Nutrition and diet

Sourdough

Also called: sourdough bread, naturally leavened bread

Sourdough is bread made with a starter of wild yeast and lactic acid bacteria instead of commercial yeast. The 12 to 24 hour fermentation breaks down most of the fructans (a FODMAP) in wheat, lowers the glycaemic response, and produces flavour acids. It is NOT gluten-free, but most people with non-coeliac wheat sensitivity tolerate it. Coeliacs cannot have it.

How sourdough differs from regular bread

  • Leavening: wild yeast plus Lactobacillus from a starter, not commercial yeast.
  • Fermentation: 12 to 24 hours minimum, often 36 to 48.
  • Bacterial activity breaks down fructans, phytic acid, and a fraction of gluten.
  • Lower post-meal glucose response than yeast bread of the same flour.
  • More flavour complexity from lactic and acetic acids.
  • Many supermarket 'sourdoughs' are not real sourdough, they use commercial yeast plus added vinegar for flavour. Look for 'naturally leavened' or 'wild yeast'.

Why people with wheat sensitivity often tolerate it

Most non-coeliac wheat sensitivity is actually fructan sensitivity, not gluten sensitivity. Fructans are short-chain carbohydrates classified as FODMAPs. Long sourdough fermentation reduces fructan content by 70 to 90 percent. So the bread that triggered bloat in regular form often does not in proper sourdough.

What sourdough is not

  • Not gluten-free. The bacteria break down some gluten but not all. Coeliacs cannot have it.
  • Not low-carb. Sourdough has the same calories per slice as other bread.
  • Not always healthier, depends on the flour. Wholegrain sourdough is meaningfully better than refined; white sourdough is similar to white yeast bread.
  • Not necessarily probiotic. Baking kills the live bacteria. Benefits come from the fermentation BEFORE baking.

How to spot real sourdough

  1. Ingredients: just flour, water, salt and starter. No commercial yeast.
  2. Heavy crust, open crumb with irregular holes.
  3. Tangy, slightly acidic flavour.
  4. Bakes well at home with about 20 minutes of hands-on time per loaf if you have a starter.

Common questions

Can people with IBS eat sourdough?
Most can, especially in moderate portions. The reduced fructan content makes it lower-FODMAP than regular wheat bread. Monash has tested several sourdoughs and rated traditional white sourdough as low-FODMAP at 1 to 2 slices.
Is sourdough OK for coeliacs?
No. Despite reduced gluten content, residual gluten remains well above the 20 ppm coeliac threshold. Specifically certified gluten-free sourdough exists but is rare.
Does sourdough spike blood sugar less?
Yes, modestly. Studies show 20 to 30 percent lower post-meal glucose vs equivalent yeast bread. The lactic acid in sourdough slows starch digestion.
Are supermarket sourdoughs real?
Most are not. UK supermarkets sell 'sourdough-style' bread made with commercial yeast plus vinegar or lactic acid. Real sourdough is from independent bakeries or made at home. Check ingredients for the absence of yeast.

Sources