a reduced risk of childhood asthma, eczema, and allergies. The reason for this association is still not entirely clear (53).

Although raw milk is more natural than processed milk, its consumption is riskier.

Milk is one of the most nutritious drinks in the world.

It’s not only rich in high-quality protein but also an excellent source of vitamins and minerals, such as calcium, vitamin B12, and riboflavin.

For this reason, it may cut your risk of osteoporosis and reduce blood pressure.

Still, some people are allergic to milk proteins or intolerant to milk sugar (lactose). Milk has also been linked to acne and an increased risk of prostate cancer.