Difference between infant formula and breast milk

Isn’t infant formula just like breast milk?

Infant formula (formula) is very different from breast milk. Human breast milk has evolved to meet the specific needs of humans and is alive with white blood cells, stem cells, and bioactive compounds. Formula allows babies to grow and develop, but it does not protect them from infections or chronic diseases. Formula usually contains plant-based fats, which are different from the animal milk fats of breast milk. Formula also has very little cholesterol, a fat that is an essential part of vitamin D and hormones. While the main sugar in breast milk is milk sugar (lactose), formula may contain other, sweeter sugars. Some formula has even been found to have higher amounts of sugar than breastmilk. Formula contains a very different mix of proteins than breast milk and its composition cannot change as the baby grows. 

A) General differences between infant formula use and breastfeeding

Breast milk has many components, which support the baby's growth and development and vary over time. It is a bioactive fluid, able to direct the baby's immune system and genes to develop normally. Breast milk is unique to each mother and responds to changes in the baby's health.

In addition, the act of breastfeeding calms babies, gives them more control over the amount of milk they take in when compared to bottling infant formula (formula), and provides helpful bacteria from the areola.

Like breast milk, formula provides nutrients allowing babies to grow and develop but there are many differences between the two. For example, formula does not protect them from infections or chronic diseases and costs more than breastfeeding. More differences are described below.

For some babies and in some situations, formula is medically necessary and even life-saving and it is important that formula is safe and affordable. But just as medication, other babies do not need it nor benefit from it.

Formula manufacturers often equate breast milk and formula to promote their products:

  • Closest to breast milk
  • Closer than ever to breast milk
  • Contains certain ingredients found in breast milk

Adding individual items such as pre- or probiotics is unlikely to substantially reduce the fundamental differences between these two products (Almeida 2021). 

B) Unique human fats

Fats in breast milk are animal milk fats and are extremely complex. Their role is not fully understood. Milk fat is organized into little balls (globules) that float in milk. The center and surface have different components. The latter contains various proteins, cholesterol, and agents used to make neurotransmitters; these have been shown to have biological effects (Brink 2020).

Formula usually contains plant-based fats, which have very different structures from those of human milk fats. Fats in formula may also come from fish, algae, eggs, and cow’s milk (Mazzocchi 2018).

C) Cholesterol

Cholesterol is a type of fat that is an essential ingredient in vitamin D and hormones. It stabilizes the cell wall and is used by the brain. Colostrum, the first milk produced right after birth, contains higher amounts of cholesterol. The amount decreases by half at about six months after delivery (Hamdan 2018).

Formula has relatively little cholesterol, and formula-fed babies tend to make more to compensate for the lack of cholesterol in their diet (Cruz 1994). The relative lack of cholesterol in formula may result in long-term changes in the way people handle cholesterol and may impact heart and blood vessel health (Babawale 2018; Delplanque 2015; Demmers 2005).

D) Live cells

Breast milk is alive with cells, such as white blood cells and stem cells, and bioactive compounds that have many functions such as preventing the growth of harmful bacteria. For this reason, unlike formula, which must be chilled right away, breast milk can safely be left at room temperatures for several hours. Breast milk contains large amounts of helpful bacteria that can prevent the growth of harmful ones.

While cow's milk has bacteria and live cells, these, along with harmful bacteria, are killed as the milk is processed.

E) Sugars

Human milk contains large amounts of specialized sugars (human milk oligosaccharides [HMOs]) that cannot be digested by the baby. Rather these feed helpful bacteria in the gut which prevents the over-growth of harmful ones. HMOs prevent infection in the gut and elsewhere, support the development of a normal immune system, and provide nutrients for growth. There are over 200 types of HMOs and these vary between mothers.

Some formula companies have added one or a few HMOs to formula. In contrast, breastfeeding babies receive a unique blend of a wide variety of HMOs which are present in large amounts. 

The main digestible sugar in breast milk and cow's milk is milk sugar (lactose). Some formula manufacturers replace lactose with other sugars. These often taste sweeter than lactose and may have other negative effects. Some formula has been found to have higher amounts of sugar than breastmilk (Bridge 2020). Soy-based formula has no lactose.

F) Whey and casein

Formula differs from breast milk in the type of protein it contains. There are two classes of protein in milk: whey and casein. While whey remains liquid in the stomach, casein turns into curds and is thought to be harder to digest. The protein in human milk is about 75% whey and 25% casein in the first months after delivery and changes to about 50% for each as lactation continues. Cow’s milk is 18% whey and 82% casein, a ratio found in some brands of formula (Martin 2016). Other brands have ratios somewhere in between the two.

G) Nitrogen-containing components

While 75% of nitrogen in breast milk is contained in protein, 25% is present in a large variety of other smaller components including protein building blocks (amino acids), gene building blocks (nucleotides), small pieces of RNA (microRNA), and certain sugars. They have many roles including being used as ingredients for more complex molecules, fighting harmful bacteria, keeping blood pressure healthy, and optimizing the baby’s growth (Dallas 2021).

By comparison, cow’s milk has 95% of its nitrogen tied up in protein and only 5% in other nitrogen-containing components (Dallas 2021).   

References

Almeida CC, Mendonça Pereira BF, Leandro KC, et al. Bioactive Compounds in Infant Formula and Their Effects on Infant Nutrition and Health: A Systematic Literature Review. Int J Food Sci. 2021 May 14;2021:8850080

Babawale EA, Jones PJ, Mercer KE, et al. Modulating Sterol Concentrations in Infant Formula Influences Cholesterol Absorption and Synthesis in the Neonatal Piglet. Nutrients. 2018 Dec 1;10(12):1848

Bridge G, Lomazzi M, Bedi R. A cross-country exploratory study to investigate the labelling, energy, carbohydrate and sugar content of formula milk products marketed for infants. Br Dent J 228, 198–212 (2020)

Brink LR, Lönnerdal B. Milk fat globule membrane: The role of its various components in infant health and development. J Nutr Biochem. 2020 Aug 3:108465

Cruz ML, Wong WW, Mimouni F, et al. Effects of infant nutrition on cholesterol synthesis rates. Pediatr Res. 1994 Feb;35(2):135-40

Dallas D, Sah BNP, Beverly RL, et al. Chapter 11 - Nonprotein nitrogen and protein-derived peptides in human milk. In: Mcguire MK, O’Connor DL, eds., Human Milk. Academic Press; 2021

Delplanque B, Gibson R, Koletzko B, et al. Lipid Quality in Infant Nutrition: Current Knowledge and Future Opportunities. Journal of Pediatric Gastroenterology and Nutrition. 2015;61(1):8-17
 
Demmers TA, Jones PJ, Wang Y, et al. Effects of early cholesterol intake on cholesterol biosynthesis and plasma lipids among infants until 18 months of age. Pediatrics. 2005 Jun;115(6):1594-601
 
Hamdan I, Sanchez-Siles LM, Matencio E, et al. Cholesterol content in human milk during lactation. A comparative study of enzymatic and chromatographic methods. J Agric Food Chem. 2018 Jun 1
 
Martin CR, Ling P-R, Blackburn GL. Review of Infant Feeding: Key Features of Breast Milk and Infant Formula. Nutrients. 2016;8(5):279
 
Mazzocchi A, D'Oria V, De Cosmi V, et al. The Role of Lipids in Human Milk and Infant Formulae. Nutrients. 2018 May 4;10(5). pii: E567