Eating Sourdough Bread Has An Unexpected Effect On Your Belly Fat

Trying to trim your midsection? You might assume that bread is off the menu. After all, bread (particularly white bread, arguably the least healthy bread) is often associated with weight gain due to its relatively high carbohydrate levels, starch content, and calories. However, not every type of bread causes your body to store fat in places like your belly. For example, sourdough bread has earned a reputation for being friendlier to the waistline.

What makes sourdough bread potentially healthier than other breads? The answer lies in its leavening ingredient. Rather than relying on prepackaged commercial yeast for leavening, sourdough bread requires the use of a "wild" starter. The starter is a mix of just flour and water that's been allowed to ferment for days, weeks, or longer. Its fermentation process is kicked off by microscopic particles of yeast that land in the flour-water mixture and begin to form lactic acid. Eventually, the starter will begin to bubble, indicating it's ready to be kneaded into dough. This foamy, fermented starter is what gives sourdough bread its tangy taste and distinctive aroma. The starter also alters the composition of the sourdough bread in two ways.

First, the starter changes the structure of the bread so it contains less gluten. This in turn lowers the bread's glycemic index (GI), meaning the bread takes longer to digest than breads made from regular commercial yeast. This puts less of a glycemic load on the body. And when you lower your glycemic load, you may find weight management easier, according to Mayo Clinic advice.

Secondly, the fermented starter gives sourdough bread probiotic powers. When probiotics are introduced into the stomach, they encourage the gut biome to work more efficiently. As the authors of a 2021 Microorganisms article conclude, the probiotic qualities of sourdough bread may aid in the digestion process and enable nutrients to flow more predictably through the system. Consequently, consumers of sourdough bread may experience decreased episodes of stomach lining inflammation and discomfort, as well as be able to absorb more nutrients from their food, including helpful magnesium.

Why single out magnesium? A study from 2022 in Frontiers in Microbiology found that mice who were given the beneficial bacteria found in sourdough bread starter absorbed more magnesium than mice that weren't given the bacteria. Although magnesium hasn't been directly linked to weight loss, a Healthline feature notes that magnesium may assist in regulating sugars. In the piece, Dr. Sherry Ross explains that a medical study showed that "taking higher amounts of magnesium helps better control insulin and glucose blood levels" as well as "helps with bloating and water retention."

Together, the lower glycemic index level and probiotics of sourdough bread may have an impact on whether or not a consumer's body stores fat or uses it for energy. For instance, a 2024 meta-analysis from Critical Reviews in Food Science and Nutrition examined the role that sourdough bread had in reducing appetite better than yeast-risen bread. The analysis findings showed that individuals who consumed sourdough bread (in contrast to those who ate commercially prepared bread) lowered their levels of blood glucose within an hour after eating. This helped keep their appetites in check due to the low glycemic nature of the sourdough bread. In another study from 2021 that was published in Foods, individuals who ate whole wheat and wheat-based sourdough bread digested their meals at a slower rate than those who ate breads made from yeast.

In other words, if reducing fat is your goal, talking with your healthcare provider about adopting a low glycemic index diet could make sense. After all, in a 2019 study in Obesity Reviews, overweight subjects who transitioned to a low glycemic index meal plan had moderate success at losing weight. That being said, they needed to substantially lower their glycemic loads to achieve results. Just how much lower of a glycemic index rating does sourdough bread have? A comparison of breads offered by MedicalNewsToday indicates that the glycemic index of sourdough is 54. For yeast-based bread, the glycemic index level is 71.

In terms of sourdough bread's probiotics, the results of a 2020 study published in Nutrients showed the bread's possible promise as a fat-fighting ally. During the trial, researchers fed mice a high-fat diet. But they injected probiotic-rich bacteria (the same bacteria strain that's found in some sourdough bread) into the bellies of a specific number of mice. By the end of the experiment, the mice who received the "good bacteria" injections gained less weight than those who didn't receive injections.

This doesn't give you the license to eat sourdough bread for every meal or snack, though. Even with all of its positive attributes, sourdough bread isn't calorie-free or low-carb. According to data from the U.S. Department of Agriculture, a single slice of sourdough bread contains 120 calories and 23 grams of carbohydrates. Therefore, if you decide to swap your regular bread for a sourdough variety, eat your slices in moderation. 

You may also want to seek out sourdough made from whole wheat to improve the bread's fiber content so you feel sated for longer. And check out which type of sourdough bread you buy, if the information is available. As a 2021 study in the Journal of Agricultural and Food Chemistry showed, San Francisco sourdough bread appeared to have a more pronounced "low glycemic load" effect than other types of sourdough bread.