How GOS/FOS prebiotics support your baby’s immune system 

GOS and FOS may sound complicated, but they’re a simple way to support your baby’s normal immunity, growth and overall development.

Quick Explanation

This article explains what GOS and FOS prebiotics are, and how they support your baby’s normal immunity, growth and overall development.




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Some terms you may hear

  • The Gut Microbiome: A complex community of beneficial bacteria that live in the gut
  • Prebiotics: nourish the 'good' or beneficial bacteria in the gut, supporting a healthy gut environment
  • GOS and FOS: galacto-oligosaccharides (GOS) and fructo-oligosaccharides (FOS) are types of prebiotics, they act as nutrients for the good bacteria in the gut
  • A mix of 90% GOS and 10% FOS in formulas has been shown to help support a healthy gut and to contribute to a well-functioning immune system, softer stools and reduced inflammation.

The Gut Microbiome: Your Baby's Gut Garden

Imagine your baby’s gut microbiota as a vibrant garden, where beneficial or ‘good’ bacteria are the flourishing plants.

These microscopic ‘plants’ are essential for digestion and supporting the immune system.

Just as a garden needs sunlight and water to thrive, these beneficial bacteria require special nutrients known as prebiotics (such as GOS and FOS).

The Role of Prebiotics

Breastmilk is recognised as the gold standard nutrition for babies, and is rich in powerful prebiotics called HMOs2 (Human Milk Oligosaccharides).


When breastmilk isn’t available, formulas fortified with GOS and FOS can offer some of these benefits2, and act as nutrients for your baby's gut flora.

They reach the intestine undigested and provide fuel to your baby’s gut microbiome by selectively helping the good bacteria to grow.

This creates a balanced and thriving gut environment which is vital from the very beginning of your baby’s life and contributes to the development of their immune system.

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What are GOS and FOS prebiotics?

GOS is naturally found in plant foods such as legumes, nuts (cashews and pistachios) and soy beans. You can find FOS in foods like onions, garlic, asparagus, banana and artichokes. 

In formula, GOS is made from lactose (a type of milk sugar) and FOS is obtained from chicory (a vegetable).

What makes GOS and FOS special is their ability to be cleverly broken down exclusively by the good bacteria.

When these good bacteria ‘eat’ GOS and FOS prebiotics, this promotes the growth of good bacteria and prevents bad bacteria from flourishing. This happens through a process called selective fermentation, which is key to maintaining a thriving gut environment. 

What is GOS and FOS in formula milk?

In 1994, Nutricia Research (the research centre behind Aptamil) developed a unique prebiotic blend of 90% GOS and 10% FOS (9:1 GOS/FOS), closely resembling the structure of HMOs found in breastmilk. 


This special 9:1 GOS/FOS blend supports the digestive system and can help to protect against harmful bacteria, as well as supporting your baby’s immune system.

Benefits of GOS and FOS for Babies


Prebiotics can also help your baby digest food better and absorb nutrients more efficiently. This contributes to a happier and more comfortable tummy for your baby.


Additionally, GOS and FOS do more than just feed the good bacteria in the gut microbiota, they also energise the cells lining the intestinal tract.

This strengthens the gut wall barrier which creates an essential defence line for the body and reduces inflammation.

Did you know that the intestine also contains the largest proportion of immune cells in the body3

Therefore, GOS and FOS not only supports the digestive system, but they also lay the foundation for a robust immune system from the earliest stages of life.

Softer Stools

Bifidobacteria is the most abundant type of beneficial bacteria growing in the guts of breastfed babies4.

As they dominate, it stops the bad or more harmful bacteria from attaching to the intestinal wall and growing in the gut.

The good news is that a number of studies show that babies who drank formula enriched with the 9:1 GOS/FOS blend had more Bifidobacteria in their stools5.  

Their stools were also softer and looked a lot more like those of breastfed babies6.  

A brief summary of the benefits of GOS and FOS:

  • Promoting Bacterial Growth: GOS and FOS are particularly effective at encouraging the growth of good bacteria like Bifidobacteria and Lactobacillus, closely mirroring the gut flora of breastfed babies.
  • Digestive Health: These prebiotics aid in digestion and nutrient absorption, ensuring your baby's tummy is happy and healthy.
  • Immune Support: The selective fermentation process of GOS and FOS is vital for gut health and immunity7.
  • Softer Stools: Studies show that babies fed with a formula enriched with 9:1 GOS/FOS are more likely to experience softer stools (similar to breastfed babies), indicating a healthy digestive system.


Breastmilk has many beneficial components and is rich in prebiotics. Understanding prebiotics like HMOs, GOS and FOS allows you to make informed nutritional choices for your baby.

The specialised 9:1 GOS/FOS blend found in some formula milk supports not just gut health and immune function but also contributes to softer stools and reduced inflammation8

It also plays a crucial role in laying the foundation for a healthy gut microbiome during the early years of life. Research suggests that nurturing a diverse and balanced gut microbiome in infancy can have long-lasting effects on overall health throughout childhood and into adulthood.

Therefore, incorporating prebiotics into your baby's diet from an early age can set them on the path to optimal digestive health and support the immune system for years to come.

  1. Imperial College Healthcare NHS Trust. (n.d.). James Kinross Q&A [online]. Available at: (Accessed: February 12, 2024).
  2. Bode L. Human milk oligosaccharides: every baby needs a sugar mama. Glycobiology 2012; 22(9): 1147–62.
  3. Imperial College London. Imperial experts’ book explains why the microbiome matters [online]. Available at: (Accessed: Febuary 13, 2024).
  4. Stanford Medicine. (2022). Breast milk shapes infant gut microbiome, Stanford-led study finds [online]. Available at: (Accessed: Feburary 13, 2024).
  5. Veereman-Wauters, G., et al. (2011). Physiological and bifidogenic effects of prebiotic supplements in infant formulae. Journal of Pediatric Gastroenterology and Nutrition, 52, 763-771.
  6. Knol, J., et al. (2005). Colon microflora in infants fed formula with galacto- and fructo-oligosaccharides: more like breast-fed infants. Journal of Pediatric Gastroenterology and Nutrition, 40, 36-42.
  7. Arslanoglu, S., et al. (2007). Early supplementation of prebiotic oligosaccharides protects formula-fed infants against infections during the first 6 months of life. The Journal of Nutrition, 137(11), 2420-2424.
  8. Mihatsch, W. A., et al. (2006). Prebiotic oligosaccharides reduce stool viscosity and accelerate gastrointestinal transport in preterm infants. Acta Paediatrica, 95(7), 843-848. 
  9. Ben, X. M., et al. (2008). Low level of galactooligosaccharide in infant formula stimulates growth of intestinal Bifidobacteria and Lactobacilli. World Journal of Gastroenterology, 14, 6564-6568. 
  10. Ben, X. M., et al. (2004). Supplementation of milk formula with galacto-oligosaccharides improves intestinal micro-flora and fermentation in term infants. Chinese Medical Journal (English), 117, 927-931
  11. Fanaro, S., et al. (2005). Galacto-oligosaccharides and long-chain fructo-oligosaccharides as prebiotics in infant formulas: a review. Acta Paediatrica Supplement, 94(449), 22-26.

Last reviewed 18th April 2024

Authored by Bahee Van de Bor

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