Sourdough fermentation has been recently rediscovered for its ability to produce a nutritional and functional bread which is beneficial for the gut and better tolerated by individuals with gastrointestinal (GI) conditions like Irritable Bowel Syndrome (IBS) and Non-Celiac-Gluten-Sensitivity (NCGS). It is specifically the fermentation process using microorganisms such as yeast, bacteria and fungi which play a key role in the functional and nutritional quality of the bread. Applying the ancient biotechnology of sourdough fermentation can help lower the glycemic response, enhance uptake of minerals, improve the bioavailability of dietary fibre,and reduce compounds in grains like gluten, a-amylase/trypsin inhibitors (ATIs), and fermentable-oli-di-mono-saccharides and polyols (FODMAPs) (1,2). The role of sourdough fermentation to reduce FODMAPs which cause GI symptoms in IBS caught my attention,and after a review of the literature I decided to embark on a pilot study of my own as part of my MSc dissertation for Nutritional Therapy.

As an IBS sufferer I have experimented with many breads over the years and tried not eating it which left me very unhappy to say the least! Bread was such an important part of my cultural heritage in Ireland where soda bread and wheaten bread were a staple in my diet. In my late teens and 20s however, I noticed a number of increasing GI symptoms when I was eating bread but did not have the information to hand to make the connection between bread and IBS. It was not until much later in my life that I began my quest to find a healthy bread which could be consumed without increasing IBS symptoms after many years of eating lack lustre gluten free bread. A visit to Pembrokeshire sparked a meeting with an artisan baker and farmer of heritage grains, Rupert Dunn who coordinates Torth y Tir, a community supported bakery. Through Rupert I came to understand that not all sourdough was equal and it was becoming clear that the length of fermentation was key to producing an authentic sourdough bread. This led me to source some traditionally fermented sourdough bread in my hometown of Cardiff and I came across a small bakery, Riverside Sourdough, with its wonderful array of breads. Mark Stevens, the passionate baker at the helm of thisvibrant business agreed to let me use their sourdough as the focus of my pilot study. What follows is a summary of myMSc dissertation supervised by senior lecturer in Nutritional Therapy, Miranda Harris at the University of Worcester. The findings provide some valuable and novel data into the impact of sourdough bread on IBS symptoms.

What are the characteristics of IBS?

IBS is the most common Functional Gastrointestinal Disorder and is characterised by abdominal pain, altered bowel patterns, abdominal bloating and distention and reduced Quality of Life (QOL), (3,4). There are 4 main subtypes, constipated dominant (IBS-C), diarrhoea dominant (IBS-D), mixed constipation and diarrhoea (IBS-M) and unsub typed(IBS-U), (5).

Studies suggest a global prevalence of 11.2% (6) with a greater prevalence in females who experience increased symptom severity and reduced QOL (7,8). The aetiology of IBS is relatively unknown but it is recognised there is a disruption in the connection between the enteric nervous system in the gut and the central nervous system; commonly known as the gut-brain axis (9,10). Symptoms can be triggered by stress, dysbiotic gut bacteria, dysregulated bile salt metabolism, inflammation in the mucosal membrane of the gut and infection (11,12).

Non-gastrointestinal symptoms are being increasingly recognised as comorbidities in IBS. Anxiety and depression are common but other physical symptoms such as headaches, dizziness, heart palpitations, back pain, shortness of breath, muscle ache, frequent urination and poor appetite have been highlighted in the literature addressing health outcomes in IBS(13,14).

A definitive diagnosis of IBS is complicated by the over-lap in gastrointestinal symptoms seen in celiac disease, food allergies, food intolerances and NCGS (15,16). Wheat is often self-reported as a trigger for GI symptoms but there is controversy surrounding which compounds are implicated; is it FODMAPs, gluten or ATIs? FODMAPS are present in wheat and many other foods and are known to trigger IBS symptoms through the slow or partial absorption in the small intestine causing increased fermentation and gas (17). A low FODMAP diet is now part of evidence based practice for IBS in conjunction with lifestyle management and pharmaceuticals (18).

Novel research has followed focusing on the application of sourdough fermentation to produce a low FODMAP and low gluten bread (19,20). Proofing times of >12 hrs have been demonstrated to reduce FODMAPs by approximately 90% in sourdough bread (21) but notably the outcome is influenced by a number of factors including grain type and interaction of the sourdough micro-organisms, lactic acid, and yeast (22,23). While a low FODMAP bread can be created and standardised in a laboratory how does this apply in real life when someone with IBS eats a traditionally fermented sourdough loaf? The long fermentation time of Riverside Sourdough bread made it an ideal candidate for this pilot study to;

‘evaluate the impact of consuming sourdough fermented bread on adults with IBS during a 4 week trial and how this impacted gastrointestinal, non-gastrointestinal symptom and QOL’.

The Trial

The pilot study was designed as a ‘before and after’, single arm intervention with a population of IBS adults (over 18 years). The study design has limitations but for a Mastersdissertation it was both cost-effective and achievable in the time scale.

Eleven participants were recruited using an inclusion/exclusion criterion based on previous studies. The study was ethically approved through the University of Worcester Ethics Committee and all collection, storage and use of data complied with the Data Protection Act 2018 and GDPR.

Participants were issued with a validated questionnaire prior to beginning the trial to assess baseline symptoms. Following collection of baseline data participants started eating a given quantity of the Riverside sourdough as part of their normal diet. No restrictions were made on diet apart from the exclusion of any other bread. The quantity requirements for the trial were as follows.

Week 1: 100g of sourdough bread. Week 2: 200g of sourdough bread. Week 3: 200g of sourdough bread. Week 4: 300g of sourdough bread

NB: 100g roughly equated to 1 large slice of sourdough bread.

The questionnaire was applied again at week 2 and the end of week 4. Data was statistically analysed using SPSS 26 and the following results were identified.

The Results

From a sample of 11 participants, 1 dropped out and 10 completed the trial. There were 9 females and 1 male with an age range between 25-55 years. IBS subtypes were mainly IBS-D (7), IBS-M (2) and IBS-C (1). Most participants were vegan and only 1 followed the low FODMAP diet.

Gastrointestinal symptoms

The key findings were a statistically significant reduction in total GI symptoms between week 1– week 4 (p=0.001). When individual symptoms were analysed, significant improvements were seen in loose stools, diarrhoea, and urgency. Furthermore, benefits were demonstrated in symptoms of constipation and pain. Pain was classified as abdominal pain, pain after eating and pain affecting sleep. The greatest benefits were seen between week 1– week 2 when participants ate 100-200g of sourdough bread.

Non-gastrointestinal symptoms

The trial measured a range of non GI symptoms based on a systematic review of the literature for IBS and co-morbidities. Once again there was a statistically significant reduction in total non-GI symptoms between week 1– week 4 (p=0.002) and symptoms of headaches, fatigue, frequent urination and muscle pain were most responsive over the 4 weeks. The most significant reduction in non-GI symptoms was also noted between week 1– week 2.

Quality of Life

In line with a reduction in GI and non-GI symptoms, QOL increased over the 4 weeks significantly (p=0.001). The greatest increase in QOL was seen between week 1– week 2 when symptoms were also responding positively within the trial.

What do the findings tell us?

It is important first of all to reiterate that as a pilot study the findings should not be over interpreted and the trial was under powered by a small sample group. However, this is the first study examining the impact of traditionally fermented artisan sourdough bread on people with IBS. The study did not measure and could not measure the level of FODMAPs in the bread due to cost and time implications. Therefore the reduction in symptoms may be related to a number of factors which are examined below.

FODMAPS and Gluten

FODMAPs are a group of sugars that are not completely broken down and absorbed in the intestines. They move slowly attracting water in the small intestine and as they enter the large intestine they are fermented by gut bacteria and produce gas (24). The primary FODMAP in wheat is fructans. A reduction in fructans through sourdough fermentation can decrease the production of hydrogen gas in the gut. (25). Previous studies have shown breath hydrogen is reduced when people with IBS eat sourdough bread and this may reduce colonic pressure which is experienced as pain and bloating (26).

Gluten is also modified through the process of sourdough fermentation and can be reduced by approx. 50% in wheat (27). The reduction in gluten may specifically help subsets within IBS who are also gluten sensitive and can tolerate smaller amounts in their diet. This would NOT apply to celiac disease. One participant in this trial had previously used gluten free bread to manage GI symptoms and was able to eat the sourdough bread with no adverse reaction.


Fibre intake was increased by eating the sourdough bread and in particular soluble fibre which is often better tolerated in IBS. Fibre is particularly beneficial for IBS-C as it helps increase the transit time of food and provides faecal bulk (28). Thus, it helps prevent that feeling of fullness and bloating common in IBS. Soluble fibre found in sourdough bread may help manage the GI symptoms by also lowering gas production which can cause pain (29).

Changes in Gut Microbiota

Research has identified changes in gas production and gut bacteria in IBS as a result of eating sourdough bread. (30). The composition of the gut microbiota in IBS is already known to be compromised and the level of dysbiosis can affect symptom severity (31,32). It is possible that the additional beneficial dietary fibre from sourdough is assisting the balance of gut bacteria in a positive manner. This would be similar to the use of other fermented foods with probiotic properties which can help modulate bacteria in the gut.

Reduction in Inflammation

Research shows that positive changes in the gut microbiota can have a beneficial effect downstream effect on immune homeostasis and inflammation (33). Consuming sourdough bread may lower inflammation in certain individuals with IBS in a similar way to probiotic foods and supplements. Studies using live cultures in food and supplements have demonstrated positive changes in the regulatory T-cells which has a role in autoimmunity, immune homeostasis and immune response. (34). This may be particularly relevant in view of the impact on non-GI symptoms such as headaches, fatigue, muscle pain and frequent urination. There is a paucity of research in this field and it is worth noting that other non-GI symptoms may not have been included in this study.

Glycemic Control/Satiety

Compared to commercially baked bread, sourdough fermented bread has the ability to lower the post prandial glycemic response (35). Lowering the post prandial glucose and insulin response can have significant benefits for preventing and treating metabolic conditions. In one study it was found that individuals with IBS had a higher prevalence of prediabetic markers (36). IBS may make it harder for the body to control the post prandial glucose response and this may result in higher blood sugars which downstream may affect the functioning of the stomach and small intestine (37). This relationship between IBS and blood sugar regulation may therefore benefit from a lower glycemic food like sourdough breadwhich can enhance gut transit and gastric emptying. Crucially, this may help non-GI symptoms such as fatigue in IBS when symptoms of pre-diabetes or diabetes is present.


The pilot study demonstrated an overall improvement for GI, non-GI symptoms and QOL when 100-200g of bread was eaten per day. This can be perhaps used as a modest guideline to trial sourdough bread in a normal diet or as part of a low FODMAP diet. For certain individuals a low FODMAP diet may have to be used to improve symptoms but this should be done under the guidance of a registered dietitian.

The mechanism behind these results cannot be defined and further research would be needed to determine FODMAPs in the sourdough bread. Further to this, the multiple health benefits of sourdough bread mean that maybe more than one mechanism is benefiting GI and non-GI symptoms in IBS. It is a complex area for research as the benefits may also be determined by subtype. This small study however did show benefit across all subtypes and this is an interesting outcome.

Sourdough bread I believe, represents a nutritious food as evidenced by the literature; an important source of dietary fibre, low FODMAP, reduced gluten, low Glycemic Index, bioavailable micronutrients and benefits for the gut microbiota. There is currently a gap in the market for a healthy low FODMAP bread and this is where long fermented sourdough bread may provide a valuable role. IBS typically causes individuals to eliminate food groups to control symptoms and from a nutritional point of view sourdough bread can offer a healthy option to fulfil requirements for carbohydrate, fibre and micronutrients.

My kitchen never feels complete now without a loaf of Riverside sourdough as it’s a staple for me and my family. It can be the basis for any meal in the day. Top with a poached egg, avocado and tomato, tinned sardines, peanut butter and blueberries or make into a tasty homemade pizza with a drizzle of olive oil, tomato puree and fresh mozzarella. There is no end to its versality and there is no disputing its unique and satisfying flavour!
Eilish Blade is a complementary therapist who works in Cardiff and Newport Pembrokeshire. She has just completed an MSc in Nutritional Therapy and will be commencing work as a Registered Nutritional Therapist from the 31st of August 2020.

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