Supplementing With Formula

With the right support and information, most mothers can make more than enough breast milk to keep their babies well fed. But what if breastfeeding is not going well or a baby seems hungry? What if there seems to be no breast milk after delivery or there are reasons for low milk supply? Or perhaps a mother is returning to work and is considering supplementing with formula. This article looks at parents’ frequently asked questions and concerns about supplementing with formula or combination feeding when their baby is breastfed.

Do I really need to give supplements?

Exclusive breast milk is the biologically normal diet for a baby and many parents do not plan to use infant formula. They want to be certain formula is really needed before giving any to their baby. There are several ways to check whether a baby is getting enough breast milk before starting formula top ups. And there are many ways to increase your breast milk supply too. See Is My Baby Getting Enough Breast Milk? and How to Make More Breast Milk for more information, and your health professional and IBCLC lactation consultant will guide you.

Baby not gaining weight

Up to 7% weight loss in the first few days is considered normal. But if your baby is not gaining weight within the normal range after this time, he may need more food. Your baby may become more and more sleepy and is in danger of becoming very weak, dehydrated or unresponsive unless he gets enough to eat. See Baby Not Gaining Weight and Understanding Your Baby’s Weight Chart for more help.

Supplements may be needed

There are lots of ways to help your baby get more breast milk such as pumping your milk to provide a top up, or improving your baby’s latch and positioning. Your IBCLC lactation consultant can help you get breastfeeding back on track as soon as possible. Even so, building a very low milk supply can take time and a full supply may not always be possible. Until you have enough breast milk to keep your baby well fed, you will need to look at alternatives. Using donor breast milk is one possibility. If donor milk is unavailable you may need to consider using a commercial infant formula for a while. Babies can and do thrive on industrial baby formula despite its imperfections. And it is important to keep your baby well fed.

Sad and sleepy baby on mother's shoulder

What are the differences between breast milk and formula?

Breast milk is very different to formula. Breast milk is a natural complete food, made fresh in the breast from a mother’s blood. It contains living cells to both protect a baby from illness and provides calories to grow. Breast milk includes friendly bacteria and enzymes to help the baby’s digestion. In comparison, formula is a man-made processed food produced in a factory with a set shelf life. It doesn’t have any living cells, immune factors or digestive enzymes and is missing a lot of ingredients compared to breast milk. The ingredients in formula compared to what is found so far in breast milk are listed in What’s In Breast Milk and What’s In Formula? (Bellybelly, 2016) or as a poster here (pdf). For much more about formula and how it is made see Maureen Minchin’s book Milk Matters: Infant Feeding and Immune Disorder.

How could supplementing with formula affect my baby?

Topping up with formula can mean:

  • A change to the balance of friendly bacteria (microbiome) living in the baby’s gut. The microbiome will change from predominantly friendly bifidus flora (bifidobacteria and lactobacilli) into the more undesirable strains that are usually found in adult guts. This reduces protection against infections and could influence long term health. Whether or not the microbiome can be reestablished with exclusive breastfeeding is not clear. Marsha Walker suggests it can return after two to four weeks of exclusive feeding 1 while Linda Palmer questions whether this is possible if any formula is given in the first seven days of life 2. Antibiotics also affect the microbiome.
  • Your baby may have an increase in allergies, becoming sensitised to cows’ milk or have an increase in atopic disease such as asthma or eczema (Walker, 2014). Inflammation, hypersensitivity or autoimmune disorder are all connected with allergy (Minchin, 2015).
  • Your baby may have an increased risk of developing diabetes3 and other health issues4.
  • Your baby may begin to prefer a bottle if he realises a bottle gives him food yet he finds himself still hungry and frustrated at the breast. See ideas below for alternative feeding methods to try to prevent this.
  • Your milk supply could drop if you do not try to build your breast milk supply alongside using formula. With the help of a breastfeeding specialist, supplementing with formula does not have to mean the end of breastfeeding.

A baby will still get some of the advantages of breast milk and the benefits of correct formation of his mouth and airways by whatever amount of breast milk and breastfeeding a mother can manage.

What is human milk fortifier?

A human milk fortifier is an adapted cows’ milk formula with extra nutrients which is added to breast milk and given to premature babies. Despite the misleading name this is not usually made from human milk (although versions are available in some areas). These human milk fortifiers (or more correctly bovine fortifiers) are intended to help premature babies grow faster which is seen as “better”. However, there are several known links between these bovine fortifiers and serious health issues for premature babies. See Human Milk Fortifiers for more information.

Formula suppliers boast of faster weight gains when their fortifiers are used, and this is a consistent finding, but it is well shown that feeding of cow products is also consistently associated with greatly increased chances of necrotizing enterocolitis, respiratory infections, other infections (sepsis), and other health risks including reduced survival. Re-hospitalizations are also more frequent in preterm infants who had been receiving formulas.

Other options

  • Skin-to-skin contact and kangaroo mother care can significantly help a premature baby’s rate of growth 5.
  • Increase the calories in breast milk by using ‘breast milk cream’, the fattier proportion of breast milk sometimes called hind milk.
  • Contact a milk bank. Milk banks usually give priority to premature or sick babies should a mother be struggling with her milk supply. Human milk is far superior for these vulnerable babies.

Can you mix breast milk and formula?

Mixing breast milk and formula in the same container is not recommended because:

  • Formula can interfere with the antibacterial benefits of breast milk.
  • Mixing milk could mean wasted breast milk if baby doesn’t finish the bottle.
  • Formula doesn’t last as long as breast milk so mixing milk would shorten the time breast milk could be stored safely.

Because breast milk is so much more valuable to your baby, the recommendation is to feed expressed breast milk supplements first rather than mixing breast milk with formula. Pausing between giving formula after breast milk will allow time for the breast milk to start to leave the stomach (e.g. between 20 minutes and one hour). Waiting will not always be practical with a hungry baby.

The research on mixing breast milk and formula

Most of the studies looking at mixing breast milk and formula have been done by studying the effects of human milk fortifier added to expressed breast milk. Studies by Chan et al 6 and Quan et al7 found that the cows’ milk protein in human milk fortifier and normal formula can prevent some of the important anti-infective properties in human milk from working. Iron and iron-enriched formula were also found to affect the antimicrobial actions of breast milk.

What is the best formula for breastfed babies?

Nobody knows. Author Maureen Minchin has studied and compared the ingredients of many formula brands and found they all contain very different ingredients. Ingredients can also change within the same brand according to the cheapest available at a certain time. Formula labels can be very vague too—failing to include potential pollutants from the manufacturing processes or the risk of bacteria in a non sterile product. Infant formula is not strictly controlled, regulated and approved by government bodies such as the United States Food and Drug Administration8. With no two formulas being the same, Minchin says that nobody knows which infant formula is ‘best’.  For further information on varieties of formula see Types of Infant Formula, NHS, 2014 and Infant Milks Overview from First Steps Nutrition Trust.

Ready to use liquid formulas

Powdered formula is not a sterile product. Wambach and Riordan9 say that ready-to-use preparations are the least risky option because they are sterile.

Low allergy formulas

Specially marketed low allergy brands of formula should not be assumed to be “safer” or “better”. Some children still react to partially hydrolysed formula10 and there is no evidence that even extensively hydrolysed formula brands prevent allergies11.

Soy formula, goat’s milk formula

See Milk Allergy in Babies for more information on these formulas which are not recommended.

Preparing formula

Current guidelines for reconstituting powdered formula can be found in How to Prepare Formula for Bottle-Feeding at Home from the World Health Organisation 2007 or the UK’s National Health Service guidelines Making up infant formula, NHS, 2014.

  • Using water that has been boiled and cooled to 70°C will kill bacteria and making fresh bottles for each feed avoids bacterial contamination and potential oxidation of the reconstituted products (Minchin 2015). Cool to body temperature before feeding your baby.
  • It is important to add the correct amount of water to the correct amount of powder. Follow the manufacturers instructions carefully and use the scoop provided. Bottle gradations can vary greatly and may not be a reliable indicator of an accurate volume. You can test the accuracy of the measurements on your bottle 12 or household jug by comparing it against the same volume measure by a large syringe (provided from your local chemist). Never dilute formula (or breast milk) with extra water.

Will topping up by bottle lead to nipple confusion?

If you do need to give your baby additional milk whether expressed breast milk, donor milk or formula you may have heard that using a bottle teat can create nipple confusion. Or you may have heard that there is no such thing as nipple confusion!

What is nipple confusion?

Sucking from a bottle teat is quite different to suckling on a breast, it feels different in the mouth and the baby’s tongue and jaw have to work in a different way to get milk. Some babies are very clever at switching back and forth between breast and bottle and can handle this difference easily. But just as sometimes a breastfed baby will refuse to take a bottle, sometimes introducing bottles can cause breast refusal. Particularly if you have low milk supply or you are using bottles before your baby has learned to breastfeed. Some babies may quickly associate the bottle with their food source and the breast with hunger or frustration. There are several ways to help avoid this nipple confusion although each has their own pros and cons.

Avoiding nipple confusion

Additional milk can be offered by a;

Baby drinking from a little cup


Although ordinarily there are lots of ways to build a mother’s milk supply before reaching for formula top ups, sometimes these can take time or not seem to help. If donor breast milk is not available, supplementing with formula may be a medical necessity—a baby needs to be fed. The health disadvantages of supplementing with formula must be weighed against the risks for a baby who is in danger of failing to thrive. Breast milk top ups are best given first and not physically mixed with formula. All formulas have different ingredients and it isn’t clear which is ‘best’ for a breastfed baby but ready made formulas are sterile while dehydrated powder isn’t. There are several ways to give supplemental milk to your baby to help avoid nipple confusion.

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