L. reuteri (2) effects of linoleic acid

This past week I’ve been spending quite a bit of time thinking about L. reuteri. One of the interesting things I’ve mentioned in the past and why I think that this particular strain is interesting out of all the other different species is because L. reuteri was a dominant species in the human gut in the middle twentieth century according to literature and samplings done during that time period. Present day this seems to not be the case. In fact, it seems to be quite rare.

One of the interesting things about L. reuteri is that the antimicrobial compound it produces, reuterin, is produced in the presence of glycerol. Glycerol as you know forms the backbone of triglycerides i.e. fat. In the lab, reuterin can be synthesized simply by culturing L. reuteri with glycerol. L. reuteri is unique in that it will thrive in 16:0 and 18:0 i.e palmitic and stearic acid growth medium.

It’s growth however, can be inhibited by excess consumption of polyunsaturated fat and in particular 18:2 or linoleic acid. While some strains have been shown to mutate in the presence of LA and evolve defense mechanisms to protect itself from LA, they don’t thrive as much as they do when LA is low. In other words LA is bactericidal/bacteriostatic. A bactericidal compound literally kills bacteria whereas a bacteriostatic compound simple inhibits growth. The effect that LA has on bacteria has been known since the early 20th century.If we take a look at these figures for sources of LA in the diet we can see that LA has dramatically increased mostly from increased soybean oil and poultry consumption.

If we take a look at these figures for sources of LA in the diet we can see that LA has dramatically increased mostly from increased soybean oil and poultry consumption.

That is a very interesting coincidence along with the falls in palmitic and stearic acid.

When bile is released it breaks down triglycerides into it’s basic components, free glycerol and 3 free fatty acids. The free glycerol would have provided substrates for L. reuteri to produce reuterin and the free fatty acids would have provided the approperiate energy substrates for L. reuteri to continue to thrive and remain dominant.

However, with declining saturated fat and meat intake and the increase in 18:2 since the middle part of the 20th century, this would have proved unhospitable to L. reuteri thus destroying any benefit to a symbiotic relationship. No more free lunch.While most bacterial strains can thrive with a variety of different energy substrates, they proliferate and dominate when they are provided with the right energy substrates that allow them to effectively compete. When you remove those things and simultaneously introduce a hostile environment they vacate.

Given the long evolutionary history we have seemed to have had with L. reuteri and the increasing amounts of carbohydrate and LA in the human diet and the decreasing prevalence of L. reuteri, I’d venture to say that this particular species is well suited to thrive in a diet low in carbohydrate and rich in fat. In other words it doesn’t need carbohydrate to thrive. I’ve often thought of the gut biomass as only being relevant in the context of diets that contain elevated amounts of ruffage. Clearly this is not always the case as L. reuteri likes glycerol, amino acids, and saturated fat, and doesn’t like LA, so as far as I’m concerned me and L. reuteri can be friends.

Given that L. reuteri thrives at physiological temperatures, culturing at 37C probably is fine.

L. reuteri (1)

L. reuteri produces a broad spectrum antibiotic compound called reuterin. The principle effect of reuterin is to kill off competing strains of bacteria and parasites. While reuterin is classed as an antibiotic the designation is somewhat misleading because it implies that L. reuteri is producing reuterin for the benefit of the host. In reality, it is produced for the benefit of itself; the benefit to the host is a convenient side effect. In other words, L. reuteri is killing off other strains of gut bacteria to plow the field for its own colonization i.e. a bit of slash and burn. While I have reason to believe the antibiotic side effect is beneficial overall, I don’t think it is without consequence if your gut is colonized by pathogens that are susceptible to reuterin.

The situational scenario I see happening is L. reuteri entering the GI tract and then opportunistically producing reuterin to kill off competitors, in response to this, the competing bacteria then release their own set of defensive chemicals, e.g. bacteriocins, endotoxin/lipopolysaccharides/lipoglycans. It is completely plausible that this thermonuclear war can lead to host discomfort with accompanying symptomology.

In my anecdotal experience with taking L. reuteri for a month, 1-2 tablets a day with meals, I had minor symptomology indicative of such a scenario. In the first week I did have one day where my stools were loose as a goose, and I intermittently had cold feet indicative of subclinical “endotoxemia”.

The second week, I had symptoms of some sort of modulatory effect on my thyroid hormone axis, feeling a little anxious and some feelings of agitation reminiscent of the times I supplemented with thyroid hormone but those feelings never overwhelmingly became my modus operandi.

By the end of the second and into the third and fourth week I had somewhat increased mucous production or the feeling of a film in my mouth and throat. I also had wild cravings. Wild cravings which I indulged in.

At the end of the fourth week the thyroid symptoms which were intermittent resolved and the mucous production most likely due to the biofilm L. reuteri establishes interacting with my own mucus production had normalized and the cravings winded down.

All throughout the experience I did notice that my digestion improved and that bloating wasn’t an issue by the 3rd and 4th week although bloating was intermittent the first and second week.

Regarding thyroid hormone, while it is possible for a direct effect on the thyroid hormone axis, in my opinion, the effect is likely indirect and a consequence of modulating the microbiome—as in—reducing the bacterial count of bacterial strains that produce chemical species that have an inhibitory effect on the thyroid hormone axis below a physiologically relevant amount.

I do think that this indirect effect is the most likely the route that L. reuteri sustains the more “youthful” hormonal pattern evidenced in the literature and is more in line with a symbiotic relationship rather than a direct effect.

All of the symptoms I had were minor compared to some of the things reported by others who have taken L. reuteri. I want to emphasize that I also spent the beginning of my life into my twenties on antibiotics and that may be why my symptoms were minor, so it is possible I simply had less harmful strains colonized in my GI tract and thus less overall harmful biomass to reduce. Do I think L. reuteri killed all those harmful strains? Not at all, I think it is more likely it reduced bacterial counts and consequently the harmful chemical species they produce below the physiological amounts required to produce symptomology. I do think those potentially harmful species are there, but now I feel they are probably low enough to avoid negative symptoms and perhaps relevantly high enough to produce a hormetic effect on the immune “system” which I view as ideal.

I do think I have been colonized by L. reuteri as the perceived benefits have continued to persist. The literature alludes to the fact that overtime counts of L. reuteri can fall requiring a “booster” after several months but I’m somewhat skeptical of this and think it probably depends on overall eating habits. Since L. reuteri seems to be found naturally in dairy and meat before we cook it, it superficially appears that that should be enough to maintain populations without “boosters”. We shall see how things develop over the coming months.

Overall, I feel happier and more exploratory and patient and I can eat more of the foods I like when I care to have them. To me that is a quality of life improvement and for some of you it might be worth exploring.