Prebiotic fibers pass through the digestive tract largely undigested. But when prebiotics enter the large intestine (colon), the gut bacteria that live there can use them as a food source.
Prebiotic Pros and Cons
On the upside, prebiotics can boost numbers of beneficial bacteria like lactobacillus and bifidobacteria. These good bacteria ferment the prebiotics they are using as a food source, which in turn produces short-chain fatty acids (SCFAs), including butyrate. These SCFAs have beneficial effects such as:
On the downside, people with digestive health problems can be particularly sensitive to prebiotics, for instance producing more flatulence when they consume higher doses [4 Trusted SourcePubMedGo to source]. Why is this? Well, if you have an overgrowth of bacteria or an imbalance in your gut microbiome, prebiotics may be feeding not only the healthy microbes but the problematic ones.
Let’s look in more detail at some of the health conditions prebiotics may help with, before considering when and why you might need to be cautious with their use.
Potential Health Benefits of Prebiotics
Though prebiotics aren’t as well researched as probiotics as yet, there are some promising outcomes, including:
Easing of chronic constipation: A meta-analysis of randomised clinical trials (the highest standard of scientific assessment available) found that inulin supplements improved stool frequency, consistency, and transit time through the digestive system. However they did not improve pain or bloating [5 Trusted SourcePubMedGo to source].
Improved colon function: A systematic review / meta-analysis (SR/MA) of nine randomised controlled trials (RCTs) found that resistant starch increased stool bulk and butyrate production in healthy adults [6 Trusted SourcePubMedGo to source].
Mood-lifting potential: An RCT found that inulin intake was helpful at improving mood in some obese subjects, though strength of response was dependent on the individual’s gut microbiome makeup at the beginning on the study [7 Trusted SourcePubMedGo to source].
Hunger curbing: An SR/MA of RCTs concluded that inulin-type prebiotics may help reduce ghrelin (the so-called “hunger hormone”) in overweight or obese people [8 Trusted SourcePubMedGo to source]. However, they did not appear to help with weight loss or weight management [9 Trusted SourcePubMedGo to source].
Eczema: An SR/MA comparing probiotics, prebiotics, and synbiotics (a combination of the two) for their effects on infant eczema found that probiotics and synbiotics reduced the incidence of eczema, but prebiotics alone had no effect [18 Trusted SourcePubMedGo to source].
Irritable bowel syndrome: A collection of SR/MAs have found little to no evidence that prebiotics are a beneficial treatment for IBS [19 Trusted SourcePubMedGo to source, 20 Trusted SourcePubMedGo to source, 21 Trusted SourcePubMedGo to source]. In one of these the effects of probiotics, prebiotics, and synbiotics on IBS symptoms were compared. It found that multi-strain probiotics with Bifidobacterium species had the greatest positive effect on overall IBS symptoms. Synbiotics helped with urgency, abdominal pain, and flatulence, but prebiotics alone were not clearly beneficial for IBS.
Sensitivity to Prebiotics
Whether or not you benefit from prebiotics may well have to do with underlying gut sensitivities.
The issue is that prebiotics, especially in large or inappropriate amounts, may feed gut bacteria in general, not just the good types. So, if the bacteria in your gut are overgrown or imbalanced, prebiotics may actually exacerbate the problem. Most prebiotic foods are also FODMAPs — belonging to the same family of fermentable carbohydrates that can kick off gut symptoms for some individuals [21 Trusted SourcePubMedGo to source]. So though prebiotics can definitely have benefits, they may also cause discomfort.
A 2016 SR/MA found that despite all of the potential benefits of high-FODMAP foods, many of which contain prebiotics, there are some cases where these types of fiber may actually cause more harm than good, specifically if you suffer from functional GI symptoms, like those that occur in IBS (irritable bowel syndrome), IBD (inflammatory bowel disease), or SIBO (small intestinal bacterial overgrowth) [22 Trusted SourcePubMedGo to source].
A 2018 RCT that compared a standard Mediterranean-style diet plus prebiotic with a low FODMAP diet plus placebo, found [23 Trusted SourcePubMedGo to source]:
Significant symptom relief in both groups after four weeks, but also more flatulence and rumbling in the prebiotic group.
An increase in bifidobacteria in the prebiotic group (but a decrease in the low FODMAPs group).
A flare of symptoms for some patients upon introduction of prebiotics, but this went away after 7-10 days.
In a 2017 RCT, 20 participants with mixed or diarrhea-dominant IBS ate a low FODMAP diet for three weeks before being given either a high dose FOS or placebo supplement for ten days. This was followed by a three-week washout period (no supplements) and then another ten days of the supplements, but switched round, so those who had placebo before now had prebiotic, and vice versa. The FODMAPs diet was continued throughout. The result showed that [24 Trusted SourcePubMedGo to source]:
All IBS symptoms improved after three weeks on a low FODMAP diet (85% patient satisfaction).
FOS produced theoretical benefits to gut health (increasing some good bacteria species and SCFAs).
However, the prebiotic also increased nausea, vomiting, headache, belching, and flatulence (placebo did not cause this effect).
It’s possible to interpret the above results in different ways, but the clinical takeaway that I’ve found suits patients best is to avoid prebiotic supplements when the gut is still very symptomatic.
In short, the more sensitive your gut is, the more careful you should be with prebiotics — the “no gain without pain” saying is not the right one here!
After your symptoms have improved, it’s fine to carefully introduce prebiotics as a boost to gut health. You may well still get a minor flare up of symptoms, but when the time is right for your microbiome to accept and benefit from prebiotics, any side effects should be minor and short-lived.
Even if you do seem to tolerate prebiotics well, more is not necessarily better, and the best prebiotic supplement may well be one that is only a modest dosage.
The further you increase your intake beyond the threshold useful prebiotic intake (likely around 3-5 grams a day) [25 Trusted SourcePubMedGo to source] the more chance you will have of running into impactful side effects.
For example, whereas low dose prebiotics may cause some bloating, higher doses can cause diarrhea, which is a much more significant side effect [26 Trusted SourcePubMedGo to source].
A good analogy here is that of using fertilizer (prebiotics) on a garden (your microbiota). While some fertilizer is good to help bacteria grow, dumping on too much fertilizer might be damaging to the overall ecosystem, potentially worsening dysbiosis (gut bacteria imbalances).
Using Diet and Probiotics to Heal Your Gut
Rather than leaping straight to prebiotics to try and improve your microbiome, the better and more fundamental place to start is your diet.
For making improvements to gut health this means:
Eating a less processed, more whole food diet to control inflammation.
Paying attention to any food intolerances you might have that could be worsening gut symptoms.
Eating in a way that helps keep your blood sugar on an even keel (less refined carbs and more protein and dietary fiber rich foods).
Finding your ideal intake of carbohydrates and prebiotics.
Because we are focusing on prebiotics in this article, let’s pay a little bit more attention to the fourth bullet point above.
Determining the right amount of carbohydrates and prebiotics for you is such an important principle because everyone’s individual tolerance level for prebiotics and fermentable carbohydrates is a bit different and can change over time.
For example, as your gut heals, say from a condition like SIBO, you might find that you can enjoy more healthy carbohydrates and prebiotics than you were previously able to.
As a general principle here, it’s best to start with the least restrictive diet and only move onto something more limited if you don’t get results.
In increasing order of restrictiveness that would usually mean:
That said, there are no real hard and fast rules here. For example for IBS specifically, the low FODMAP diet is highly effective and you might want to try this first.
What About Probiotics?
Whereas prebiotics taken too early in your gut healing program might cause problems, research shows the same is not true for probiotics.
Diet is always the first place to start in your gut healing journey, but probiotics can also be introduced early on without any problems. For most patients, changes to diet and use of a multistrain probiotic can produce symptom relief within a couple of weeks.
Scientific studies show a wide variety of benefits from taking probiotics, including:
There’s very little research comparing prebiotic types. But as with any time you are choosing a supplement, look for a reputable brand that uses high-quality manufacturing processes, and check the ingredients and dosage are suitable for you. It’s a good sign if the product has been tested in independent clinical trials too.
One study suggested that galacto-oligosaccharides (found in the supplement Bimuno) may be favorable because they seem to [40 Trusted SourcePubMedGo to source]:
More specifically boost healthy bifidobacteria than other prebiotics
Produce this beneficial effect at lower doses
In theory, at least this could mean more benefits with fewer issues for a sensitive gut. However, more research is needed.
Tying It All Together
Prebiotics are like a fertilizer for your good bacteria, and they have some quite good documented health benefits. However, whether you will benefit is very individual, and some trial and error might be needed to help find what is the best probiotic supplement (and dosage) for you.
The best advice for most patients with gut health issues is to bide your time and only introduce prebiotics after you are already well on the road to recovery.
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