Milk is a highly nutritious liquid formed in the mammary glands of mammals to sustain their newborns during their first months of life.

This article focuses on cow’s milk.

A huge variety of food products are made from cow's milk, such as cheese, cream, butter, and yogurt.

These foods are referred to as dairy or milk products and are a major part of the modern diet.

This article tells you everything you need to know about cow’s milk.

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The nutritional composition of milk is highly complex, and it contains almost every single nutrient that your body needs.

One cup (240 ml) of whole cow’s milk with 3.25% fat provides (1):

  • Calories: 149
  • Water: 88%
  • Protein: 7.7 grams
  • Carbs: 11.7 grams
  • Sugar: 12.3 grams
  • Fiber: 0 grams
  • Fat: 8 grams

Milk proteins

Milk is a rich source of protein — providing approximately 1 gram of this nutrient in each fluid ounce (30 ml), or 7.7 grams in each cup (240 ml) (1).

Proteins in milk can be divided into two groups based on their solubility in water.

Insoluble milk proteins are called casein, whereas soluble proteins are known as whey proteins.

Both of these groups of milk proteins are considered to be of excellent quality, with a high proportion of essential amino acids and good digestibility.

Casein

Casein forms the majority — or 80% — of proteins in milk.

It’s really a family of different proteins, with alpha-casein being the most abundant.

One important property of casein is its ability to increase the absorption of minerals, such as calcium and phosphorus (2).

It may also promote lower blood pressure (3, 4).

Whey protein

Whey is another family of proteins, accounting for 20% of the protein content in milk.

It’s particularly rich in branched-chain amino acids (BCAAs) — such as leucine, isoleucine, and valine.

Whey proteins have been associated with many beneficial health effects, such as decreased blood pressure and improved mood during periods of stress (5, 6).

Whey protein is excellent for growing and maintaining muscles. As a result, it’s a popular supplement among athletes and bodybuilders.

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, 13).

Carbs

Carbs in milk are mainly in the form of the simple sugar lactose, which makes up around 5% of milk.

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.

SUMMARY Milk is an excellent source of high-quality protein and different fats. Carbs make up around 5% of milk — mainly in the form of lactose, which some people cannot digest.

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).
  • Phosphorus. Dairy products are a good source of phosphorus, a mineral that plays an essential role in many biological processes.

Sometimes fortified with vitamin D

Fortification is the process of adding minerals or vitamins to food products.

As a public health strategy, fortifying milk products with vitamin D is common and even mandatory in some countries (17).

In the United States, 1 cup (240 ml) of vitamin-D-fortified milk may contain 65% of the daily recommended allowance for this nutrient (18).

SUMMARY Milk is an excellent source of many vitamins and minerals, including vitamin B12, calcium, riboflavin, and phosphorus. It’s often fortified with other vitamins, especially vitamin D.

More than 50 different hormones are naturally present in cow's milk, which are important for the development of the newborn calf (19).

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 (20).

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.

SUMMARY Milk contains a wide variety of hormones that promote the development of the newborn calf. Only one of them — insulin-like growth factor 1 (IGF-1) — has potential health effects in people.

Milk is one of the most nutritious foods you can find.

It has been widely studied and seems to have several important health benefits.

In particularly, cow’s milk may positively affect your bones and blood pressure.

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.

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 a higher bone density (15).

The high calcium and protein content of milk are the two main factors believed responsible for this effect (21).

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 (22, 23).

It’s thought that the unique combination of calcium, potassium, and magnesium in milk are responsible for this effect (24, 25).

Other factors may also play a part, such as peptides formed during the digestion of casein (3, 4).

SUMMARY Being a rich source of calcium, milk may promote increased bone mineral density, cutting your risk of osteoporosis. Milk and its products have also been linked to reduced blood pressure.

The health effects of milk are complex — some components in milk are quite beneficial, while others may have adverse effects.

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 (26).

Lactose intolerance is most prominent in parts of Asia, Africa, and South America, where its estimated to affect 65–95% of the population (27).

In Europe, the estimated prevalence is 5–15%, with people in Northern Europe being the least affected (27).

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 (28).

Most often, allergic symptoms are caused by whey proteins called alpha-lactoglobulin and beta-lactoglobulin, but they can also be due to caseins (29).

The main symptoms of milk allergy are skin rash, swelling, breathing problems, vomiting, diarrhea, and blood in stools (28, 30).

Acne

Milk consumption has been associated with acne — a common skin disease characterized by pimples, especially on the face, chest, and back (31, 32, 33).

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 (33, 34, 35).

Milk and cancer

Many observational studies have looked at the association between milk and cancer risk.

Overall, the evidence is mixed, and very few conclusions can be drawn from the data.

However, a fair number of studies indicate that dairy consumption may increase the risk of prostate cancer in men (36, 37).

Conversely, numerous studies have found a link between dairy consumption and a lower risk of colorectal cancer (38, 39, 40).

As a general recommendation, excessive consumption of milk should be avoided. Moderation is key.

SUMMARY Many people are intolerant to lactose, and some are allergic to whey or casein. Milk has also been linked to other adverse effects, such as an increased risk of acne and prostate cancer.

Virtually all milk sold for human consumption is processed in some way.

This is done to increase the safety and shelf life of milk products.

Pasteurization

Pasteurization is the process of heating milk to destroy potentially harmful bacteria that are occasionally found in raw milk (41).

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 (42).

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 (43).

SUMMARY To increase its shelf life and safety, commercial milk is pasteurized and homogenized.

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 (44, 45, 46).

Homogenization — the process of breaking the fat globules in milk into smaller units — has no known adverse health effects (43).

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 (47).

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

In healthy cows, milk does not contain any bacteria. It’s during the milking process, transport, or storage that milk gets contaminated with bacteria — either from the cow itself or the environment.

Most of these bacteria are not harmful — and many may even be beneficial — but occasionally, milk gets contaminated with bacteria that have the potential to cause disease.

Although the risk of getting ill from drinking raw milk is small, a single milk-borne infection may have serious consequences.

People are usually quick to recover, but those with weak immune systems — such as older adults or very young children — are more susceptible to severe illness.

Most public health advocates agree that any potential health benefits of drinking raw milk are outweighed by possible health risks resulting from contamination with harmful bacteria (48).

SUMMARY Raw milk has not been pasteurized or homogenized. Drinking raw milk is not recommended, as it may be contaminated with harmful bacteria.

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.

At the end of the day, moderate consumption of cow’s milk is healthy for most people — but you should avoid drinking it in excess.