Are there carbs in fermented foods?: A Comprehensive Guide to Carbs, Probiotics, and Diets

November 10, 2025 •

5 min read

The process of fermentation, carried out by microorganisms like bacteria and yeast, uses carbohydrates as a primary energy source. This metabolic activity is precisely why the answer to 'Are there carbs in fermented foods?' is nuanced, as the final carbohydrate content is almost always lower than in the unfermented raw ingredients.

Quick Summary

Fermentation naturally alters carbohydrate content by converting sugars and starches into organic acids, resulting in a reduced carb count compared to raw ingredients. The final level depends on the food type, initial sugar content, and fermentation duration. Many fermented products are excellent for low-carb diets, but awareness of added sugars is essential.

Key Points

Carbohydrate Reduction: The fermentation process naturally reduces the carbohydrate content of foods by allowing bacteria and yeast to consume sugars and starches.
Factors for Carb Levels: The final carbohydrate count in fermented foods is influenced by the original ingredients, the fermentation duration, and any post-fermentation sweeteners.
Low-Carb Options: Many fermented vegetables like sauerkraut and kimchi, as well as plain, full-fat dairy products like yogurt and kefir, are naturally low in carbohydrates and suitable for low-carb diets.
Glycemic Index: Fermentation can lower a food's glycemic index, leading to a slower, more controlled release of glucose into the bloodstream, which is beneficial for blood sugar management.
Beneficial for Gut Health: Incorporating fermented foods into a low-carb diet can provide essential probiotics to support a healthy gut microbiome, which may be at risk on a restrictive diet.

Understanding the Fermentation Process and Carbohydrates

Fermentation is an ancient preservation method involving the metabolic action of bacteria and yeasts. These microorganisms essentially 'pre-digest' the food by feasting on the sugars and starches—the core carbohydrates—present in the raw ingredients. As they consume these compounds, they produce byproducts such as lactic acid, acetic acid, and carbon dioxide. The result is a food that is not only preserved but often has a tangy flavor and, critically, a lower overall carbohydrate count.

This principle applies across many types of fermented foods. In yogurt, the lactose (milk sugar) is consumed by bacteria. In sauerkraut, the natural sugars in the cabbage are the food source for the lactobacillus bacteria. This metabolic activity is the reason properly fermented foods, particularly vegetables and dairy, are often much lower in carbs than their unfermented counterparts.

How Fermentation Reduces Carbohydrates

The reduction in carbohydrate content is not a uniform process and depends on several key factors:

Initial Ingredients: The starting material's natural carb level is foundational. Fermenting naturally low-carb vegetables like cabbage will result in an end product with very few carbs, whereas fermenting a starchy root vegetable like beetroot, while reducing carbs, will leave a higher residual amount.
Fermentation Time: The duration of fermentation is crucial. A longer fermentation period allows the microbes more time to consume the available carbohydrates, resulting in a lower final sugar and carb count. For homemade kefir, for example, fermenting for 48 hours can result in a significantly lower carbohydrate level than a shorter 24-hour ferment.
Added Sugars: Be mindful of store-bought fermented products, especially flavored varieties. Manufacturers often add sugar post-fermentation to improve palatability, which will increase the carbohydrate content. Always check labels for 'live and active cultures' and be wary of added sweeteners.

Carbohydrate Content Across Different Fermented Foods

The final carbohydrate count varies significantly depending on the food type. Here’s a breakdown of some popular fermented items:

Fermented Dairy: Plain, unsweetened yogurt and kefir have their lactose partially consumed by bacterial cultures. The remaining carb content is relatively low, especially in products fermented for longer durations. Low-fat or fat-free versions often have more sugar added for flavor and texture, so opt for full-fat, plain options on a low-carb diet.
Fermented Vegetables: Sauerkraut and kimchi, made from cabbage, naturally contain very few carbohydrates. Fermentation further reduces this count, making them exceptionally low-carb. A one-cup serving of sauerkraut, for instance, might contain just 4–6 grams of total carbohydrates, with the net carbs being even lower due to fiber.
Fermented Soy: Miso and tempeh are made from fermented soybeans and provide an excellent source of protein with a relatively low carbohydrate count.
Fermented Beverages: The carbohydrate content of kombucha is variable. The yeast and bacteria of the SCOBY (Symbiotic Culture of Bacteria and Yeast) consume most of the initial sugar, but some residual sugar remains, especially in shorter ferments. Look for unsweetened or very low-sugar varieties for low-carb diets.
Fermented Grains: Sourdough bread undergoes a fermentation process that reduces its glycemic index (GI), causing a more gradual and controlled release of glucose into the bloodstream. While still a carbohydrate-based food, the fermented version is generally considered a better option for blood sugar management than regular bread.

Fermented Foods: A Carb Comparison Table


Food (per 100g)	Carb Content (Approximate)	Notes
Raw Cabbage	6g	Baseline for Sauerkraut and Kimchi.
Green Sauerkraut	4g	The fermentation process reduces carbs.
Plain Yogurt	3.6g (Net)	Bacteria consume lactose. Flavored versions contain added sugar.
Plain Kefir	4.48g (Net)	Kefir typically has slightly more carbs than yogurt. Longer fermentations reduce this.
Kombucha	Varies widely	Can range from very low to moderate depending on residual sugar and added ingredients.
Tempeh	12.7g	A moderate-carb, high-protein soy product.

The Impact of Fermentation on Glycemic Index

Beyond simply reducing the carbohydrate count, fermentation can also significantly lower a food's glycemic index (GI). The GI measures how quickly a food causes blood sugar levels to rise. This is particularly beneficial for individuals managing blood glucose or those on low-carb diets. For instance, lactic acid produced during fermentation can inhibit enzymes like α-amylase, slowing down the digestion and absorption of sugars.

Furthermore, fermentation can increase the amount of resistant starch, a type of carbohydrate that is not easily digested by the human body. Resistant starch acts like soluble fiber and passes to the large intestine, where it feeds beneficial gut bacteria. This dual action of carb reduction and GI modulation makes fermented foods a health-conscious choice.

How Fermented Foods Fit into a Low-Carb or Keto Diet

For those following low-carb or ketogenic diets, fermented foods can be an excellent addition. They not only provide beneficial probiotics for gut health, which can be neglected on restrictive diets, but they also come with a reduced carbohydrate load.

A low-carb friendly guide to fermented foods:

Prioritize Plain, Unsweetened Varieties: Always opt for plain yogurt, kefir, and kombucha. Added sugars can quickly negate the low-carb benefits.
Stick to Vegetables: Sauerkraut, kimchi, and pickles (brine-fermented, not vinegar-pickled) are naturally low in carbs and high in fiber, making them ideal additions.
Check Labels Carefully: Read the nutrition information to be aware of any added sugars or flavorings that increase the carb count, especially for store-bought products.
Consider Fermented Soy: Miso and tempeh can be included in moderation. Miso is a great low-carb flavor enhancer, while tempeh offers protein and fiber.
Use Sourdough Sparingly: While having a lower GI, sourdough is still a carb-dense food and should be consumed in limited quantities, especially on strict keto diets.

Conclusion

Yes, fermented foods contain carbohydrates, but the fermentation process significantly alters their composition by converting sugars and starches. The microbes do the work for you, often resulting in a product with a lower overall carb count and a reduced glycemic impact compared to its raw form. Factors like fermentation time and the presence of added sugars are key to determining the final carbohydrate levels. By choosing unsweetened and properly fermented options, particularly vegetables, these probiotic-rich foods can be a valuable and beneficial part of many dietary plans, including low-carb and ketogenic lifestyles.

Fermentation is a natural process that not only preserves food but also enhances its nutritional profile.

Frequently Asked Questions

No, not all fermented foods are low in carbs. While the fermentation process typically reduces carbohydrate content, the starting ingredient is a major factor. Fermented vegetables are generally low-carb, but products from higher-carb sources like starchy legumes or grains will have higher residual carbs.

Fermentation reduces carbs because the microorganisms involved, such as bacteria and yeast, consume the carbohydrates (sugars and starches) in the food for energy, converting them into organic acids like lactic acid, as well as carbon dioxide.

Plain, full-fat yogurt and kefir both contain relatively low amounts of carbs, but commercial varieties can differ. Kefir, especially if fermented longer, can have slightly lower lactose than yogurt due to its more extensive fermentation process involving yeasts and bacteria. Always opt for unsweetened versions and check nutrition labels.

Yes, sauerkraut does have carbs, but significantly fewer than raw cabbage. For example, fresh cabbage can have around 6g of carbs per 100g, while fermented sauerkraut has been shown to contain about 4g per 100g. Much of the remaining carb content comes from dietary fiber.

Kombucha's carb count is highly variable. While the SCOBY consumes much of the sugar, some residual sugar remains. Always check the label, as many commercial brands add extra sugars or juices. Look for unsweetened options for the lowest carb count.

Sourdough bread is not typically considered keto-friendly, as it is still primarily a carbohydrate-based food. However, its fermentation process lowers its glycemic index compared to regular bread, making it a better option for blood sugar management.

It is crucial to check for added sugars because many flavored fermented products, particularly yogurts, kefirs, and kombuchas, have high levels of added sweeteners that increase the final carbohydrate count and negate the low-carb benefits of fermentation.