Fiber and Prebiotics: Are They All the Same?

March 03, 2024 8 min read

Fiber and Prebiotics: Are They All the Same?

At Layer Origin Nutrition, and indeed many other organisations, the terms fibre, prebiotics or prebiotic fibre are used interchangeably, but this can lead to confusion. Although fibre and prebiotics are important for health, there are some distinct differences.

In this article, we’ll get to work deciphering these differences between the two.

What is fibre?

Fibre is a type of carbohydrate. It is known as ‘indigestible’ because the human body cannot break it down. So, it passes through most of your digestive system relatively intact, until it reaches your colon, where it can be fermented by your gut microbiota.

However, not all fibres are fermentable, instead, these types pass through the colon and bulk out your stools, making them easier to pass. Fibre can be defined into two types, both of which are beneficial for health, but have different functions. They are solubleand insoluble.

Soluble fibre

Soluble fibre is the type that dissolves in water to create a gel, slowing digestion. This type of fibre is associated with lowering blood cholesterol and sugar levels, so may lower the risk of developing diabetes[i].

Soluble fibre sources





Brussels sprouts


Flax seeds


Sweet potato


Insoluble fibre

Insoluble fibre, as its name suggests, doesn’t dissolve in water. Instead, it travels to your colon where it attracts water to bulk out your stools. This is important because it helps to promote normal bowel function and regularity and prevent constipation[ii].

Insoluble fibre sources



Green beans



Whole wheat flour


Did you know?Our Organic Apple Peel Powder is a great source of both soluble and insoluble fibre, perfect for proper digestion.

What are prebiotics?

Prebiotics are special types of fibre that act as nourishment or food for the beneficial bacteria residing in your gut. In doing so, the process of fermentation, or the breakdown of these fibres by your microbes, yields magical metabolites like short-chain fatty acids (SCFAs) and vitamins, that are not only beneficial for your digestive tract but also other vital organs and processes throughout the body[iii].

Are all fibres prebiotic?

The short answer is no but all prebiotics are dietary fibre.

Confused? Don’t be.

It just means that some fibres aren’t broken down by your gut bacteria, but they still have good effects. For example, they may go on to bulk up your stools to stop you from feeling bunged up[iv].

Types of prebiotics

The concept of “prebiotics” is relatively new having been first introduced in 1995 by Glenn Gibson and Marcel Roberfroid[v].

To be considered a prebiotic there are three criteria that the fibre must satisfy. They are:

  1. It should be resistant to the pH of the stomach, unable to be hydrolysed by human enzymes and not absorbed by the gastrointestinal tract (GI)
  2. The fibre must be fermented by gut microbes and
  3. It must increase the growth and/or activity of the gut bacteria, resulting in health benefits[vi]

Currently, the three most common types of prebiotics are fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), and trans-galacto-oligosaccharides (TOS), but there are others, such as resistant starches and human milk oligosaccharides, which we will investigate further, next.


Although inulin and FOS are related compounds, they are not entirely the same. Despite this, you may sometimes read that inulin is a type of fructo-oligosaccharide. What is true, is both are a type of fructan (naturally occurring carbohydrates) and both have prebiotic effects.

The main difference between them is their structure. FOS are shorter chain molecules that are arranged in a line whereas inulin is longer with a cross-linking structure[vii].

Inulin is readily available in powder form and is found in over 36,000 plant-based foods, including:

  • Chicory root
  • Garlic
  • Jerusalem artichokes
  • Onions
  • Whole wheat

Inulin is known to have bifidogenic properties, specifically stimulating the growth of Bifidobacteria[viii]. But it’s also known to lower blood sugar, regulate the metabolism of fat, lower the risk of colon cancer, and even have benefits for depression[ix].

Fructo-oligosaccharides (FOS)

Even though inulin and FOS are distinct from one another, they do share common sources and functions, which is why they are often discussed together.

FOS is naturally found in foods like:

  • Asparagus
  • Bananas
  • Chicory root
  • Garlic
  • Leeks
  • Onions

Fructo-oligosaccharides are naturally low in sugar, so are often used as a low-calorie alternative to sweeteners. Aside from their use to sweeten food, FOS also have numerous other health benefits, mainly because of their prebiotic activity.

A study by Jinno et al., (2017) involving 84 pregnant women, found the administration of 8 grams of FOS per day from the 26th week of pregnancy until one month after birth saw a significant increase in Bifidobacteriaspecies compared to a control group. The same study also noted an increase in bowel movements In the FOS group compared to the placebo group, which suggests that FOS also has an anti-constipation effect[x].

Other studies have shown that FOS may have an immune-modulating function, too. For example, Jalil et al., (2008) demonstrated that the administration of a FOS/inulin mix increased the efficacy of a Salmonella vaccine given to mice. Overall, the study found that FOS may afford some protection against Salmonella in animal models[xi].

Galacto-oligosaccharides (GOS)

Galacto-oligosaccharides or GOS is a term given to carbohydrates that are made up of oligo-galactose and some lactose and glucose[xii]. Just as with other prebiotics, GOS travels to the gut undigested, where it can be fermented by your good gut bacteria.

GOS has been shown to have numerous health benefits. A study by Johnstone et al., (2021) examined the effect of dietary supplementation of GOS on the mood and wellbeing of 64 healthy women. The researchers found that GOS had a positive effect on participants who experienced self-reported trait anxiety. They also noted an increase in Bifidobacteriaabundance in the gut[xiii].

GOS can also provide relief from constipation, particularly in adults who experience low stool frequency[xiv].

Did you know?At Layer Origin our PureHMO® Tri-Prebiotic™ Powder combines the power of GOS, FOS, and HMOs to feed the different strains of probiotics in your gut and increase the diversity of your microbiome.

Resistant starches

As their name suggests, resistant starches are starch molecules that can pass through the body without being digested. Generally, starches are long chains of glucose found in foods like potatoes and grains, but resistant starch works similarly to soluble fibre.

It is important for the production of short-chain fatty acids by your gut microbiota, with the resistant starch acting as a form of sustenance for the bacteria residing there. It’s also associated with an improved tolerance to glucose and improved insulin sensitivity[xv].

Resistant starch is found in the following foods:

  • Cooked and cooled potatoes, rice and pasta
  • Grains
  • Legumes
  • Unripe bananas

Human milk oligosaccharides (HMOs)

HMOs are an important prebiotic consisting of a complex mixture of oligosaccharides that are unique to human breast milk. They can resist digestion and the acidic and hostile environment of the stomach to reach the colon.  Here, they are fermented by probiotic bacteria, yielding SCFAs and supporting microbial growth[xvi].

HMOs have several other important functions, including:

  • Promoting a diverse microbiome
  • Supporting the immune system
  • Anti-adhesive properties, protecting the host from harmful pathogens
  • Strengthening the intestinal barrier

There are over 200 different HMOs that have been isolated from human breast milk. At Layer Origin, we provide a wide range of PureHMO® products designed to help you seamlessly support your gut health. Our products are human-identical milk oligosaccharides (HiMOs) and include:

  • 2’-Fucosyllactose (2’-FL)
  • Lacto-N-neotetraose (LNnT)
  • Lacto-N-tetraose (LNT)
  • 6'-Sialyllactose (6'SL)
  • 3'-Sialyllactose (3'SL)

Are prebiotics and probiotics the same?

No. Probiotics are the beneficial microbes, mainly bacteria, that occupy your gut and confer health benefits while prebiotics are the energy source or food, these microbes need to grow, survive, and thrive. Both are equally important for your gut health but have different functions. You can find out more by reading our “What are prebiotics and how do they differ from probiotics?” article.


Although fibre and prebiotics are similar in terms of their overall function to promote good gut health, there are some distinct differences, and indeed there are differences between the different types of fibre and prebiotics.

It’s important to remember though, that to achieve optimal gut health, it’s essential to incorporate a wide variety of fibre, both soluble and insoluble, and prebiotic foods and/or supplements into your diet.

Written byLeanne Edermaniger, M.Sc. Leanne is a professional science writer who specializes in human health and enjoys writing about all things related to the gut microbiome. 


[i] Chen C, Zeng Y, Xu J, Zheng H, Liu J, Fan R, Zhu W, Yuan L, Qin Y, Chen S, Zhou Y, Wu Y, Wan J, Mi M, Wang J. Therapeutic effects of soluble dietary fiber consumption on type 2 diabetes mellitus. Exp Ther Med. 2016 Aug;12(2):1232-1242. doi: 10.3892/etm.2016.3377. Epub 2016 May 20. PMID: 27446349; PMCID: PMC4950069.

[ii] Ho KS, Tan CY, Mohd Daud MA, Seow-Choen F. Stopping or reducing dietary fiber intake reduces constipation and its associated symptoms. World J Gastroenterol. 2012 Sep 7;18(33):4593-6. doi: 10.3748/wjg.v18.i33.4593. PMID: 22969234; PMCID: PMC3435786.

[iii] Davani-Davari D, Negahdaripour M, Karimzadeh I, Seifan M, Mohkam M, Masoumi SJ, Berenjian A, Ghasemi Y. Prebiotics: Definition, Types, Sources, Mechanisms, and Clinical Applications. Foods. 2019 Mar 9;8(3):92. doi: 10.3390/foods8030092. PMID: 30857316; PMCID: PMC6463098.

[iv] Fiber [Internet]. 2023 [cited 2024 Jan 7]. Available from:,it%20is%20easier%20to%20pass.

[v] Gibson GR, Roberfroid MB. Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. J Nutr. 1995 Jun;125(6):1401-12. doi: 10.1093/jn/125.6.1401. PMID: 7782892.

[vi] Hutkins RW, Krumbeck JA, Bindels LB, Cani PD, Fahey G Jr, Goh YJ, Hamaker B, Martens EC, Mills DA, Rastal RA, Vaughan E, Sanders ME. Prebiotics: why definitions matter. Curr Opin Biotechnol. 2016 Feb;37:1-7. doi: 10.1016/j.copbio.2015.09.001. Epub 2015 Sep 29. PMID: 26431716; PMCID: PMC4744122.

[vii] Niness KR. Inulin and oligofructose: what are they? J Nutr. 1999 Jul;129(7 Suppl):1402S-6S. doi: 10.1093/jn/129.7.1402S. PMID: 10395607.

[viii] Meyer D, Stasse-Wolthuis M. The bifidogenic effect of inulin and oligofructose and its consequences for gut health. Eur J Clin Nutr. 2009 Nov;63(11):1277-89. doi: 10.1038/ejcn.2009.64. Epub 2009 Aug 19. PMID: 19690573.

[ix] Qin YQ, Wang LY, Yang XY, Xu YJ, Fan G, Fan YG, Ren JN, An Q, Li X. Inulin: properties and health benefits. Food Funct. 2023 Apr 3;14(7):2948-2968. doi: 10.1039/d2fo01096h. PMID: 36876591.

[x] Jinno S, Toshimitsu T, Nakamura Y, Kubota T, Igoshi Y, Ozawa N, Suzuki S, Nakano T, Morita Y, Arima T, Yamaide F, Kohno Y, Masuda K, Shimojo N. Maternal Prebiotic Ingestion Increased the Number of Fecal Bifidobacteria in Pregnant Women but Not in Their Neonates Aged One Month. Nutrients. 2017 Feb 26;9(3):196. doi: 10.3390/nu9030196. PMID: 28245628; PMCID: PMC5372859.

[xi] Benyacoub J, Rochat F, Saudan K-Y, Rochat I, Antille N, Cherbut C, et al. Feeding a diet containing a fructooligosaccharide mix can enhance salmonella vaccine efficacy in mice. The Journal of Nutrition. 2008;138(1):123–9. doi:10.1093/jn/138.1.123

[xii] Niittynen L, Kajander K, Korpela R. Galacto-oligosaccharides and bowel function. Scand J Food Nutr. 2007 Jun;51(2):62–6. doi: 10.1080/17482970701414596. PMCID: PMC2607002.

[xiii] Johnstone N, Milesi C, Burn O, van den Bogert B, Nauta A, Hart K, et al. Anxiolytic effects of a galacto-oligosaccharides prebiotic in healthy females (18–25 years) with corresponding changes in gut bacterial composition. Scientific Reports. 2021;11(1). doi:10.1038/s41598-021-87865-w

[xiv] Schoemaker MH, Hageman JHJ, Ten Haaf D, Hartog A, Scholtens PAMJ, Boekhorst J, Nauta A, Bos R. Prebiotic Galacto-Oligosaccharides Impact Stool Frequency and Fecal Microbiota in Self-Reported Constipated Adults: A Randomized Clinical Trial. Nutrients. 2022 Jan 12;14(2):309. doi: 10.3390/nu14020309. PMID: 35057489; PMCID: PMC8780623.

[xv] Bojarczuk A, Skąpska S, Mousavi Khaneghah A, Marszałek K. Health benefits of resistant starch: A review of the literature. Journal of Functional Foods. 2022;93:105094. doi:10.1016/j.jff.2022.105094

[xvi] Okburan G, Kızıler S. Human milk oligosaccharides as Prebiotics. Pediatrics & Neonatology. 2023;64(3):231–8. doi:10.1016/j.pedneo.2022.09.017


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