Prevotella in the gut appears to improve glucose tolerance

Last week we wrote about a study that showed that the glycemic response from foods was a function of the microbiome, and alluded to the fact that the microbiome likely affects many aspects of metabolism.  Another paper was published this week, in the journal Cell Metabolism, that describes which bacteria are responsible for some of these effects.  The authors describe how Prevotella improve glucose metabolism in healthy human subjects.

The scientists gave 39 subjects white bread and barley bread for three consecutive days and measured their glucose and insulin responses to the diets.  For the most part, the barley bread was associated with an improved response over white bread, but some of the individuals’ responded with a much more stark improvement than others.  The scientists then measured the gut microbiomes of each individual and noted that the microbiome changed in the most responsive individuals, and this change was characterized by an increase in Prevotella (specifically Prevotella copri) and methanogenic archaea.  The opposite effect was seen in the individuals that responded least to the barley bread intervention.  The scientists then confirmed these results in mice.  Mice that were given fecal microbiota transplants from human responders, or P. copri probiotics had improved glycemic responses to high fiber diets than control mice.

Prevotella comes up in a lot of microbiome literature as a bug seen in ‘traditional’ societies that eat a lot of fiber.  This paper demonstrates that many of the genes from Prevotella are crucial to digest the complex fibers and that this may stimulate an improved glycemic response.  Collectively, many papers now support the idea that Prevotella is a critical bacterium to a ‘healthy’ microbiome.

Helminths may increase sensitivity to insulin

Different helminth eggs

Countries that are becoming more exposed to Westernization have experienced many positive health impacts, such as decreases in infectious disease rates.  At the same time, however, there have been some negative consequences, such as increases in type 2 diabetes (T2DM) patients in these developing countries.  T2DM is linked to disruptions in energy balance and increases in systemic inflammation.  Interestingly, helminth infections – i.e., the parasitic worms that can reside in the intestines – have been previously shown to enhance glucose tolerance in animal models as well as induce anti-inflammatory immune responses.  Researchers sought to explore this relationship in humans, hypothesizing that insulin resistance is lower in subjects with soil-transmitted helminth infection. 

A homeostatic model assessment for insulin resistance (HOMAIR) test was used to examine insulin resistance in 646 adult study participants on Flores Island in Indonesia.  Soil-transmitted helminth (STH) infection is common on this island.  The HOMAIR model measures insulin in blood samples in a well-validated insulin-resistance assay.  Stool samples were also collected from the subjects, and microscopy and PCR were used to detect various helminth species. 

Of the 646 participants, 424 were STH-infected while 222 were not.  In the STH-infected cohort, participants were further categorized by how many different species were found.  Body mass index and waist to hip ratio were significantly lower in the STH-infected group, suggesting STH-infection may be beneficial toward glucose metabolism.  Furthermore, there was an association between the number of distinct STH species present and HOMAIR.  For every additional species found in a subject, there was an incremental decrease in homeostatic insulin resistance. 

These experiments display an interesting causal relationship between STH species and insulin resistance, however there were certainly limitations.  No association was found between subjects in systemic inflammation in infected versus non-infected groups, failing to elucidate modulations of inflammatory pathways that could be correlated with the observed trends.  Additionally, the changes in insulin resistance may be related to a change in body-mass index rather than helminth infection.  Specifically, participants located in more rural areas may have more active, healthier lifestyles, and would be subsequently leaner and thus more sensitive to insulin.  On top of this, patients with helminths tend to exhibit lower weight in general as these parasites significantly affect metabolism. 

Despite these limitations, this study points to an interesting relationship that is deserving of more examination.  This epidemiology research will impact global health policy and can offer good perspective as more nations around the world are on the path toward development.  

Does eating fermented foods help you lose weight?

Kimchi is a Korean food that traditionally consists of fermented cabbage and spices.  It is a staple in the South Korean diet, and is one of the most frequently consumed fermented foods.  The presence of bacteria in the kimchi has led many to speculate that it can exert a positive influence on the microbiome, and kimchi is believed to have anti-obesity effects.  In order to test this hypothesis researchers from South Korea conducted a clinical trial in which they put obese women on a kimchi diet.  The women were split into two groups, one of which consumed fermented kimchi, while the other consumed non-fermented kimchi.  A summary of the study was recently published by Molecular Nutrition and Food Research.

Surprisingly, fermentated kimchi did not appear to affect the women’s body measurements or specific health indicators when compared to the non-fermented version.  For example, women on both diets had similar decreases in weight, waist circumference, body fat, blood pressure, and cholesterol. There were some important differences though, fermented kimchi increased fasting insulin levels and fasting blood glucose.

The scientists also measured the two groups’ gut microbiomes and blood gene-expression in the study.  The group that ate fermented kimchi had higher abundances of Bacteroides and Prevotella in their microbiomes, and an increased Bacteroides/Firmicute ratio, which has been linked to weight loss.  Bifidobacterium longum, a major lactic acid bacterium that ferments kimchi, has also been linked to weight loss, and to this end, a significant correlation between an increase of this bacterium in the microbiome and decrease in waist circumference was observed.    In addition, a gene known as Acyl-CoA synthetase long-chain family member 1 was found to be significantly upregulated in subjects consuming fermented kimchi compared to those consuming fresh kimchi. This gene plays an important role in metabolism, and it is important in breaking down fatty acids. A second gene, aminopeptidase N (ANPEP) was also expressed more in subjects consuming fermented kimchi.  ANPEP is important for regulating inflammation, and has been associated with a healthy blood pressure.

Overall, this study showed fermented kimchi possibly has beneficial effects on metabolism and immunity when compared to the non-fermented variety. While this study is limited by its small sample size, among other factors, it still shows that the bacteria involved in the fermentation process could benefit us in more ways than we currently know.  These bacteria not only make kimchi taste good, but they may make us healthy too!