How Long Does It Take Babies to Digest Breastmilk vs Formula?
Parents often notice a big difference between how often their breastfed vs formula-fed baby wants to eat. Breastfed babies seem to feed “all the time,” while formula-fed babies may go longer between bottles. This can make some parents worry:
“Is my supply low?”
“Why is my baby always hungry?”
“Is formula more filling than breastmilk?”
The truth is, the difference isn’t about one being “better” or “worse,” it’s about how quickly each type of milk is digested and leaves your baby’s stomach. And yes - breastmilk really does digest faster than formula!
How Baby Digestion Works
Newborns don’t have the same digestive systems as adults. Their stomachs are tiny, their digestive enzymes are still developing, and their intestines are learning to handle food outside the womb.
Here are a few key facts about your baby:
Your newborn’s stomach on day 1 only holds about 5–7 ml (a teaspoon). By day 10, it stretches to about 60–80 ml (2–3 oz).
Gastric emptying (how quickly milk leaves the stomach) is influenced by milk type, volume, and composition.
Your baby’s body is designed for frequent feeds, which helps stabilise blood sugar, maintain hydration, and support brain development.
This is why timing feeds by the clock can be misleading. What matters is what’s happening inside their tummy.
Why Does Breastmilk Digests Faster?
Breastmilk is uniquely designed for human babies and that includes being easier to digest.
Gastric emptying time: Around 48–120 minutes (1–2 hours) on average [3].
Protein type: Breastmilk is higher in whey protein than casein. Whey forms a softer, looser curd in the stomach, while casein makes a thicker, harder-to-digest curd [4].
Built-in enzymes: Breastmilk contains lipase and amylase, which help babies break down fat and sugar efficiently [1]. Formula has to rely on the baby’s own enzymes, which are immature in the early weeks.
Dynamic composition: Breastmilk changes during a feed and across the day, which can influence how quickly it digests [3].
This is why breastfed babies feed frequently. It’s not that they’re “hungry all the time” or that your supply is inadequate or less “fatty”. It’s that their food is being digested efficiently and their small stomachs need refilling often.
Why Does Formula Takes Longer?
Infant formulas are designed to be nutritionally complete, but they don’t digest the same way as breastmilk.
Gastric emptying time: On average 2.5–4 hours [2,3].
Protein type: Many formulas are casein-dominant or have a higher proportion of casein than human milk [4]. Casein curds are firmer and sit heavier in the stomach.
Lack of live enzymes: Babies have to do all the digestive work themselves [1].
Consistency: Formula is uniform, which means it doesn’t change mid-feed or throughout the day, like breastmilk does. This steadiness contributes to a slower, heavier digestion.
This is why formula-fed babies may go longer between feeds. They feel fuller because the milk physically takes longer to leave the stomach. But “fuller” doesn’t automatically mean “more satisfied” - some babies actually show more spit-up, wind, or discomfort, as the day goes on, because of the harder-to-digest curd.
Mixed Feeding: Why You May Notice a Difference
Families who combine breastfeeding and formula feeding often notice clear differences in their baby’s feeding rhythm depending on which milk is given.
After a breastfeed: Babies may want to feed again in 1–2 hours because breastmilk digests quickly. This is completely normal and not a sign of low supply.
After a formula feed: Babies may last 3–4 hours because formula digests more slowly and sits heavier in the stomach.
This can sometimes be confusing or even unsettling for parents. One feed might feel “constant” while the next seems to last much longer. It’s easy to interpret that as something being wrong with your breastfeeding or that your baby doesn’t appear to be “satisfied” with your breastmilk, but in reality, it’s just the natural difference in how the two milks are digested.
Some parents also notice changes in:
Comfort: Babies may be more settled after a formula feed but can also be gassier or spit up more.
Sleep: Longer gaps can sometimes mean longer stretches of sleep, but not always or it can be very hit and miss. That is because digestion isn’t the only factor that drives sleep.
Interest in the breast: If formula is given frequently, some babies may seem less eager at the breast, not because they dislike it, but because their stomach feels full for longer or has become accustomed to that “fuller” feeling.
The key takeaway: Mixed feeding creates different rhythms, and that’s okay. It doesn’t mean breastmilk isn’t “enough.” It simply reflects the way each milk type digests.
Why This Matters for Parents
Understanding digestion times doesn’t just explain why babies feed differently — it also helps take away a lot of guilt, doubt, and unnecessary stress.
If you’re breastfeeding
Your baby feeding every 1–2 hours is not always a supply issue, it’s biology.
Your baby’s stomach is doing exactly what it’s meant to do by digesting breastmilk quickly and asking for more.
Frequent feeds are normal and help establish and maintain supply.
If you’re formula feeding
Longer gaps are expected, and it doesn’t mean your baby is “better fed” or more satisfied, it may just mean that formula digests more slowly.
If your baby is refluxy, windy, or unsettled, it may be linked to how hard their tummy is working to break down formula curds, not something you’re doing wrong or that they’re intolerant to the certain formula you are using.
If you’re mixed feeding
It’s normal to see very different rhythms: short gaps after a breastfeed, longer gaps after a bottle.
This doesn’t mean your breastmilk is “not enough.” It simply reflects the different digestion speeds.
Sometimes, the contrast can make parents doubt their breastfeeding. The truth is your body and your milk are working exactly as they should.
For parents who want to exclusively breastfeed but feel “stuck” in the top-up trap
This is a really common story we see too often in our practice. A baby is given formula in the hospital - sometimes because of blood sugar concerns, sleepiness after birth, or weight loss or due to difficulties latching and/or lack of hospital support. Suddenly, parents find themselves topping up every feed with formula because their milk hasn’t “come in” yet and you’re finding that you’re milk volume is struggling to catch up, so it feels impossible to stop the formula (known as the “top up trap”).
Here’s the good news: it is possible to return to exclusive breastfeeding in most cases. Understanding digestion is part of the puzzle:
Babies may take longer to want the breast after formula because their tummies are full for longer.
If you interpret that longer gap as your milk not being “enough,” it can keep the cycle going.
With support, paced top-downs, and a clear plan, many babies can transition back to the breast as supply is supported and formula is gradually reduced.
The key is recognising that feeding patterns are shaped by digestion, not by “failure.” With the right guidance, you’re not trapped, there’s a pathway back to the feeding journey you want.
Takeaway: Different Isn’t Better or Worse
At the end of the day, breastmilk and formula nourish babies differently, but both support growth and development. The biggest difference lies in digestion speed.
Breastmilk: Designed for human babies, digests in about 1–2 hours, which means frequent feeds are the biological norm.
Formula: Takes about 3–4 hours to digest, which means babies may go longer between feeds but may also experience more digestive effort or discomfort.
Neither is “better” or “worse.” They’re just simply different. What truly matters is whether your baby is:
Feeding comfortably and without distress.
Growing along their own curve.
Content and alert in their awake periods.
Supported by a feeding approach that works for your family.
Closing Thoughts
Feeding can feel overwhelming when you’re told so many different things like “feed every three hours,” “just give a bottle,” “your milk isn’t enough,” or “formula will keep them fuller.” The truth is far more nuanced. Babies don’t read the rules, and their digestion doesn’t fit into rigid schedules.
Knowing how digestion works helps you:
Understand your baby’s natural feeding rhythm.
Recognise that frequent feeding at the breast is normal, not a sign of failure.
Avoid guilt when comparing breast and bottle feeding patterns.
Feel empowered to make choices that suit your baby and your family.
And if your journey hasn’t gone as planned, whether you’re mixed feeding, topping up, or wanting to return to exclusive breastfeeding, please know that support exists and change is possible. You are not trapped, and you are definitely not alone!
At The Gentle Village, our role is to walk with you through these decisions with compassion, evidence, and care, so you feel confident in feeding your baby, whatever path you choose.
If you need support with breastfeeding, bottle feeding, or mixed feeding, we’re here to help. Because every baby deserves an individualised approach and every parent deserves support.
References
Hamosh, M. (1996). Digestion in the newborn. Clin Perinatol, 23(2), 191–209.
Cavell, B. (1981). Gastric emptying in infants fed human milk or infant formula. Early Human Development, 5(2), 187–193.
Brezinka, C., et al. (1994). Gastric emptying in breastfed and formula-fed infants measured by ultrasound. Acta Paediatr, 83(9), 872–876.
Mason, S. J., et al. (2006). Gastric emptying and milk composition: The role of whey and casein. Acta Paediatr, 95(6), 738–743.