New study suggests gut microbiome directly influences BMI, triglyceride, and HDL levels

Molecular structure of cholesterol

The microbiome has long been associated with cardiovascular disease, especially after studies showing differences between the gut microbiomes of obese and slim individuals.  The mechanisms by which the microbiome may be influencing heart disease are still unknown, but there are a few mechanisms that have been identified.  For example, as has been previously discussed on this blog, trimethylamine N-oxide (TMAO) in the blood is an independent risk factor for atherosclerosis, and is produced by gut bacteria from choline and carnitine.  In addition, systemic, chronic inflammation is associated with heart disease, and our avid readers will know that the microbiome can cause chronic inflammation in the vagina, gut, and mouth.  Overall though, a direct relationship between specific bacteria and heart disease has not been shown.  A recent epidemiological study though, did just that.  The researchers, mostly from the Netherlands, were able to identify specific species that were associated with higher BMIs, as well as those that were directly correlated with HDL cholesterol levels.  They published their results in the journal Circulation Research.

The scientists measured the genomes, microbiomes, BMI, and blood lipids of 1500 adults.  Their results showed that higher overall diversity and richness of the gut microbiome was associated with a lower a lower BMI (healthier state), lower triglycerides (healthier state), and higher level of HDL cholesterol (healthier state).  The diversity was not, however, associated with total cholesterol nor LDL levels.  The researchers then identified specific bacteria associated with these health indicators.  There are too many to list in this blog, so we encourage interested readers to take a look at the article.  Some examples though: Akkermansia, Christensenellaceae, and Tenericutes were each associated with low BMI, low triglycerides, and high HDL (all healthy states), while Eggerthella was associated with high BMI and high triglycerides, and Butyricimonas was associated with high BMI, high triglycerides, and low HDL (all unhealthy states).  Finally, the researchers sought to determine just how important the microbiome was to overall BMI, triglyceride levels, and HDL levels by incorporating the host genetics, age, and gender into their calculations.  They showed the 4.5% of the variance in BMI, 6% of the variance in triglycerides, and 4% of the variance in HDL is directly attributable to the microbiome.

These study results reaffirm the importance of the microbiome to our overall health, and even quantitatively show its influence on specific health indicators.  The authors do not attempt to explain why specific bacteria would cause variation in these metrics, although as previously mentioned some mechanisms have already been demonstrated.  To check to see which other diseases these bacteria have been associated with, use the search tool, or click the tags below to see all the blog articles that mention them.

Breastfeeding plays an important role in microbiome development

As soon as a child is born, his or her microbiome is continually being shaped by external factors such as diet and bacterial exposure. The first few years of life are critical in microbiome development as these early years will shape the composition of bacteria that will inhabit that individual’s body for years to come. Infant dietary habits play a critical role in this development.  Breast milk has high nutritional content and is important in passing immunological factors from mother to child, as well as nutrients that are essential for gut colonization by bacteria. A team of scientists led by a group at University of North Carolina School of Medicine published in Frontiers in Cellular and Infection Microbiology on early changes and development of the microbiome in infants with different feeding and daycare habits.

Stool samples were collected from nine infants, some of which were exclusively breastfed (EBF) and some of which were non-exclusively breastfed (non-EBF). The infants were followed over a period of time from 2 weeks to 14 months, and samples were collected before and after the introduction of solid foods. The samples were tested for differences in bacterial composition.

The scientists found that infants that were solely breastfed and did not receive formula had guts that were more prepared for the introduction of solid foods. When solid foods were introduced to their diets, the microbial shift was much less dramatic than the shift for infants who were breastfed while also receiving formula.

Analysis showed that non-EBF infants had greater microbiome species diversities compared to EBF infants. Also, non-EBF infants showed lower abundances of Bifidobacterium and greater abundances of Eggerthella compared to EBF infants. Bifidobacterium is a bacterium that is associated with good digestion. After introduction of solid foods, however, EBF infants showed an increase in Eggerthella abundance, and non-EBF infants showed an increase in Bifidobacterium abundance.

In a second part of the study, researchers considered day care attendance when comparing the microbiome of the infants. They found that attending daycare resulted in a more diverse microbiome, but feeding habits were the most important factor for microbiome composition after the introduction of solid foods. 

It is clear from this study, in addition to others  we have discussed, that there are many factors contributing to microbiome diversity and species richness. This study highlights the important role that diet plays on early microbiome development. What was quite interesting was that while many studies often equate a more diverse microbiome with health, the infants that were exclusively breastfed had less diverse microbiomes yet they were more prepared for the introduction of solid foods.  This study only included nine participants and should be expanded to include a greater number of infants to better understand this relationship, but it can still help inform the conversation around breastfeeding versus formula feeding.