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The Truth About Sourdough | Not Healthier! — Transcript

by Novita Listyani · 8,046 words · 856 segments · language en · Watch on YouTube

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0:00Hey everyone, Seraphine here,
0:01and today, we’re going to break down the halo of sourdough.
0:05If you know sourdough, then you probably know how good it is.
0:08Sourdough is widely
0:10used to make the bread taste better, improve the texture and raise its quality.
0:14In the case of some flours like rye,
0:16sourdough acts as an improver to achieve baking ability.
0:20But for all the fanfare around it, here is one inconspicuous fact
0:25about sourdough that you may want to know: as of today, scientific research
0:29has not yet established a clear nutritional or health
0:33benefit for sourdough bread in comparison to yeast-leavened bread.
0:37That’s not my opinion, that is the conclusion
0:39of this systematic review on the nutritional benefits of sourdoughs
0:43that pointed to conflicting evidence and inconsistent results,
0:47or beneficial effects that showed no significant differences.
0:51This scientific review was published in 2022.
0:55Another paper published in July 2023 also agreed with these findings,
1:00and here I quote, “Overall, we conclude that
1:02although a broad range of sourdough
1:04related health benefits are praised in publications, social media
1:08and by bakers, a sound evidence base for measurable effects on health related
1:13clinical endpoints has not been established.”
1:17Clinical endpoints in this statement refer to well-defined clinical endpoints
1:21such as diabetes risk reduction, improved weight management, reduction
1:25of gluten intolerances and improved bone mineral density.
1:30Also from the paper, “there appears to be a clear discrepancy
1:33between observations in vitro/vivo tests with experimental sourdoughs
1:38and supporting data on health effects from human clinical studies.
1:43Because of this situation, health authorities such as EFSA (EU)
1:46or FDA (United States) have thus so far
1:49not approved the use of any sourdough health benefit claim.”
1:53Likewise, the Great Britain Nutrition and Health Claims Register includes
1:57none specific to sourdough or different types of wheat.
2:01So, what gives?
2:03Haven’t we been told, all these years, to believe that sourdough bread is somehow
2:07superior compared to yeast-leavened bread?
2:09In so many aspects, from sensory and functional to nutritional benefits,
2:14including tolerability for that matter, it has been almost like a consensus
2:18that sourdough bread is just simply better.
2:21Now, before we continue, I want to say that this video isn’t
2:24meant to be a negative video about sourdough per
2:26se, rather it’s meant to be a video to properly clarify
2:26what sourdough’s confirmed benefits actually are based on scientific evidence,
2:26so, to that end, most of our discussion will be based on these two reviews.
2:26Let’s get started and I want to begin by looking at how sourdough is perceived.
2:26Within the bread category,
2:47sourdough breads are considered to be unique.
2:49They are perceived to be natural, and from the perspective of food
2:53marketing, these breads have the so-called “health halo” effect.
2:57To illustrate this effect,
2:58you might see the label of sourdough on a package of bread
3:01and think to yourself, this must be healthy for me
3:04even if you have no idea what the actual health benefits
3:08of the bread are or what other ingredients it might have.
3:12More formally, the health halo effect refers to the act of overestimating
3:16the overall favorable nutritional profile of an item based on a single claim.
3:21This is something that brands know all too well, as food marketing
3:25has been known to effectively use health and nutrition claims made on packaging
3:30to create health halos that make food appear healthier than it
3:34is, which in turn can lead to over consumption, hence more sales
3:39for the producers with questionable benefits for consumers.
3:43However, consumer perceptions aside,
3:45without conclusive clinical data on the health benefits of sourdough bread,
3:49food authorities aren’t likely to accept any health claims on sourdough.
3:54One major thing to consider
3:55is that there is no consensus on the definition of sourdough.
3:59Sourdough can mean a range of different starters with different bacteria and more.
4:03As this review put it, “Apart
4:05from commonalities, such as a high level of lactic acid bacteria
4:09and higher levels of activity, sourdoughs differ in composition
4:13with respect to microbiota subclasses, enzymes and metabolic activity,
4:18and the proportion of the flour that is fermented.” In short,
4:21sourdough is a one-size-fits-all glossary with no established
4:25and internationally recognized legal definition.
4:28Which is part of why any health benefit claims on sourdough have,
4:32so far, been denied.
4:34But that hasn’t stopped people
4:36from spreading around health claims that haven’t been officially confirmed.
4:40So, let’s have a closer
4:41look at some of the health claims that are widely spread around
4:45and see if there is any claim that can stand up to scrutiny.
4:49Let’s start with the claim that sourdough fermented breads
4:52are better digestible than yeast-leavened breads.
4:55Now, we have to ask, what does “better digestible” actually mean?
5:00As explained in this review, “Dependent of the factor of measure (time
5:04or quantity) ‘better digestibility’ can relate to less time
5:08required for a component to be completely digested
5:10or that quantitatively more of the food is digested
5:14and consequently less undigested matter passes into the colon.”
5:17Basically, “better digestible” could mean that it takes less time to digest
5:17or that more of it is completely digested before it goes into the colon.
5:18So, it is of crucial importance to define what the term,
5:22“better digestible,” stands for.
5:24“Depending on what we define as ‘digestibility’,
5:27the parameters to be studied can be very different,
5:29which will influence the conclusions regarding health benefits.”
5:34When time is the dependent factor, we can look at appetite and basically,
5:38how full we are after eating the bread, more formally, appetite rating and satiety
5:42markers that are closely associated with the gastric emptying rate.
5:47Now, to be clear, the gastric emptying rate is a measure of the delivery speed
5:51of moving the gastric contents of the stomach into the duodenum.
5:55Gastric contents to be delivered include liquids, digestible
5:58solids, and indigestible food residues.
6:01Now, we can get to the paper.
6:03To systematically review the clinical evidence related to the benefits
6:07of sourdough-fermented bread on health, the authors of this scientific review
6:11searched online for articles that met a predefined set of criteria.
6:15They found 573 articles, of which 25 clinical trials were eligible,
6:20out of this 25, they found 7 studies that focused on appetite markers
6:24as a primary or secondary outcome included a total of 147 healthy subjects.
6:30A total of 7 studies focused on gastrointestinal health parameters;
6:34among which, 4 focused on 90 healthy subjects and 3 investigated
6:39the effects of sourdough breads with a reduced content of fermentable
6:43oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP)
6:47or reduced gluten content, in individuals
6:50suffering with irritable bowel syndrome (IBS) with 170 subjects.
6:55Of the 7 studies that focused on appetite and satiety,
6:58they found conflicting evidence and although some benefits were shown,
7:02the effect of sourdough per se cannot be identified.
7:06“In 5 studies comparing sourdough breads with their yeast counterparts,
7:10no significant differences in any of the satiety parameters assessed
7:14were observed.” In contrast, one study found sourdough bread ingestion
7:18induced a significantly higher appetite and a significantly lower
7:22satiety than those induced by baker’s yeast bread.
7:26In another trial, gastrointestinal perceptions
7:29showed that the feeling of hunger was significantly lower and the feeling for
7:33satiety was higher between 45 and 240
7:37min after ingestion of a sourdough croissant
7:40in healthy subjects than those found after ingestion of its yeast counterpart.
7:45As for gastric emptying, in many references, organic acids
7:49added to food have been shown to have the potential to reduce the gastric
7:53emptying rate and increase meal-induced satiation However, two
7:57studies, with one using paracetamol as an indirect marker
8:01and the other using a C-octanoic acid breath test, showed no differences
8:05in the rate of gastric emptying
8:07after ingesting breads made with different ferments.
8:10So, when it comes to appetite and satiety and the associated gastric emptying,
8:15we can only say with the available studies as our references,
8:18the results show conflicting evidence, we can’t confirm the claim of ‘better
8:22digestibility’ that relate to less time required for a component
8:26to be completely digested.
8:28Thus, the claim that sourdough bread is “better digestible”
8:31in this respect is questionable at best.
8:34Now, if by “better digestible” it’s meant to indicate quantitatively
8:39more of the food is digested, there are many additional parameters
8:43we have to consider, and it is highly related to the claim
8:46that sourdough fermentation improves the nutritional profile of bread
8:50and reduces the content of components that may cause gastrointestinal complaints
8:54in susceptible individuals.
8:56Some people who experience discomfort eating breads made using baker’s
9:00yeast might say that they can enjoy eating genuine sourdough bread.
9:05Using this review as our reference again, we learned that “These claims
9:09are predominantly based on in vitro studies that document
9:13the degradation of (potentially) harmful or anti-nutritive factors,
9:17or an altered digestibility of macronutrients and micronutrients.”
9:22Quick note here, in vitro literally means in glass in Latin,
9:26which makes sense because it means studies done in test tubes and etc.,
9:30outside of a living organism,
9:32on the other
9:32hand, in vivo is the one that means it’s done in a real living organism.
9:36So, when these in vitro studies document the breakdown of potentially
9:40harmful factions or the altered digestibility
9:43of nutrients, they’re doing it on systems outside of a real body.
9:48And as explained in this review,
9:49we can actually quantify a certain aspect of this, we can measure
9:52some of the changes that are happening, and here I quote, “for components
9:56which may cause adverse reactions, the degradation of anti-nutritive factors
10:00during sourdough fermentation
10:02or during proofing of straight dough bread can be quantified.
10:06This includes phytate, lectins, amylase-trypsin inhibitors (ATIs),
10:10rapidly fermentable non-absorbed carbohydrates (FODMAPs), and gluten.”
10:15We can also measure vitamins, phenolic compounds and minerals
10:20that have been synthesized
10:21by the fermentation medium or released from the food matrix in sourdough bread
10:26and compare the
10:27results to straight dough bread.
10:30Here is the issue, though, when we’re talking about in vitro or animal data,
10:35for that matter, for them
10:36to be actually valid in the prediction of the human in vivo situation,
10:41these conditions have to be, at least, ‘very similar’ to the human situation.
10:46For example,
10:46even though rats and mice are frequently utilized, they have major differences.
10:51As explained in the review,
10:52despite promising development in mechanical models, differences
10:56in the set-up and procedures of in vitro studies make direct
11:00quantitative comparisons of data across studies difficult, not to mention
11:04“in vitro studies generally result in data on the nutrient content
11:07within the test digestion system,”
11:10the authors also point out that bio-accessibility
11:13is not the same as bio-availability, although the two terms
11:16are often used interchangeably.
11:18So, more technically, when it comes to nutrients,
11:21the bio-accessibility of a nutrient is defined as the amount of nutrient
11:25that is released from its matrix in the gastrointestinal tract,
11:28becoming available for absorption — for example, entering the blood stream —
11:32while the bioavailability of a nutrient is the amount of nutrient
11:36that can be absorbed and stored by the body’s organs
11:39and tissues and participates in metabolic processes.
11:43For practical purposes, in vitro models are often used to estimate
11:46what might happen in the human body, but they can lack certain important parts.
11:52In the case of digestion and nutrient absorption, the in vitro
11:56model lacks the cells that line the intestines, the epithelium,
12:01that may either consume or convert such molecules to other compounds.
12:06Case in point, as mentioned in the review, “small peptides are readily degraded
12:10by enterocyte proteases and extremely small quantities may pass into the blood.
12:16There they become subjected to hydrolysis by proteases, resulting in very short
12:20half-lives and concentrations too low to induce a biological effect.
12:25Accordingly, the presence of peptides in an in vitro digest has little relevance
12:29for their in vivo absorption and post absorption bioactivity.” So, in general,
12:34what we can take away from this is that sometimes those attention-grabbing
12:38benefits coming from in vitro studies may not necessarily contribute
12:42to any clinically relevant health benefits.
12:44And what that means for the health claim of sourdough being “better
12:48digestible” in the sense of
12:49more of the food being digested, or the rate at which it’s digested,
12:54is that we have to ask whether that really affects human health?
12:58Now, this is a question that is a lot more complex than it sounds
13:02because it involves many aspects of human health and other issues,
13:06it is to a certain extent what we’re going to talk about in the rest of this video,
13:10so let’s start with the resistant starch. Resistant starch
13:14is a carbohydrate that doesn’t get digested in your small intestine,
13:19the reason that it’s often considered “good” is that it, kind of,
13:22acts like fiber and it feeds your good gut bacteria.
13:26Food processing or baking may transform a fraction of starch
13:30into resistant starch, causing a reduction in the glycemic potential.
13:34Sourdough fermentation is often said to increase the resistant
13:38starch content, so let’s take a look at the evidence.
13:41Well, at the fermentation state, available data shows mixed outcomes.
13:45One study reported a fermentation-induced increase
13:49in resistant starch, whereas another found no difference.
13:53There is also another study
13:54that found no resistant starch formation during fermentation
13:57but a 3-fold jump during the subsequent step from proofed loaf to bread.
14:02All studies with the exception of one showed a distinct
14:05but small increase in resistant starch in sourdough bread.
14:09“Nonetheless, the storage time may have a significant impact
14:13on the resistant starch content.
14:15The increase in resistant starch may be caused by the presence of acids,
14:19which promoted starch retrogradation after heat application during the baking step.
14:24However, the degree of gelatinization, porosity and other compounds
14:28may also have an impact.” This is actually pretty good, “but
14:32quantitatively the increases were low and not shown to result
14:36in measurable health effects.” So, now, about resistant starch
14:40and the effect of sourdough on GI or glycemic index.
14:44Glycemic index is a measure of how fast a food can make your blood sugar go up.
14:48It’s generally a good thing if it’s lower.
14:50And with sourdough, “Several studies reported a lower
14:53GI and an improved insulin response of sourdough bread.
14:57Several underlying mechanisms such as the previously discussed
15:00resistant starch content, have been proposed.” So,
15:04it’s often suggested that sourdough bread
15:07results in a lower glycemic index (GI) than yeast-fermented bread.
15:11Well, to save you time, there’s no conclusive clinical
15:14data to support such a claim, as mentioned here.
15:17Examining the problems with many of the studies, “This may result
15:21from improper control conditions, in which other variables than only sourdough vs.
15:26yeast dough making differ, such as comparing a rye sourdough bread
15:30with a yeast wheat bread.
15:31In such a comparison also grain type used, flour characteristics, fiber content
15:37and bread structure will impact on the glycemic response.”
15:41So, a lot of these studies are not making an apples-to-apples comparison.
15:45But that’s not even the worst of it, look, a study was said to compile “data
15:50from 22 studies with in vivo challenges, and concluded that the average
15:55GI of sourdough bread was significantly lower compared to straight dough bread.
16:00However, none of these 22 study sources were cited making a critical evaluation
16:05of the study conditions and inclusion criteria for combining the results
16:09impossible.” The citation pointed to this paper.
16:13From this review we also learned, “More than 50% of the studies
16:17comparing sourdough bread with white wheat bread
16:19did not find significant differences in the glycemic response
16:23of healthy individuals between the groups.” Let’s zoom in on the details.
16:27Among the 20 clinical studies assessing the effect of sourdough
16:31bread on glucose response, either as a primary or as a secondary outcome,
16:36“14 focused on healthy individuals, 2 focused on individuals
16:40with obesity or who were overweight, 2 focused on both healthy and hyperglycemic
16:45individuals, 1 focused on subjects with impaired glucose
16:48tolerance, and 1 focused on individuals with type 2 diabetes.
16:52In total, measures of glucose response were available for 369 individuals.”
16:57Among the healthy subjects, “a total of 14 studies had measures
17:01of glycemic response available for 263 healthy subjects.”
17:05One study found the glucose response was significantly lower
17:09in the sourdough group than in the control group, two other studies found glucose
17:13response was significantly decreased in the sourdough group compared with that
17:17in the yeast group.
17:18“However, no significant differences in glucose response over the assessment
17:22period were observed in 5 other trials.”7 studies compared the effect of sourdough
17:28bread based on wholegrain wheat or rye on glucose response
17:32with that of baker’s yeast white wheat bread in healthy subjects.
17:372 studies found a significant reduction in glucose response over the assessment
17:42period, whereas the other 5 trials
17:45found no identifiable difference.
17:48As for subjects with obesity or metabolic diseases, there were 6 studies,
17:52including a total of 78 subjects with impaired glucose metabolism.
17:57One study indicated a significant reduction in glucose AUC,
18:00area under the curve, another study highlighted a significantly lower
18:06glucose iAUC, incremental Area Under Curve.
18:09Two other studies found no evidence of a difference in glycemic parameters
18:14between whole-grain sourdough bread and white wheat bread
18:18whether in normoglycemic or hyperglycemic
18:21individuals or individuals with type 2 diabetes.
18:25In another trial “including subjects with obesity
18:28and those who were overweight, the observed glucose iAUC
18:32with sourdough white wheat bread was significantly lower
18:36than that observed with white wheat or whole wheat yeast bread.
18:41Using commercial bread, the same research team found that sourdough white
18:44wheat bread was not different from baker’s yeast white wheat bread
18:49regarding its effect on glucose response in subjects who are overweight
18:53when breads were matched for delivering 50 g of carbohydrates.
18:57However, when breads were matched for mass, the glucose iAUC of the sourdough
19:02bread was significantly higher than that of the white wheat bread.”
19:06So, the conclusion is that the effect of sourdough
19:10fermentation on GI is not substantiated, as mentioned here.
19:15Seeing all this data, what really troubles me, at this point, is
19:19how many of the sourdough health claims are actually true?
19:24We have another one to check here.
19:26Some say sourdough bread has some health benefits for cardiovascular health.
19:32Again, using this review as our reference, we saw a total of 7 clinical studies
19:37investigating the effects of sourdough bread on cardiovascular health
19:40parameters as a primary or secondary outcome.
19:44Four studies focused on 73 healthy subjects, and 3 studies
19:48focused on 42 individuals with metabolic impairments.
19:51In one trial, the investigators examined the influence of whole-grain sourdough
19:55bread consumption compared with that of white wheat bread consumption
20:00on a biomarker of cardiovascular disease
20:03that may be altered by dietary carbohydrates.
20:06After a 6-week consumption period,
20:09no significant differences could be observed between the groups.
20:12In another, no differences in blood lipids or inflammatory parameters were reported
20:17between the sourdough and yeast bread groups; however, LDL
20:21cholesterol was significantly decreased compared with baseline in both groups.
20:26No impact of sourdough bread compared with that of white wheat bread on blood
20:31lipids was observed in 4 other studies 2 involving healthy subjects,
20:35one involving individuals with impaired
20:37glucose tolerance, and one involving subjects who were overweight.
20:43“However, in another randomized controlled trial
20:46including healthy subjects, a significant decrease
20:49in both total and LDL cholesterol levels was found after consumption
20:53of whole wheat sourdough bread compared with that after consumption of white wheat
20:58yeast bread.” So, in conclusion, when it comes to cardiovascular health,
21:03no significant differences between groups for all markers, one, and only one, study
21:09observed a significant decrease in both total and LDL cholesterol levels.
21:14And that’s another claim down, it’s further fueling my skepticism.
21:19Now, aside from these claims, there are also many panacea-like claims
21:23about sourdough in the context of addressing adverse reaction
21:27to wheat components and irritable bowel syndrome (IBS).
21:30Okay, the commonly known types of adverse reactions to wheat components are:
21:35celiac disease, wheat allergy, and non-celiac wheat sensitivity.
21:39These are considered to be gluten-related disorders.
21:42Let’s have a quick rundown of these disorders
21:45before we talk about the effects of sourdough on them.
21:49Start with celiac disease, CD.
21:52The pathogenesis of this disorder is autoimmune.
21:55“It is an autoimmune disorder in people when the indigestion of gluten
22:00leads to problems in the body.” The estimated global prevalence
22:04of celiac disease is 1%, but regional prevalence may vary.
22:08Uptake of this disorder is oral.
22:10Peptides from gliadins and glutelins have been shown to be the triggers.
22:14A gluten-free diet is the suggested therapy.
22:18Wheat allergy is typically
22:19an allergic reaction to the seed storage proteins found in wheat.
22:23It is more common in children and can be associated with a severe reaction
22:27such as anaphylaxis and wheat-dependent, exercise-induced anaphylaxis.
22:32It is “characterized by T helper type 2 activation
22:36which can result in immunoglobulin
22:40E (IgE) and non-IgE mediated reactions.”
22:42This disorder affects 0.2–1% of the population and children
22:46appears to have a higher prevalence of this disorder compared to adults,
22:50especially if wheat was introduced after 6 months of age.
22:55“The increased prevalence in children compared to adults can be explained
22:59by the fact that most patients outgrow their allergy by the age of 16
23:04years.” Known uptakes of this disorder are oral, respiratory
23:08and through the skin or percutaneous.
23:10Depending on the type of the allergic reaction,
23:13it could be triggered by gliadins, glutelins and/or
23:16non-gluten proteins such as amylase-trypsin inhibitors (ATIs).
23:20The suggested therapy is a wheat-free diet.
23:23Non-celiac wheat sensitivity (NCWS) is defined as a condition
23:27of self-reported unspecific immune-based reaction
23:31following the ingestion of wheat or other gluten-containing foods,
23:35after exclusion of celiac disease, and IgE-mediated wheat allergy.
23:40The term non-celiac wheat sensitivity actually used to be called non-celiac
23:45gluten sensitivity, but due to a strong focus on FODMAPs
23:49leading some groups to conclude that it was FODMAPs instead of gluten
23:53causing sensitivity symptoms, the non-celiac gluten sensitivity
23:57was changed to non-celiac wheat sensitivity to reflect that.
24:02“observational studies from across the globe suggests that approximately 10%
24:06of the population is self-reporting wheat sensitivity.” Quoting from the paper,
24:11“The major reason for this is that self-reported symptoms
24:14may, to a large extent, be due to belief, which is strongly influenced
24:20by the effects of social media news as well as socio-economic factors.”
24:24In one study, for example, investigating 392 patients
24:28complaining of gluten-related symptoms; the researchers found 26 [6.63%]
24:32cases of celiac disease, 2 [0.51%] cases of wheat allergy
24:36and 27 [6.88%] were diagnosed with non-celiac wheat sensitivity.
24:40The remaining 337 patients [85.96%]
24:43did not experience any change of symptoms with a gluten-free diet.
24:47So, the authors concluded self-perceived gluten-related symptoms
24:50are rarely indicative of the true presence of symptoms due to gluten consumption.
24:56The pathogenesis of non-celiac wheat
24:59sensitivity is unspecific or partially immune-based.
25:03Uptake of this disorder is oral.
25:05Wheat components that might trigger this sensitivity are amylase-trypsin
25:09inhibitors (ATIs), gluten and FODMAPs, predominately fructans.
25:14Suggested therapy is either wheat-free or strong reduction of wheat in diet.
25:20“Irritable bowel syndrome (IBS) is a functional bowel disorder
25:24in which abdominal pain or discomfort is associated
25:27with defecation and/or a change in bowel habit.
25:31Sensations of discomfort (bloating), distension, and disordered defecation
25:35are commonly associated features.” “IBS
25:38represents the most commonly diagnosed functional gastrointestinal disorder
25:43with an estimated global prevalence of about 1 in 10,
25:47ranging from 7 to 21%.” Because it is a cluster of symptoms
25:52caused by multiple pathologies, accurate diagnosis of IBS
25:56is difficult, and prevalence estimates are often based on self-diagnosis.
26:01“There is still no standardized test or biomarker for diagnosis,
26:06an examination of the detailed patient history is essential for an appropriate
26:09diagnosis.” So, pathogenesis of IBS is diverse and not clear.
26:14Uptake is usually oral.
26:16FODMAPs, amylase-trypsin inhibitors (ATIs), and gluten are potential triggers.
26:20Exact triggers are hard to be defined.
26:23“Most patients assume that their symptoms are caused by specific foods,
26:26in particular foods rich in rapidly fermentable carbohydrates
26:30such as fruits, vegetables, pulses and grains” Gluten-free and low
26:34FODMAP diet are usually suggested for people suffering from IBS.
26:39Okay, after the summary of the disorders, now let’s have a look at the components
26:43that cause these adverse reactions.
26:46Start with cereal grain proteins.
26:48According to their solubility, cereal grain proteins have been traditionally
26:51classified into four so‐called Osborne fractions: albumins, globulins,
26:57prolamins, and glutelins [Osborne, 1907], along with residual proteins.
27:00Albumins, soluble in water and dilute salt solutions;
27:04Globulins, soluble in dilute salt solutions; Prolamins, soluble in aqueous
27:04alcohols, [for example, 60% ethanol or 50% propanol,] but insoluble
27:04in water and salt solutions; Glutelins, soluble
27:10in dilute acid.
27:15A quick glance at the solubility of these fraction, and if you have
27:18been baking with long fermented dough using poolish or sourdough;
27:22you may well be familiar with the byproducts that come with it,
27:25such as ethanol and organic acids; from this, it wouldn’t
27:29be hard to speculate which of these fractions
27:31would be influenced by long fermentation, including sourdough naturally.
27:35But, wait, before jumping to conclusions, let’s gather more information first.
27:40So, of these four factions, the first two, the albumin and globulin fractions
27:45“mainly contains regulatory, metabolic, and protective
27:49proteins such as enzymes and enzyme inhibitors.”
27:52They are easy to distinguish and their names are still used today.
27:56On the other hand, the remaining 2 factions are a bit
27:59more complicated to specify.
28:01Quoting from this review
28:02article, “prolamins were recognized as a defined group present
28:05only in cereal grains with the name being based on their high contents
28:10of proline” and glutamine, and in fact, prolamins are given
28:13specific names in different cereal species, such as gliadin
28:17in wheat, hordein in barley, secalin in rye, and so on.
28:22Now, the final faction, glutelin, is actually more difficult to define.
28:26This is because it basically comprises “all proteins which are insoluble
28:30in the three previous solvents but can be solubilized
28:34under conditions of extreme pH.” So, proteins that do
28:37not fit into the previous 3 factions end up in here.
28:40Hence, glutelin proteins are actually a mixture of unrelated proteins, some
28:44being “insoluble structural and metabolic proteins such as those bound
28:48to membranes and cell walls”, but these are the minority.
28:52Taking it straight from the review, “the major glutelin components are in fact
28:56prolamin subunits which are not extractable
28:58with alcohol/water mixtures”, and this is because of their presence
29:02as high molecular mass polymers that are stabilized by inter-chain
29:06disulphide bonds.
29:06In wheat, you are probably familiar with the glutelin faction,
29:11where it goes by the name glutenin.
29:13Glutenin is present in about equal amounts to the gliadins
29:16in wheat, and together, these two groups make gluten.
29:19With these factions now clear, there is one more piece
29:22of information to add, traditionally, the proteins in wheat
29:25have been divided into 2 groups, prolamin and non-prolamin proteins.
29:29In this case, the prolamins consist of the gliadins and glutenins,
29:33while non-prolamins consist of the other proteins
29:36including salt and water-soluble globulins.
29:39Now, as we have mentioned before, prolamin proteins are high in proline
29:44and glutamine, and that’s what makes them the main storage proteins.
29:48During gastrointestinal digestion, the enzymes, chymotrypsin or pepsin,
29:53present in the human intestine
29:55can only partially digest the proline-rich sections, consequently,
29:59this can easily trigger adverse reactions in predisposed individuals.
30:03Many food allergens are heat-stable proteins
30:06that have molecular properties, such as disulfide bonds, protein glycation,
30:11the ability to bind lipids etc., that can provide conformational stability.
30:15These properties can protect food allergens from degradation by heat,
30:19proteases, or acid hydrolysis, thus, enhancing the uptake of intact
30:24protein in the gastrointestinal tract, not a good thing.
30:27It shouldn’t be surprising that a large number
30:30of wheat allergens can be found among the group of prolamins.
30:34Undigested gluten peptides contain repeated amino acid
30:39sequences, also referred to as CD-active epitopes.
30:43These are antigen molecules to which immune cells recognize,
30:47and therefore, when exposed to the gut epithelium,
30:50they may give rise to a cascade of immune and inflammatory responses.
30:55Among these molecules is immunodominant* 33-mer gliadin peptide that has been found
31:01to be highly resistant to proteolysis despite prolonged exposure.
31:0533-mer gliadin peptide “has frequently been described as the most important
31:11CD-immunogenic sequence within gluten.” It’s a big deal
31:15when it comes to these wheat allergens that triggers our immune response.
31:19Citing this paper as a reference, this review stated,
31:22“The number, type, and distribution of epitopes may influence the potency
31:27of the inflammatory and immune responses involved in the etiology of CD.” Besides
31:33prolamins, non-prolamin proteins make up a small proportion of cereal proteins.
31:38Several of these proteins, though,
31:39may cause adverse physical reactions in sensitive people.
31:43Among them, “ATIs and non-specific lipid transfer proteins (nsLTPs) can sensitize
31:48susceptible atopic patients after ingestion or inhalation.”
31:53ATIs are also thought to be involved in the cause of non-celiac wheat sensitivity.
31:57Amylase/trypsin inhibitors (ATIs) are a group of proteins
32:01that are present in the seeds of all cereals and are the most abundant
32:05proteins in the water soluble or albumin fraction of wheat.
32:09Like gluten proteins, ATIs are primarily present in the endosperm, and they are
32:14also found in isolated vital wheat gluten, which is a common addition to foods.
32:19Non-specific lipid transfer proteins (nsLTPs) belong to a group of structurally
32:23related proteins that are often referred to as α-class proteins.
32:27They are good examples of true food
32:29allergens, in the sense that they are capable of sensitizing, i.e.
32:33inducing specific immunoglobulin E (IgE), as well as, of eliciting severe symptoms.
32:39These proteins have a very stable structure
32:42that gives nsLTPs their extreme resistance to proteolysis,
32:46heat denaturation and other forms of processing.
32:49This stability allows the allergen to reach the gastrointestinal
32:53immune system in an immunogenic and allergenic conformation,
32:57allowing sensitization and induction of systemic symptoms.
33:00This stability is a recurring theme in problematic food allergens
33:04and such stability also explains the presence of such allergens
33:07in processed foods.
33:09In addition to proteins, wheat contains fructans.
33:12Fructans are recognized as health-promoting food ingredients;
33:16and as indigestible carbohydrates, fructans are classified as FODMAPs.
33:21FODMAPs are considered potential triggers of IBS
33:24and maybe even of non-celiac wheat sensitivity.
33:27As one example, lactose is a non-digestible disaccharide
33:31to approximately 70% of the world population, while approximately
33:3615% are “ fructose-malabsorbers, meaning that ingested fructose
33:40is not completely absorbed in the small intestine or is absorbed
33:44only completely when glucose is also present at the same time.”
33:48FODMAPs are a little bit complicated health-wise, because as a soluble dietary
33:53fiber and fermentable carbohydrate, they are beneficial to human health,
33:57“however, whether FODMAPs ingestion is beneficial
34:00or harmful is dose and individual dependent.” “A quantity of >15
34:04g of FODMAPs per day results in quantitative effects on osmosis induced
34:09liquid accumulation in the terminal small intestine
34:11and on fermentation in the terminal cecum and colon, which may cause bloating,
34:16flatulence and abdominal discomfort in susceptible people.
34:19“ Low-fructan meals may help reduce
34:22intestinal gas formation and alleviate symptoms in IBS patients.
34:27But as with many aspects of health,
34:29we need to pay attention
34:30to a more balanced picture, taking this quote from this paper,
34:33“Non-starch polysaccharides from wheat are a major source
34:36of dietary fiber in for example, breakfast cereals and breads.
34:40Hence, reduction of FODMAP intake
34:43will be associated with reduction of fiber intake, unless specific effort
34:47is made to replace with low FODMAP fibers such as rice bran or oats.
34:51Since dietary fiber is important for laxation, a risk of reducing
34:56fiber intake is constipation, which can complicate symptoms in patients
35:00following the low FODMAP diet.” So, a balanced diet is still very important.
35:04Now, let’s have a look at the reduction of these potentially harmful components
35:09by sourdough fermentation.
35:10To clarify, there are many types of sourdough
35:13in baking applications, but as a home baker,
35:15we’re going to limit ourselves to only one type that we use most frequently,
35:19the type-I sourdough, of which the inoculum is done by back
35:23slopping, it’s usually used as the sole leavening agent.
35:26Typically, around 20–30% of the flour
35:29in a bread dough is subjected to a relatively long fermentation time,
35:33more than 6 hours, and proofing time generally exceeds 2 hours.
35:37Key bacterium includes Fructilactobacillus sanfranciscensis,
35:40and other potential bacteria here.
35:44Key wild yeast include Kazachstania humilis, other yeasts are S.
35:49cerevisiae, K. exigua etc.
35:51It’s also noted that, “Amateur bakers at the household level
35:55include more extensive interruptions of the continuous back-slopping process
36:00and use only 5–10 back-slopping cycles per month.
36:04The microbial consortia in these sourdoughs depends on the diverse
36:08fermentation conditions of the individual bakers.” “Lactobacilli other than Fl.
36:14sanfranciscensis are likely to predominate and S.
36:17cerevisiae is the most prevalent yeast.” Sourdough fermentation has the potential
36:22to alter the quantity and structure of wheat components,
36:25which may affect the way these components
36:27are presented to the intestinal epithelium and immune system.
36:32From the review, “Although there is no validated strategy
36:35for producing cereal-based sourdough-fermented foods
36:38with lower levels of allergens and triggers of CD and NCWS,
36:43experimental sourdoughs have shown reductions
36:46that potentially may reduce adverse reactions.”
36:49Now, when talking about sourdough, we would be remiss not to mention
36:53protease activity and how it might change protein digestion.
36:57Due to a low pH, less than pH 4.5, type I sourdough,
37:02the type we home bakers normally use, exhibit significant proteolysis.
37:06These acidic conditions activate endogenous proteases in the flour.
37:11These endogenous enzymes along with the lactic acid bacteria’s
37:15proteolytic enzymes induce significant degradation of peptides,
37:19including toxic gluten epitopes, this breakdown results
37:23in an almost linear increase in amino acids with fermentation time,
37:27which contributes to the better flavor and taste of sourdough bread.
37:31To add to the proteolytic activity, “reducing power generated by sourdough
37:35microbes impacts protein stability and proteolytic degradation.”
37:39Gluten proteins are essentially weakened by certain lactobacilli
37:43that “accumulate reduced glutathione, or produce other low-molecular
37:48weight thiols that interact with glutathione to reduce intra-
37:51and intermolecular disulfide bonds”, this, of course, also impacts bread volume.
37:56In a species like Fructilactobacillus sanfranciscensis, the glutathione
38:00reductase “has been found to enhance the degradation of wheat
38:04germ agglutinin and allergenic ovotransferrin in sourdoughs”.
38:07In terms of health benefits, “the reduction of disulfide bonds to thiol
38:12groups decreases the resistance to proteases and potentially alleviates
38:17adverse events such as inflammation, immune and allergic responses
38:21that are dependent on proteins with an intact tertiary structure,
38:24either for activity or for passage through the intestinal tract.”
38:28It has to be noted though that” the reduction of intramolecular
38:31thiol groups during the breadmaking process,
38:35however, has been documented only for type I sourdoughs.” Now, the review continues
38:40by explaining what goes on during protein digestion
38:44and why it can sometimes cause problems for our immune system.
38:48Starting at the top, after we take a bite of our food
38:50and consume it, “protein digestion takes place via the combined action
38:55of stomach acid and gastrointestinal enzymes
38:58(pepsin, trypsin, chymotrypsin), in combination with brush border
39:02peptidases.” These enzymes are supposed to breakdown the protein that we ate,
39:07but sometimes, specific protein and peptides can resist being broken down
39:12because of the “lack of specific gastrointestinal enzymes
39:16required for their complete degradation.” You should not be surprised
39:20that gluten proteins are an excellent example of this.
39:24This is because grain proteins like gluten are particularly high
39:27in disulfide bonds and/or proline.
39:31Our gastrointestinal tract “lacks the proline-specific peptidases
39:35required to cut the post-proline bonds in the gluten peptide chains,
39:39resulting in incomplete digestion and leaving proline-rich
39:43gluten fragments intact.” This is a problem because these “fragments
39:47induce immune responses and inflammation, causing CD.”
39:52The fragments are commonly called “toxic gluten peptides (epitopes)
39:56that can be recognized by the immune system.” Quoting from our reference, “A
40:00reduction of gluten epitope levels in food by proline-specific peptidases
40:05during food processing, may help reduce adverse reactions.” So,
40:09the way we make our food could help us limit these reactions and indeed,
40:13“Many lactobacilli as well as fungi, including Aspergillus oryzae,
40:18express proline-specific peptidases that cleave peptide bonds
40:22adjacent to proline.”* This is pretty good, but
40:25before we get ahead of ourselves, the authors continue by stating, “However,
40:29sourdough products available on the market are generally not processed in this way,
40:34and there is no data to support the claim that sourdough breads
40:38reduce the risks of developing celiac disease.” So, in the end,
40:42the only truly effective treatment for celiac disease
40:46is a strict adherence to a lifetime gluten-free diet.
40:50Now, let’s talk about the conversion of FODMAPs.
40:53In vitro trials demonstrated that sourdough fermentation
40:56can significantly reduce the FODMAP content in bread, with certain microbiota
41:01being able to almost completely degrade it, meaning that sourdough bread
41:06could potentially be better for IBS patients
41:09by mitigating gas formation related intestinal discomfort.
41:13That being said, though, it has to be noted that Baker’s yeast
41:16fermentation alone is also very effective in reducing FODMAP content
41:21and in vivo clinical evidence supporting the safety of the resulting
41:25low-FODMAP bread in patients with IBS remains to be confirmed.
41:30A research team investigated the effects of sourdough
41:33bread on IBS symptoms comparing control bread that was prepared
41:37using traditional rye sourdough and low-FODMAP rye bread
41:41that was prepared using a specific Lactobacillus strains which resulted in
41:46rye bread with a clearly lower FODMAP (fructan and mannitol) content.
41:50They found no significant differences in IBS severity score (SS)
41:55or IBS quality of life values between traditional sourdough
41:59and low-FODMAP sourdough rye breads in 87 subjects with IBS.
42:05However, abdominal symptom scores and hydrogen breath concentrations
42:09significantly improved in the low-FODMAP bread group.
42:13A subsequent study by the same team confirmed sourdough
42:16baking reduces the quantities of both ATIs and FODMAPs found in wheat,
42:21but the sourdough bread was not tolerated better than the yeast-fermented bread.
42:26However, the score related to non-GI symptoms (such
42:29as tiredness, joint symptoms, and decreased alertness)
42:32was significantly higher in the low-FODMAP sourdough group than in the yeast group.
42:38One randomized controlled trial reportedly used sourdough fermentation
42:42with specific Lactobacillus strains and fungal proteases to lower
42:47gluten content in wheat bread, and then assessed
42:50whether the resulting product would reduce gastrointestinal symptoms
42:54in patients with IBS, compared with normal-gluten bread.
42:58The study reported a significant decrease in gastrointestinal symptoms
43:02for the gluten-reduced sourdough bread when compared with yeast bread
43:06that had normal gluten content, but they did not report
43:10any changes in IBS-Severity Score or IBS quality of life scores.
43:14Another study comparing a regular rye sourdough with a specific sourdough
43:19containing unique lactobacilli that efficiently metabolize fructans
43:23showed no significant improvement of symptoms.
43:26From all these results, we can see that “the clinical relevance
43:29of sourdough bread for FODMAP-sensitive individuals remains unclear
43:33and the effects may be more dependent on the composition of the overall diet.”
43:38Thus, this is another sourdough health claim that remains questionable at best.
43:44Okay, let’s talk about the reduction of anti-nutritive compounds and contaminants.
43:49Starting with phytate or its phytic acid.
43:52Phytic acid is often labelled an anti-nutrient
43:55because it binds to minerals like iron and calcium, becoming phytate,
43:59and since we lack the phytase enzyme to break it down, this
44:03phytate passes through our system, taking along with it all those minerals.
44:08Whole wheat flour, for example,
44:09has quite a bit of minerals but some of them are bound in phytates,
44:13and this makes them, in theory, pretty difficult to access.
44:17In fact, since phytic acid is capable of bonding to “minerals
44:21and trace-elements that are part of fluxes between blood and gut”,
44:25consuming phytates could actually result in a net negative balance.
44:30To put it simply, you could consume a phytate
44:32which is phytic acid bound to some minerals,
44:35and then as it passes through your stomach, the phytic acid
44:38binds to whatever other minerals or trace elements it meets,
44:42and when it finally passes through your system, you could end up
44:45with less minerals and trace elements than before you ate the phytate.
44:49This may not be a very big deal for healthy people with varied diets
44:54but in the case of those with mineral deficiencies,
44:57this can be a real problem, and one of the touted benefits of sourdough
45:01fermentation is that it reduces phytate content, as this paper notes,
45:05and I quote “ Long-term SD fermentation, with a mutual effect of acidification
45:10(which stimulates flour endogenous phytases)
45:12and the presence of phytates expressing microbiota, results
45:16in significantly higher PA degradation, compared to short term yeast
45:21fermentation.” Reading up to here,
45:23you may think that this is it, case closed, this is a clear health
45:26benefit from sourdough fermentation and there’s nothing more to it.
45:30But it’s actually more complicated than that.
45:33Starting with the degradation, the same paper states that, “the
45:37benefit of the need for use of selected lactobacilli for this purpose
45:41is challenged by data from Leenhardt et al., who showed that only moderately
45:46acidifying the dough with lactic acid (not less than pH 5.5),
45:51in the absence of lactic acid bacteria, resulted in similar
45:55PA degradation compared to the use SD fermentation alone.”
45:59These are pH levels that we can actually reach with yeast too
46:03as long as we let it ferment for long enough.
46:05So, phytate degradation may not really require sourdough fermentation.
46:09But if we continue with the paper, things get more complicated,
46:13because even though in vitro digestion studies do generally confirm
46:17that fermentation-induced acidification of dough reduces
46:20phytate content and increases the amount of free ionized minerals,
46:25this improved bio-accessibility which potentially facilitates
46:28the bio-availability of minerals, does not necessarily result
46:33in an improved mineral status of the human body.
46:36The paper continues by stating, “The latter is the longer-term
46:40effect of digestion and the absorption of multiple meals
46:44passing the entire gastrointestinal tract, and the subsequent distribution
46:48and excretion of absorbed/non absorbed minerals.
46:52This encompasses much more than the digestion of a single test meal in vitro
46:57in a simulated intestinal compartment, where many in vivo factors
47:00(neural regulation, blood flow, hormonal responses,
47:01gut epithelium associated factors, microbiota metabolism, etc.) are absent.
47:02” Additionally, let’s not forget that our stomach acid is very low in pH,
47:07and after the ingestion of bread, phytates “may be partially broken down due
47:13to phytase activity induced by acid exposure in the stomach.”
47:17This is paired with microbiota activity in the colon where pH reduction due
47:21to fermentation of dietary fibers also happens, “ significant PA degradation
47:26can take place, resulting in the solubilization of mineral complexes,
47:31an increase in ionized free minerals and their colonic absorption.”
47:35Showing the complexity of this matter, one in vitro study
47:39“showed that the fermentation induced decrease in phytate
47:42and the increase in ionized minerals (bio-accessibility)
47:45cannot be directly generalized to better absorption/bio-availability.
47:49” While the study confirmed that whole-grain sourdough bread had a greater
47:55phytate degradation than yeast bread (respectively sourdough 100% vs.
47:59yeast 75%).
48:00It was shown that neither the yeast nor the sourdough bread resulted in increased
48:05ferritin levels, a measure of iron uptake, in cultured intestinal cells.
48:09Of course, in vitro, as mentioned, has its limitations.
48:13So, we turn to in-vivo studies.
48:15One such study “ observed that the consumption of a low-phytate
48:18wholegrain bread in a total diet context, compared to a high-phytate
48:23wholegrain bread, did not improve iron status in humans.
48:27Others observed no significant effects in iron absorption from meals prepared
48:32using genetically modified maize containing 30–50%
48:36less phytic acid, compared to regular maize.”
48:39Adding to these studies, it’s also known that other ingredients or foods in a diet
48:44can influence mineral absorption, such as how calcium can interfere
48:48with iron absorption.
48:49Taking it from the paper, “Thus, PA is only one of many factors
48:54influencing overall mineral uptake by the human body
48:57and the reduction of PA levels in food alone,
49:00without consideration of other factors,
49:02may slightly increase total bio-accessibility but
49:05may be ineffective in reducing the prevalence of mineral deficiencies.”
49:09Taking another quote from the paper’s conclusion, “The available evidence
49:13clearly indicates that, for the enhancement of iron absorption
49:17in individuals who have a marginal mineral intake,
49:20the fortification of flour (foods) is more effective
49:24than fermentation-induced PA degradation during food processing alone.
49:28Although fermentation conditions vary widely, and the fortification of flours
49:32can be realized with high precision and within narrow ranges.
49:36A combination of fermentation and fortification may nevertheless
49:40potentiate positive effects.” The authors also make clear
49:43that, “In Western countries, it is increasingly recommended
49:47to consume a diet rich in whole grains, legumes, vegetables, seeds and nuts,
49:52which seems controversial since most of these are relatively high in PA.
49:57However, there is no doubt that this is associated with improved health outcomes.
50:02The advice to avoid the consumption of whole grain foods
50:05because they contain PA is unjustified.” Now, another anti-nutritive compound,
50:11wheat germ agglutinin, as present in raw cereal materials,
50:15is a lectin with the potential to reduce nutrient absorption
50:18and cause digestive problems, such as NCWS.
50:23This study found that fermentation
50:24with homofermentative and heterofermentative lactobacilli
50:28reduces the content of WGA in wheat sourdoughs.
50:32Previous reports on wheat germ fermentation assumed that WGA
50:37was denatured during baking, but comparison of its thermal stability
50:41and the crumb temperature during baking suggests
50:43that it might not be fully denatured in all products.
50:47All things being said though, the actual impact of WGA on health
50:51and NCWS “remains controversial because adverse effects
50:56were observed in vitro, but suitable in vivo studies
50:59remain elusive.” Thus, this study showing the reduction of WGA content due
51:04to sourdough fermentation “is likely to add one piece to the large
51:08but rather incomplete puzzle
51:09that relates wheat components and sourdough fermentation
51:12to the (in)tolerance of wheat products in NCWS and irritable bowel syndrome.”
51:19As a prime example of something that can really annoy our bodies, “ATIs
51:23are relatively heat and acid stable as well as digestion resistant.
51:27As a result, they remain
51:28largely intact during food processing and during gastrointestinal transit.”
51:32As if that wasn’t enough,
51:33they can also inhibit digestive enzymes, and “induce innate immune responses
51:38and inflammation, which is why they are suspected to play a significant
51:41role in the etiology of CD and NCWS.”
51:46Now, there are several studies examining the fate of ATIs
51:50during sourdough fermentation but “these studies have only investigated
51:54the degradation resulting
51:55from fermentation in dough samples and not in the baked bread”.
51:59To add to that, “extraction protocols that do not account
52:02for denatured or aggregated proteins in bread
52:05were frequently used or model systems with protein fractions were examined.
52:10Therefore, data of effects of the consumption of ATIs
52:14by humans, as present in heat-processed cereal foods, analyzed appropriately,
52:19are required for drawing valid conclusions.” For another popular claim,
52:23sourdough fermentation
52:24is often suggested to promote gut microbiota and health as well.
52:28However, a recent review pointed out eminent knowledge
52:31gaps which limits developments of a personalized nutrition.
52:35So, for now, at least, it remains an inconclusive benefit clinically.
52:40In conclusion: Let’s read the words from these authors:
52:44“Although this review revealed that sourdough fermentation alone
52:48did not result in a direct and measurable health benefit, the sum of changes
52:53in structure of ingredients and metabolic products might have indirectly
52:57positive effects for human nutrition and wellbeing of consumers.
53:01Furthermore, increased shelf life of sourdough bread and reduced
53:05susceptibility for spoilage contribute to food safety.”
53:08Also, “Sourdough fermentation particularly allows replacement of hyper-palatable
53:13baked goods, which are high in sugar, fat, and salt and were shown
53:17to increase the ad libitum food intake, with more wholesome recipes.
53:22This beneficial impact on bread quality also relates to superior whole-grain
53:26or fiber-enriched products and thus supports a healthy nutrition
53:30and lifestyle.” So, it’s not like sourdough has no benefits
53:34or that we should avoid sourdough, heck no, sourdough is pretty good, and
53:40there are real, sensory, and functional benefits to baking sourdough bread.
53:44However, we have to be pretty careful with some of the health claims of sourdough
53:48and we have to make sure we aren’t misled by the “health
53:51halo” effect propagated by food marketers.
53:54Especially when considering that there are real consequences
53:57to those who suffer from gluten related disorders, wheat sensitivities and IBS.
54:03Sourdough is sourdough, it’s not a synonym
54:06for healthy, at least not yet.
54:10Okay, that’s it for today, thanks for watching and bye!

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