If you haven’t noticed yet, a running theme/theory on this blog is the importance of pH in determining the microbial makeup of a person’s GI. The acidity level of one’s gut is what gives rise to particular species of bacteria, and I now believe it is the main determinant of whether one maximizes the benefits of supplementing with Resistant Starch and other fibers. The human gut is full of saccharolytic (carbohydrate-degrading) bacteria, and I believe what determines which ones get fed is pretty simple: whichever ones happen to be present. And again, it’s pH that largely decides that. If a bacteria is not adapted to a particular pH, it won’t survive, plain and simple. Like putting a human on a planet that doesn’t contain any oxygen. Now, this may sound a little circular — after all, it’s fermentable fiber that lowers pH. We’ll get to that soon, I promise!
For now, I wanted to do a quickie post that I think will give another angle on pH that I think is a little more tangible, since people are quite familiar with probiotics and fermented foods.
For a while now, I’ve been aware of research showing that the survivability of probiotics is greatly increased when taken with, or just prior, to a meal. And it is particularly the fat in the meal that increases the survivability. This study showed that quite clearly:
Enumeration during and after transit of the stomach and duodenal models showed that survival of all the bacteria in the product was best when given with a meal or 30 minutes before a meal. Probiotics given 30 minutes after the meal did not survive in high numbers.
The protein content of the meal was probably not as important for the survival of the bacteria as the fat content. We conclude that ideally, non-enteric coated bacterial probiotic products should be taken with or just prior to a meal containing some fats.
I hadn’t given this a ton of thought, until recently, when it occurred to me that the same pH principle applies here. The reason Lactic Acid bacteria (LABs) in probiotics and fermented food survive better is because of the pH buffering effect of food, and particularly fat. The stomach and its acids provide a very harsh environment for bacteria, as they should — that’s how we keep a lot of pathogens out. The stomach’s fasting gastric pH is about 1.5. That’s very low, even for the acid-loving LABs. What’s ideal? Broadly speaking, it looks like survivability grows and hits its peak at around a pH of 5. L. plantarum hits its peak at 4.8, in that study. And here’s a chart of L. plantarum growth in sauerkraut, which confirms that.
How does that line up with the effect of food on stomach acidity? Like so:
Humans secrete approximately 2.5 liters of gastric juice each day, generating a fasting gastric pH of 1.5, which increases to between pH 3.0 and 5.0 during feeding.
Well would you look at that. And when you look at how fermented foods are traditionally consumed, it makes perfect sense. Fermented dairy seems like quite a probiotic package, with its protein and fat content providing what is likely a pretty good pH buffer for LABs. And in the case of sauerkraut and kimchi, we know that these foods are traditionally consumed as condiments as part of larger meals that most often include meat and fat.
So it seems that if you are looking to maximize the effect of fermented food consumption it would be wise to consume some sausage with that sauerkraut, and some Korean BBQ with that kimchi.
More broadly, I think this illustrates what an important and universal principle pH is for the gut microbiome. What I found interesting in researching this was that among LABs, L. plantarum (who we’ve talked about quite a bit) seemed to be one of the most acidophilic. Which is in keeping with what’s been argued here — that L. plantarum is a pretty important commensal, and that acidophilia is a pretty good determinant of commensalism. Looks like L. plantarum is pretty well equipped to survive GI passage (but not without a little fat!).
And of course, LABs like L. plantarum seem to return the favor. If they can make it past that harsh acidic environment, their lactic acid production has a pH-lowering effect in the gut. We’ve gone at length about immunomodulation as the primary benefit of probiotic consumption, but I have to believe that this is a major benefit as well. But probably not to the same extent as fermentable fiber consumption.
Lastly, the effect of fat on pH lines up pretty well with the research showing the darker side of that effect — that meals with fat can increase circulating endotoxins, and that the consumption of fiber along with the fat negates this effect. In other words, this isn’t an excuse for a fat free-for-all. I’ve been running a personal experiment to test out this phenomenon, and it’s been quite interesting. I’ll post on that soon. In the meantime, I’ll leave you with Heisenbug’s corollary:
Eat fat. Always with plants. Sometimes the fermented kind.