Breast Milk vs Formula Pros and Cons

Mothers considering the merits of formula vs. breast milk have mostly weighed nutritional qualities, which are similar though not identical. In addition to its nutritional value, breast milk helps the baby establish a healthy gut microbiome (Frontiers in Immunology, Feb. 28, 2018). Babies fed formula also miss out on the immunological protection available through breast milk (Nutrients, May 11, 2016). Scientists have identified another reason to feed newborns breast milk if at all possible. It helps to protect infants from bacteria with antibiotic resistance.

Antibiotic-Resistant Bacteria in Babies Fed Formula

Bacteria that do not respond to antibiotics are especially dangerous for newborn babies. Doctors have long blamed antibiotics administered early in life for encouraging antibiotic resistance.

A new study suggests, however, that formula feeding may also contribute to greater numbers of antibiotic resistant bacteria (American Journal of Clinical Nutrition, online Oct. 22. 2021). The scientists studied the genomes of gut bacteria in 46 neonates. Babies fed formula instead of breast milk had more bacteria considered potentially pathogenic. In addition, these bacteria had 69 percent more antibiotic resistance genes. Overall, breastfed infants had more Bifidobacteria and other beneficial types of bacteria than infants getting formula.

Pediatricians have known for a long time that breastfeeding promotes more microbial diversity for little babies. Nearly five years ago, we were fascinated to read such a study.

Breastfeeding Helps Babies Get the Right Bacteria in Place

The scientists examined microbial samples from more than 100 pairs of mother and infants (Pannaraj et al, JAMA Pediatrics, July 2017 ). They found that important microbes in the babies’ stool matched bacteria in their mothers’ milk and on their mothers’ skin.

The milk microbes that colonized the infants’ digestive tracts were associated with more diverse microbial communities. This is how breastfeeding gives them a good start, presumably making for better digestive health both in infancy and at later ages.

In response to this report, Ellie posed an interesting question:

“For years, low income and minority women have not breastfed their babies while educated women have embraced breast feeding. At the same time, obesity has grown in the lower income, minority population. Is anyone doing a study on beneficial bacterial derived from breast feeding and non-breastfed lower income children?”

So far as we know, that particular question has not been answered through research. Lack of maternity leave or breaks to pump breast milk makes it far more difficult for low income women to establish or continue breast feeding.

Does Breastfeeding Increase the Risk for Osteoporosis?

So far, we have been emphasizing the benefits of breastfeeding. Are there downsides to consider? Certainly, not every mother has a job that accommodates breastfeeding or pumping breast milk for the baby to consume while the mother is absent. One concerned grandmother is pleased that her daughter is breastfeeding the baby but worried about the risk for osteoporosis.

Q. My daughter just had a baby and she is breastfeeding. I’m proud that she is giving my grandchild such a good start in life, but I am surprised that she has not been told to take mineral supplements. Doesn’t lactation take a toll on the mother’s bones?

A. Your daughter is giving her baby the best possible nutritional start. She’ll do better for herself and the baby if she follows a diet rich in omega-3 fats. (Of course, she should be careful not to consume fish such as king mackerel, shark, tilefish, swordfish and bigeye tuna, which may be high in mercury.) She also needs more iodine and choline than usual. Those are found in dairy products, eggs and some types of seafood. Iodized table salt also provides iodine, while beans, peas and lentils can offer choline.

Dairy products contain calcium, and for some women that is sufficient. Other women have trouble consuming enough calcium and getting adequate vitamin D, especially if they or their infants can’t tolerate dairy products (Annals of Nutrition and Metabolism, Feb. 21, 2025).  Vitamin D supplements can help her provide adequate vitamin D to the baby and keep her own calcium levels normal (Breastfeeding Medicine, Spring 2006).  Her doctor should be able to advise her on a suitable dose by checking her serum 25-hydroxyvitamin D.

Breastfeed for at least Six Months

Pediatricians in the US encourage parents to breastfeed babies for at least six months. Sometimes parents try to introduce solid foods too early. But there is a balance to be found. Mexican researchers have reported that prolonged breastfeeding, two or three years total duration, can increase the mother’s risk of osteoporosis after menopause (Menopause, March 2011). However, they did not analyze data regarding the women’s diet or supplements during lactation.

Learn More

You can learn more about the importance of diversity in the gut microbiome, not for babies but for adults, from our interview with Dr. Robynne Chutkan, author of The Microbiome Solution.