FOR THE LAST year or two, people have been talking a lot about the bacteria we carry in our guts and elsewhere in our bodies – fecal transplants, fermented foods, probiotics, and so on. Along those lines, I got an interesting e-mail from a reader recently, wondering whether the difference between “responders” and “non-responders” to the endurance-enhancing effects of beet juice could be explained by differences in gut micro biome – that is, in the mix of friendly bacteria contained in their digestive tract. It’s an intriguing idea, and it got me thinking more generally about whether and how microbiome composition might affect athletic performance.
As if on cue, there’s a study in this month’s Journal of Strength and Conditioning Research, from researchers at National Taiwan Sport University, investigating the effect of intestinal microbiota on exercise performance…in mice. The advantage of using mice is that you can really control what’s in their guts. The researchers compared normal mice (SPF) with “germ-free” mice stripped of all intestinal bacteria (GF), and with germ-free mice whose intestines had then been recolonized by a single strain, Bacteroides fragilis (BF). Here’s how they all fared in a time-to-exhaustion swimming test:
So in this case, having “normal” gut bacteria is the best option; having all your gut bacteria wiped out is the worst option; and having at least one gut bacteria is better than nothing. Why? The researchers focus on the possible role of gut bacteria in enhancing the body’s antioxidant response, and they do indeed show that antioxidant activity was reduced in the germ-free mice.
There are also a number of other possible explanations, since gut bacteria play a role in food digestion and absorption, determining how much energy can be extracted and utilised during exercise. The germ-free mice also had less muscle tissue and smaller livers; the researchers casually cite one obscure study claiming that muscle mass doesn’t affect endurance performance, which seems fairly unconvincing. To me, the message is that your microbiome does affect performance, but it’s not clear how, or whether it’s a direct or indirect effect.
(And it’s worth noting that some preliminary research published last year suggests that it goes the other way too: exercise affects your microbiome in a positive way, producing greater diversity.)
Which brings us back to beet juice, whose key ingredient is nitrate, which is converted by friendly bacteria in the mouth to nitrite, which is then converted to nitric oxide, which is what boosts endurance. In this case, then, it’s your oral microbiome rather than your gut microbiome that matters. There’s already some interesting research from back in 2008 showing that, if you use an antibacterial mouthwash, you completely wipe out the benefits of ingesting nitrate. Here’s a graph from that study, showing nitrite levels after ingesting nitrate, with and without prior mouthwash:
But is nitrate-to-nitrite conversion simply an on-or-off process, or do people have varying efficiency in the conversion, depending on what particular bugs they have living in their mouths? I asked Andrew Jones, the University of Exeter scientist who has been one of the leaders in beet juice research. Here’s what he replied:
It turns out that there are umpteen types of oral bacteria that process nitrate to a greater or lesser extent, and there is massive variation in both the quantity and the balance of these colonies between individuals. The effects of age, diet, health and training status on the oral microbiome is pretty much unknown, but the implications of this for using nutrition to influence health could be really important. I think you’ll see quite a few studies on this topic over the next few years.
So the obvious question is: what do we do right now to enhance the quality of our oral and gut microbiomes? Not using antimicrobial mouthwashes is certainly one thing to consider; upping your intake of fermented foods and probiotics may be another. But I think it’s worth concluding with some wise words from near the end of Michael Pollan’s New York Times Magazine article on his microbiome:
My first reaction to learning all this was to want to do something about it immediately, something to nurture the health of my microbiome. But most of the scientists I interviewed were reluctant to make practical recommendations; it’s too soon, they told me, we don’t know enough yet. Some of this hesitance reflects an understandable abundance of caution. The microbiome researchers don’t want to make the mistake of overpromising, as the genome researchers did. They are also concerned about feeding a gigantic bloom of prebiotic and probiotic quackery and rightly so: probiotics are already being hyped as the new panacea, even though it isn’t at all clear what these supposedly beneficial bacteria do for us or how they do what they do…