GOS (galacto-oligosaccharides) is a prebiotic made from lactose that feeds Bifidobacterium gut bacteria in formula-fed infants. It is structurally similar to the oligosaccharides in breast milk. Clinical trials show GOS raises Bifidobacterium to breastfed infant levels.
FOS (fructo-oligosaccharides) is a prebiotic made from chicory root. It is a different structure from GOS and the evidence for FOS alone producing the same Bifidobacterium increase is considerably weaker. FOS adds benefit when combined with GOS but is not a substitute for it.
The difference matters because most formula brands list both on the same label as if they were equivalent. They are not. GOS is the prebiotic the EU has designated as the reference standard for infant formula. FOS alone is not.
GOS (galacto-oligosaccharides) and FOS (fructo-oligosaccharides) are prebiotics added to baby formula to feed beneficial gut bacteria - primarily Bifidobacterium. They are not the same thing, the evidence behind each is very different, and most formula labels use both terms as if they were interchangeable. They are not.
You have probably read the word "prebiotics" on a formula tin and felt vaguely reassured. That is exactly what the label was designed to do. The problem is that "prebiotics" tells you almost nothing - it is a category, not an ingredient. And the difference between the prebiotics inside that tin could be the difference between a gut that looks like a breastfed baby's and one that does not.
There are three things formula brands add to try to support your baby's gut. All three appear on labels in very similar language. The science behind them is not similar at all.
Why does GOS and FOS in formula matter?
It starts with your baby's gut bacteria.
Your baby's gut in the first months of life is not just digesting milk. It is building an immune system. Roughly 70% of immune function is shaped in the gut lining during infancy - and the bacteria that colonise it first have a disproportionate influence on everything that comes after. Allergies, eczema, gut sensitivity, even how the immune system responds to infections years later. It all has roots here.
In a breastfed baby's gut, one type of bacteria dominates: Bifidobacterium. It makes up 60 to 90% of all gut bacteria in the first months of life. This is not random. Breast milk contains over 200 types of complex carbohydrates - called human milk oligosaccharides - that exist for a single purpose: to feed Bifidobacterium specifically, while starving the bacteria you do not want.
Formula-fed babies have significantly less Bifidobacterium. Cow's milk - the base of most formula - has almost none of those oligosaccharides. Everything that formula brands add under the "prebiotics" banner is an attempt to compensate for that gap. The question is which ones actually work. For a deeper look at what that gap actually means for your baby's immune development, see our guide on what baby formula does to your newborn's gut bacteria.
What is GOS in baby formula?
The prebiotic with the real evidence.
GOS is made by taking lactose - milk sugar - and converting it enzymatically into longer chains. Because it starts from lactose, it ends up structurally similar to what is in breast milk. Your baby's gut bacteria recognise it. Bifidobacterium ferments it efficiently. This is not a coincidence - it is chemistry working in your favour.
The clinical evidence for GOS is the strongest of any prebiotic in formula. In a randomised trial of 371 infants, babies on GOS formula had Bifidobacterium levels statistically indistinguishable from breastfed babies. Babies on the same formula without GOS did not. The difference was not marginal.
Ben et al. (2008) - 371 term infants, randomised. GOS at 2.4 g/L raised Bifidobacterium and Lactobacilli to breastfed infant levels. Clostridium - the bacteria associated with colic and gas - fell. Gut acidity improved. No effect on growth, crying or vomiting.
A second large Italian trial across six centres found the same thing - and added something that will interest you if your baby has colic: babies on GOS formula had significantly less colic than those on unsupplemented formula. The likely reason is that more Bifidobacterium means less Clostridium, which produces the gas implicated in colic pain. Another gut-comfort pathway relevant for colicky babies is the A1/A2 beta-casein mechanism in cow milk formula, which is a separate but complementary route to gut inflammation.
Coccorullo et al. (2014) - multicentre RCT, 362 infants across six Italian centres. GOS formula matched breastfed babies for Bifidobacterium. Colic was significantly lower in the GOS group. Clostridium counts fell.
GOS does three things for your baby's gut that no other prebiotic in formula replicates:
- Feeds Bifidobacterium directly: GOS is structurally similar to human milk oligosaccharides, so your baby's gut bacteria recognise it. In clinical trials it raised Bifidobacterium to breastfed infant levels.
- Softens stools and reduces constipation: GOS improves stool consistency in formula-fed infants, producing a softer, more frequent pattern closer to that of breastfed babies.
- Reduces colic: More Bifidobacterium means less Clostridium, the bacteria that produces the gas implicated in colic pain. A multicentre Italian trial of 362 infants found significantly less colic in the GOS group.
- Supports immune development: A healthy Bifidobacterium-dominant gut in the first months of life is associated with lower rates of allergy, eczema, and immune dysregulation in childhood.
Several organic brands add GOS to their infant formula. On the European side: HiPP Dutch Goat, Jovie Goat, Pure Goat, Kendamil Organic, Kendamil Goat, and Löwenzahn Goat. On the US side: Nara Organic Whole Milk, and Happy Baby Organics (which adds GOS alongside FOS and a probiotic strain). On the label it will appear as "galacto-oligosaccharides" or "galacto-oligosaccharides from lactose" (sometimes "galacto-oligosaccharide syrup"). Holle Goat does not add GOS, relying instead on the oligosaccharides naturally present in whole goat milk, which are structurally related but present in much smaller quantities. Some well-known US formulas, including Bobbie Original, do not add GOS, FOS, or probiotics at all.
What is FOS in baby formula?
Not the same as GOS, despite what the label implies.
FOS comes from chicory root. It is a real prebiotic - but its structure is different from GOS, and different from what is in breast milk. Bifidobacterium can ferment it, but not as selectively. FOS feeds a wider range of gut bacteria, including some you are less interested in encouraging.
The evidence for FOS alone producing the same Bifidobacterium increase as GOS in formula-fed infants is considerably weaker. Multiple reviews have found GOS consistently outperforms FOS on its own. FOS does add something when combined with GOS - but it is not a substitute for it.
FOS appears as "fructooligosaccharides," "fructo-oligosaccharides," or "chicory root extract." If that is the only prebiotic listed, you are looking at FOS alone. GOS and FOS together - often at a 9:1 ratio - is a stronger combination. FOS alone is not the same as GOS.
Some US formulas also list polydextrose as a prebiotic. It is a synthetic fibre with modest effects in infants and is not comparable to GOS.
The EU reflects this distinction in law. Under Regulation 2016/127, GOS from lactose is the reference prebiotic for Stage 1 formula. FOS is permitted but restricted. The regulator does not treat them as interchangeable. The research does not either.
Is GOS or FOS better than probiotics in formula?
Probiotics are live bacteria - usually Bifidobacterium or Lactobacillus strains - added directly to the formula. The logic is appealing: instead of just feeding the bacteria already in your baby's gut, deliver more of the right ones directly.
The catch is survival. Getting live bacteria through manufacturing, powder processing, months of shelf storage, and then dissolved into warm water - with enough still alive to do anything useful - is genuinely hard. By the time a tin reaches your kitchen, viable bacterial counts can be far lower than the label suggests.
Heppner et al. (2024) compared probiotic formula directly with GOS formula. The result: GOS formula produced higher stool Bifidobacterium levels than the probiotic formula. Feeding the bacteria already in the gut turned out to be more effective than adding new ones.
That does not mean probiotics are useless. Certain specific strains - particularly Bifidobacterium longum and Lactobacillus rhamnosus GG - have solid clinical evidence for specific benefits: fewer infections, less antibiotic-associated diarrhoea, modest reductions in allergy risk. The strain matters enormously. "Added probiotic cultures" on a label is not the same as a named, validated strain at a proven dose.
Most European organic goat milk formulas (including HiPP Dutch Goat, Jovie Goat, Pure Goat, Kendamil Organic, Kendamil Goat, and Löwenzahn Goat) rely on GOS as their prebiotic strategy and do not add probiotic cultures. Given the Heppner finding above, this is defensible: the evidence that added GOS raises Bifidobacterium to breastfed-infant levels is stronger than the evidence for commercial probiotic formulas. Happy Baby Organics is an exception on the US side; it adds Bifidobacterium breve M-16V alongside GOS and FOS, which is one of the more studied strains in infant nutrition research. The theoretical best combination is GOS plus a named probiotic strain at a validated dose, but most commercial formulas either rely on GOS alone or do not publish the strain and dose detail needed to evaluate a probiotic addition properly.
How major formulas compare on prebiotics and probiotics
| Formula | GOS | FOS | Probiotic | Prebiotic profile |
|---|---|---|---|---|
| Happy Baby Organics Stage 1 (US) | ✓ Yes | ✓ Yes | ✓ B. breve M-16V | GOS + FOS + probiotic |
| HiPP Dutch Goat Stage 1 | ✓ Yes | ✗ No | ✗ No | GOS added |
| Jovie Goat Stage 1 | ✓ Yes | ✗ No | ✗ No | GOS added |
| Kendamil Organic Stage 1 | ✓ Yes | ✗ No | ✗ No | GOS added |
| Kendamil Goat Stage 1 | ✓ Yes | ✗ No | ✗ No | GOS added |
| Löwenzahn Goat Stage PRE/1 | ✓ Yes | ✗ No | ✗ No | GOS added |
| Nara Organic Whole Milk (US) | ✓ Yes | ✗ No | ✗ No | GOS added |
| Pure Goat Stage 1 | ✓ Yes | ✗ No | ✗ No | GOS added |
| Holle Goat Stage 1 | ✗ No | ✗ No | ✗ No | Goat milk oligosaccharides only |
| Little Spoon (US) | ✗ No | ✓ Yes | ✗ No | FOS only - weaker evidence |
| Bobbie Organic Original (US) | ✗ No | ✗ No | ✗ No | No added prebiotics or probiotic |
| Typical US cow milk formula | Rarely | Variable | Variable | Limited / mixed |
A note on Holle Goat: it does not add GOS. Goat milk naturally contains a small amount of oligosaccharides that cow's milk does not, so Holle Goat relies on what is already in the milk rather than supplementing it. Not the same as added GOS supplementation, but not nothing either. The research on added GOS specifically is what produced the breastfed-infant Bifidobacterium levels discussed above.
If a formula says "prebiotics" and you want to know whether it is actually doing something: look for GOS specifically. That is the one with two large randomised trials, breastfed-infant Bifidobacterium levels as the outcome, and the EU's own regulatory standard behind it.
FOS alongside GOS is a bonus. FOS alone is not equivalent. Probiotics are worth having if the strain is named - not just listed as "added probiotic cultures." And "prebiotics" on its own, with no further detail, tells you almost nothing at all. For the broader picture of formula quality, including recall safety and supply chain considerations, see our main formula coverage.