Gut bacteria and Soylent


It’s a well known fact that different people have different gut bacteria, and these bacteria can have different effects on the foods that we eat. Best known example is the difference between vegetarians and omnivores. Further, recent studies, including the highly publicized study on gut bacterial breakdown of carnitine in meat into a biomarker for atherosclerosis suggests that these bacteria have a large effect on what actually enters the body (which is different from what we eat). I understand that this is so far a one-man (and very busy) operation, but is there any effort to at least qualify changes in bacterial cultures in the gut, especially with a diet with a single component?

This is pretty much the only thing that gives me pause with this experiment. Since you’re only consuming the one thing, would this not incentivize only a relatively small set of species to flourish, which may result in increased numbers of oligocultures that wouldn’t be a problem with a diverse diet?


Excellent point. Gut bacteria seem to be very unique to each individual, making me pessimistic concerning the effectiveness of my probiotics. This would be an excellent thing to study closely with the funds hopefully soon to be raised.

That said, I believe most species of studied gut bacteria are able to feed on fiber and oligosaccharides, which Soylent has in spades (my latest formula has 40g of fiber). I don’t know how individual bacteria would respond to the other compounds in cultural foods or meats but fiber seems a safe bet for the health of the gut bacteria of most individuals.


This is an excellent item to investigate a little further, as gut bacteria also has a flow-on effect into mood and brain function. 90% of serotonin is produced in the gut, and then moves to the brain, so the life-affecting potential of changes in gut bacteria would be well worth considering.


this was one if the things that had me questioning as well, not enough to stop me from trying mind you. but reading that there is 10x the amount of bacterial cells vs human, caused me to think if we might be missing nutrients to feed them as well. though Rob’s response here, just quailed any ambiguity I had about this. via la Soylent! :wink:


Rob, but what made you change your mind from the following statement you made in a blog post:

Believe it or not the optimal amount of fiber I found is only 1.2g. I know the FDA recommends much more, but that’s probably assuming a more conventional diet.

and what is the ratio of soluble an insoluble fiber that you are using?


In relation to this, I’m worried about the type of fiber to use.

I know for instance that most fiber destroys my stomach. My specific flora/bacteria seems to offgas (read: cause flatus) a lot when I even consume a small amount of certain fibers. For instance, those 5g fiberone bars make me so gassy i’m uncomfortable and I often have very loose (read: super aerated) BMs.

I am fine with methyl cellulose as a fiber, but since that passes straight through, that would not be ideal, correct? My gut flora reacts with the fiber by consuming it while producing gas as a by-product. Would methyl cellulose effectively starve those bacteria?


My girl has similar gut issues from the sounds of your post. I will ask her to jump in on this discourse, as she just found a supplement that seems to be working to harmonize gut function after years and years of problems. might be able to offer some anecdotal advice.


The fiber I used was interfering with the absorption of the maltodextrin. I now use a different source so I can use much more. Detailed information coming in my 3 month blog post shortly.


There’s a range of insoluble fibers around these days that pass through and in some cases, partially ferment in the lower bowel, which is a good thing, but produces gas. Inulin is an example, as well as glucomannan. There’s plenty of others too. My average day currently sees upwards of 20/30g of fiber, I eat 2-3 cans of black/red beans per day. I’m accustomed to it, having eaten slow carb for 2 years now.


you could also throw in some probiotics to “balance out” the varying gut bacteria for a more controlled experiment across different people. no harm.


Excited to hear this. I know I personally found that more fiber was a necessity.


The Wiki article here explains that serotonin is used in the gut to regulate digestion, but that the serotonin in the central nervous system is synthesized there. ( This would suggest that levels of serotonin in the gut would not directly impact mood. Have you come across a source that says otherwise? It would be good to know more about.

Then there are a few more good points in this wiki article in the “Effects of food content” section - a higher tryptophan to phenylalanine and leucine ratio increases serotonin, and a higher carb to protein ratio can do the same. It should be possible to adjust this ratio in a soylent mix.


Interesting, I’ve read elsewhere of a more substantial connection. I don’t have those refs on hand, but quickly found;
Also: "Some beneficial bacteria that have taken up residence in the gut will actually increase GABA receptors in the brain. When there are more GABA receptors in the brain, more GABA is being put to good use. This is a good thing, especially since a decrease in GABA receptors has been associated with mood disorders, like chronic depression."
REFERENCES (not sure which sorry):
Javier A. Bravo, et al. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. PNAS 2011 : 1102999108v1-201102999.
Lyte, M. Probiotics function mechanistically as delivery vehicles for neuroactive compounds: Microbial endocrinology in the design and use of probiotics. Bioessays. doi: 10.1002/bies.201100024.
Hurley, Dan. Your Backup Brain. Psychology Today. Dec 2011. 80 - 86

This article isn’t specific to serotonin, but discusses a more impactful link:


One aspect I haven’t seen brought up anywhere with respect to Soylent is the fact that fiber often ferments into butyric acid. The caloric value of this fermentation is something like 2.5 calories per gram of fiber.

But of course it depends on the individual’s gut biome.

@rob, uBiome may be interested in working with you. I can put you in touch with Jessica Valenti, one of the cofounders.


What you eat has a big impact on your gut flora - they subsist on the contents of your lower intestine and the balance of the population changes depending on what you eat.

I’m pretty sure that gut flora aren’t only interested in fibre - they’re opportunistic bacteria and will evolve to eat whatever is around, changing themselves and their populations to suit the available food.

Anything you eat that doesn’t get digested and absorbed further up the gut, ends up passing through the lower intestine - the colon - where most intestinal flora live. Different people and nationalities, with different diets, have gut flora that has adapted to match. Difference in diet predicts most of the difference (~60%) in gut flora between people.

@nthmost mentioned Butyric acid which is produced by intestinal flora - amongst many other things. These contribute quite substantially to caloric intake - rodents raised in a sterile environment and lacking a microbiome require ~30% more calories to maintain weight than controls.

Gut flora also mediate other metabolic effects such as the syntheses of vitamins like biotin and folate, as well as absorption of ions including magnesium, calcium and iron.

Gut flora also have a big impact on health, regulating the immune system in the gut, protecting against opportunistic infections by pathogens, preventing inflammatory bowel disease, allergies, etc.

TLDR: gut flora are a large and important part of the Human organism and they change if you change your diet. A major change of diet, like Soylent, cannot fail to have an effect on your microbiome - probably a fairly pronounced one, especially if you keep it up long term.

This isn’t necessarily a bad or good thing - it entirely depends on the outcome - but it would be one of my major concerns with long term soylent use.

I can also see that Soylent might be an ideal way to change your gut flora on purpose. I used to have Ulcerative Colitis - but I cured it by changing the balance of my gut flora through diet. Doing this while eating whole food is very hard, requires enormous strictness and takes years of work - individual bacteria don’t eat much, so you have to be very strict - and while it’s easy to affect your gut flora through diet, it takes a long time to completely change it for good.

Soylent could make that process much easier by allowing you to finely control what ends up in the lower intestine and therefore deliberately change the bacterial population much more quickly and easily.

TLDR;TLDR: @rob, I think you might have the makings of a much more accessible/workable treatment for IDB/IBS/Colitis/Crohns on your hands.

Please note, the original version of this post had lots of links to references, but although I’m apparently only allowed to have two links per post, it wouldn’t work unless I took all of them out. I can supply the rest in follow up comments if anyone is interested.


lol @ tldt;tldr :smile: please post more, and thanks for the write up, Fascinating as I had not attributed the impacts of this on IDB/IBS/Colitis/Crohns great correlation you make.


Thanks - I’ll try and see if Discourse will let me post some links.

Edit: Okay, one link at a time :frowning: