Is sourdough bread low carb?

Sourdough bread has become increasingly popular in recent years, partially due to claims that it has a lower glycemic index and may be a better choice for people monitoring their carbohydrate intake. But is sourdough bread actually low carb? Here’s a comprehensive look at the carb content of sourdough bread and how it compares to other breads.

What is sourdough bread?

Sourdough bread is made using a fermented starter dough that contains wild yeast and bacteria. This starter dough helps create sourdough bread’s signature tangy flavor and allows the bread to rise without the need for commercial yeast. The fermentation process also breaks down some of the gluten in the wheat flour, making sourdough bread easier to digest for some people.

Traditional sourdough starters take days or even weeks to ferment and develop complex flavors. Many modern commercial bakeries now use faster methods to make sourdough breads quickly, but they may lack some of the complex flavor and health benefits of traditionally fermented sourdough.

Carb and calorie content of sourdough bread

Like most breads, the main calories in sourdough come from carbohydrates. A 1-ounce slice (about 28g) of sourdough bread contains approximately:

  • Calories: 75-80
  • Total carbohydrates: 15-17g
  • Fiber: 1-2g
  • Sugars: 1-2g
  • Protein: 2-3g

This carb count is quite similar to most other breads. For example, one slice of white bread also contains about 15-17g total carb and 75-80 calories.

So despite its unique flavor and texture, sourdough bread is not significantly lower in total carbs or calories compared to other breads.

Does the glycemic index matter?

The glycemic index (GI) measures how quickly a food causes spikes in blood sugar. Foods with a high GI cause rapid spikes, while low GI foods cause a more gradual rise.

Some research indicates that sourdough bread has a lower GI than other breads, possibly because the fermentation process breaks down more of the starch. The glycemic index of sourdough bread can vary but often falls in the low to moderate range:

  • White sourdough bread: GI 54-56
  • Whole wheat sourdough bread: GI 45-53

In comparison, regular white bread scores at a GI of about 70-75. This suggests sourdough bread may be slightly preferable for blood sugar control compared to some other breads.

However, glycemic index is just one measurement. The total carb content of a food still matters most when calculating daily carb intake.

Net carbs in sourdough bread

Net carbs refer to the grams of total carbohydrate minus grams of fiber. Because fiber is not digested and absorbed, net carbs give a more accurate idea of a food’s real-world impact on blood sugar.

An average 1-ounce slice of sourdough bread contains about:

  • Total carbs: 15-17g
  • Fiber: 1-2g
  • Net carbs: 14-15g

So sourdough bread contains only 1-2g less net carbs than total carbs per slice. This negligible difference means sourdough is not actually very low in net carbs compared to other bread options.

How many carbs are in a serving of sourdough bread?

Here are the carb counts for standard serving sizes of sourdough bread:

Serving Total carbs Net carbs
1 slice (1 oz) 15-17g 14-15g
1 medium slice (1.5 oz) 22-26g 21-23g
1 large slice (2 oz) 30-34g 28-30g

As you can see, carb content adds up quickly if eating larger servings or multiple slices. Two medium-sized slices would contain over 40g total carbs.

Sourdough bread glycemic load

Glycemic load accounts for both the GI and the carb content in a given serving of food. It provides a more practical look at how the food impacts blood sugar in real-life portions.

Glycemic load is calculated by multiplying the grams of carbohydrate in a serving by the food’s GI score. Compared to regular white bread with a high GI of 75:

  • 1 slice white bread has a glycemic load around 13.
  • 1 slice sourdough bread has a glycemic load around 8.

This indicates that sourdough bread in typical serving sizes has a mildly lower glycemic load than regular bread. However, both bread types are still high glycemic load foods overall.

Sourdough bread and the keto diet

The keto diet restricts net carbs to 20-50g per day to achieve ketosis. This carb count includes all sources, not just bread.

With 14-15g net carbs in one slice, sourdough bread can quickly use up a large portion of a keto dieter’s daily carb allowance. Eating two or three slices could easily knock someone out of ketosis.

Low-carb diets like keto emphasize nutrient-dense whole foods over processed grain products. So breads of any kind are very restricted on keto, even if technically low enough in carbs to fit into daily macros.

Sourdough compared to other breads

How does sourdough bread compare to other breads in terms of carb content?

Here are the net carbs for 1-ounce slices of different breads:

Bread type Net carbs
White 15g
Wheat 13g
Sourdough 14-15g
Rye 12g
Pumpernickel 14g
Gluten-free 18g

Most breads contain a similar carb content per slice. Sourdough is comparable to wheat, white, and pumpernickel bread. The only minor differences come from the addition of fiber-rich ingredients like whole grains or seeds in some breads.

Tips for lowering carbs in bread

There are some ways to reduce the carb content when enjoying bread:

  • Choose thin slices instead of thick cut bread.
  • Opt for small or medium slices rather than large pieces.
  • Look for lower-carb gluten-free bread options under 15g net carbs.
  • Create “open-faced” sandwiches on just one slice of bread.
  • Use lettuce wraps or keto “buns” made of fathead dough instead of bread.

Health benefits of sourdough bread

Despite not being very low carb, sourdough bread does offer some potential health benefits:

  • Lower glycemic response – The fermentation may improve the bread’s glycemic profile.
  • Increased digestibility – The process breaks down gluten and starches, making it easier to digest for some.
  • Probiotics – Traditionally fermented sourdough contains probiotic bacteria that support gut health.
  • Nutrient bioavailability – Sourdough bread may make nutrients like iron, zinc, and B vitamins more available for absorption.
  • Antioxidants – Sourdough develops antioxidants during fermentation that fight inflammation and oxidative stress.

However, processed commercial sourdough bread made with yeasts and additives likely loses many of these benefits compared to authentic sourdough.

Sourdough bread recipes

Traditional sourdough recipes use just flour, water, salt, and the starter culture. But many modern recipes incorporate ingredients for flavor and texture:

  • Whole wheat – Adds a hearty, nutty taste with extra fiber.
  • Rye or pumpernickel – Imparts a dark color and rich flavor.
  • Seeds – Top with poppy, sesame, or caraway seeds for crunch.
  • Herbs – Mix in rosemary, thyme, or garlic for an aromatic bread.
  • Olives, sun-dried tomatoes – Knead in chopped olives, tomatoes, or other savory ingredients.

The additions above can provide more nutrients and fiber. But be mindful that ingredients like seeds, nuts, and dried fruit will also add more carbs to the final bread.

Is sourdough keto-friendly?

Sourdough bread is not keto-friendly and should be avoided on a ketogenic diet. A few slices could use up your entire carb allowance for the day.

Many keto bread recipes mimic the taste and texture of bread using alternative low-carb ingredients:

  • Almond flour – Ground almonds make grain-free, low-carb flour.
  • Coconut flour – Very high fiber flour substitutes for wheat.
  • Psyllium husk – Adds fiber and gives a chewy texture.
  • Xanthan gum – Helps bind and give structure to baked goods.
  • Fathead dough – Cheese and egg based dough can be shaped into buns or pizza crust.

These creative recipes allow keto dieters to enjoy “bread” and sandwiches without going over their carb limits.

Low-carb sourdough alternatives

Some low-carb packaged bread alternatives provide a sourdough taste with fewer net carbs:

  • ThinSlim Foods Bakery On Main Sourdough Bread – 7g net carbs per slice
  • Franz Keto Sourdough Bread – 5g net carbs per slice
  • Aldi L’Oven Zero Net Carb Sourdough Bread – 0g net carbs per slice

Note that specialty low-carb breads often come in smaller slices. Pay attention to serving sizes, as two regular slices may be equivalent to three low-carb slices.

Is sourdough bread paleo?

The paleo diet avoids all grains, even whole grains, as well as commercial dairy products. So conventional sourdough bread made with wheat flour and cows’ milk is not paleo-friendly.

However, there are modified paleo sourdough recipes that use allowed ingredients:

  • Almond flour, coconut flour – Nut and seed-based flours replace grain flours.
  • Honey or maple syrup – Natural sweeteners stand in for refined sugar.
  • Nut milk, coconut milk – Substitute for conventional dairy products.

Paleo sourdoughs require extra modifications since they lack gluten. Baking with starch powders or xanthan gum can help bind and give rise.


Sourdough bread is not significantly lower in carbohydrates or calories compared to most other breads. One slice of sourdough contains about 15 grams total carbs and 14 grams net carbs.

The fermentation process may give sourdough bread some glycemic and digestibility advantages. But its total carb content per serving is quite similar to regular bread.

Sourdough bread is too high carb to fit into a keto diet. Low-carb bread alternatives can provide the sourdough taste with fewer digestible carbs.

Overall, sourdough bread is a better choice than mass-produced white bread but still should be eaten in moderation as part of a healthy diet.

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