Prebiotic Fibres – What Are They? A Guide to Food For Your Gut Microbiome.
Many of us have heard the term ‘prebiotic fibres’ before. We’ve seen it on ingredients lists in supplements, we’ve heard nutritionists talk about them when they recommend plants in the human diet, and we hear all sorts of things about what they can do for the human body and the effects they have. But how many of these claims are true? And what do they actually do?
At BetterGuts we love prebiotic fibres, and use them in both of our flagship supplements, for reasons you’ll see, so let’s take a little trip together into the world of prebiotics to find out what they are, where they come from, and what they can do for you.
So, what are they?
‘Prebiotic fibres’ is a name given to a group of different compounds, all derived from plants. They’re complex compounds in their natural form, and like a lot of fibre, your body can’t actually break them down and digest them on its own. But, that doesn’t mean they’re not useful to your gut! You see, although your digestive system can’t break them down, a lot of the time the bacteria in your gut can. In fact, they often feed on these prebiotic fibres, hence the name ‘prebiotic’. It’s for this reason that a lot of the study in this area looks at levels of bacteria after people eat these fibres.
There are a few different types of prebiotic fibre, we’ll focus on two key ones here, Fructooligosaccharides, or FOS, and Xylooligosaccharides, or XOS for short. These two, along with GOS (galactooligosaccharide), are the most heavily studied prebiotic fibres out there for their effects on your gut microbiome. FOS has been studied since the mid 1980s, and has a solid 40 years of research behind it. For the longest time it was accepted as the go to example of a prebiotic fibre, and for many people it still is. XOS on the other hand has been studied since the 90s, but didn’t really get much recognition until a bit later, with a lot of the research ramping up in the 2010s and the EU approving it as a ‘novel food’ in 2019, so while it’s got a lot of research behind it, that research is a bit more recent. Let’s look at them one at a time.
FOS
FOS is a non-digestible carbohydrate fibre, mostly made up of fructose, that’s right, the sugar often found in fruit. It’s naturally occurring in plants, and turns up in a few different foods such as chicory root, garlic, onions, leeks, asparagus, bananas, and even some grains. When it’s produced for use in supplements it’s often made from chicory root inulin, which is cut down using enzymes to produce the FOS. This is what your gut microbes would do if you ate chicory root, as they need to break it down into FOS too before they eat it.
It’s been studied very heavily for how it interacts with the human gut, and how your gut microbes react to it, but we’ll get into that in just a moment. First, let’s look at the other major player…
XOS
Just like FOS, XOS is derived from plants. In fact, to get a little technical, it is typically derived from Xylan, a compound found in a variety of different plant fibres. Typically XOS can come from a number of foods we often consume as humans, such as bamboo shoots, various types of fruit and vegetable, honey, and milk. It turns up in other places as well though, such as corn cobs, and can even be found in some varieties of wood!
Much like FOS, XOS is produced by taking the main compound it comes from, Xylan, and chopping it down into XOS using enzymes. It’s been studied very heavily for how it interacts with the human microbiome, what your gut bacteria do with it, and what the effects can be. It typically is broken down much more slowly than FOS, making it a more gentle prebiotic fibre.
So, now that we know what they are, let’s have a look at what they actually do…
So, what do they do? Show me the science!
Both FOS and XOS have been heavily studied in a wide variety of randomised control trials, the gold standard in medical testing, to have a look at how they affect the gut and the microbiome inside it. Typically FOS ferments in the gut a lot faster than XOS, so a lot of studies have actually compared them to each other as well as combining them. Here are a few areas they’ve been studied and what they found.
One major study compared the two by giving some people XOS, some people FOS, and some people nothing at all as a control group, to see how they react individually. They found that while both the prebiotic fibres helped to boost levels of Bifidobacteria in the gut, the XOS reduced constipation, and seemed to boost the Bifidobacteria at a lower dose. This points to something we already know, that FOS ferments a lot faster than XOS does, but interestingly, shows that XOS is better at feeding Bifidobacteria (the same family as BB12). To be clear, they both feed your gut bacteria, but some bacteria only eat one or the other, not both.
There are a number of different studies that looked at FOS and XOS individually as well, and found that they both boost levels of Bifidobacteria in the gut, so we know they can both work together, but at different speeds.
But you might be thinking, ok but what does this actually mean for me? Well, let’s look at some of the studies that measured other markers.
One interesting study combined FOS and XOS together, alongside a few other prebiotic fibres, to see not just which bacteria ate them, but what the effect of that was. They gave them to people with a certain variety of bowel cancer (colorectal cancer) before and after they had an operation to see what the effects were. They found that both before and after operation the people who had taken the prebiotics had increased levels of immune markers (IgG and IgA, among others). In other words, their immune system was more active and dealing with threats more readily!
Another study showed that these prebiotic fibres, combined with others, helped to reduce inflammation, with a drop in IL-8 (an inflammatory biomarker) found in one study in particular. This is important as a reduction in inflammation is something often associated with certain bacteria, BB12 being one of them, so it suggests that by feeding that bacteria themselves, the prebiotic fibre helped to reduce inflammation.
Alright, what does all this mean?
The science shows clearly that both FOS and XOS can boost the gut microbiome and levels of specific bacteria in it, leading to clearly high levels of beneficial bacteria, especially Bifidobacterium species. But, we know that they feed some of the same microbes, but also some different ones, so they both have a job to do!
They also ferment at different rates. We know that FOS can break down much faster and more aggressively, which is great for short term impact, but once it’s gone it’s gone. The benefit of the XOS is that it breaks down more slowly, so it’s benefits aren’t all at once, but they last for a bit longer.
Not only all of this, but the research into these fibres is often double blind, randomised control. This is the highest standard in medical clinical testing, se we know it’s science we can trust!
We should also note that FOS has been around as a supplement for a long time, and has been studied for years. XOS on the other hand is a slightly newer kid on the block, and is still classed as a ‘novel food’ by the EU, even though it has already got a body of science behind it that’s hard to argue with!
In other words, these fibres feed your gut bacteria, and those bacteria go on to look after you. In fact, sometimes when your bacteria break down these fibres, the chemicals they produce lead to positive benefits, so it’s directly linked. It’s important to remember that these fibres aren’t just there to feed the bacteria that we produce either, they feed the bacteria that already live in your gut too! It’s a great chain!
It’s for this reason that we decided to use both of these fibres in our LGG and BB12 supplements at BetterGuts. We know that our bacteria have a huge body of gold standard science behind them, but we didn’t want to send them in without any food! So, by packaging in prebiotic fibres shown to feed these bacteria, we know that we’re sending in our live cultures with a packed lunch. And not only that, but a packed lunch that they can share with the other beneficial bacteria in your gut. That way, they can get straight to work!
References (the science) – Don’t just take our word for it:
- Yi W, Wang Q, Xue Y, Cao H, Zhuang R, Li D, Yan J, Yang J, Xia Y, Zhang F. Xylo-oligosaccharides improve functional constipation by targeted enrichment of Bifidobacterium. Food Sci Nutr. 2023 Nov 27;12(2):1119-1132. doi: 10.1002/fsn3.3827. PMID: 38370040; PMCID: PMC10867466.
- Xie X, He Y, Li H, Yu D, Na L, Sun T, Zhang D, Shi X, Xia Y, Jiang T, Rong S, Yang S, Ma X, Xu G. Effects of prebiotics on immunologic indicators and intestinal microbiota structure in perioperative colorectal cancer patients. Nutrition. 2019 May;61:132-142. doi: 10.1016/j.nut.2018.10.038. Epub 2018 Nov 29. PMID: 30711862.
- Yuan Cui, Dingwei Kuang, Jing Wang, Shaoye Huo, Peng Li, Lin Lu, Yuhuan Wei, Lihong Wang, Xiaojing Zhong, Yunhua Zhao, Jianying Niu, Weibing Wang, Chunhai Shao, Effect of soluble dietary fiber on gut microbiota and derived metabolites in stage 3 to 5 chronic kidney disease patients: A randomized controlled trial, Journal of Functional Foods, Volume 116, 2024, 106181, ISSN 1756-4646, https://doi.org/10.1016/j.jff.2024.106181.
- Bouhnik Y, Raskine L, Simoneau G, Paineau D, Bornet F. The capacity of short-chain fructo-oligosaccharides to stimulate faecal bifidobacteria: a dose-response relationship study in healthy humans. Nutr J. 2006 Mar 28;5:8. doi: 10.1186/1475-2891-5-8. PMID: 16569219; PMCID: PMC1448190.
- Tandon D, Haque MM, Gote M, Jain M, Bhaduri A, Dubey AK, Mande SS. A prospective randomized, double-blind, placebo-controlled, dose-response relationship study to investigate efficacy of fructo-oligosaccharides (FOS) on human gut microflora. Sci Rep. 2019 Apr 2;9(1):5473. doi: 10.1038/s41598-019-41837-3. PMID: 30940833; PMCID: PMC6445088.
- Finegold SM, Li Z, Summanen PH, Downes J, Thames G, Corbett K, Dowd S, Krak M, Heber D. Xylooligosaccharide increases bifidobacteria but not lactobacilli in human gut microbiota. Food Funct. 2014 Mar;5(3):436-45. doi: 10.1039/c3fo60348b. PMID: 24513849.
- Yang J, Summanen PH, Henning SM, Hsu M, Lam H, Huang J, Tseng C-H, Dowd SE, Finegold SM, Heber D and Li Z (2015) Xylooligosaccharide supplementation alters gut bacteria in both healthy and prediabetic adults: a pilot study. Front. Physiol. 6:216. doi: 10.3389/fphys.2015.00216
- Ma R, Bai Y, Huang H, Luo H, Chen S, Fan Y, Cai L, Yao B. Utility of Thermostable Xylanases of Mycothermus thermophilus in Generating Prebiotic Xylooligosaccharides. J Agric Food Chem. 2017 Feb 15;65(6):1139-1145. doi: 10.1021/acs.jafc.6b05183. Epub 2017 Feb 3. PMID: 28067041.
