Milk and Milk Products (Dairy Products)

Children and adolescents should be encouraged to consume milk products because this is the period of their lives in which they are building their peak bone mass and developing lifelong habits. This article highlights the benefits of milk and milk products, as well as common misconceptions.  

A production plant for processing dairy products is called a dairy or a dairy factory. Dairy products are generally defined as food products that are produced from milk. They are rich sources of energy. Raw milk for processing generally comes from cows, but occasionally from other mammals such as goats, sheep, and water buffalo. Water is the main constituent of milk (about 90%).

Milk of various types (including whole milk, skim milk, buttermilk), yoghurt, cheese (e.g. Swiss cheese, cheddar cheese, cottage cheese), and ice cream are dairy products. Of all milk products, milk, yoghurt and cheese are the best sources of calcium.

Dairy products and alternatives such as calcium-fortified soy products are nutritious foods, and provide benefit when consumed as part of a nutritionally balanced diet which includes all of the 5 food groups:

Meat/chicken/fish/alternatives; andA small amount of fats and oils.

The functions of a food are served specifically through its nutritionally important components, including proteins, carbohydrates, lipids, minerals, vitamins and water. Cow's milk is the preferred choice for most people. It provides 67 kilocalories and has a protein content of 3.2 grams per 100 millilitres. Milk proteins include casein (about 80%) and whey (about 20%). Whey has a higher nutritional value than casein.

Once fat and casein have been removed from milk, it consists mainly of whey, which contains the soluble milk salts, milk sugar and the remainder of the milk proteins. Whey proteins consist of a number of specialised proteins, the most important being beta lactoglobulin (50% of whey) and lactoglobulin.

Milk proteins have a high biological value but, unlike egg proteins, they lack sulphur-containing amino acids. The proteins in cow's milk have balanced amino acid profiles and good digestibility, making it the obvious choice when it comes to feeding the family. Casein in cow's milk combines with calcium to form caseinogen. A higher proportion of calcium and casein in cow's milk makes it more difficult to digest than human milk. Some people cannot drink fresh milk because they are lactose intolerant, but can consume sour milk because it contains less lactose.

The nutrient composition of milk makes it a time-tested liquid that is indispensable for the maintenance of optimal nutrition, especially for the young. The major nutrients in milk aside from protein include the following:

Fat

Milk and milk products also contain fat. Cow's milk contains fat that is in the form of glycerides. The fat in cow's milk is a poor source of essential fatty acids.

The fat content of milk varies:

Whole milk contains 3.9 g fat per 100 ml,Semi-skimmed milk provides 1.7 g fat per 100 mlSkim milk provides 0.2 g fat per 100 ml1% milk, a blend of skimmed and semi-skimmed milk, has recently become available. It contains 1 g fat or less per 100 ml.

Carbohydrates

The main carbohydrate in milk is a disaccharide called lactose. It is made up of two simple sugars – glucose and galactose – and is sweeter than sucrose (found in cane sugar). Lactose supports the absorption of calcium and phosphorus and the synthesis of some B complex vitamins in the small intestine. In the human body, an intestinal enzyme called lactase digests lactose. Some people are unable to produce enough lactase, inhibiting lactose digestion. This undigested lactose is then broken down in the large intestine by bacteria, causing the formation of gas, bloating, pain and diarrhoea. This condition is called lactose intolerance.

Lactose intolerance is the inability to digest significant amounts of lactose, the major sugar found in milk. Lactose intolerance poses a problem for some people, but can be managed. People who have trouble digesting lactose should avoid dairy products that are not compatible with their system. Many people with this condition can enjoy milk, ice cream and other such products if they eat them in small amounts or eat other food at the same time. Additionally, lactase liquid or tablets can help digest the lactose.

Lactase deficient individuals may tolerate milk with cereals or cooked as custard more than liquid milk. Some dairy foods contain less lactose than others, and may be better for people who suffer from lactose intolerance. These include:

Fermented milk products, including some yoghurts, mature cheeses (like cheddar cheese) and butter, generally pose no problems.Since heating breaks down some of the lactose, heated milk products such as evaporated milk may be preferred to unheated foods.

Vitamins and minerals

Milk and milk products are an excellent source of vitamins and minerals, particularly calcium. Milk has significant amounts of vitamin A and B vitamins such as thiamine, riboflavin and nicotinic acid, but is a poor source of vitamin C and vitamin E. It also contains vitamin B12.

The important minerals in milk are calcium, phosphorus, sodium and potassium. It is, however, a poor source of iron. Calcium is a mineral that the body needs for numerous functions, including building and maintaining bones and teeth, blood clotting, the transmission of nerve impulses, and regulation of the heart's rhythm.

How much calcium do you consume?

Calcium is found in many foods, in particular dairy products and to a lesser degree bony fish, nuts and legumes, fruit and vegetables. It plays an important role in building and maintaining healthy bones and teeth.

Individuals need to consume sufficient amounts of calcium throughout their lifespan.  Calcium requirements increase throughout childhood, peak during puberty, then stabilise until an individual is approximately 50 years old, when bone mass deteriorates and more calcium is required.

Click here to calculate your required calcium intake

Milk and dairy products are the major food source of calcium and protein in most developed countries, including Australia. One litre of milk can provide approximately 1200 mg of calcium, representing more than the daily requirement for calcium. Calcium in milk is in a bioavailable form and is readily absorbed. The absorption of calcium is enhanced by vitamin A and lactose.

Adequate intake of calcium is necessary for growth in childhood, and for the prevention of diseases like osteoporosis in adulthood. Research evidence points to an association between decreased calcium intake and osteoporosis.

  

Calcium is also needed in the diet to control hypertension. A number of studies have reported an inverse association between dietary calcium intake and blood pressure. The most powerful research strategy is the randomised controlled trial. Findings from such clinical trials indicate that an increased calcium intake lowers blood pressure and the risk of hypertension. However, another trial in which researchers followed 193 men and women split into two groups, one taking a placebo and the other taking calcium carbonate tablets twice daily, reported that calcium had no significant effect on blood pressure.

Despite its nutritional value, some people are sceptical of milk consumption, mainly because of the fat and cholesterol content, and the risk of atherosclerosis (clogging of the arteries) or coronary heart disease (CHD). However, there is insufficient scientific evidence to support this caution. In 2004, Dairy Australia Seminar Series, a review of the epidemiological evidence on milk and cardiovascular disease presented by Professor Peter C Elwood, showed that milk drinkers have a reduced risk of cardiovascular disease (CVD) compared to those who drink little or no milk, despite the fact that most of the milk drank was regular fat milk. The review further concluded that there was no evidence of an increase in vascular disease; rather, the incidence of stroke and heart disease was about 15% lower in the subjects with the highest intakes of milk. Evidence from cohort studies suggests that though milk consumption raises cholesterol level, milk is protective against vascular disease.

The biggest setback to using milk and dairy products is that the public in general, and teenagers and women in particular, tend to avoid milk and dairy products because of their fat content.

A 300 ml glass of full cream milk contains 10 g of fat, of which 6.3 g is saturated fat, and can contribute about 770 kJ of energy. In contrast, a 300 ml glass of skim milk only contains 0.6 g of fat (a reduction of 94%), 0.3 g of saturated fat, and 440 kJ (a reduction of 43%). Therefore, consuming skim milk and low fat yoghurt instead of whole milk will allay the fear of health risks associated with dairy fat.

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It has been documented that, in most countries, milk consumption has fallen over the past 20–25 years. A reduction in milk consumption may impact on nutritional needs, especially of calcium. It appears that the positive nutritional and health contributing values of dairy products far outweigh concerns regarding cholesterol.

Like any other food, overconsumption may be associated with health risks. The key word in the choice and consumption of any food is moderation. At moderate levels, calcium and dairy products have benefits beyond bone health, including possibly lowering the risk of high blood pressure and colon cancer.

A daily intake of three glasses of skim milk, over cereal at breakfast, in hot beverages and in milk dishes like custard, and one or more portions of low fat yoghurt or low fat cottage cheese, is sufficient to meet your milk requirements. The US Department of Agriculture's Food Guide Pyramid recommends that individuals two years and older eat 2–3 servings of dairy products per day.

A serving is equal to:

1 cup (8 fl oz; 250 ml) of milk 8 oz (250 g) of yoghurt1.5 oz (40 g) of natural cheese (e.g. cheddar) 2.0 oz (60 g) of processed cheese

It is generally recommended that children, pregnant women, older people and those who are unwell avoid unpasteurised milk and milk products. Individuals who are allergic or intolerant to milk and dairy products may try to avoid them. For such people, eating dairy products such as yoghurt in small quantities may be helpful.

Milk and milk products should be stored in a refrigerator to slow down the growth of micro-organisms, such as mould on cheese. Milk, cheese and yoghurt should be stored and used by the date specified on the packaging.