Does Sourdough Really Help With Blood Sugar? What the Science — And Our Customers — Say

If there is one question we hear more than any other at the bakery, it is this: 'Is your bread better for my blood sugar?'. It is a fair question, and as a scientist I would rather answer it honestly than sell you a slogan. So let's see what the research actually shows, where it is solid, where it is still debated, and what our own customers keep telling us.

Why sourdough should be gentler

When you eat ordinary bread, enzymes in your gut break its starch down into glucose quickly, and your blood sugar rises in a sharp spike. Sourdough changes that chemistry in a few measurable ways.

During the long fermentation, lactic acid bacteria produce organic acids — mainly lactic and acetic acid. Those acids slow the rate at which your body breaks down starch into glucose, and they in turn lower the pH in the small intestine. This lower pH dampens the activity of the enzyme α-amylase responsible for digesting starch. Fermentation also increases resistant starch, a slow-digesting fraction that behaves more like fibre than sugar. In a 2021 study in the journal Foods, researchers baked eight sourdough breads under different conditions and measured starch digestion directly. The best loaf — whole wheat, fermented in warm conditions with selected strains — showed nearly a 30% lower estimated glycemic index than ordinary bread, with resistant starch reaching around 16 grams per 100 grams.

In plain terms: the acid in real sourdough acts as a natural brake on the blood-sugar spike. Energy is released more gradually.

The honest part

Here is where I will be straight with you, because you deserve it. A lot of that evidence comes from laboratory and test-tube measurements. When researchers look specifically at human trials, the picture is more mixed. A careful 2023 review in Frontiers in Nutrition found that the clinical data on sourdough and glycemic index are inconsistent — some studies show a benefit, some show none — and concluded the effect is not yet firmly proven in people. Other factors, like the type of grain, how coarse the flour is, and how much fibre the loaf contains, can matter as much as the fermentation itself.

So I will not tell you our bread lowers anyone's blood sugar. What I can tell you is that the mechanism is real and well described, and that slowly fermented bread is exactly the kind the mechanism favours.

What our customers keep telling us

This is where the story gets personal. Many of you have told us that your blood sugar does not spike after eating our Extended Fermentation Sourdough the way it does after ordinary bread. A number of you have gone further and tracked your HbA1c — the measure of how well blood sugar has been managed over the previous two to three months — and seen it drop after switching to our bread.

Those are not controlled clinical trials, and I would never dress them up as one. But they are real experiences, from real people, and they line up beautifully with what the science predicts should happen. When the mechanism and the lived experience point the same way, that is worth paying attention to.

If you are managing your blood sugar, this is not medical advice, and your own doctor knows your numbers better than a loaf of bread does. But if you would like to try the difference for yourself, our Extended Fermentation Sourdough is the one to start with — no added sugar, high in acid, and made the slow way for exactly this reason.

Sources: Demirkesen-Bicak et al. (2021), Foods, 10(3), 514. D'Amico et al. (2023), Frontiers in Nutrition, 10, 1230043. Arora et al. (2021), Trends in Food Science & Technology, 108, 71–83.