From FODMAPs to fibre: navigating dietary treatments for IBS

Irritable bowel syndrome (IBS) is a common gastrointestinal issue marked by abdominal pain, bloating, diarrhoea and constipation. This chronic condition can lead to anxiety, depression and a reduced quality of life. With no definitive trigger or treatment, managing IBS can be challenging. However, diet changes can positively influence IBS. In this podcast episode, I’ll outline evidence for various approaches, from supplements like probiotics right through to low-FODMAP diets.

Links referred to in the podcast

• Review of nutritional interventions in IBS https://pubmed.ncbi.nlm.nih.gov/39110917

Episode transcript
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Transcript

Irritable bowel syndrome (IBS) is a common gastrointestinal issue marked by abdominal pain, bloating, diarrhoea and constipation. This chronic condition can lead to anxiety, depression and a reduced quality of life. With no definitive trigger or treatment, managing IBS can be challenging. However, diet changes can positively influence IBS. In this podcast episode, I’ll outline evidence for various approaches, from supplements like probiotics right through to low-FODMAP diets.

Irritable bowel syndrome is a common gastrointestinal disorder affecting up to 1 in 5 people. Symptoms of IBS include abdominal bloating, pain, flatulence, diarrhoea and altered bowel habits. People with IBS report a poorer quality of life compared to people without IBS, with diet being a key factor impacting their lifestyle. The condition can be difficult to diagnose because other conditions share the same symptoms. Currently, there is no specific diagnostic test for IBS.

The cause of IBS is unknown, but environmental factors such as changes in routine, emotional stress, infection and diet are all known to trigger an attack. With no definitive cause of IBS, treatment is mostly focussed on managing the symptoms. Dietary changes such as increasing the amount of fibre eaten, eliminating potential ‘problem foods’ such as gas-producing beans or cabbage, spicy foods or removing dairy foods and wheat from the diet can work for some people. A range of medications are sometimes prescribed to manage IBS, while stress management techniques can also help some.

For a condition that affects so many people, there are few effective treatments that are well supported by evidence. In an attempt to combine that research in one place, an umbrella review has just been published. An umbrella review is simply a review of reviews so it is probably one the most comprehensive ways to look at the full research field.

The types of studies in the reviews were randomised-controlled trials and all up, 175 different trials involving over 35,000 people with IBS were looked at which described the effect of 11 different types of nutritional interventions. The nutritional interventions included probiotics, prebiotics, a low-FODMAP diet, fibre, glutamine, a glutamine-free diet, peppermint oil, aloe vera, vitamin D, curcumin, and Tong Xie Yao Fang which is a traditional Chinese medicine formula. In all the studies, the effect of the nutritional intervention was compared to a placebo.

The primary outcomes of interest were IBS symptoms, IBS severity and abdominal pain. The secondary outcomes were stool consistency and quality of life. And I’ll link to the review in the show notes. https://pubmed.ncbi.nlm.nih.gov/39110917

Now, I’m not going to go into a lot of detail about all those different types of nutritional interventions as you can do your own reading on each of them from the paper if any interest you. What I will cover though are the ones that had the strongest evidence for a benefit. And the list was fairly short. And these were a low-FODMAP diet and probiotics which both had a moderate certainty of evidence for a benefit. The other supplements could show some level of improvement for some of the IBS symptoms, but overall, the effects were small with a low level of evidence for certainty. So, I’ll focus more on a low-FODMAP diet and probiotics for the remainder of this podcast.

FODMAP is an acronym for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols and includes carbohydrates such as lactose, fructose and fructans (which are long chains of fructose molecules such as inulin) and sugar alcohols. FODMAPs are found in many foods including wheat, milk, pears, plums, onions, garlic and legumes.

FODMAPs can be poorly absorbed in some people, leading to their accumulation in the small intestine where they then pass into the large intestine. Once there, they can draw more water into the bowel which increases the chance of diarrhoea. FODMAPs can also increase gas production from their fermentation by colonic bacteria. These effects of FODMAPs in the bowel explain many of the symptoms reported in IBS.

Previous review papers on a low-FODMAP diet in IBS have also supported its benefit in managing some of the symptoms of IBS. And in some of those reviews, they could even look at the effect of following a high-FODMAP diet versus a standard diet which gave a big jump in IBS symptom scores so that adds further credence to their role in triggering IBS.

Despite the clinical benefits of the low-FODMAP diet, a potentially negative impact on the gut microbiota is a concern. The levels of beneficial Bifidobacteria are lower when following a low FODMAP diet which is most likely due to reduced consumption of fermentable carbohydrates. 

The impact of the low-FODMAP diet on the gut microbiota is only one of the challenges. The low-FODMAP diet is complex to follow and may lead to lower fibre, iron and calcium intakes. Extensive food knowledge and label reading are required to identify suitable foods and is why it is advised to seek education and support from a dietitian for anyone considering trialling a low-FODMAP diet.

Another emerging treatment for IBS are probiotics. Probiotics may improve IBS symptoms by inducing favourable changes in the gut microbiota and their metabolite production and may interact with the intestinal immune and nervous systems. Therefore, they may modulate gut motility, inflammation and gut hypersensitivity through these mechanisms.

There is though not a lot of clarity for which bacterial species or strain and the form they are found in which are best to use. Previous reviews on this topic found that certain single-strain formulations, such as Lactobacillus plantarum DSM 9843 improved IBS symptoms, but other strains did not. It seems though that at a genus level it is Lactobacillus, Bifidobacterium and Bacillus that appear to be the most effective bacteria in the management of IBS symptoms. But it is the evidence for Lactobacillus that is considered the highest quality.

For someone wishing to trial probiotics to manage IBS, consider selecting one product at a time and then monitor the effects and choose a product containing a strain that has some clinical evidence for a benefit in IBS. And give the probiotic time to work; a minimum of 4 weeks at the dose recommended by the manufacturer is advised.

So, let’s wrap all this up. As a gastroenterologist once said to me, IBS is code for “We don’t know” and that is a fair call to make as the underlying cause or causes of IBS can be so varied. Diet and lifestyle changes are one place to start to help manage IBS and is where there are dietary strategies shown to improve IBS symptoms that can be tried and these could include peppermint oil, certain probiotic formulations, psyllium supplementation, avoiding trigger foods such as spicy foods and caffeine, and of course a low-FODMAP diet. As it is unlikely one dietary strategy will benefit everyone with IBS, then it may be a matter of trialling different approaches. This is where getting professional help and support from a dietitian can help, especially with the more involved approaches such as a low FODMAP diet.

So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.

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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.