Why can I eat sourdough but not regular bread? The science of fermentation

October 5, 2025 •

3 min read

According to Monash University research, many people who experience digestive issues after eating regular bread are actually reacting to fructans, not gluten. The lengthy fermentation process used in traditional baking is precisely why can I eat sourdough but not regular bread?, making it a more tolerable option for sensitive guts.

Quick Summary

Traditional sourdough is often easier to digest than regular bread because its slow, natural fermentation process reduces fermentable carbohydrates (fructans) and partially breaks down gluten. This changes the bread's composition, making it more tolerable for many with sensitive stomachs or IBS.

Key Points

Long Fermentation: The slow, extended fermentation process of traditional sourdough, lasting 12-24+ hours, is key to its digestibility, unlike fast commercial bread.
Fructans, Not Always Gluten: Many people with non-celiac wheat sensitivity are reacting to fermentable carbohydrates (FODMAPs) called fructans, not necessarily gluten.
Pre-digested Fructans: Sourdough's lactic acid bacteria break down fructans during fermentation, significantly reducing the trigger for IBS symptoms like bloating and gas.
Partial Gluten Breakdown: While not gluten-free, sourdough fermentation partially hydrolyzes gluten proteins, making them potentially easier to digest for those with mild sensitivities.
Improved Nutrient Absorption: The acidic environment of sourdough fermentation activates enzymes that degrade phytic acid, improving the bioavailability of minerals like zinc, magnesium, and iron.
Beware of 'Faux' Sourdough: Many commercial sourdoughs use shortcuts like baker's yeast and additives, bypassing the beneficial long fermentation. Check ingredients for a simple list of flour, water, and salt.

The core difference: Slow vs. fast fermentation

Traditional sourdough relies on a slow, natural fermentation using a live starter culture of wild yeasts and lactic acid bacteria, often taking 12 to 24 hours. This contrasts with commercial bread, which uses fast-acting baker's yeast for a rapid rise in just a few hours. This extended fermentation period in sourdough is key to its unique properties and digestibility.

The fructan factor: The real culprit for many

Recent research indicates that digestive discomfort from wheat, for those without celiac disease, is often due to fructans rather than gluten. Fructans are FODMAPs that are poorly digested and can cause gas, bloating, and other IBS symptoms when fermented by gut bacteria. The long fermentation in sourdough significantly reduces fructan content as lactic acid bacteria 'pre-digest' them, while regular bread's rapid process does not.

Gluten modification, not elimination

Sourdough is not gluten-free and is not suitable for individuals with celiac disease. However, for those with non-celiac gluten sensitivity, the extended fermentation can partially break down gluten proteins into smaller fragments, potentially making it easier to digest for some.

The bonus of better nutrient absorption

Sourdough fermentation also enhances nutrient availability. The acidic environment created by lactic acid bacteria activates phytase, an enzyme that degrades phytic acid. Phytic acid, found in wheat flour, can hinder the absorption of minerals like zinc, magnesium, and iron. By reducing phytic acid, sourdough improves the bioavailability of these minerals.

Buyer beware: Real vs. "faux" sourdough

Authentic sourdough with digestive benefits comes from traditional, long fermentation. Many commercial products use shortcuts like adding commercial yeast, bypassing this crucial process. To identify genuine sourdough, look for simple ingredients (flour, water, salt), a distinct tangy flavor from slow fermentation, and a dense, chewy texture.

A comparative look at sourdough vs. regular bread


Feature	Traditional Sourdough	Regular Commercial Bread
Leavening	Wild yeast and lactic acid bacteria from starter	Fast-acting commercial baker's yeast
Fermentation	Slow, often 12-24+ hours	Quick, often 1-2 hours
Fructan Content	Significantly reduced due to long fermentation	High, as quick fermentation doesn't break them down
Gluten Structure	Partially broken down by lactic acid bacteria	Intact, unaltered gluten proteins
Phytic Acid	Reduced by active phytase enzyme, improving mineral absorption	High, hindering mineral bioavailability
Digestibility	Easier for many with sensitive guts or IBS	Potential trigger for digestive discomfort

Introducing sourdough into your diet

If digestive issues have led you to avoid bread, traditionally made sourdough might be a good option. Consider these tips:

Start slow: Begin with small portions to see how your body reacts before increasing.
Choose wisely: Look for artisanal bakers or bakeries emphasizing long fermentation. Check labels for minimal ingredients in pre-packaged options.
Go whole grain? Whole grains have more fiber but also higher fructans. White or spelt sourdough might be better tolerated than whole wheat initially. You can explore FODMAPs and sourdough fermentation further on the Monash University website.
Track your reaction: Monitor how you feel after eating and consider a food journal to identify your tolerance levels.

Conclusion: The slow, scientific solution

The ability to eat sourdough but not regular bread often stems from the scientific magic of long fermentation. This process, involving wild yeast and lactic acid bacteria, transforms the flour by reducing fructans, modifying gluten, and enhancing nutrient absorption. Choosing authentic sourdough means opting for a product that is often gentler on the digestive system.

Frequently Asked Questions

No, traditional sourdough is not gluten-free and is unsafe for people with celiac disease. While fermentation reduces gluten, it does not eliminate it entirely, and any trace amount can cause intestinal damage. Only sourdough made with certified gluten-free flour in a gluten-free environment is safe for celiacs.

Real sourdough uses a live starter culture and a long, natural fermentation process. Commercial sourdough often uses fast-acting baker's yeast and additives to speed production and mimic flavour, skipping the beneficial fermentation stage that breaks down irritants.

The lactic acid bacteria in the sourdough starter feed on the fructans and other carbohydrates in the flour during the long fermentation period. This 'pre-digestion' reduces the fructan content in the final bread, making it less likely to cause digestive symptoms.

FODMAPs are fermentable short-chain carbohydrates that are poorly absorbed by the gut. For sensitive individuals, gut bacteria quickly ferment these compounds, producing gas and causing symptoms like bloating, pain, and gas.

While the sourdough starter contains beneficial bacteria, the high heat of baking kills most of the live organisms. However, the fermentation process creates prebiotics and other compounds that feed the good bacteria already in your gut, supporting gut health.

Sourdoughs made from white or spelt flour are often easier to tolerate for those sensitive to fructans because these flours naturally contain lower levels of the carbohydrate compared to whole wheat or rye. However, traditional fermentation of even whole wheat sourdough still greatly reduces FODMAPs.

Look for local, artisanal bakeries and ask about their fermentation process. When buying packaged bread, check the ingredients for a simple list of flour, water, and salt. Avoid products with commercial yeast or extra additives.