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Is there a difference between breastfed babies and formula fed babies?

Yes, there are measurable differences. Breastfed and formula-fed babies tend to grow at different rates, have different gut bacteria, and breastfed babies have somewhat lower rates of infections, with some studies also finding small cognitive advantages.

Most of these differences are on average across large groups and don't predict what will happen for any one baby, especially since many studies can't fully separate the effects of feeding from other family factors.

Strength of evidence

Good

Major differences (like infection rates and gut bacteria) come from systematic reviews and large cohort studies; some outcomes like IQ come from a large randomized trial, but many findings are observational and affected by socioeconomic and family confounders.

What the evidence says

Growth: In the first couple of months, breastfed and formula-fed babies grow similarly. After about 2-3 months, formula-fed babies tend to gain weight and length a bit faster than breastfed babies, and often carry more body fat later in the first year. This is a big reason WHO growth charts (based on breastfed babies) differ from older reference charts that mixed feeding types.

Immunity and infections: Breast milk contains antibodies and other immune-supporting substances that formula doesn't fully replicate. Reviews and observational studies consistently find fewer infections such as ear infections, colds, and gut infections among breastfed babies, though the amount of protection reported varies between studies.

Gut bacteria: Breastfed and formula-fed babies develop noticeably different populations of gut bacteria, with formula feeding linked to more potentially harmful bacteria in some studies. The long-term health impact of these differences is still being studied.

Development and long-term health: Some studies, including a large randomized trial of breastfeeding support, found modestly higher intelligence test scores in breastfed children, though many observational studies on this topic are confounded by parental education and home environment. Formula feeding has also been linked to differences in hormones related to appetite and fat storage, which may play a role in future obesity risk, but this research is still evolving.

Sources

✓Reviewed by CH, MD, FRCPC

Reviewed by a specialist physician certified by the Royal College of Physicians and Surgeons of Canada, who has read this answer against the sources listed above and confirmed it reflects them. That is not medical advice about your child. How we review

Answer checked July 31, 2026

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