NUTRITION HOTLINE
By Reed Mangels, PhD, RD
QUESTION: Like many others, I've been making sourdough bread since the start of the pandemic. My family is vegan and we wondered if there was any nutritional advantage to sourdough bread.
S.F., via emailM
ANSWER: The main nutritional advantage associated with sourdough breads compared to quick breads (like biscuits and banana bread) and to yeast-raised breads is that some minerals are better absorbed from sourdough breads. To appreciate this advantage, it helps to be familiar with phytates.
Phytates are substances found in whole grains, legumes, seeds, nuts, and vegetables. They are a storage form of the phosphorus which a plant needs to grow. Humans are not able to digest phytates. Phytates in plants firmly attach to minerals. Our digestive system is not able to digest phytates and is not able to remove the minerals from the phytate-mineral complex. That means that those minerals can't be absorbed or that they are poorly absorbed.
Iron and zinc absorption are especially affected by dietary phytates, but phytates can also reduce the absorption of calcium, magnesium, and copper. When wheat flour is refined, most of the phytates are removed but so are many of the minerals. Thus, using refined (white or all- purpose) flour is not a solution to the reduced mineral absorption from whole grain flour. Besides, many people feel breads made with whole wheat and rye flour taste better.
When sourdough bread is made, wild yeasts and bacteria work together to leaven the dough and to create an acidic environment that is hostile to other bacteria and yeast. The acidic environment appears to allow naturally occurring enzymes in the flour to break down the phytates in the flour. 1 When the phytates are broken down, the minerals, including iron and zinc, that were attached to the phytates are released. This means that we can absorb these minerals. The long fermentation time typical of sourdough production gives the enzymes time to break down the phytate-mineral complexes.
Sourdough fermentation has been shown to be more effective than yeast fermentation in reducing the effect of phytates. In one study, sourdough fermentation reduced the phytate content of whole wheat bread by 62% compared to a 38% reduction with yeast fermentation. 2
REFERENCES:
1 Reale A, Konietzny U, Coppola R, Sorrentino E, Greiner R. The importance of lactic acid bacteria for phytate degradation during cereal dough fermentation. J Agric Food Chem. 2007;55(8):2993-2997.
2 Lopez HW, Krespine V, Guy C, Messager A, Demigne C, Remesy C. Prolonged fermentation of whole wheat sourdough reduces phytate level and increases soluble magnesium. J Agric Food Chem. 2001;49(5):2657-2662.
