Eating more vegetables appears to improve microbiome-mediated health indicators

There are many diets that have been rigorously shown to decrease metabolic syndrome (obesity, diabetes, etc.) and are generally associated with a healthy lifestyle, such as vegetarian, vegan, and Mediterranean diets.  The one thing they share in common is a high consumption of plant material, and a low consumption of meat.  There are mechanistic reasons for why high veggie - low fat diets should improve health, and many researchers now believe this is partly due to the gut microbiome that these diets create.  In order to help demonstrate the microbiome-mediated health benefits of a high vegetable – low meat diet, a team of researchers from Italy recently measured the microbiome and specific metabolites produced by the microbiome in 153 individuals.  They then compared these results with the diet that the individual had consumed prior to the measurements, and confirmed that these ‘healthy’ diets were creating ‘healthy’ microbiomes.  They published their results in the journal Gut.

The scientists asked 51 vegans, 51 vegetarians, and 51 ominivores individuals to self-declare their eating habits over the past seven days, and then sampled their stool and urine for bacteria and metabolites.  They learned that amongst the different types of diet the individuals’ overall microbiome diversities were relatively similar.  However, they did show that Bacteroidetes were more prevalent in vegetarians and vegans than in ominvores, and that a higher Firmicutes to Bacteroidetes ratio existed in the guts of ominvores than in vegans and vegetarians.  In addition, the abundance of Prevotella, which is normally associated with health, was positively correlated with overall vegetable intake, and on the contrary Ruminococcus was negatively associated with a high vegetable diet.

The scientists also measured specific metabolites in the individuals.  They discovered that short chained fatty acids (SCFAs), which are normally implicated with health, were associated with the consumption of fruits, vegetables, and legumes.  In addition, there were positive associations between SCFAs and specific populations of bacteria, such as Prevotella.  On the other hand, the metabolite trimethylamine oxide (TMAO), which is a microbiome metabolite whose concentration is directly related to atherosclerosis and other diseases, was significantly lower in vegetarian and vegan diets compared to omnivore diets. It was also directly associated with the abundance of the aforementioned Ruminococcus. 

These relationships between SCFAs and veggies are unsurprising, because SCFAs are the byproducts of bacteria breaking down the complex glycans found in fiber.  In addition, the TMAO is produced by gut bacteria from carnitine and choline, two molecules that exist in red meat and eggs, among other things.  Regardless though, this study should remind us that our diet can shape our microbiome and have lasting health effects.  This study only reinforces that a diet high in veggies that feeds the microbiome is probably a healthy choice.

Antibiotic use in livestock is increasing and leading to greater antibiotic resistance

We’ve talked extensively about antibiotic resistance on the blog but we haven’t focused much on the impact that antibiotics given to livestock have on humans. Farmers give low doses of antibiotics to farm animals in order to not only prevent illnesses in their animals, but also to promote growth within their livestock. Animals being produced for food account for about 80% of antimicrobial use in the United States and bacteria in the animals become resistant to these antibiotics in the same fashion that they do in humans. As antibiotic use rises, more bacteria are becoming resistant and these bacteria are passed from animals to humans through the environment, consumption, and direct contact. An international research team from Europe, India, Africa, and the United States mapped the global consumption of antimicrobials in livestock.

The results were published in the Proceedings of the National Academies of Science (PNAS) and compared the use of antibiotics in livestock in 2010 to the projected use in 2030. The authors found that the global use of antibiotics in livestock will increase 67% in the 20 years between 2010 and 2030. This is largely a result of an increase in demand for meat by middle class individuals in countries like Brazil, Russia, India, China, and South Africa (BRICS). These BRICS countries have shifted their livestock production systems to be more cost-effective by increasing the use of antimicrobials to ensure the health of their animals and to promote growth.

This increase in antimicrobial use in animals is a compounded annual growth rate of 2.6% annual which is almost three times the annual growth rate of the human population (.98%) during the same time period. The authors found that in 2030, if new regulations are not put into place, approximately 30% of all antimicrobial use will be accounted for in the livestock industry in China.

Many countries, and specifically those in the developing world, do not regulate the use of antimicrobials in livestock production. While directly linking antibiotic use in animals to drug resistant infections in humans is very complex, it can be inferred that increase in antibiotic use leads to antibiotic resistant bacteria, and we have seen evidence of this in practice. In countries like India, where bacterial diseases are very prevalent and a major public health concern, antibiotics are a key factor in fighting these illnesses.  Increased resistance to bacteria by increased use of antibiotics in farm animals will only increasingly prevent the effectiveness of antibiotics in humans.  

The study authors call for global action to decrease the use of antibiotics used in animals that are raised for meat consumption. While the authors do state that this analysis was based on limited available data, largely in developed nations, the global trends of antibiotic use in livestock is concerning.