Suche
Relation
T. Korem, D. Zeevi, N. Zmora et al. Bread influences clinical parameters and induces gut microbiome-associated personal glycemic responses.Cell metabolism. 2017;25(6):1243-1253.
Draft
Randomized crossover study
Participant
Twenty healthy participants, 9 men and 11 women, aged 18 to 70 years.
Study parameters assessed
Participants were randomized into 2 groups. One group ate industrially produced white bread with sourdoughSaccharomyces cerevisiae(baker's yeast), the other ate traditionally ground whole-grain sourdough bread (the study did not specify which organisms the sourdough contained). Participants in each group consumed bread containing 50 g of available carbohydrates every morning for a week, plus additional consumption of this type of bread ad libitum throughout the day. Participants were instructed not to consume other wheat products during this time. After a two-week washout period, the groups rotated for another week.
Primary outcome measures
glucose metabolism (quantified by oral glucose tolerance test) and waking glucose levels; Secondary outcome measures included blood chemistry, thyroid-stimulating hormone (TSH), lipids, and blood pressure. Stool was collected on days 1, 6, 20, and 27 and analyzed for the presence of microbial species.
Key insights
Overall, no significant difference was found in the primary outcome measures between the consumption of conventional white bread and wholemeal sourdough bread. In fact, a large interpersonal variability was found in the postprandial glucose response (PPGR) to the two types of bread - 10 participants had a lower glycemic response to white bread and 10 had a lower response to sourdough.
Practice implications
Although the sample size and duration are small, this study is intriguing because it examines the relationship between microbiome composition and glycemic response. While no significant difference was found overall in the glycemic response to the white bread compared to the whole wheat sourdough bread, there were interpersonal differences. Some people consistently had a higher glycemic response to white, some to sourdough. When stool flora composition was analyzed, each individual's microbiome was predictive of their glycemic response. Additionally, each person's microbiome remained relatively constant throughout the testing period, regardless of what type of bread the person ate.
Previous studies have shown that several factors influence PPGR for bread products. Steaming bread instead of baking it, for example, lowers its glycemic index. The structure of the bread itself can also influence glycemic response: One study found that compact products like pita bread and pasta had a lower peak glucose and insulin response compared to bread with a porous structure.1Prolonged proofing also increases porosity and therefore the glycemic index.2Adding or replacing fiber and grains such as inulin, oat fiber and rye flour to traditional wheat bread can also reduce the glycemic response.3-5Data on whether sourdough reduces glycemic response compared to yeast bread is mixed. While all of this is very useful information for advising patients on how to eat healthily to support healthy blood sugar levels, this study opens up the opportunity to take our advice a step further into the realm of individualization.
This new understanding of the microbiome offers doctors the opportunity to use data from patients' stool samples to individualize their nutrition and supplementation plan.
The connection between the gut microbiota and blood glucose regulation, including metabolic syndrome and type 2 diabetes, has become increasingly clear in recent years. The presence of certain bacteria in the gut appears to be associated with increased inflammation, obesity and insulin resistance, while others are associated with reduced inflammation and metabolic balance.6.7
An article from 2015 inDiabetologyNotes: “LactobacilliSpecies, on the other hand, correlate positively with fasting glucose and glycosylated hemoglobin (HbA1c) levelsClostridiumSpecies are negatively correlated with fasting glucose, HbA1c and insulin levels. A recent study suggests that higher blood glucose concentration can be predicted by a reduction in the proportion of anaerobes, particularly Bacteroides.”8In this study, 2 were the bacteria that informed the glycemic response prediction modelCoprobacter fastidiosus(Phylum Bacteroides) andBacterium Lachnospiraceae3_1_46FAA (class Clostridia). In a rat studyLachnospiraceaeThey have also been found to contribute to the onset of type 2 diabetes.9
This new understanding of the microbiome offers doctors the opportunity to use data from patients' stool samples to individualize their nutrition and supplementation plan. Unfortunately, however, few of us are currently able to obtain complete microbiome studies at relative abundance, and the tools to interpret these data in a clinically relevant manner do not yet exist on a large scale. On the other hand, blood sugar control is not only predicted by the presence or absence of certain species – it is related to the composition of the microbiome as a whole. Reduced genetic diversity in the microbiota as well as a general decrease in butyrate-producing bacteria are also associated with an increased incidence of metabolic disorders.7.10With this in mind, helping people understand how to eat in their environment and live in ways that increase exposure to many different microorganisms is a less daunting task and relevant to any patient hoping to improve their glucose tolerance.
We are not yet able to individualize our nutritional plans to people's microbiome, but we have good tools to increase its genetic diversity. Of course, while the gut flora remained largely the same in each person during this study, other studies have shown dietary changes that promote the growth of different types of bacteria. Prebiotics have been shown to reduce postprandial and fasting glucose and improve insulin sensitivity.10For example, melanoidins, the product of the Maillard reaction that occurs when starch and protein are baked together and form the browned component of the bread crust, have been found to decrease enterobacteria, which promotes inflammation, and increase bifidobacteria, which may improve glucose tolerance.11-13Inulin and other polysaccharides such as fructooligosaccharides have also been shown to increase the production of bifidobacteria.14
The other good news is that general dietary supplementation with commercial probiotic formulations and fermented foods can also positively impact blood sugar. Meta-analyses of studies in people with type 2 diabetes and metabolic syndrome have shown that patients supplemented with probiotics (unspecified type) had both lower fasting blood glucose and HbA levels1C.15-17Probiotic supplementation has also been shown to increase insulin sensitivity and reduce inflammation. Interestingly, a meta-analysis showed that the effects were greater for fermented milk products than for encapsulated strains, suggesting a preference for the greater diversity of bacteria in food sources.18.11This supports the idea that greater variety is better for blood sugar control. Taking this idea even further, several studies have suggested fecal transplantation as another viable therapy for diabetes.19.20
While the primary measurements of this study showed no significant overall difference in glycemic response to the different types of bread consumed, data from each person's microbiome was used to predict individual response. This gives us a new factor to consider when helping patients control their blood sugar. By looking at the balance and diversity of gut flora, we can further individualize treatment to help patients improve and maintain metabolic health.