Is exclusive breastfeeding better than breast milk+formula, in developed countries?

Question

I would like to know whether exclusive breastfeeding is shown to be better than a combination of breast milk and formula, in developed countries.

The current advice of the World Health Organization (WHO) is that six months of exclusive breastfeeding leads to best health outcomes for the child. This means that the child is fed on demand, only with breast milk, for a full six months. Solid foods and liquids other than milk are not recommended.

I have seen this same recommendation on all the baby websites I've looked at (here is one example), and it has been repeated to me by a pediatrician, different nurses, and a lactation specialist, all in The Netherlands.

Formula-feeding (with no breast milk alongside it) leads to more hospitalizations for gastric and breathing problems.

However, there are two ways to non-exclusively breastfeed:

1) Introduce solid food before an infant is a full six months old. Evidence from the UK suggests that introducing solids earlier than six months has no adverse health outcomes. In fact, children who are exclusively breastfed are at a higher risk for iron deficiency.

2) Introduce formula alongside breast milk. This is the topic I am interested in.

I am looking for evidence that compares exclusive breastfeeding to half-breast milk, half-formula, in developed countries.

The WHO has to give recommendations that are not only simple and clear, but that pertain to the whole world. I am skeptical about how well this recommendation for exclusive breastfeeding translates into the wellbeing of children in developed countries. Is there evidence to support the WHO's recommendations?

Answer 1

This prospective study in the UK found a serious risk of neonatal necrotising enterocolitis amongst formula-users.

• A. Lucas, T.J. Cole. Breast milk and neonatal necrotising enterocolitis, The Lancet, Volume 336, Issues 8730–8731, 22 December 1990, Pages 1519–1523

In a prospective multicentre study on 926 preterm infants formally assigned to their early diet, necrotising enterocolitis developed in 51 (5·5%). Mortality was 26% in stringently confirmed cases. In exclusively formula-fed babies confirmed disease was 6-10 times more common than in those fed breast milk alone and 3 times more common than in those who received formula plus breast milk. Pasteurised donor milk seemed to be as protective as raw maternal milk.

I tried to read this report which looked at meta-analyses on breastfeeding research, which seemed very relevant, but was unable to confirm from it whether this stood up to further review.

• Breastfeeding and Maternal and Infant Health Outcomes in Developed Countries, Agency for Healthcare Research and Quality, U.S. Department of Health and Human Services, April 2007.

Note: This only looks at one type of problem, and is not a measure of overall health outcomes of the child and mother. It also doesn't show causality.

Answer 2

I'm not aware of any studies on mixing breastfeeding with other nutrition, other than what you already mentioned; that introducing solids for the age-group 4-6 months doesn't seem to cause any measurably worse outcomes.

But there are plenty of studies on the effect of feeding a new-born only formula, the result from these are that breastmilk is moderately better, especially for very young children (first 1-2 months). If studies on mixes where done, I think the expected result would be that being fed a mix of breastmilk and formula, gives results somewhere in-between being fed only one of these.

Also please note that "better" is commonly poorly defined: it is known that having stressed-out overworked, underslept parents gives worse outcomes than having the caretakers be more balanced. And using formula obviously is "better" in atleast this sense: it makes it possible for the mother to get a break, and for the father to be more involved. I would expect this benefit to be largest for those couples where the woman experiences a lot of problems and/or stress about breastfeeding.

I suspect the reason for the lack in studies is the fact that the formula-breastmilk difference is already small, and searching for a even smaller needle in the haystack might have questionable cost-benefit.