Sourdough bread is known for its chewy texture, mildly tangy flavour and rustic crust. Made using a natural fermentation process with wild yeast and lactic acid bacteria, it has gained popularity not just for its taste but also for its potential health benefits. Despite its artisanal appeal, sourdough bread like all bread, contains calories, and the amount per slice depends on the ingredients, portion size and baking method.

Calories in a Slice of Sourdough Bread by Size and Recipe

A standard slice of white sourdough bread weighing about 40 to 50 grams typically contains 120 to 150 calories. The calorie count comes mainly from the flour, with most sourdoughs made using white or a mix of white and wholemeal flour.

Heavier, artisan-style sourdough slices, often thicker and denser, can contain closer to 180 to 200 calories per slice, especially if they include olive oil, seeds or whole grains. Wholemeal sourdough, while slightly higher in fibre, is similar in calorie count to white versions, usually around 140 to 160 calories per slice depending on the size.

Pre-sliced supermarket sourdough often features smaller portions and more uniform slices, with some containing as few as 90 to 110 calories per slice. However, the serving size on the label might not reflect how much people eat in one go, especially if the bread is used for toast or sandwiches.

Nutritional Breakdown of Sourdough Bread

Sourdough bread is primarily made from flour, water and salt, fermented using a natural starter rather than commercial yeast. A typical slice provides around 20 to 30 grams of carbohydrates, including small amounts of natural sugars formed during fermentation. Protein content ranges from 3 to 6 grams per slice, depending on the flour used, with wholemeal versions containing slightly more.

Fat content is minimal unless added separately during baking, and fibre content is moderate—usually around 1 to 2 grams in white sourdough and 2 to 4 grams in wholemeal sourdough. The fermentation process can also reduce gluten content and make some nutrients like B vitamins and minerals more bioavailable compared to conventional breads.

Benefits of Eating Sourdough Bread

Sourdough bread offers more than just great flavour. Its natural fermentation process may help support gut health by promoting beneficial bacteria and making it easier to digest. The fermentation also lowers the phytic acid content, which can improve the body’s ability to absorb minerals such as iron, magnesium and zinc.

The lower glycaemic index of sourdough bread compared to standard white bread means it has a more gradual effect on blood sugar, helping reduce spikes and crashes. This can be especially useful for people with insulin sensitivity or those trying to manage appetite and energy levels.

Wholemeal and seeded sourdoughs offer more fibre, which supports digestion, improves satiety and contributes to heart health when eaten as part of a balanced diet.

Downsides of Eating Sourdough Bread

While sourdough is often marketed as a healthier bread, it still contains a significant amount of refined carbohydrates if made with white flour. This means it can still contribute to high calorie intake if portion sizes aren’t managed, especially when served with butter, oil or cheese.

Some sourdough breads sold in supermarkets are not traditionally fermented and may be labelled “sourdough” despite being made with added yeast and vinegar. These versions may lack the nutritional benefits of authentic sourdough and can contain additives or preservatives.

People with gluten sensitivity should also be cautious. Although sourdough fermentation can reduce gluten, it is not gluten-free and should be avoided by those with coeliac disease unless specifically made with gluten-free flour.

How Sourdough Bread Fits Into Your Diet

Sourdough bread can be part of a balanced diet when eaten in moderation and paired with nutrient-dense foods. Topping a slice with protein-rich ingredients like eggs, hummus or cottage cheese adds satiety and balances the carbohydrate content. It also works well as part of meals with leafy greens, lean meats or oily fish.

If you’re counting calories, keeping to one or two slices and watching toppings is key. For those trying to increase fibre intake, opting for wholemeal sourdough or adding seeds such as chia or flax can boost nutritional value without significantly raising calories.

Because sourdough is satisfying and more flavourful than standard bread, many people find they need less of it to feel full.

Glycaemic Index of Sourdough Bread

Sourdough bread has a lower glycaemic index than conventional white bread, typically ranging from 48 to 55, depending on the flour type and fermentation time. This slower digestion helps moderate blood sugar levels and can improve energy stability throughout the day.

The fermentation process creates organic acids that slow down the rate at which glucose enters the bloodstream. Wholemeal sourdough has an even lower glycaemic impact due to its higher fibre content.

Pairing sourdough with protein or healthy fat, such as eggs or avocado, further reduces the glycaemic load and helps keep you fuller for longer.

How Sourdough Bread Is Made and What It Contains

Traditional sourdough is made using just three ingredients: flour, water and salt. A sourdough starter—made from fermented flour and water—is used instead of yeast. This starter contains wild yeast and lactic acid bacteria, which ferment the dough over several hours or days.

During this time, the dough develops its characteristic tangy flavour and chewy texture. Longer fermentation times allow for more breakdown of gluten and phytic acid, potentially improving digestibility and nutrient availability.

Some sourdoughs may include seeds, olive oil, herbs or whole grains for added texture and nutrition. It’s worth checking ingredient lists if you’re buying pre-made versions, as not all sourdoughs are made using traditional methods.

Healthy Alternatives to Sourdough Bread

If you’re looking to switch things up, rye bread, wholegrain bread or sprouted grain bread offer similar benefits with different flavours and textures. For those needing gluten-free options, buckwheat, millet or rice flour breads are available, though they don’t usually have the same fermentation profile as sourdough.

For a lower-carb alternative, lettuce wraps, roasted sweet potato slices or seed crackers can replace bread in meals while offering more fibre and nutrients with fewer carbohydrates.

Summary

A slice of sourdough bread contains between 120 and 200 calories depending on size, flour type and added ingredients. It delivers a good mix of carbohydrates and protein, with moderate fibre and minimal fat. Thanks to its natural fermentation process, sourdough may offer improved digestibility and a lower glycaemic impact than conventional breads. While not calorie-free, sourdough can be a healthy, satisfying option when portioned sensibly and combined with balanced toppings. Choosing wholemeal or traditionally made varieties ensures you get the most nutritional value from every slice.

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