What Happens to Your Blood Sugar When You Eat Sourdough Bread Regularly?

Sourdough bread is often touted as a healthier choice than other types of bread – and when it comes to blood sugar, that reputation may hold up. Although research is limited, experts say sourdough could be a smart option if you’re watching your blood sugar.

Gathering reliable evidence on the health effects of sourdough can be tricky, said Elizabeth Holt, MD, PhD, an endocrinologist at UCSF Health who specializes in treating tumors of the endocrine system. Human studies use different types of sourdough flour, all with their own microbial compositions, making comparisons difficult.

Several variables also influence blood sugar response, such as individual metabolism, portion size and what is consumed with the bread, added Beth A. Czerwony, MS, RD, CSOWM, LD, a registered dietitian at the Bariatric and Metabolic Institute and the Institute of Digestive Diseases and Surgery at the Cleveland Clinic.

However, available research indicates that sourdough is more blood sugar-friendly than some other breads.

A major factor is sourdough’s glycemic index, a scale of 0 to 100 that measures how quickly a food raises blood sugar. The GI of sourdough is around 55, compared to around 83 for bread made from 100% white wheat flour and around 75 for whole wheat barley bread.

“Eating sourdough bread in place of unfermented bread, such as white or wheat bread, may help stabilize blood sugar levels when combined with a healthy diet,” says Jessica Brantley-Lopez, MBA, RDN, dietetics internship director at the VA Hospital in Loma Linda, California.

Unlike other breads, sourdough is made with probiotics, or beneficial bacteria and yeast found in sourdough.

Although these microbes don’t survive the high heat of baking, they play a role in how sourdough affects blood sugar, said Sheri Gaw, RDN, CDCES, a California-based registered dietitian nutritionist and certified diabetes care and education specialist. During the unique sourdough fermentation process, probiotics consume some of the sugars in the flour and also produce organic acid that slows stomach emptying. This helps delay digestion and causes blood sugar to rise more gradually after eating.

Additionally, some varieties of sourdough, especially whole-grain versions, also contain fiber, which can further slow the absorption of carbohydrates and help smooth out sugar spikes, added Lorena Alarcon-Casas Wright, MD, professor of clinical practice in the division of endocrinology at UW Medicine.

Holt doesn’t suggest eating more sourdough just because it might be better for blood sugar control than other breads. “The negative impact of increased calorie and carbohydrate consumption could offset the benefits of glucose,” she said.

Additionally, she added, more human research is needed to fully understand the effects of sourdough. For example, we still do not know whether regular consumption of a refined sourdough made from white flour is better for blood sugar levels than regular consumption of whole-grain bread made from baker’s yeast.

Still, if you’re choosing between breads with otherwise similar ingredients, Holt said sourdough is probably the better option. But keep in mind that portion sizes and your overall eating habits are most important when it comes to blood sugar levels.

“A diet consisting of a variety of lean proteins, beans, legumes, fruits and vegetables is key to overall blood sugar control and longevity,” Brantley-Lopez said.