Fats

Due to their fast growth rate, babies require three to four times more energy per kilogramme of body weight than adults. Fat contains a lot of calories and is a very concentrated source of energy, accounting for half the energy content of breast milk. This high energy density is important because babies have a limited stomach capacity. Fat also acts as the carrier for the fat-soluble vitamins A, D, E and K. Breast milk and most infant formula milks also contain essential fatty acids and long chain polyunsaturated fatty acids (LCPs), including arachidonic acid (AA) and docasahexaenoic acid (DHA).

Carbohydrates

The main carbohydrate is lactose, a natural milk sugar that provides 40 per cent of the energy content of breast milk. Breast and infant formula milks also contain oligosaccharides, a type of carbohydrate consisting of linked sugar units. Also included are fructo-oligosaccharides and galacto-oligosaccharides.

Proteins

Protein is required for growth as well as the maintenance of muscles and bones. There are two main proteins: casein and whey, which occur in breast milk in a ratio of 40:60.

• Whey protein forms a soft curd which is easily digested. In breast milk, whey protein also contains other important proteins: lactoferrin, lysozyme, alpha-lactalbumin, and immunoglobulins
• Casein protein has coagulating properties, so forms a firmer curd that may take longer to digest.

Vitamins

• Vitamin A: contributes to the normal function of the immune system, maintenance of normal vision and skin, and helps the body metabolise iron
• Vitamin D: needed for calcium absorption, vitamin D contributes to the normal function of the immune system and helps maintain normal teeth, muscle function and bones
• Vitamin E: helps to protect cells from oxidative stress
• Vitamin K: helps maintain normal bones and blood clotting
• Vitamin C: contributes to the normal function of the immune and nervous systems. Increases iron absorption
• B vitamins: are important for energy metabolism.

Minerals

• Calcium: is needed for the maintenance of normal bones and teeth, and contributes to normal blood clotting and muscle function
  Phosphorus: contributes to the maintenance of normal bones and teeth  
• Zinc: contributes to normal cognitive function, the metabolism of fatty acids and vitamin A, and the maintenance of normal bones, vision and immunity
• Selenium: protects cells from oxidative damage
• Iodine: is important for growth and normal cognitive function
• Iron: contributes to normal cognitive function.
  The iron content of breast milk is low as babies are generally able to rely on their own stores until four to six months of age. At this age, babies need a dietary source of iron. Iron is more efficiently absorbed from breast milk than infant formula milk, which is why infant formula milk contains higher levels.

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