A Dietitian’s guide to fermented foods and IBS

If you are wondering if fermented foods are good for IBS, then you are in the right place. 

Fermented foods are a hot topic, with much discussion about how they are beneficial for gut health. But are fermented foods good for people with IBS? 

In this article, we answer this question along with what fermented foods are, whether they are good for our gut and who needs to avoid them.

What are fermented foods?

Fermentation is the breakdown of sugar without oxygen, producing acids, alcohol and gas. 

You produce fermented foods when microorganisms, such as bacteria or yeast, are added to a food source and starved of oxygen (1).

For example, when bacteria (aka kefir grains) is added to milk and left in a sealed container, it ferments and produces kefir, a fermented milk drink (1). 

Attention is drawn to fermented foods in recent years due to their proposed health benefits, including improved gut health.

Examples of fermented foods include:

• Kefir
• Yogurt
• kombucha
• sauerkraut
• Sourdough
• Kimchi
• Miso paste
• Tempeh

Are fermented foods good for our gut?

People often see fermented foods as a source of probiotics, however, this is not true. 

The problem is that they do not regularly test fermented foods to see if they contain beneficial microbes known as probiotics.

Even if they contain beneficial microbes, we do not know if they end up reaching our gut alive.

However, this does not mean fermented foods have no benefit to our gut health.

For example, one study finds that a fermented milk drink may prevent antibiotic-associated diarrhea (2). 

Antibiotic-associated diarrhea develops by upsetting the balance of good and bad bacteria in your gut (3). 

As well as this, a lot of fermented foods are vegetables which means they count towards our 30 plant points per week. 

Research shows that having 30 different plants in your diet per week is optimal for your gut health (4).

Yogurt can also improve digestive health. This claim is based on its calcium content which allows enzymes to function normally (5). 

In some cases, fermenting foods can also make them easier to digest. 

For example, in the process of making kefir, lactose is broken down into galactose and glucose making it easier for people with lactose intolerance to digest (6).

We need more research specifically on the effects of fermented foods on our gut, as currently there is very little.

Who should not eat fermented foods?

Although fermented foods have some health benefits, they may not be suitable for everyone. 

Fermented foods are often high in a compound known as histamine due to the fermentation process. 

Histamine is important for the functioning of our immune system. 

Cells release histamine in response to injury and it is involved in inflammatory and allergic reactions (7). 

If you have a histamine intolerance, avoiding these foods or consuming them in small quantities may be best. 

For more information on histamine intolerances see our article, A low histamine diet.

If you are immunosuppressed, we recommend that you avoid fermented foods as they contain live microbes which may cause you to become ill (8).

Are fermented foods good for IBS?

Below, we discuss different types of fermented foods in the context of IBS.

Sauerkraut

Sauerkraut is shredded cabbage that is fermented. 

One study finds that consumption of either pasteurized or unpasteurized sauerkraut can significantly improve IBS symptoms.

The study also shows that supplementation of sauerkraut in the diet significantly alters the gut microbiome composition, which may be related to a possible prebiotic effect.

Although promising, the study has a small sample size of 34, meaning we do need more research before firm conclusions are drawn (9). 

Kimchi

Kimchi consists of fermented vegetables including cabbage and radish and originates from Korea (10).

One study finds that when those with IBS eat kimchi (210g daily), symptoms including abdominal pain, desperation, incomplete evacuation and bloating are significantly improved (11).

The low FODMAP serving of kimchi is also much smaller than the study dose (210g). Kimchi is low FODMAP at 47g (12). 

Sourdough bread

Sourdough is a naturally leavened bread, meaning it does not use yeast or other raising agents.

Water and flour are left to ferment; this is added to more flour and you cook this resulting in sourdough.

Although there are no studies on IBS and sourdough consumption, if you suffer from IBS, you may find you can digest this bread more easily than conventional yeast risen bread.

This is because the fermentation process helps break down FODMAPs (called fructans) making it easier to digest for people with IBS to digest (13). 

Spelt sourdough is classified as low FODMAP at 2 slices (12).

For more information on the low FODMAP diet and sourdough bread, see our article Is sourdough bread low FODMAP?. 

Kefir

Kefir is a fermented milk drink from the Caucasus Mountains near the Black Sea and has been used for hundreds of years (14).

There are currently no studies looking at the effect of kefir on IBS. 

However, a pilot study looks at the effect of kefir consumption on functional constipation. 

It finds that stool frequency and stool consistency significantly improved, as well as a reduced need for laxatives in people with functional constipation (15).

For more information on kefir and IBS, see our article, Will kefir help IBS?. 

Are fermented foods bad for our gut?

No, particular fermented foods are beneficial for our gut including those with IBS.

Anecdotally, some people report symptoms of bloating or abdominal discomfort when they first start eating fermented foods. 

This bloating and discomfort is because you introduce new microbes into your system.

(15)

If this is the case for you, reduce the portion size and build up slowly. 

How can I incorporate fermented foods into my diet if I have IBS?

If you are following a low FODMAP diet, it can be hard to incorporate fermented foods into your diet. 

Some fermented foods, such as yogurt and kefir, will not be appropriate for the low FODMAP diet due to the lactose content. 

Here are some fermented foods that are low FODMAP in varying amounts:

• Miso (1 tablespoon)
• Tempeh (1 slice)
• Kimchi. (⅓ cup)
• Spelt sourdough (2 slices)

(12)

Depending what your IBS triggers are, you may want to try some of these practical suggestions too:

• Replace milk for kefir or yogurt with your cereal/granola
• Add kimchi and/or miso paste to stirfries
• opt for kombucha over other carbonated beverages
• Use kombucha as a mixer on a night out!
• Add kefir or yogurt into a smoothie
• Serve kefir or yogurt with a curry dish
• Add sauerkraut to your sandwiches

Summary

Fermented foods are produced when microorganisms, such as bacteria or yeast, are added to a food source and starved of oxygen (1). 

Fermented foods may benefit our gut health and help alleviate IBS symptoms. However, we need more research to confirm this.

You may need to avoid fermented foods if you are immunocompromised or have a histamine intolerance.

Fermented foods can easily be incorporated into your diet using the above suggestions.

 If you are following a low FODMAP diet make sure you stick to low FODMAP portions.