The idea that feeding is either breastfeeding or formula feeding, with nothing in between, does not reflect how most families actually feed. Mixed feeding – combining breastmilk and formula in whatever proportions work for a given family – is the reality for a substantial proportion of UK babies, and the fact that it is often presented as a failure state of breastfeeding rather than a legitimate approach does parents a disservice.
Many families choose to mix feed for entirely straightforward reasons: to allow a partner to share night feeds, to provide flexibility when the mother returns to work, to manage when breastfeeding is difficult, or simply because it suits their family. Understanding how mixed feeding affects supply and how to approach it intentionally – rather than accidentally reducing supply while intending to continue breastfeeding – allows families to make it work the way they want it to.
Healthbooq (healthbooq.com) covers feeding choices in the first year.
How Mixed Feeding Works
Breastmilk supply is governed by the principle of supply and demand: milk is produced in response to its removal (by feeding or expressing). More frequent, more complete removal means more milk; less frequent removal means the body produces less. This is why introducing formula can affect supply.
When formula is given as a replacement feed (instead of a breastfeed, at a time when the baby would otherwise have fed at the breast), the breast is not stimulated for that feed. If the formula replaces one feed per day, one less stimulation occurs and supply adjusts downward slightly. If formula replaces multiple feeds, supply reduces proportionally.
When formula is given as a top-up after a breastfeed (to add volume on top of what the baby has already taken at the breast), the impact on supply is lower because the breast has already been stimulated for that feed – but if the baby was going to have fed again soon, the top-up delays the next feed, which does have a small effect on supply.
When Formula Is Introduced
Early in the newborn period, when supply has not yet established: this is the highest-risk period for supply disruption. The first weeks of breastfeeding are when supply calibration happens, and frequent breastfeeding during this period is what establishes long-term supply. Formula given in the first 1-2 weeks for reasons other than medical necessity (birth weight loss above 10%, hypoglycaemia, severe maternal illness) can compromise supply before it has established.
After 4-6 weeks: supply is usually established. Introduction of an occasional formula feed at this point is less likely to reduce supply substantially, particularly if the breast is expressed when formula is given.
When returning to work or choosing planned mixed feeding: expressing milk when the baby takes formula maintains supply for those feeds. Introducing one formula feed at a time and allowing supply to adjust gradually is more manageable than rapid changes.
Minimising Supply Impact
If the intention is to continue breastfeeding as the primary form of feeding with occasional formula, expressing when formula is given maintains stimulation and prevents supply reduction. A pump session at the same time as a formula feed signals to the body that milk is still needed.
If the intention is to reduce breastfeeding gradually and increase formula, doing so slowly – reducing by one feed per week or less – allows supply and engorgement to adjust comfortably and reduces the risk of mastitis (breast infection that can occur when milk is not regularly removed).
Formula Choice
Any first-stage infant formula (Stage 1, suitable from birth) is appropriate for mixed feeding. There is no benefit to switching between brands or using "comfort" formulas unless there is a specific clinical indication. Follow-on formula (Stage 2, marketed from 6 months) is not necessary and confers no advantage over Stage 1 formula.
Hypoallergenic formula (extensively hydrolysed or amino acid based) is prescribed for confirmed or strongly suspected cow's milk protein allergy; it is not appropriate for general mixed feeding.
Supporting Breastfeeding Alongside Formula
A breastfeeding specialist (NHS infant feeding team, lactation consultant, NCT breastfeeding counsellor, La Leche League) can help families who want to mix feed while maintaining a good supply, or who have encountered difficulties. The aim is to give families information about what will affect supply so they can make choices with accurate expectations.
Key Takeaways
Mixed feeding (also called combination feeding) involves giving a baby both breastmilk and infant formula. It is very common – approximately 24% of infants in the UK are receiving both breast milk and formula at 6 weeks. Mixed feeding is a valid and positive choice for many families. The main risk to be aware of is that formula top-ups can reduce milk supply by reducing the frequency and completeness of breast stimulation; introducing formula judiciously – ideally replacing a full feed rather than topping up after breastfeeds – minimises this effect. The timing of when formula is introduced, and the reason for introducing it, significantly affects how it interacts with breastfeeding.
