Appendix: Breast Milk Substitutes

There are situations, albeit rare, in which breastfeeding is impossible due to health problems of the mother or baby. There may also be various other reasons why a new mother decides not to breastfeed. In such cases, as previously discussed, experts advise against using cow’s milk as a substitute for human milk during the first year of life. Instead, they recommend using infant formula—a processed product, mostly derived from cow’s milk but modified to resemble human milk as closely as possible.

What They Contain

Currently, it is not possible to fully replicate human breast milk, which, in addition to fats, carbohydrates, proteins, vitamins, and minerals, contains many bioactive molecules and beneficial bacteria. The function of these elements is not yet fully understood, and the milk’s composition changes from day to day—even throughout the same day—to meet the baby’s needs. However, infant formula can approximate its nutritional profile fairly closely.

The cow’s milk used as the base for formula is too rich in energy and proteins for infants, so it is skimmed and diluted, with the addition of polyunsaturated fats from vegetable sources, vitamins, iron, and other minerals.

Formulas are also available that are based on soy or rice milk for babies who are allergic to cow’s milk proteins, as well as formulas made with hydrolyzed proteins—broken down at a molecular level to improve digestibility. In recent years, formulas supplemented with probiotics (specific strains of beneficial bacteria that support the infant’s gut flora) and prebiotics (carbohydrates that nourish these bacteria and are not absorbed by the intestines) have also become available.

WHO Guidelines

There are three categories of formula designed for the different stages of a baby’s development: Formula 1 (infant formula): from 0 to 6 months, Formula 2 (follow-on formula): from 6 months to 1 year, Formula 3 (growing-up milk): from 1 to 3 years. The composition of infant and follow-on formula is strictly regulated by WHO guidelines, first issued in 1981 and recently updated by the Nutrition Committee of the European Society for Pediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) on behalf of the WHO.

Each nutrient has a minimum and maximum allowed concentration, similar to those found in human milk. Iron content, however, is higher than in breast milk.

ESPGHAN has also published guidelines on the introduction of probiotics and prebiotics in infant and follow-on formulas. Adding these microorganisms increases the presence of bifidobacteria and lactobacilli in the gut flora of bottle-fed infants, making it more similar to that of breastfed infants. This results in softer stools, more frequent bowel movements, and a reduced risk of constipation and diarrhea.

Unlike formula 1 and 2, formula 3 (growing-up milk) is not regulated and varies widely between brands.

Generally, these commercial formulas have high energy and protein levels, similar to cow’s milk, and often contain added sugars and flavorings. Most are fortified with iron, vitamin D, and omega-3 fatty acids.
At this stage (1 to 3 years), children eat a variety of foods, and milk or formula is no longer a staple but just one food among many. According to ESPGHAN experts, after the first year of life, mothers who do not breastfeed can choose between cow’s milk, formula 3, or continuing with formula 2. The only advantage of some formula 3 products is their higher content of vitamin D, iron, and omega-3s, which can also be provided through other foods.

How Babies Grow on Formula

One of the main reasons cow’s milk is not suitable as a breast milk substitute during the first year is its high energy, fat, and protein content. Babies fed cow’s milk tend to grow more rapidly and are at higher risk of becoming overweight or obese. This is why WHO and ESPGHAN have set strict limits on the energy content of infant formulas.

Despite this, experts have noted that bottle-fed babies still tend to gain weight more rapidly than breastfed babies, particularly in the first few weeks of life. The typical early weight loss seen in all newborns is less pronounced in formula-fed babies—they lose less weight and regain it faster. Although this might seem beneficial, it could actually contribute to an increased risk of overweight later in life. This phenomenon is partly because infant formula has an energy content similar to breast milk after the milk has come in, but significantly higher than colostrum, which is the baby’s only food in the first days when breastfeeding. Furthermore, colostrum is produced in small quantities. Therefore, a formula-fed newborn has access to more food right from birth—especially since sucking from a bottle is easier than from the breast.

To reduce the risk of excessive weight gain in formula-fed infants, experts recommend feeding on demand, just like with breastfeeding, and paying close attention to hunger and satiety cues. Parents should not insist on finishing the bottle if the baby repeatedly refuses after drinking most of it.

Bottle Preparation

Infant formula is sold in ready-to-use liquid form or as powder to be mixed with water. It is not sterile and may contain bacteria that can be harmful to infants. Proper preparation and storage are essential to avoid contamination and bacterial growth.

WHO guidelines outline the correct procedure: Wash and sterilize all equipment (bottles, teats, containers, scoops) before use with hot water and soap, using a brush to remove residue. Then boil the equipment or use a sterilizer. Wash hands thoroughly and clean the preparation surface.

Boil water and let it cool slightly to at least 70°C (158°F). Pour the correct amount into the bottle and add the powder using the scoop provided, following the package instructions. Close the bottle and shake vigorously to dissolve the powder. Cool the bottle under running water to feeding temperature. Test it on the inside of your wrist—it should be warm, not hot.
Ideally, feed the baby immediately. If the formula needs to be prepared in advance, cool it quickly and refrigerate it at no more than 5°C (41°F), for no longer than 24 hours. To reheat, place the sealed bottle in hot water for no more than 15 minutes. Do not use a microwave, as it can heat unevenly and cause burns. Always discard any leftovers.