Sourdough bread is often promoted as a healthier choice than other bread types—and when it comes to blood sugar, that reputation may hold up. Though research is limited, experts said sourdough could be a smart option if you’re watching your blood glucose.
Gathering reliable evidence on sourdough’s health effects can be tricky, said Elizabeth Holt, MD, PhD, a UCSF Health endocrinologist who specializes in treating tumors of the endocrine system. Human studies use different types of flour for sourdough starters, all with their own microbial compositions, making comparisons difficult.
Multiple variables also influence blood sugar response, such as individual metabolism, portion size, and what’s consumed alongside the bread, added Beth A. Czerwony, MS, RD, CSOWM, LD, a registered dietitian at the Bariatric and Metabolic Institute and Digestive Disease and Surgery Institute at Cleveland Clinic.
Still, the available research does point to sourdough being more blood sugar-friendly than some other breads.
A major factor is sourdough’s glycemic index, a scale from 0 to 100 that measures how fast a food raises blood glucose. Sourdough’s GI is around 55, compared to about 83 for bread made from 100% white wheat flour and around 75 for barley whole-wheat bread.
“Eating sourdough bread in place of non-fermented bread, such as white or wheat, can help stabilize blood sugars when paired with a healthy diet,” said Jessica Brantley-Lopez, MBA, RDN, dietetic internship director at the VA Hospital in Loma Linda, California.
Unlike other breads, sourdough is made with probiotics, or beneficial bacteria and yeasts in the starter.
Although these microbes don’t survive the high heat of baking, they do play a role in how sourdough affects blood sugar, said Sheri Gaw, RDN, CDCES, a California-based registered dietitian nutritionist and certified diabetes care & education specialist. During sourdough’s unique fermentation process, the probiotics consume some of the sugars in the flour and also produce organic acid that slows stomach emptying. This helps to delay digestion and leads to a more gradual rise in blood sugar after eating.
Additionally, certain sourdough varieties, especially whole-grain versions, also contain fiber, which can further slow the absorption of carbohydrates and help blunt sugar spikes, added Lorena Alarcon-Casas Wright, MD, a professor of clinical practice in the division of endocrinology at UW Medicine.
Holt doesn’t suggest eating more sourdough solely because it might be better for glucose control than other breads. “The negative impact of increased intake of calories and carbohydrates might offset any benefits to glucose,” she said.
Plus, she added, more human research is needed to fully understand sourdough’s effects. For example, it’s still unclear whether regularly eating a refined white-flour sourdough is any better for blood sugar than consuming a whole grain bread made with baker’s yeast on a routine basis.
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 size and your overall eating pattern matter most when it comes to blood sugar.
“A diet that has a variety of lean proteins, beans, legumes, fruits, and vegetables is key to overall blood sugar control and longevity,” Brantley-Lopez said.
