Dr. Bray Links

Tuesday, October 14, 2014

(Re)Becoming Human

This is some very interesting research on the gut microbiome. When doctors say take more probiotics, it's like telling you to  go take one of those vitamin pills for hypertension - but which one and how much? We  need to be more exacting with our recommendations with creating a healthy gut microbiome to be helpful.

"It's also interesting to note that while the most dominant group of bacteria in the American Gut is the genus Bacteroides – by a country mile – this group of bacteria is a minor, minor player in the Hadza gut. Almost non-existent. The prevailing wisdom is that these bacteria are driven by our high protein-fat and sugary diet. However, I think it has a lot more to do with our absence of dietary fiber and resulting alkaline guts (see Going Feral). As my own self-experiments have shown, I can turn my Bacteroides up or down with the amount of fiber in my diet irrespective of the amount of other macronutrients like fat. To me at least, I think the dominance of Bacteroides in the western gut has to do with pH levels, which is "mainly" driven by fermentation of dietary fiber (fermentation of fiber equals more SCFAs and thus a more acidic colonic environment which strains of Bacteroides don't like). So with the average American eating less than 20g of fiber a day – pitiful – we are likely lugging around the most alkaline guts in human history which in turn is allowing certain species of Bacteroides (and some opportunistic pathogens) to flourish. Again, if we squint for a moment and lean on the gut of the Hadza, then maybe we shouldn't let Bacteroides dominant our gut – and by doing so, who else is getting nudged out or down and potentially dragging us closer to ill health? I suspect the Hadza keeo Bacteroides levels low with their high, daily levels of dietary fiber which keeps their colonic environment very acidic. In addition the high protein-fat and sugary argument doesn't hold with the Hadza either as they will often gorge on meat-fat and eat piles of sugary honey for weeks on end during the wet season – and we see no blooms in Bacteroides when we sample during these periods. It's the Fiber, Stupid!

Some of our initial sequencing data on the Hadza reveal extraordinary diversity of certain groups of bacteria – one that sticks out, among many – is the genus Prevotella. Currently there are only two described/sequenced species of Prevotella derived from the human gut: P. copri and P. stercoreaStrikingly, the Hadza appear to harbor dozens of species! This is interesting as Prevotella have been linked/correlated to enhanced susceptibility to arthritis and some otherissues. So, is the diversity of Prevotella species in the ancestral Hadza beneficial, benign, or possibly even problematic? It's exciting to think that we all once harbored this diversity of Prevotella but have lost it through our western diet and lifestyle. At the moment we don't know what to make of the Hadza diversity of this important genus, but we are working on it. Stay tuned.

Oxalobacter formigenes is another species of bacteria that most of the Hadza carry and that the rest of us in the western world have more or less lost. Oxalobacter, as an oxalate-degrading gut microbe, has gained attention in recent years for its ability for preventing calcium oxalate kidney stones. Graduate students Amanda PeBenito and Lama Nazza in Marty Blaser's lab at NYU have been looking at Oxalobacter levels in our Hadza samples and have found that most of the Hadza still carry this important microbe – and acquire it at a young age. Conversely, Oxalobacter seems to be disappearing from our western guts and may be at the root of rising levels of kidney stones. Less the 15% of Americans still carry this important microbe and almost no kids are acquiring now – according Amanda and Lama's research. Since Oxalobacter is sensitive to penicillin's, our overuse of some western medications may be the problem. (Click here for a PDF of a poster recently presented at an NIDDK conference by Amanda and Lama showing some of the Hadza data)"

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