Milk is the only naturally occurring food on this planet that offers you almost all the nutrients that exist. That is what makes it a complete food offering health benefits that span across almost all body systems.

The composition varies in different animals and in different species of the same animal but the differences are mostly quantitative, all the nutrients being mostly present.

Humans mostly consume cow milk but also that of buffalo, goat, and sheep depending on which part of the world you live in.

Milk is regarded as a complete food because it is rich in macronutrients and micronutrients such as proteins, fat, carbohydrates, all vitamins and minerals essential for supporting life and maintaining good health.

Incidentally, milk is about 85 to 95 percent water. Cow’s milk is 87 % water and 13 % dry matter.

Two essential nutrients in milk that make milk very nutritious to the body are carbohydrates and proteins.

The composition can vary between different breeds with the variation being high in fat, slight in protein, while lactose remains largely stable.

Whole milk is milk that is largely left untouched. Then you have the reduced-fat milk in which fat is present 2% by weight and lastly there is the low-fat milk in which fat is present 1% by weight. Skim milk is milk in which all the fat is removed.

In cow’s whole milk, fat constitutes about 3 to 4 percent of the solid content, protein about 3.5 percent and lactose 5 percent.

Buffalo,s whole milk is very high in fat content, which is on average twice as high as that of cow milk. The fat-to-protein ratio in buffalo milk is about 2:1. Buffalo milk also has a higher casein-to-protein ratio and high calcium content.

Table showing composition of various types of cow milk in an 8-ounce serving

Skim Milk Low-Fat Milk Whole Milk
Calories 83 102 146
Carbs 12.5 g 12.7 g 12.8 g
Protein 8.3 g 8.2 g 7.9 g
Fat 0.2 g 2.4 g 7.9 g
Saturated Fat 0.1 g 1.5 g 4.6 g
Omega-3s 2.5 mg 9.8 mg 183 mg
Calcium 306 mg 290 mg 276 mg
Vitamin D 100 IU 127 IU 97.6 IU

Calories

The calories in your food, including milk, provide energy to your body to perform various actions. These calories in milk are provided by the macronutrients proteins, carbohydrates and fats.

Proteins provide four kcal/gram, carbohydrate four kcal/gram, and fat nine kcal/gram. The calorie content, therefore, depends on the macronutrient content of your food.

Whole milk provides the most calories while skim milk provides fewer calories due to its low-fat content.

Calories are important for the body and you should know about their functions. Every function that is being performed in the body requires calories, be it the metabolism at the cellular level, or breathing or the pumping of the heart. Without calories, these essential functions would stop.

Water

Cow’s milk is about 87% water and acts as its good source in the diet. Water is a major component of the human body and is essential to maintain body temperature.

It is again necessary for metabolism. It also helps in keeping you hydrated and prevents dehydration, which can cause fatigue, mental impairment, cramping, and a decreased athletic performance. 

It maintains blood volume and helps to transport nutrients to the tissues and organs and carrying away the waste from the various parts of the body for elimination.

It is a major component of the fluids that lubricate the joints to facilitate their movements.

Carbohydrates

Milk contains approximately 4.9% of carbohydrates in the form of lactose. They are the main source of energy for body activity.

Lactose is split into glucose and galactose by the hormone lactase and then absorbed in the small intestine.  People who suffer from lactase deficiency are not able to digest lactose  and they suffer from lactose intolerance.

The brain gets its energy only through glucose. Lack of glucose in the blood can lead to muscle fatigue and improper functioning of the brain.

Besides providing energy, carbohydrates play an important part in hormonal regulation.

Milk Fat

Milk fat in cow’ milk is made up of about 65% saturated, 30% monounsaturated, and 5% polyunsaturated fatty acids. It is one of the most complex fats known and varies from animal to animal.

Milk fat consists mainly of triacylglycerols, which are present in globular form and each of these fat globules is surrounded by a complex membrane consisting of unsaturated phospholipids, proteins, and glycoprotein.  

It is an important source of bioactive fatty acid conjugated linoleic acid (CLA), which has a number of health benefits such as anticarcinogenic, antiatherogenic, immunomodulating, and anti-obesity properties.

Vitamin D, a fat-soluble vitamin, is also present in the fat. The more the fat content, the more vitamin D your milk contains.

Similarly, the content of omega-3 fatty acids is directly proportionate to the fat content of your milk. Omega-3 fatty acids exhibit many health benefits including improving heart and brain health. These fatty acids also lower the risk of cancer.

Milk Protein

The milk of all mammals is rich in protein in view of the requirement of the newly-born. The proportion, however, varies from animal to animal and from breed to breed of the same animal..

For example, buffalo milk contains 11%  more protein than cow milk. However, while the amount of content varies, the type of protein remains the same.

Milk proteins have a high nutritional value because they contain all the nine essential amino acids in adequate quantities.

Proteins in milk are of two types: casein and whey in the proportion of 80% and 20%.

The concentration of protein in cow’s milk is on average 3.2%, with about 2.6% caseins and 0.6% whey proteins

Caseins consist of three subcategories (alpha α, beta β, and kappa κ) and exist in the form of a colloidal suspension (micelle).

Serum (whey) proteins, unlike casein, are soluble molecules in the aqueous phase of milk. They consist of four main subcategories: α-lactalbumin, β-lactoglobulin, bovine albumin serum, and proteosis-peptones.

Many consider whey as the best source of protein because of the nature of its excellent chain of amino acids and its high natural and organic value.

Vitamins in milk

Milk contains water-soluble vitamins and fat-soluble vitamins.

The water-soluble vitamins include

  • thiamin (vitamin B1)
  • riboflavin (vitamin B2)
  • niacin (vitamin B3)
  • pantothenic acid (vitamin B5)
  • vitamin B6 (pyridoxine)
  • vitamin B12 (cobalamin)
  • vitamin C and
  • folate

While milk is a good source of thiamin, riboflavin and vitamin B12, it contains minute amounts of niacin, pantothenic acid, vitamin B6, vitamin C, and folate.

Milk also contains fat-soluble vitamins A, D, E, and K. The amount of content of these vitamins in the milk or its dairy products depends on the amount of fat present in the milk.

Whole cow’s milk contains 3.5% fat, reduced-fat milk contains 2% fat, low-fat milk contains 1% fat, and skim milk contains no fat.

Due to the reduced content of the fat in the latter three types of milk, they contain lesser amount of the fat-soluble vitamins.

They, therefore, have to be fortified with vitamin A (mandatory) to equal its content of whole milk. This is because the other fat-soluble vitamins are easy to get from a diet of nuts, seeds, vegetables, fish and eggs.

Whole milk contains 5 percent of your daily requirement of vitamin A and 24 percent of your daily requirement of vitamin D.

After the reduced-fat milk is fortified with vitamin A and D, it contains 9 percent of your daily requirement of vitamin A and 29 percent of your daily requirement of vitamin D.

Minerals in milk

Your body needs a small amount of trace minerals. They include iron, manganese, copper, iodine, zinc, cobalt, fluoride and selenium. And, milk has all 22 minerals that are necessary to the human diet. 

Milk is a rich source of calcium, magnesium, phosphorus, potassium, selenium, and zinc. It also contains small amounts of copper, iron, manganese, and sodium. 

Calcium, magnesium, and phosphate are present as salts bound with the protein and this does not affect the nutritional availability of these minerals.

Enzymes in milk

Enzymes are proteins that act as biological catalysts. Enzymes in milk come from several sources.

  • They are originally present in the native milk
  • They may form due to contamination from airborne bacteria or from bacteria that are added to ferment the milk
  • They are present in the somatic cells in milk. These are predominantly the white blood cells that help to fight infection of mastitis ( inflammation of the mammary gland in the breast or udder).

There are several enzymes found in milk and the functions of many are still not well-defined. These enzymes present in milk do not help in the digestion of milk in the human stomach. That is done by the enzymes secreted in the stomach itself.

Some of the important milk enzymes are:

  • Lipases
  • Proteases
  • Alkaline phosphatase
  • Lactoperoxidase

Lipase in milk breaks down the fat into fatty acids and glycerol for easier digestion. It is present as lipoprotein lipase. Pasteurization inactivates the lipase in milk and increases its shelf life.

Proteases are enzymes that break down the proteins. The main protease present in milk is plasmin. Some of the proteases lose their property due to heating and can make the milk bitter. This enzyme is important during the manufacture of cheese.

Alkaline phosphatase enzyme is naturally present. It is heat sensitive and is inactivated when milk is properly pasteurized. This acts as a test to find out whether the milk is properly pasteurized or adulterated with raw milk after pasteurization.

Lactoperoxidase is a very heat stable enzyme present in milk with mild antibacterial properties. Its presence in milk inhibits the growth of microorganisms in raw milk.

However, when combined with hydrogen peroxide and thiocyanate its antibacterial properties become stronger.

Lysozyme is another enzyme present in small amounts and also exhibits some antibacterial properties.

Iodine

The amount of iodine in milk and dairy products differs and depends greatly on the iodine content in the cattle feed.

Based on a comprehensive study, one cup of milk can provide 59–112% of the recommended daily amount of iodine.

Dairy products such as yogurt and cheese also provide your body with a good amount of iodine.

One cup of plain yogurt provides roughly about half of the daily recommended amount of iodine. Among the cheese types, cottage cheese provides more iodine. One cup of cottage cheese gives your body 65 mcg, while one ounce of cheddar cheese provides about 12 mcg of iodine.  

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