Some new evidence brings us closer to the possibility that I was.
That’s from a 10-day experiment conducted by American Gut/Human Food project founder Jeff Leach, which he posted on the project’s Facebook page. In addition to consuming a high protein/fat paleo-ish diet, Jeff professes to normally consume a very high plant fiber diet. For 10 days, Jeff dropped fiber consumption entirely but kept the rest of his diet the same. And those are the results — a complete reversal of Firmicutes and Bacteroidetes. Less noticeable, but no less interesting, is the reversal of Actinobacteria and Proteobacteria.
This is relevant on many levels.
First, this helps lay to rest, once again, the unsubstantiated hypothesis that high firmicutes are connected to obesity. Here, we see it’s a direct result of fiber fermentation in the gut.
Second, this reversal is EXACTLY the same reversal we saw in the cigarette smoking study I posted recently: cessation of smoking results in a rise in Firmicutes and Actinobacteria. And I posited that a reasonable assumption is that picking up the smoking habit does the reverse.
So now we have two completely different actions that are generally regarded as healthful — eating plants and quitting smoking — leading to precisely the same shift in microbiota.
Lastly, this experiment supports (but doesn’t yet prove) the case I made in my posts exploring the Resistant Starch experiment — that for Resistant Starch to be the holy grail in restoring a healthful gut microbiome, we should be seeing some changes in Firmicutes, and specifically the Clostridia clusters IV and XIVa (“Ruminococcaceae” & “Lachnospiraceae” on these gut reports). “Tatertot” Tim’s results, after extended supplementation with Resistant Starch in the form of raw, unmodified potato starch, did not show this — he had higher than average Bacteroidetes & lower than average Firmicutes. Michael Pollan and Jeff Leach — plant-lovers both — had the reverse. (But Tim’s reports DID show much higher than average Actinobacteria, specifically Bifidobacteria, which may explain why Resistant Starch is leading to many beneficial effects. I touched on that here and at the end of the smoking study post.)
But again, that assumes that a high Firmicutes/low Bacteroidetes ratio is necessarily healthful and should be sought out. Right now we can only confidently say that it is not detrimental and is a result of plant consumption. If anything, the Resistant Starch experiment shows (with the extremely limited data we have so far) that beneficial effects can be realized without this ratio.
But the fact that both smoking cessation AND plant consumption lead to this ratio certainly tips us further toward that conclusion. And there is plenty of more evidence that paints a very convincing picture, in my opinion:
What else do we know about Firmicutes and Bacteroidetes?
- Besides the obesity link, I have yet to see anything correlating high firmicutes to disease.
- Quite a few disease-specific studies correlate high bacteroidetes to more disease (Type 1 Diabetes, IBD, Obesity, Metabolic Disease)
- Firmicutes are almost exclusively gram positive. They do not produce endotoxins, and so they cannot contribute to endotoxin-induced inflammatory disease.
- Bacteroidetes are ALL gram negative. All endotoxin producers.
- Firmicutes — specifically the butyrate-producing Clostridia clusters — live in the mucosal lining of the intestine. It’s where all the butyrate production is, the preferred energy source for colonocytes. They seem to be the guardians and nourishers of the gut barrier.
- Bacteroidetes, conversely, are predominant in the luminal space — the hollow space within the large intestine.
Those last four points seem especially illustrative to me. Here is the (speculative) picture they paint: it seems to me that if Firmicutes/Clostridia — the intestinal barrier’s front line of defense — aren’t guarding the mucosal barrier, endotoxin-producing Bacteroidetes have free reign to opportunistically bloom and invade. Not outright bad guys (after all, they are at least the second largest group in most people), but hey, if their natural antagonistic counterparts decide to go on vacation, they have no choice. Ecosystems 101.
Again, highly speculative. Just a hypothesis. Hypotheses aren’t meant to be believed, they’re meant to be tested. And until someone lends me an RV and a gallon of methylamine, that will have to wait.