Gastric bypass surgery alters microbiome which possible contributes to weight loss

Schematic of Roux-en-Y anastomosis.

Roux-en-Y gastric bypass surgery and vertical banded gastroplasty are two types of bariatric weight loss surgeries that are highly effective in promoting weight loss.  The mechanisms for their efficacy are complex and not completely known, but both surgeries are shown to reduce caloric intake, suppress hunger and increase gastric emptying.  Little is known about how the microbiome changes during these surgeries, and how this change may effect subsequent weight loss.  A team of Swedish scientists investigated this topic and showed the gut microbiota undergo important changes.  They published their results in the journal Cell Metabolism.

The researchers compared the microbiomes of women that were obese and hadn’t had surgery with those who were of similar BMI presurgery, but had undergone surgery at least nine years earlier.  They observed some major differences in the women’s microbiomes, with the post-operative women had much higher levels of Gammaproteobacteria and lower levels of Firmicutes.  When the scientists looked at actual genetic variations they found many differences.  Some notable differences were a decrease in short chain fatty acid (SCFA) and in increase in trimethylamine N-oxide (TMAO) creation in women who had surgery.  As we have written about in this blog before, SCFAs are often associated with health, while TMAO is a risk factor for some cardiovascular diseases.  Interestingly, when they took the microbiomes from both groups of women and transferred them into germ-free mice, the mice receiving microbiomes of women that had undergone surgery gained less weight than the mice that received microbiomes of obese women.

Gastric bypass surgery is often a last resort for folks that have severe obesity.  While not normally considered, the microbiome is drastically affected by this procedure. The microbiome is certainly altered by the procedure, and it appears that it may even be helping keep the weight off.  However, there may be some negative microbiome-mediated consequences as well, derived from alterations to micrbiome metabolism, such as an increased level of TMAO.  Like all surgeries, folks undergoing this one need to balance the risks and rewards of the procedure, and hopefully after this study, the microbiome will be considered.

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!