No, people on gluten-free diets currently cannot safely eat sourdough breads made with wheat, rye or barley flour, even if they are fermented. The good news is that researchers have discovered that "fully fermented" sourdough baked goods, made with a specialty wheat flour treated with specific good bacteria and enzymes did not have toxic effects on a small group of Celiacs participating in a recently published study.
The Italian study was designed to assess how 13 Celiacs responded to eating baked goods made with wheat flour treated with lactobacilli and fungal protease. The study, Safety for Patients with Celiac Disease of Baked Goods Made of Wheat Flour Hydrolyzed During Food Processing was published in the January 2011 issue of the journal Clinical Gastroenterology and Hepatology.
The wheat flour used to prepare the baked goods for the study was "manufactured with sourdough lactobacilli and fungal proteases." Lactobacilli is a "friendly" bacteria. A form of lactobacilli, lactobacillus acidophilus is commonly used to ferment yogurt. Fungal proteases are groups of enzymes that break down (hydrolyze) the bonds that hold large protein molecules together. Gluten is a large protein molecule.
The 13 study participants had confirmed Celiac disease and were divided into 3 groups. Each group was fed 200 grams (about 7 ounces) of baked goods a day. The baked goods were prepared from specialty wheat flour treated (hydrolyzed) with sourdough lactobacilli and fungal proteases and finally, the baked goods were prepared three different ways:
- "Natural flour baked goods which contained 80,127 ppm gluten"
- "Extensively hydrolyzed flour baked goods which contained 2480 ppm residual gluten"
- "Fully hydrolyzed baked goods which contained 8 ppm residual gluten"
PPM = parts per million of gluten in the sample food. The FDA has not yet ruled on gluten-free labeling but may eventually follow the European Union's lead and allow 20 ppm gluten in foods labeled gluten-free. This is a level that is believed to be safe for most, but not all Celiacs.
Five participants ate 200 grams of baked goods made from "fully hydrolyzed wheat flour for 60 days." This group of Celiacs exhibited no signs of gluten toxicity. Methods used to assess gluten damage in the participants included anti–tissue transglutaminase antibody blood tests and small bowel biopsy.
Participants that ate the baked goods prepared with "natural flour" and "extensively hydrolyzed flour" suffered varying degrees of gluten toxicity. Some participants had to drop out of the study due to adverse reactions to gluten.
The findings of this study and others like it are encouraging but larger studies are needed to confirm that specially treated wheat flour can be used to prepare safe baked goods for people with gluten intolerance, Celiac disease and dermatitis herpetiformis.
The study was small with only 13 participants and methods used to assess gluten damage in the participants -- blood tests for anti–tissue transglutaminase antibodies and small bowel biopsy have potential for false negative results. This means that these tests have potential to miss these markers of gluten toxicity.
A good explanation of how this happens comes from Dr. Dennis Lee, Medical Editor at MedicineNet.com. "Patients with deficiency of one type of antibody, IgA (they are born that way) will have low endomysial antibodies and anti-tissue transglutaminase antibodies since they are IgA-type antibodies."
"Patients who have self-treated themselves with a gluten-free diet for weeks to months before having these tests done can have abnormal blood tests revert to normal."
Based on the findings of this study, fermented sourdough bread prepared with ordinary, grocery store wheat flour and baker's yeast should not be eaten by Celiacs or people with gluten intolerance or dermatitis herpetiformis.
Researchers at the Department of Food Science, Food Technology and Nutrition, National University of Ireland, Cork, Ireland say, "The use of sourdough in GF baking may be the new frontier for improving the quality, safety and acceptability of GF bread."
Again, this is great news but it does not mean that we can safely bake, buy or eat sourdough bread with any assurance that it contains low, non-toxic levels of gluten. Hopefully, soon we can!
Read the Study Abstract: