Scientists studying how fiber influences the microbiome | Hacker News Reader

Scientists studying how fiber influences the microbiome

nytimes.com

115 pointsHillaryBriss11 comments

Maybe someone with a knowledge of nutrition and medicine can clear this up for me.

As I understand it, there are two types of fiber that are lumped into the term "dietary fiber": soluble fiber and insoluble fiber. I believe that both are fermented in the large intestine but soluble fiber is the one that primarily supports flora through fermentation, while insoluble fiber is used for more of a physical effect, to draw water into the stuff that's going through. Apparently soluble fiber also helps to increase the viscosity of the stuff going through the stomach, which slows digestion (considered to be a good thing).

One of the studies mentioned in the article uses inulin (soluble fiber -- the kind you'd find in a supplement like Benefiber). With regards to regulating sugar, metabolism, and gut flora I imagine that soluble fiber is the one we should be focusing on. Yet it seems rare to distinguish the two.

I know that both fibers are often found in the same food (typically fruits and vegetables) but some processes (like juicing) remove insoluble fiber while leaving the soluble fiber intact. So it's commonly believed that juice "doesn't have fiber", which is untrue.

Isn't it time we start distinguishing between the two when we talk about the health effects? Am I just completely wrong in how I understand this?

Thanks for this comment. I totally forgot about this when I posted mine. You're understanding of soluble/insoluble matches mine although I think soluble does contribute to drawing water into the stool and giving it shape. Edit - Soluble fiber dissolves in water and forms a gel - insoluble absorbs water and provides a fibrous matrix. Both are involved in stool firming

Seems most supplements are soluble in nature. So maybe if you need to speed digestion or solidify loose stools you should focus on getting some insoluble fiber naturally rather than relying on supplements? Definitely seems like an important distinction

AIUI, insoluble fiber didn't get fermented. Insoluble fiber basically means cellulose; to digest cellulose, you need some pretty serious engineering, like four stomachs [1], or a huge caecum [2], or, er, a two-pass process [3]. Humans don't traditionally have any of those, so we don't digest cellulose to a significant degree. There are other components of food classified as insoluble fiber, but the only significant one is lignin, at on the order of 10-20% of the mass of cellulose [4], and that's so hard to digest you basically have to be a fungus to do it [5]. Apparently even termites don't break it down much.

Soluble fibres are oligosaccharides with weird bonds that we can't break down, but that bacteria can. They're nothing like insoluble fibre, except that they come from plants. They're polymers, but this is biology, every other thing is a polymer. They're not really even fibrous. We absolutely should distinguish them.

This review is pretty accessible, and covers a lot of ground:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3614039/

I would write more, but i'm going to cook some lentils instead!

[1] https://en.wikipedia.org/wiki/Ruminant

[2] https://en.wikipedia.org/wiki/Equine_nutrition#The_cecum_and...

[3] https://en.wikipedia.org/wiki/Cecotrope

[4] http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.1981....

[5] https://en.wikipedia.org/wiki/Lignin#Biodegradation

I think the main reason we can't break down cellulose is because we don't have the enzymes to do so. It's not as if cellulose is actually all that different to polysaccharides we are able to digest, it simply has beta 1->4 glycosidic bonds [1] between the glucose molecules instead of alpha 1->6 glycosidic bonds that are digestable by humans.

edit: upon some more skimming of the review article, even with the enzymes we may not have the conditions in which cellulose could be degraded, hence the "four stomachs" and other methods.

[1]: https://en.wikipedia.org/wiki/Cellulose

As someone who has recently been battling IBS after coming back from a trip it's become pretty clear to me that gut bacteria/micro fauna/whatever plays a significant role in our health that Western medicine is only just beginning to understand. I'd wager in another few decades we will see a whole bunch of new treatments based around an improved understanding of the gut.

It's unfortunate because I (anecdotally) see Doctors dismiss gut micro-fauna balance as quackery, especially since alternative medicine often points to it as a source of trouble (e.g. Candida overgrowth). Sadly it's common to see conventional doctors attack straw-men when discussing alternative medicine's view on the gut rather than acknowledging what we do/don't know. Not saying 'alternative' medicine is right but it's clear to me a healthy gut is critical to a healthy person. I crave more scientifically backed data - I've really begun to appreciate how impacted quality of life becomes when you're dealing with chronic digestive issues.

Adding fiber and probiotics to my diet has helped me tremendously. Shocker - eating green, healthy looking things instead of fast food poison makes me feel better too. After a fair bit of research this probiotic seemed like the best value with a solid strain list. Probably best to refrigerate as soon as possible though.

https://www.amazon.com/gp/product/B00JEKYNZA/ref=oh_aui_deta...

Also found this article helpful. https://www.ncbi.nlm.nih.gov/pubmed/22504002

The problem is that so much of what alternative medicine points to is quackery, even if they get the system potentially correct.

I've worked a bit in gut microbiome stuff, and a bunch of the things alt medicine advances about it still fall in the "That's not how any of this works..." realm.

Oh, absolutely. It's just that I'd rather read more interesting insight on what we do know rather than a tangential attack on how Autism and gut yeast can't be related. I guess it's similar to a lot of more controversial topics where the dialogue is often narrated by extreme viewpoints rather than the more reasonable middle ground

Definitely tangential to the main point, but I don't really think it's accurate what one of the biologists implies about McDonald's food:

> “It’s basically what you’d get at McDonald’s,” said Dr. Bäckhed said. “A lot of lard, a lot of sugar, and twenty percent protein.”

As far as I can tell, McDonald's stopped frying their french fries in lard back in 1990 and other products before then. (See http://articles.chicagotribune.com/1990-07-24/business/90030... .)

Fast food has plenty of nutrition problems, but it doesn't seem helpful to make up ones that don't actually exist.

Maybe he just used the wrong word since he's from Sweden, though.

Given that the rest of the sentence refers to sugar and protein, he probably means fat. Non-native speaker and/or mildly inaccurate translation. Lard isn't really worse for you than other fats anyway, so I'm not sure why he'd focus on that.

Which is a shame really as the tastiest chips are fried in lard, or better still, beef dripping. Not very accommodating to vegans however.

The most common food other than fries McDonalds is known for would be hamburgers. I’m guessing that’s what they’re thinking of as a source of animal fat. Possibly he meant tallow, as in beef tallow, which is also what they used to fry their fries in. Now they use an additive to replace the flavor, while using vegetable oil.

https://www.wired.com/2014/07/whats-inside-mcdonalds-french-...

It wouldn’t shock me to hear someone referring to tallow as lard.

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