While sourdough might seem like just another type of bread you can make or buy, it actually used to be one of the only options. Until the development of commercial yeasts in the 1800s, sourdough, made with naturally occurring yeasts and lactic acid bacteria, was the main type of leavened bread consumed worldwide.

Sourdough undergoes natural fermentation rather than relying on additives found in baker’s yeast. This means that compared to other breads, it is easier to digest, has less of an impact on blood sugar, and is potentially more nutritious.

The fermentation process used to create sourdough helps to degrade gluten, a protein found more heavily in grains such as wheat, barley, and rye that is resistant to digestion.

In addition to lower levels of gluten, sourdough has lower levels of other compounds known to cause gastrointestinal issues, including FODMAPs, phytates, tannins, and trypsin inhibitors.

This means that sourdough may be easier to digest and result in fewer gastrointestinal symptoms compared to commercially leavened bread. A 2023 review of 25 studies bears this out, showing that people reported significant improvements in gastrointestinal comfort switching from bread made with baker’s yeast to sourdough bread.

The fermentation process used to make sourdough produces organic acids, such as lactic and acetic acids, which help slow the absorption of starch in the digestive tract. When food is digested slowly, glucose is released more gradually into the bloodstream, preventing a significant spike in blood sugar levels after eating.

This means that compared to other breads, sourdough is low on the glycemic index (GI), a classification system that ranks carbohydrate-rich foods on a scale of 0-100 according to their impact on blood sugar levels. The GI estimates how quickly food is digested and absorbed into the bloodstream.

The GI for a 30-gram (g) serving of bread made with white wheat flour is 71, while the GI for a 30g serving of sourdough bread is 54.

Anti-nutritional factors found in whole wheat or grain breads, such as phytates, tannins, and trypsin inhibitors, can make it harder to absorb nutrients from food. Phytates, in particular, are able to bind to minerals like magnesium, calcium, and iron, blocking their absorption in the digestive tract.

The fermentation process used to make sourdough breaks down anti-nutritional factors like phytates. In fact, some studies suggest that certain sourdough formulations can degrade over 96% of the phytic acid in the dough.

Here’s the nutrition breakdown for a medium-sized 59-gram slice of sourdough made with enriched white flour:

• Calories: 188
• Carbs: 36.5 grams (g)
• Fiber: 1.8 g
• Protein: 7.67 g
• Fat: 1.26 g
• Iron: 2.28 milligrams or 13% of the Daily Value (DV)
• Copper: 0.088 mg or 10% of the DV
• Folate: 82.6 micrograms (mcg) or 21% of the DV
• Thiamine: 0.252 mg or 21% of the DV
• Niacin: 3.17 mg or 20% of the DV
• Riboflavin: 0.218 mg or 17% of the DV
• Manganese: 0.33 mg or 14% of the DV
• Selenium: 17.5 mcg or 32% of the DV
• Zinc: 0.619 mg or 6% of the DV

While sourdough contains less gluten than other breads made with wheat flour, it’s not gluten-free and isn’t safe for people with celiac disease or those who are sensitive to gluten-containing foods.

If you’d like to enjoy sourdough but can’t eat gluten, choose a gluten-free sourdough product. Gluten-free sourdough bread is made with gluten-free flours such as those made with millet, sorghum, teff, quinoa, and buckwheat. Keep in mind that gluten-free sourdough will have a different texture than sourdoughs made with wheat flour, as gluten adds a chewy and airy texture to baked goods.

Sourdough is a tangy-tasting bread made with naturally occurring yeasts and lactic acid bacteria. 

Studies show that sourdough has less of an impact on blood sugar levels compared to refined breads made with baker’s yeast and may be easier to digest as it contains lower levels of gluten, FODMAPs, and anti-nutrient compounds.

Nutrition varies depending on ingredients used, but most sourdough provides a good source of several vitamins and minerals, including B vitamins and selenium. 

Though sourdough makes a healthy choice for most people, those who need to avoid or restrict gluten, such as people with celiac disease and gluten intolerance, should avoid sourdough made with gluten-containing flours.