Is sourdough bread better for blood sugar than regular bread?

Yes. Sourdough bread has a GI of approximately 54, compared to around 75 for regular white bread. The fermentation process produces lactic and acetic acids that slow starch digestion and glucose absorption. Studies consistently show a 20-30% lower blood sugar response from sourdough compared to conventional white bread made from the same flour.

How many calories are in a slice of sourdough bread?

A medium slice of sourdough bread (approximately 40g) contains around 95 kcal, with 17.4g of carbohydrates and 3g of protein. This is broadly comparable to other bread types — the key advantage of sourdough is not fewer calories but a slower, lower blood sugar response due to fermentation.

Glucose: MediumNOVA 3

Nutritional Information for Sourdough Bread

Q: Is sourdough bread ultra-processed?

Authentic sourdough bread is NOVA 3 (processed), not ultra-processed. It should contain only flour, water, salt, and sourdough culture. However, some mass-produced 'sourdough-style' breads use dried sourdough powder alongside commercial yeast, emulsifiers, and dough conditioners — which would push them to NOVA 4. Always check the ingredients: a short list with recognisable ingredients indicates genuine sourdough.

Q: What is the glycemic index of sourdough bread?

Sourdough Bread has a glycemic index of 54, which is classified as Low GI. Sourdough bread has a medium GI of approximately 54 â€” substantially lower than regular white bread (GI ~75). The lactic and acetic acids produced during sourdough fermentation slow gastric emptying and modify starch structure, reducing the speed of glucose absorption. Rye and seeded sourdough variants tend to score even lower. However, it is still bread with 43g carbs per 100g, so portion control matters.

Sourdough bread is a fermented bread made with a live starter culture rather than commercial yeast. At around 238 kcal per 100g with 43g carbohydrates, it is calorie-dense like all bread — but the sourdough fermentation process gives it a genuine SpikeSaver advantage. With a medium GI of approximately 54, sourdough produces a significantly lower blood sugar response than white bread (GI ~75), thanks to organic acids produced during fermentation that slow starch digestion.

Nutrition per 100g

Nutrient	Per 100g	Per serving
Energy	238 kcal / 1007 kJ	95 kcal
Protein	7.5g	3g
Carbohydrates	43.4g	17.4g
of which sugars	2.7g	—
Fat	2.8g	1.1g
of which saturated	0.2g	—
Fibre	4.7g	—
Salt	0.78g	—

Serving size: 1 medium slice (~40g) · Source: Tesco product page, October 2025

Glucose impact

Glycemic Index

Medium

Glucose risk

Sourdough bread has a medium GI of approximately 54 — substantially lower than regular white bread (GI ~75). The lactic and acetic acids produced during sourdough fermentation slow gastric emptying and modify starch structure, reducing the speed of glucose absorption. Rye and seeded sourdough variants tend to score even lower. However, it is still bread with 43g carbs per 100g, so portion control matters.

Processing level

NOVA 2-3 (processed)

Traditional sourdough bread is made from flour, water, salt, and a live sourdough starter — all NOVA 2 culinary ingredients combined into a NOVA 3 processed food. Authentic sourdough does not require commercial yeast, emulsifiers, or preservatives. However, some supermarket 'sourdough' products use dried sourdough powder alongside commercial yeast and may include dough conditioners or emulsifiers, pushing them towards NOVA 4. Check the ingredients list: a genuine sourdough should list only flour, water, salt, and sourdough culture.

Sourdough Bread at Tesco

Source: Tesco product page, October 2025

Tesco Finest White Sourdough Loaf 400G

£1.95*NOVA 3 (processed)

Tesco Finest Rye & Mixed Seed Sourdough Loaf 400G

£1.95*NOVA 3 (processed)

Tesco Finest Part Baked White Baguettes with Sourdough 2 Pack 250g

£1.85*NOVA 3 (processed)

Jason's Recipe No 01 The Great White Straight Up Sourdough Loaf 450g

£2.15*NOVA 3 (processed)

Tesco Sourdough Bread Mix 500G

£1.00*NOVA 2 (processed culinary ingredient)

*Prices were correct at the time of collection and may have since changed. Check Tesco.com for current pricing.

What to watch for when shopping

Not all 'sourdough' at Tesco is equal. The Tesco Finest White Sourdough Loaf and Rye & Mixed Seed Sourdough are both genuine sourdough products at NOVA 3 with clean ingredient lists. The Rye & Mixed Seed variant is the better SpikeSaver choice — rye flour and seeds add fibre (6.7g/100g vs 4.7g) which further slows glucose absorption. Watch out for part-baked products which may have higher carbs (58g/100g for the baguettes). The bread mix at £1.00 is great value if you want to control the process yourself.

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