Sourdough Bread Nutrition: What's Actually in a Slice

sourdough bread nutritionsourdough bread caloriessourdough nutritional valuesourdough bread proteinsourdough minerals

Nutrition labels tell you what's in the bread. They don't tell you what your body can actually use. That distinction matters with sourdough, because fermentation changes the equation.

What's in a typical slice

A standard slice of sourdough bread (about 64 grams, or roughly 2 ounces) made with bread flour contains approximately:

- Calories: 120-150 - Protein: 5-6g - Carbohydrates: 24-28g - Fiber: 1-2g (higher with whole-grain flour) - Fat: 0.5-1g - Sodium: 200-300mg (depends on how much salt you use) - Iron: 1.5-2mg - Calcium: 20-30mg

These numbers look pretty similar to regular white bread. And on paper, they are. The differences between sourdough and conventional bread aren't about what's listed on the nutrition label -- they're about bioavailability, which is a fancy word for "how much of this your body can actually absorb."

How fermentation changes the nutritional picture

Here's where sourdough gets interesting. The raw numbers on a nutrition label don't account for phytic acid, which binds to minerals and carries them through your digestive tract unabsorbed.

Sourdough fermentation breaks down 50-80% of the phytic acid in flour. That means the iron, zinc, magnesium, and calcium listed on the label are significantly more bioavailable in sourdough than in yeasted bread. You're eating the same nutrients on paper, but absorbing more of them in practice.

Fermentation also partially breaks down starches into simpler sugars, which sounds like it would raise the glycemic index -- but the organic acids produced simultaneously slow down digestion. The net effect is a lower glycemic response despite the pre-digested starches.

Protein quality changes too. The protease enzyme and bacterial proteolysis break down some proteins into free amino acids, which are more readily absorbed. This doesn't change the total protein count, but it does change how efficiently your body uses it.

Sourdough vs. white bread vs. whole wheat

Comparing sourdough to other breads gets complicated because "sourdough" describes a process, not a flour type. You can make sourdough with white flour, whole wheat flour, or anything in between.

White sourdough vs. white yeasted bread: similar calories, protein, and carbs. The sourdough wins on mineral absorption (phytic acid reduction), glycemic response (lower GI), and digestibility (partially broken-down gluten and FODMAPs).

Whole-wheat sourdough vs. whole-wheat yeasted bread: same advantages as above, but more pronounced. Whole-wheat flour has more phytic acid, so the fermentation's phytase activation makes a bigger difference. The fiber content is similar between both.

Whole-wheat sourdough vs. white sourdough: the whole-wheat version has more fiber (3-4g per slice vs. 1-2g), more minerals to begin with, and more B vitamins. The fermentation benefits apply to both, but whole-wheat sourdough is nutritionally the strongest option.

If you're optimizing for nutrition, whole-grain sourdough with a long fermentation is the clear winner. If you're optimizing for taste and texture, a blend of 80% bread flour and 20% whole wheat hits a sweet spot that most people enjoy.

The mineral story

Bread flour contains meaningful amounts of iron, zinc, magnesium, and smaller amounts of calcium, phosphorus, and selenium. Whole-grain flour contains significantly more of all of these.

But here's the thing most nutrition articles miss: the form of iron in bread (non-heme iron) is already harder for your body to absorb than the iron in meat (heme iron). Phytic acid makes it even harder. By breaking down phytic acid, sourdough fermentation can roughly double the absorption rate of non-heme iron from bread.

For people who rely heavily on plant-based foods for their iron intake, this is a meaningful difference. One study estimated that switching from yeasted bread to long-fermented sourdough could increase daily iron absorption by 15-20% for people who eat bread as a dietary staple.

Zinc absorption follows a similar pattern. Zinc is critical for immune function and wound healing, and it's one of the nutrients most affected by phytic acid binding. Sourdough fermentation substantially improves zinc bioavailability.

Frequently asked questions

How many calories are in a slice of sourdough bread?

About 120-150 calories per slice (roughly 64g), depending on the flour used and how thick you slice it. This is comparable to regular white bread or whole-wheat bread.

Is sourdough bread a good source of protein?

A slice has about 5-6 grams of protein, which is decent for bread but not exceptional. The fermentation does improve protein digestibility by breaking some proteins into free amino acids, making them easier for your body to use.

Does sourdough bread have more fiber than regular bread?

The fiber content depends on the flour, not the fermentation method. Sourdough made with white flour has roughly the same fiber as regular white bread (1-2g per slice). Use whole-grain flour and you'll get 3-4g per slice.

Is sourdough bread keto-friendly?

No. A slice of sourdough has 24-28 grams of carbohydrates, which would use up most or all of a typical keto dieter's daily carb allowance. The lower glycemic index helps with blood sugar, but it doesn't reduce the carb count.

Is Sourdough Bread Healthy? What the Science Actually Says

An honest, evidence-based look at sourdough bread's health benefits -- from digestibility and glycemic response to nutrient availability. No hype, just research.

7 Benefits of Sourdough Bread (Backed by Science)

The real, evidence-backed benefits of sourdough bread -- from better digestion and longer shelf life to improved flavor and nutrition. No miracle claims.

Sourdough vs Yeast Bread: What's the Difference?

A side-by-side comparison of sourdough and commercial yeast bread -- how they're made, how they taste, and why the differences matter more than you think.