Sourdough bread glycemic index and glycemic load
Sourdough bread has a high glycemic index of 72 (the median of 4 lab tests, range 54 to 82) in the 2021 International Tables, where pure glucose is 100. A serving of 1 oz (28 g) has 14.1 g of carbs minus fiber, which gives a glycemic load of about 10.
Glycemic load by portion
| Portion | Carbs | Fiber | Carbs minus fiber | Glycemic load |
|---|---|---|---|---|
| 1 oz (28 g) | 14.7 g | 0.6 g | 14.1 g | 10 |
Glycemic load = GI 72 × carbs minus fiber ÷ 100. Carbs from USDA FoodData Central, Bread, french or vienna (includes sourdough). USDA lists sourdough together with French and Vienna bread.
Every standardized test
| Food as tested | GI | Category | Country |
|---|---|---|---|
| Sourdough wheat bread | 54 | low | Australia |
| Sourdough Vienna bread, Bakers Delight™ (Bakers Delight Holdings, Australia) | 66 | medium | Australia |
| Sourdough Cob Bread (Fine Breads of Australia, NSW, Australia) | 77 | high | Australia |
| Sourdough bread (50% whole wheat wheat, 50% white wheat, sourdough starter (70% wet weight), 80... | 82 | high | New Zealand |
The tables' own average for this food: 70 (mean of five foods).
Glucose = 100. Low 55 or less, medium 56 to 69, high 70 or more (category cut-offs from the International Tables). Only tests that followed the ISO 26642:2010 method: at least 10 healthy adults, a portion with 25 or 50 g of available carbs (Supplemental Table 1).
Compared with similar foods
| Food | GI | Portion | Carbs minus fiber | Glycemic load |
|---|---|---|---|---|
| Corn tortilla | 49 | 1 oz (28 g) | 10.9 g | 5 |
| Pita bread | 62 | 1 pita, large (2.1 oz, 60 g) | 32.1 g | 20 |
| White bread | 71 | 1 slice (1 oz, 27.3 g) | 12.8 g | 9 |
| Sourdough bread | 72 | 1 oz (28 g) | 14.1 g | 10 |
| Whole wheat bread | 75 | 1 slice (1.1 oz, 32.1 g) | 11.9 g | 9 |
Same group in the International Tables (Bread), each at its usual US portion. A low GI with a big portion can give a higher glycemic load than a high GI with a small one.
How much the glycemic index tells you
Researchers and health bodies do not agree on how much weight to give the glycemic index of single foods.
- Level E The World Health Organization examined the glycemic index, found it inconsistent, and refused to build guidance on it. Carbohydrate intake for adults and children: WHO guideline, 2023
- Level C A year after the World Health Organization set the glycemic index aside, a meta-analysis of cohorts each over a hundred thousand people linked high glycemic index diets to more diabetes, heart disease and death. Lancet Diabetes & Endocrinology, 2024
- Level C Glycemic index and glycemic load, the other two ways of judging carbohydrate, held up far worse than fiber in the same analysis. Reynolds et al., The Lancet, 2019
What studies found about sourdough bread and blood sugar
- Level A A 2026 systematic review of 27 studies in healthy people judged the evidence that sourdough beats yeast bread for blood glucose and insulin as neither sufficient nor convincing. Frontiers in Nutrition, 2026
- Level B After 6 weeks, whole grain wheat sourdough bread lowered the glucose response to a glucose drink by 19% versus white bread in adults with high glucose and insulin, without changing fasting values. Nutr Metab Cardiovasc Dis, 2012
- Level B Whole wheat bread made with 10% sourdough had a glycemic index of 50 to 56 with most starters, against 70 for the same bread without sourdough. Int J Food Sci Nutr, 2011
- Level B In 24 adults, sourdough rye crispbread lowered hunger versus refined wheat crispbread, but unfermented rye gave the lowest insulin response, partly because fermentation broke down viscous fiber. Br J Nutr, 2017
- Level E The EU did not authorize a claim that high-fiber sourdough rye bread reduces after-meal glucose responses. EU Register on nutrition and health claims, claim POL-HC-8470, snapshot 2026-09-21
Some studies above score foods against white bread, not glucose, as 100, so their numbers are not on the same scale as the ones at the top of this page. Levels: A is a meta-analysis of trials, B a randomized trial, C an observational study, D lab or animal work, E an expert position. How we grade evidence.
Keep exploring
Sources
- Atkinson FS, Brand-Miller JC, Foster-Powell K, Buyken AE, Goletzke J. International tables of glycemic index and glycemic load values 2021: a systematic review. Am J Clin Nutr 2021;114(5):1625-1632, Supplemental Table 1, PMID 34258626, doi:10.1093/ajcn/nqab233 (accessed 2026-10-12)
- USDA FoodData Central, SR Legacy (2018): Bread, french or vienna (includes sourdough), FDC ID 172675
- USDA FoodData Central, SR Legacy (2018): Tortillas, ready-to-bake or -fry, corn, FDC ID 175036
- USDA FoodData Central, SR Legacy (2018): Bread, pita, white, enriched, FDC ID 174915
- USDA FoodData Central, Foundation Foods (release 2025-12-18): Bread, white, commercially prepared, FDC ID 325871
- USDA FoodData Central, Foundation Foods (release 2025-12-18): Bread, whole-wheat, commercially prepared, FDC ID 335240
- Evidence cards: each study above links to its source. Card review dates are listed in our methodology.
Sources checked 2026-10-12. Bioma Learn provides information, not medical advice.