Yogurt is a fermented milk product made by adding a harmless bacteria culture to milk.
As with all dairy products it naturally contains many nutrients essential to growth, development and maintenance of the human body.
Numerous different types and flavours of yogurts are now available and the market is continually growing.
Yogurt can be given to children as part of a weaning diet, included in packed lunches, used in the cooking of sweet and savoury dishes or just as a quick nutritious snack.
As with milk, yogurt has been associated with many health benefits and provides an important and popular addition to the diet.
a) Macro nutrients in Yoghurt.
The energy/calorie content of yogurt depends upon the type of yogurt consumed.
Natural yogurts made with semi skimmed or skimmed milks usually have a lower calorie content compared with natural yogurts made with whole milk, due to the lower fat content.
However, flavoured yogurts are usually higher in added sugars than natural yogurts and are consequently higher in calories.
Therefore flavoured, whole milk yogurts tend to have the highest calorie content whilst low fat natural yogurts are lowest.
The protein in yogurt and milk is of high quality as it provides all of the amino acids the body needs to function correctly. The protein content of yogurt is usually slightly higher than in milk because of the addition of non-fat dry milk during processing.
Interestingly the protein present in yogurt tends to be more readily digested than the proteins present in milk. This is due to the pre-digestion of milk proteins that occurs through the action of the bacteria present in yogurt.
The milk proteins in yogurt also have a higher content of the amino acids proline and glycine compared with milk and these proteins have additional functions in the body including enhancing calcium absorption and boosting the immune system.
It is also important to note that the nutritional value of milk proteins is not affected by the fermentation process.
The form of carbohydrate found in yogurt and all dairy products is the sugar known as lactose.
Lactose is digested by the enzyme lactase into glucose and galactose which are then absorbed and used to produce energy.
Before fermentation, the lactose content of yogurt is about 6%. Once the fermentation process begins, lactose is digested by up to 20-30% into its absorbable components, glucose and galactose.
This process lowers the lactose concentration in yogurt compared with milk and partly explains why individuals who have difficulty digesting lactose are able to tolerate yogurt better than milk .
The fat content of yogurts varies depending on the product, ranging from approximately 10% fat for full fat Greek style yogurts, 3% fat for whole milk yogurts, 1.7% fat for low fat yogurts and non-fat varieties containing less than 0.3% fat.
The fat present in milk goes through many biochemical changes during yogurt production. The homogenisation and fermentation processes result in the breakdown of some of the fat into fatty acids which increases the digestion and absorption of the yogurt end product.
Yogurt has also shown to have increased concentrations of conjugated linoleic acid (CLA), a naturally occurring fat, which is believed to boost the immune system and protect against cancers.
Water soluble vitamins
The vitamin content of yogurts is variable depending on the type of yogurt and method of production, but remains fairly similar to milk for the majority of vitamins.
Yogurt is a provider of several B vitamins particularly, riboflavin (vitamin B2) and thiamin (vitamin B1).
Riboflavin is necessary for the release of energy from foods and healthy membranes and skin.
A 150g serving of whole milk plain yogurt and low-fat plain yogurt will provide 31% and 30% of an adult’s daily B2 requirement respectively.
Thiamin (vitamin B1) is necessary for carbohydrate metabolism, neurological and cardiac function.
A 150g serving of whole milk plain yogurt and low-fat plain yogurt will provide 23% and 45% of an adult’s daily B2 requirement respectively.
Vitamins B12 and B6 are often significantly reduced in yogurt compared with milk. This is mainly due to the metabolism of S. thermophilus which uses up these B vitamins and leads to reduced content in the final product. However some varieties of yogurt are still useful dietary providers of these nutrients.
Some lactic acid bacteria species such as S. thermophilus and Bifidobacteria actually synthesise certain vitamins such as Folic acid and depending upon the bacterial strain used, the folate content of yogurt can be significantly increased compared with milk .
Fat soluble vitamins
Whole milk yogurt is also a provider of the fat soluble vitamins A and E.
Vitamin A is necessary for normal eye function, while vitamin E is an antioxidant which protects cell membranes and is needed for the immune system.
c) Minerals in yoghurt
Yogurt is a good source of calcium, which is essential for the healthy growth and maintenance of teeth and bones amongst other important functions.
A 150g serving of whole milk fruit yogurt provides 26% of the calcium required daily by an adult (19-50 yrs) and 41% of the calcium required by a child (4-6 yrs).
The reason that milk, yogurt and other dairy foods are good providers of calcium is because they contain significant amounts of calcium in a bioavailable (easily absorbed) form.
Whilst other foods may also contain calcium, they may not necessarily be good providers because their calcium content per serving is low, because the calcium they provide isn’t available for absorption and use by the body (i.e. bioavailable), or as a result of both these factors.
For example, whilst spinach contains calcium, its bioavailability is poor and, hence, it would be necessary to eat 11 servings, or 963g, of spinach in order to absorb the same amount of calcium that is available from one small-pot of yogurt.
In addition the acidity of yogurt is thought to increase the absorption of certain minerals including calcium, phosphorous and magnesium even further compared with other dairy products and may reduce the inhibitory effect of some compounds such as phytic acid which is known to interfere with mineral absorption (particularly calcium).
Studies have also suggested that calcium from yogurt may lead to greater bone mineralization than calcium from non fermented dairy products in animals, however, there are no published studies that show this effect in humans at present.
Yogurt is also a provider of phosphorus.
Phosphorus serves many functions in the body and is necessary for healthy bones and teeth as well as energy production, cell membrane structure, tissue growth and regulation of pH levels in the body.
A 150g serving of whole milk plain yogurt and low-fat plain yogurt will provide 47% and 40% of an adult’s daily phosphorus requirement respectively.
Yogurt is a good source of iodine. Iodine is necessary for the functioning of hormones such as thyroxine produced by the thyroid gland. These hormones regulate the rate of metabolism (how quickly the body burns energy and the rate of growth).
A 150g serving of whole milk plain yogurt and low-fat plain yogurt will provide approximately 68% and 36% of an adult’s (aged 19-50 years) daily iodine requirement respectively. A 150g serving of whole milk plain yogurt and low-fat plain yogurt will provide a child aged 6 years with all (158%) and 85% of the recommended daily requirement for iodine respectively.
Magnesium, potassium, zinc, selenium, iron and chloride are also found in yogurt.