Is sourdough bread healthy? That’s a question we hear a lot. Clinical research that has examined whether or not sourdough bread is “good for you” should be considered, to date, preliminary; most studies have been small or lacked strong enough controls. However, the early research is promising: sourdough bread appears to exert a physiological benefit in the gut that likely enhances your metabolic health and possibly also your cardiovascular and immune health.
Certain types of sourdough bread may also lessen the uncomfortable gastrointestinal symptoms experienced by some individuals that suffer from irritable bowel syndrome (IBS) or gluten intolerance. Since whole-grain versions are good sources of daily fiber, these sourdough breads may have the added benefit of helping you feel full longer, which can assist in weight management efforts. However, we caution that bread, in general, is carbohydrate-rich and densely caloric, and weight management — so important for maintenance of multiple health indicators — may be best achieved when bread is eaten in moderation.
The fermentation “craze”
For centuries, fermented foods have been prepared and consumed all over the world. But only in recent years have a bevy of fermented foods undergone a resurgence in popularity, in part due to their possible health benefits.
Defined by scientists, fermented foods are foods or beverages produced through controlled microbial growth and the conversion of food components through enzymatic action. Meat and fish, dairy, vegetables, soybeans, other legumes, cereals and fruits can all be fermented, sometimes as a method of preserving them; at other times as a way of enhancing taste or texture. Diary foods such as yogurt and cheese have been studied extensively. Scientists are in earlier stages of studying non-dairy fermented foods such as kefir, kombucha, sauerkraut, tempeh, natto, miso, kimchi and sourdough bread. (Kefir has been studied the most, and has been shown to be beneficial for lactose malabsorption and the eradication of H. pylori, an infection that causes severe diarrhea and abdominal pain.)
Some of these non-dairy fermented foods are fermented naturally — such as sauerkraut, kimchi, and certain fermented soy products. Others — including sourdough bread, kefir, kombucha and natto — are produced via the addition of “starter cultures.”
What is sourdough bread, and how is it made?
The art of making sourdough bread is quite ancient, but it has been dwarfed over the past few decades by highly industrialized bread-making processes using baker’s yeast leavening agents. By contrast, traditional sourdough bread relies on a starter culture of flour and water, where the flour’s native lactic acid bacteria and yeasts produce the fermentation. Making the sourdough starter takes on average seven days and involves replenishing the microbes with fresh flour and water daily. The microbial content of the sourdough starter depends on the traditional practices used, which not only affects taste and texture, but the bread’s nutritional profile. In general, several species within the Lactobacillus, Leuconostoc, Weissella, Pediococcus and Streptococcus genera have been identified in sourdough starters, with Lactobacillus species the most prevalent and Lactobacillus sanfransiscensis considered one of the most important.
Once the starter is ready, a small portion is added to the sourdough base ingredients to initiate the sourdough fermentation process, commonly referred to as “backslopping.” During fermentation, microbial and enzymatic-led conversions of cereal carbohydrates, proteins, lipids and phenolic compounds occur. While we won’t delve further into the chemical reactions that take place, suffice to say that the microorganisms’ and enzymes’ activity are interlinked in numerous and complex ways.
What’s the nutritional profile of sourdough bread?
Ultimately, the nutritional quality of sourdough bread depends on all the ingredients that go into it and how the fermentation and baking is staged. There are literally hundreds of different formulations. One big factor: the type of grain used in the fermented dough. Sourdough bread can be made with many different types of flour, including refined white flour, whole-grain wheat or rye flour, or processed wheat flour; and many store-bought versions include added yeast, added salt, ascorbic acid, vinegar, oil, and even added sugars. Thus, reports that list the nutritional values per one slice of sourdough bread are, frankly, pretty useless. Here’s but one example, from a store-bought Beckmann’s “Organic Sourdough,” which says it’s made from unbleached wheat flour, whole wheat flour (so we can’t tell how much of each), sea salt, organic gluten, organic enzymes, organic cultured wheat starch and vitamin C (trace amounts):
Serving size: 1 slice (43 grams)
Total Fat: 0% of Daily Value (DV)
Cholesterol; 0% of DV
Sodium: 206mg (9% of DV)
Total Carbohydrate: 24g (9% of DV)
Dietary Fiber: 1g (4% of DV)
Total Sugars: 0g
Calcium: 5mg (0% of DV)
Iron: 0.5mg (3% of DV)
Potassium: 39mg (1% of DV)
What might seem notable about the above data is that, overall, sourdough bread doesn’t seem like a health super-food. And it probably isn’t, in that it’s caloric-rich (who eats just one slice), has a fairly high sodium level, doesn’t appear to have a huge amount of fiber, and the mineral and vitamin content appears fairly modest. But the numbers above don’t tell the story of what sourdough bread does when it interacts with your gut microbiome, which we’ll discuss in a later section.
But isn’t “whole-grain” bread the healthiest?
Before we discuss sourdough bread specifically, let’s first step back and talk about where breads fit into the health discussion these days. It’s interesting to note that in the Dietary Guidelines for Americans, 2020-2025, there is a chapter on the place of grains in a healthy diet, but sourdough bread is not mentioned. The extent of the commentary:
“Healthy dietary patterns include whole grains and limit the intake of refined grains. At least half of total grains should be whole grains…. Grain-based foods in nutrient-dense forms limit the additions of added sugars, saturated fat, and sodium. A food is a 100% whole-grain food if the only grains it contains are whole grains….Shifting from refined to whole-grain versions of commonly consumed foods—such as from white to 100% whole-wheat breads, and white to brown rice where culturally appropriate—would increase whole-grain intakes and lower refined grain intakes to help meet recommendations.”
Leading medical organizations, such as Cleveland Clinic, also recommend whole-grain foods, summing up that “eating whole-grain foods within an overall healthy diet helps to lower your risk for many diseases, including stroke, diabetes, heart disease, asthma and colorectal cancer. Whole-grains are also rich in protein, fiber, B vitamins and many other nutrients that help to lower blood pressure, reduce gum disease, strengthen the immune system and help control weight.”
So with these ringing endorsements, it may make some wonder why we should bother to consider breads other than those made of 100% whole grain flour. Our response: Yes, the overall body of research supporting the health benefits of whole-grain foods is solid, but (a) sourdough bread can be a whole-grain food option, and possibly with additive health benefits; and (b) not all population groups can tolerate consumption of whole grains, due to gastrointestinal issues, which might be lessened with sourdough breads.
Is sourdough bread healthy? The unique health benefits of sourdough bread
Here are the probable health benefits associated with consumption of sourdough bread:
1. Sourdough bread may modulate your glucose response to bread.
The generally accepted medical view is that your long-term health benefits from a relatively steady and healthy blood glucose level. Carbohydrate foods, like breads, can cause your blood glucose levels to rise, or even spike if consumed in high quantities. So scientists and healthcare professionals alike suggest you consider avoiding foods with a high glycemic index (GI), a tool first created in 1981 that assigns carbohydrate foods a number: the lower the GI number, the less likely the food might be to cause an increase in blood glucose. (Another index, glycemic load (GL), tells you how quickly a food causes glucose to enter the bloodstream and how much glucose you’ll get per serving. See our report, Glycemic Index vs Glycemic Load, to learn more about how GI and GL can be analyzed concurrently for optimal nutritional guidance.)
A common type of sourdough bread has a GI rating of 54 and a GL rating of 8, while bread made from white wheat flour has a GI rating of 71 and a GL rating of 9. Therefore, it has been hypothesized that sourdough bread may help you keep your blood sugar levels more stable than if you were to eat white bread. A cautionary note: Scientists warn, and rightly, that we should be careful using (and probably should not rely upon) these indexes, because foods with similar carbohydrate contents don’t necessarily impact blood glucose levels in similar ways. (HbA1c assays provide better information, which is why individuals with diabetes are often recommended to get such tests.)
Fortunately, there is considerable in vivo (human clinical trial) evidence supporting the notion that the “postprandial glucose response” is lowered by sourdough fermentation, although the exact mechanism of action is still highly debated and yet to be confirmed.
Interestingly, a 2009 clinical review concluded that white wheat sourdough bread fared no worse (relative to glucose response) than whole-grain sourdough bread, leading the authors to hypothesize that it’s not necessarily the insoluble fiber level in bread that influences glycemic response; rather, the fermentation process may, in some way, alter the chemistry of your gut microbiome in a way that mitigates the rise in blood glucose.
The evidence regarding sourdough bread’s efficacy in lowering postprandial insulin response is less clear. Most of the studies that show benefit used very dense sourdough breads, including those prepared in a more artisanal manner (e.g., shorter bread rising period) — suggesting that there can be an effect of physical structure of bread on postprandial insulin response, resulting from the retarded glucose release and absorption. (See our later section on sourdough bread types.)
2. Sourdough fermentation appears to improve the nutritional quality of bread.
It has been thought for some time that the lactic acid bacteria present during fermentation represent potentially probiotic microorganisms in your gut that seem to generate bioactive peptides and polyamines –– with potential beneficial effects on cardiovascular, immune and metabolic health.
Importantly, lactic acid bacteria can convert phenolic compounds (such as flavonoids) to biologically active metabolites. The bacteria also break down phytic acid, an element in commercial baker’s-yeast-produced (non-sourdough) bread that tends to block our ability to absorb many of the vitamins and minerals (such as potassium, magnesium, folate) in the food.
A 2018 metabolic profiling study hypothesizes that “sourdough fermentation contributes to the beneficial health effects of whole grains by increasing the amount of several bioactive compounds, such as BCAAs, small peptides, and microbial phenolic acid metabolites, in the baked products.” In other words, whole-grain bread is healthy; sourdough whole-grain bread may be even healthier. The authors also noted that the effect is more profound in rye sourdough compared to wheat, likely attributable to the more extensive metabolism occurring in a typical rye sourdough.
3. For some individuals, sourdough bread may be easier to digest.
Scientists speculate that over the past few decades, a change in bread making processes from a traditional long fermentation process to a short, incomplete fermentation may have contributed to bread intolerance through its effects on fermentation in the colon.
Irritable bowel syndrome (IBS) is now so common that an estimated 10-20% of adults and adolescents suffer worldwide from this disorder. IBS is characterized by abdominal pain or discomfort, disturbed bowel habits and altered stool characteristics. While it’s clear that the causes of IBS are likely multifactorial, in many cases a disturbance of gastrointestinal microbiota seems to play a role, and many IBS sufferers have difficulty tolerating the consumption of many types of bread.
One reason bread can be difficult to digest, for many, is the high amount of “FODMAPS” bread contains, including wheat bread. FODMAPS is an acronym for “fermentable oligosaccharides, disaccharides, monosaccharides and polyols” — molecules fermented in the colon to short-chain fatty acids (SFCA), which are generally thought to exert multiple beneficial effects on human health. Prebiotic, fibrous foods — like vegetables — also fall into the FODMAPS sphere, and yet we know they have significant health benefits. However, over-consumption of certain FODMAPS foods can irritate the gastrointestinal (GI) tracts of certain individuals at certain times and in combination with certain other foods. (Unfortunately, information about FODMAPS content in food is very limited, and individual responses to these foods vary greatly and so may depend on an individual’s genetic make-up, health status, environmental and other factors.)
As a 2019 review paper summed up, sourdough fermentation can lower the content of non-digestible oligosaccharides fructans and raffinose, which are the FODMAP subgroups most commonly found in breads.
While the in vitro (test tube) work is highly promising, we must caution that clinical studies are rather preliminary. An important 2016 study demonstrated that sourdough rye bread caused less GI symptoms (abdominal pain, flatulence, stomach rumbling, intestinal cramps) in IBS sufferers, but the bread used was specifically created to have a lower-FODMAP level than the sourdough breads commonly marketed or made at home.
Sourdough bread may also be easier to digest if you are “gluten intolerant.” While sourdough bread does contain gluten — and so is not recommended if you have celiac disease (a disorder wherein you have no gluten tolerance), scientists theorize that sourdough fermentation increases the interaction between starch and gluten proteins resulting in the creation of a barrier which limits starch bioavailability and enzyme accessibility. In other words, as a Mayo Clinic blog reports, for those with “gluten intolerance” (more commonly known as non-celiac gluten sensitivity), the sourdough process may increase tolerance for consuming the bread, according to Alessio Fasano, director of the Center for Celiac Research at Massachusetts General Hospital. Adds Peter Green, director of the Celiac Disease Center at Columbia University, the long fermentation process to make sourdough bread the old fashioned way does reduce some of the toxic parts of gluten for those that react to it.
Unproven claims about sourdough bread
Sourdough bread and its constituent microorganisms have also been suggested to exhibit antimicrobial, anti-hypertensive, and cholesterol lowering properties. However, these observations are based on in vitro studies examining the impact of sourdough-extracted bacteria, rather than of baked sourdough bread, and in vivo studies have been contradictory.
Different bread flours merit attention, too; but research is ongoing
Much research still needs to be done to determine which bread flours (and other ingredients) and which bread-making and baking processes produce the healthiest products. As mentioned previously, some scientists are finding that the more dense sourdough breads, including those prepared in a more artisanal manner (e.g., shorter bread rising period) — are associated with the most distinct metabolic benefits.
- A 2018 study opined that sourdough whole-grain rye has a considerably better metabolite profile than does whole-grain wheat bread.
- A study showed that, in adult patients with type 2 diabetes, breads made of sprouted grains and produced with sourdough fermentation exhibit lower blood glucose incremental AUC (iAUC) compared with whole grain or white wheat sourdough fermented breads.
- One of the better, lowest GI values has been demonstrated in a wheat sourdough bread enriched with dietary oat and rye fiber.
- Pumpernickel rye bread, consumed heavily in Germany and Scandinavia, has been shown to promote lower postprandial glucose and insulin responses in T2D patients compared both with white bread and whole wheat grain bread.
So, is sourdough bread healthy? Much scientific research remains to be done to determine the exact benefits of sourdough bread, which kinds are best, and why they work as they do. But the initial results are promising, and point to likely benefits for blood glucose management, nutritional merit and digestive comfort. Since whole-grain foods are already a gold-standard food group, why not consider the potential additive benefits of a sourdough whole-grain bread — as long as it’s consumed in moderation so as not to exceed your overall caloric goal and desired proportion of calories deriving from carbohydrate sources.