Is Sourdough Keto?

The Ingredient Breakdown

To understand why sourdough fails the keto test, we need to look at the flour used. The primary ingredient in almost all commercial sourdough is enriched wheat flour. This is a refined carbohydrate that acts as the primary fuel source for the yeast during fermentation. While the fermentation process (using fermented wheat flour and yeast) does lower the bread's glycemic index by consuming some of the sugars and producing lactic acid, it does not eliminate the starches. These starches are complex chains of glucose, which your body breaks down into sugar, spiking insulin and disrupting ketosis.

Additionally, ingredients like wheat gluten are added to improve texture and rise. While gluten itself is a protein, it is inextricably bound to the carbohydrate-heavy starch in the wheat kernel. You cannot separate the gluten from the carbs in a standard loaf. Therefore, every slice of sourdough comes with a heavy load of net carbs that is incompatible with a keto lifestyle.

Nutritional Value

A standard slice of sourdough bread typically contains between 15 to 20 grams of net carbohydrates. On a keto diet, the daily limit is usually around 20 to 50 grams of net carbs. Eating just one slice could consume nearly your entire carb allowance for the day, leaving no room for vegetables or other nutrient-dense foods. Furthermore, while sourdough is often praised for being lower in sugar than other breads, the enriched wheat flour is essentially a complex sugar once digested. It provides a quick burst of energy followed by a crash, which is the exact blood sugar rollercoaster the keto diet aims to avoid. It is also relatively low in fat, which is the opposite of what a keto diet requires for energy.