Breads · Glycemic index

Does sourdough bread spike blood sugar?

Not much in a small portion. Sourdough bread has a high GI of 70, but a 28 g serving (1 oz) has a low glycemic load of 10. Sourdough is often described as low-GI, but wheat sourdoughs averaged 70 in the 2021 tables — only a little below regular white bread. The acidity of the dough may help slightly; the type of flour matters more.

Key numbers

Glycemic index: 70; High GI
Glycemic load: 10; Low GL
Available carbs: 14 g; 0.6 g fiber
Serving: 1 oz; 28 g · fresh

GI vs GL for sourdough bread

The glycemic index (GI) compares how fast the carbohydrate in a food raises blood sugar against pure glucose (100), using a fixed amount of carbohydrate. The glycemic load (GL) adds the other half of the story — how much carbohydrate a normal serving actually contains: GI × available carbs ÷ 100. For sourdough bread: 70 × 14 g ÷ 100 ≈ 10.

That figure is an average reported in the 2021 international GI tables (“Sourdough wheat breads, mean of five foods”). Sourdough results range widely: individual wheat sourdough tests in the University of Sydney database run from 50 to 82, and a sourdough rye bread tested 48. The five-bread average is the fairest single figure.

Eating a different amount? Work out the glycemic load of your portion.

How to eat sourdough bread with less of a spike

Choose rye or wholegrain sourdough over white sourdough; a sourdough rye tested 48 and a stoneground wholemeal sourdough 59.
Cut thin slices — carbohydrate scales with the weight of the slice, and artisan loaves are easy to cut thick.
Top it with olive oil, eggs or avocado rather than jam or honey.

Lower-GI swaps

Compare with

See all 67 foods in the glycemic index table

Frequently asked questions

What is the glycemic index of sourdough bread?

Sourdough bread has a glycemic index of 70, which is high. That figure is an average reported in the 2021 international GI tables (“Sourdough wheat breads, mean of five foods”). A 28 g serving (1 oz) contains about 14 g of available carbohydrate, giving a glycemic load of 10 (low).

Is sourdough bread good for prediabetes?

Sourdough is not the blood-sugar fix it is sometimes marketed as. A wholegrain or rye sourdough is a better bet than a white sourdough loaf, and one slice with protein beats a basket of bread.

Is sourdough bread low GI?

Usually not. Five wheat sourdough breads averaged a GI of 70 in the 2021 international tables, which is in the high band. Individual loaves have tested anywhere from about 50 to 82, so some sourdoughs — particularly wholegrain and rye versions — do better.

Sources

GI values come from the international GI tables; carbohydrate and fiber per serving are calculated from USDA FoodData Central.

Data last checked September 30, 2026.