Only about 5% of women have a medical or surgical reason that means they're unlikely to produce enough milk. Perceived low supply is far more common than actual low supply, and it has two main causes: misreading normal newborn behaviour, and comparing breastfed babies to bottle-fed ones. Breastfed babies genuinely drink less — and that is a feature, not a fault.
Most women are anxious that they have a low milk supply — but it's actually quite unlikely that there's a fundamental reason for this. So why does it feel like such a common phenomenon?
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Misinterpretation of infant cues
This is a huge reason women believe they have a low milk supply — in my experience, it is the number one reason women begin to feel under-confident and reach for that bottle of formula.
A newborn baby knows no other reality than his mother. He has been used to being tightly held, rocked, protected from light, noise and temperature variation. He has been surrounded by white noise, drip fed from the placenta, and is never apart from his mother. Suddenly, after a long and sometimes difficult process for both, he is launched into the harshly lit, loud, cold and wide open space of his crib.
It's the concept of the fourth trimester, and we need to better understand the adaptation from womb to world to fully read infant cues in the first few weeks.
That baby is unlikely to settle anywhere but his mother's arms — probably where he feels most at ease is suckling at her breast. Colostrum smells very similar to amniotic fluid, and her breast is near her heart, which he has heard and felt beating for many months. This is partly why many babies feed very frequently, or even non-stop, at some point in the first few days.
And sometimes babies cry. Some babies cry a lot. In some cases it isn't clear why — but one thing we know is that they tend to stop when held close and allowed to breastfeed as often as they like.
This is confusing for new mothers, because they perceive most infant crying as a cry for feeds. So they become disheartened that their baby is seemingly unsatisfied at the breast.
Why the comparison is unfair
If they observe women around them formula feeding, they'll probably notice that those babies sleep for longer stretches. They begin to question whether they have sufficient milk — because when they see their own constantly feeding, crying baby alongside a formula fed baby feeding infrequently and settling after most feeds, the apparently logical conclusion is that the formula fed baby is getting enough and theirs isn't.
Here's what's actually happening. The reason formula fed babies tend to sleep for longer stretches in the early days is that the larger volumes commonly fed to them will overfill the newborn's tiny stomach. The response to being overfull is either vomiting, or falling asleep — much like adults do after over-eating. It isn't necessarily a sign of contentment. It's a physiological response to the volume of liquid the baby now has to digest.
So babies often want to feed constantly in the first 3–5 days. This is normal, and understandable.
There is something absolutely primal about the need to feed your baby, and women's worst fear is usually that they are starving their baby — so that tends to be the first conclusion they jump to. Meanwhile women and health professionals tend to compare breastfed baby behaviour to formula fed baby behaviour, and assume breastfeeding is going wrong when the breastfed baby behaves differently.
Our society is very used to seeing bottle fed babies. Health professionals and the public alike generally believe that the volumes fed to formula fed babies are the physiological norm, and therefore that breast milk volumes are inadequate.
Reason 1: breastmilk is nearly 100% bio-available
Formula fed babies drink more milk than breastfed babies. In fact, even babies fed breastmilk in a bottle drink more than breastfed babies. There are three reasons for this — and the first is bio-availability.
Breastmilk is nearly 100% bio-available, meaning babies can extract nearly all the nutrients from it. Volumes are therefore generally lower, and also more consistent than for formula milk. Initial volumes are much, much smaller than the amounts commonly fed to formula fed babies, and women often compare their expressed volumes unfavourably with formula quantities.
After the initial establishment of a mature milk supply, which takes about 2–4 weeks, a breastmilk supply will remain at relatively constant volume all the way through to starting solids at around six months. Babies naturally grow more slowly from about 12 weeks, and the nutritional composition of breastmilk adapts as the baby matures — so they don't need to keep drinking more and more as they get bigger.
This is in direct contrast to formula fed babies, who need more and more milk as they grow, because a certain proportion of their milk simply cannot be digested or extracted from. This is part of why their stool is smellier, and why they are approximately 1kg heavier than breastfed babies by the age of one. That has come to be seen as a sign of health and privilege — but being heavier at age one is associated with increased risk of diabetes and obesity, so far from being a good thing, it is actually harmful.
Reason 2: the mechanism of bottle feeding
When babies drink from a bottle, they cannot regulate the flow of milk as well. When you have liquid pouring into your mouth you have three options: drink it, choke on it, or dribble it. Most babies opt for options one and three, for obvious reasons.
So bottle fed babies drink more simply because it keeps flowing into their mouths. The feed is generally fast, so the baby doesn't get the message that they're full until long after the feed has finished. We are training our babies to over-eat before they're even responsible for what they eat — we override their full and contented feelings and keep feeding them in order to "finish the bottle". This is also true of babies fed expressed milk in a bottle; it's the speed and mechanism of suckling that's responsible.
Reason 3: fat, leptin and appetite regulation
When breastfeeding, babies receive an increasing proportion of fat as the feed progresses. They also receive increasing amounts of an appetite-regulating hormone called leptin, which causes the baby to feel satisfied and full at the right time so they don't over-eat. It chemically signals the baby to finish feeding.
This is another reason you should never take a baby off the breast until they spontaneously release it themselves. That way you know they've had what they need. It doesn't mean they won't want the other side — it just means they've finished the first.
When you feed a baby expressed milk, the milk does not change as the feed progresses — it's more homogenised, so babies don't get that chemical signal in the same way. It is not possible to produce an artificial form of leptin, so it is not present in formula milk at all.
What this means in practice
- Breast milk volumes are initially much lower than the amounts fed to formula fed babies
- When breastfed babies require supplements for medical or other reasons, people tend to give an amount suitable for a formula fed baby
- Bottle fed babies drink more than breastfed babies — regardless of what's in the bottle
- Formula milk does not contain leptin, which regulates appetite and protects against obesity and diabetes
- The mechanism of bottle feeding does not allow babies to regulate their appetite, or control the flow of milk
So two of the most common reasons women believe they have a low milk supply are the misinterpretation of infant cues, and the fundamental physiological differences in milk volumes between breast and bottle fed babies.
Increasingly we live in a society which loves to compare. It's really important that any comparisons we make serve to normalise breastfeeding, because this is the biological norm. When we can do this across all sectors of society — the media, health professionals, popular parenting literature — maybe then women will have more faith in their own ability to make plenty of milk for their babies.
If you're concerned about supply, a full feeding assessment is the right next step rather than supplementing on a hunch. Check the six signs a baby is feeding well, and find an IBCLC through Lactation Consultants of Great Britain.
Common questions
How many women actually have low milk supply?
About 5% have a medical or surgical reason meaning they're unlikely to produce enough. Perceived low supply is far more common than actual low supply.
Why do formula fed babies sleep longer?
Because the larger volumes typically fed overfill a newborn's tiny stomach. Falling asleep is a physiological response to that volume, not necessarily a sign of contentment.
Do breastfed babies drink less than bottle fed babies?
Yes — even when the bottle contains expressed breastmilk. Breastmilk is nearly 100% bio-available, and bottle feeding overrides the baby's ability to regulate flow and appetite.
When does milk supply settle?
A mature supply takes about 2–4 weeks to establish, then stays at a relatively constant volume until solids start at around six months.
About the author
Dr Lyndsey Hookway is an International Board Certified Lactation Consultant, paediatric nurse, health visitor and researcher, and a published author on infant sleep and feeding. She is a co-founder of the Holistic Sleep Coaching Program and teaches on Babyem's accredited programmes.
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Babyem's accredited training teaches practitioners how to tell perceived low supply from actual low supply — and what to do about each.