Understanding Sourdough and FODMAPs
For those following a low FODMAP diet, navigating bread can be challenging. Many traditional breads are off-limits during the elimination phase because they contain high levels of fructans, a type of fermentable carbohydrate. However, sourdough bread is a notable exception due to its unique preparation method. Unlike commercial breads that use quick-acting yeast, authentic sourdough relies on a slow, natural fermentation process. This allows the beneficial bacteria and wild yeasts in the starter to break down the fructans in the flour, resulting in a finished product with a significantly lower FODMAP content. This is great news for individuals with Irritable Bowel Syndrome (IBS) or other digestive sensitivities who miss enjoying a piece of toast or a sandwich. Not all sourdough is created equal, and the low FODMAP status and serving size are highly dependent on the flour used and the duration of fermentation.
Low FODMAP Sourdough Serving Sizes by Type
The most authoritative source for low FODMAP guidance is Monash University in Australia, which has laboratory-tested various sourdough varieties. Their research reveals specific serving sizes for different types of sourdough that are considered low FODMAP. These portion sizes are critical for managing symptoms, as consuming larger amounts may introduce a higher level of FODMAPs that could trigger digestive distress. It's always a good idea to cross-reference with the latest Monash University FODMAP app for the most current information.
White Wheat Sourdough
Based on Monash University's testing, a low FODMAP serving of white wheat sourdough is up to two slices, or approximately 109 grams. This makes it a great option for a satisfying sandwich or toast for breakfast. The long fermentation of the wheat flour effectively reduces the fructan content to a manageable level for most people on the low FODMAP diet.
Wholemeal Wheat Sourdough
Similar to its white counterpart, wholemeal wheat sourdough also has a generous low FODMAP serving size. The tested amount is also two slices, weighing around 97 grams. The sourdough process works just as well on wholemeal flour to reduce the fructan load, allowing for a higher-fiber option.
Spelt Sourdough
Sourdough made from spelt flour is another excellent low FODMAP choice. The recommended serving size is two slices. If purchasing spelt sourdough, it's beneficial to confirm that it is made with 100% spelt flour, as some varieties may mix with other high-FODMAP flours. Spelt itself is often better tolerated than modern wheat, and the sourdough process makes it even more gut-friendly.
Oat Sourdough
Not all sourdoughs are equal, and oat sourdough is a clear example. While the process still helps, the low FODMAP serving size for oat sourdough is notably smaller—only one slice, or about 26 grams. Consuming two slices would introduce a moderate level of GOS (a type of FODMAP), which could cause symptoms. This emphasizes the need to be mindful of the specific ingredients and portion sizes.
Sourdough Varieties to Avoid
On the other end of the spectrum, certain flours, even when prepared as a sourdough, are still high in FODMAPs. This includes rye sourdough and kamut sourdough, which are typically high in fructans and should be avoided during the elimination phase of the diet.
The Crucial Role of Long Fermentation
The magic behind low FODMAP sourdough lies in the fermentation. The traditional, long-fermentation process allows the lactobacilli and yeast in the starter culture to metabolize and break down the carbohydrates in the flour. Specifically, they consume the fructans. This process doesn't happen with the rapid-rise yeast used in most commercial breads, which is why those products are typically high FODMAP. A genuine sourdough can take anywhere from 12 to 24 hours to ferment and rise properly. This extended timeframe is what gives the microorganisms ample opportunity to do their work. A shorter rise, even with a sourdough starter, may not be sufficient to reduce the FODMAP content to a safe level. For this reason, homemade sourdough with a proven long-fermentation technique or certified brands offer the greatest assurance of low FODMAP status. For more detailed information on FODMAP testing, consider visiting the Monash University FODMAP website.
Comparing Sourdough and Standard Bread on a Low FODMAP Diet
| Feature | Low FODMAP Sourdough Bread (Wheat/Spelt) | Standard Commercial Bread (Wheat) |
|---|---|---|
| Key Ingredient | Wheat or spelt flour | Wheat flour |
| Leavening Agent | Slow-fermenting starter culture | Fast-acting commercial yeast |
| FODMAP Content | Low in fructans due to long fermentation | High in fructans, which are not broken down sufficiently |
| Low FODMAP Serving Size | 2 slices (approx. 97-109g) | 1 slice (approx. 24g) |
| Digestibility for IBS | Often well-tolerated during elimination phase | Likely to cause symptoms due to high fructan load |
| Best Practice | Check for certification or confirm long fermentation | Stick to small, measured portions if tolerated |
Practical Tips for Sourdough on a Low FODMAP Diet
Beyond knowing the serving sizes, there are other practical considerations when incorporating sourdough into your diet. First, if buying from a store, look for certified low FODMAP products. Both Monash University and the FODMAP Friendly program certify products that meet their low FODMAP criteria, and this is the most reliable way to ensure you're getting a safe product. Second, if baking your own sourdough, use a reputable recipe that specifies a long, slow fermentation time. Finally, always listen to your body. Even with the tested low FODMAP servings, individual tolerance can vary. When reintroducing sourdough, start with a small portion and see how you react before increasing your intake. The ultimate goal is to find what works best for your unique digestive system.
Conclusion
For many on a low FODMAP diet, the question of "how many slices of sourdough bread is low in FODMAP" has a welcome answer. Two slices of traditional wheat or spelt sourdough bread are generally considered safe during the elimination phase, as confirmed by Monash University's testing. This is thanks to the long fermentation process, which naturally reduces the fructan content. It is crucial, however, to be aware of the flour type, as oat sourdough has a smaller safe serving size of one slice, and some varieties like rye should be avoided. By focusing on certified low FODMAP options, understanding the role of fermentation, and paying attention to individual tolerance, you can safely enjoy this delicious and gut-friendly bread.
