Psyllium husk is a non-fermenting (no gas or bloating) soluble dietary fiber that improves both constipation and diarrhea (such as with IBS), normalizes blood sugar, reduces LDL (“bad”) cholesterol, and can help with weight loss. Each type of dietary fiber has different effects, and a “high fiber” diet in general won’t necessarily provide the same benefits.
I’m sharing this because I’ve always heard that “dietary fiber” helps with various things, but different dietary fibers actually do different things. This article helped me get a gears-level understanding of what fiber actually does and why specific foods have the effects they do. For example, psyllium fiber helps with my Irritable Bowel Syndrome[1] but every other type of fiber I’ve tried makes it worse (insoluble fiber causes more irritation, and fermentable soluble fiber causes gas), and I didn’t really understand why until reading this.
At a high level (read the article for details and citations):
Psyllium is a dietary fiber that’s soluble but doesn’t ferment.
It forms a gel that traps water (helping with both constipation and diarrhea[2]) and also bile (reducing LDL/”bad” cholesterol[3][4][5]).
The gel slows down digestion, which normalizes blood sugar, increases GLP-1[6], and makes you feel full longer (and helps modestly with weight loss[7]).
The lack of fermentation means it makes it all the way through your body and out, and doesn’t produce gas.
Soluble fiber helps modestly with blood pressure, likely as a secondary effect of weight loss.
In comparison to other dietary fibers:
Insoluble fiber (like in wheat bran) doesn’t form a gel but if it’s sufficiently coarse, it can help with constipation through the magic of irritating your intestinal lining (but psyillium helps more, without the irritation).
Soluble fermentable fiber (like beta-glucans in oats or pectin in fruits) can slow down digestion and have similar effects on blood sugar and cholesterol, but doesn’t help with constipation or diarrhea because they don’t make it that far in the process.
This article doesn’t go into it, but fermentable fiber has other benefits like helping your gut microbiome and has a larger effect on cholesterol, so don’t take away from this that fermentable fiber is useless.
Suggestions if you want to try psyllium supplements:
My preferred form of psyllium is to take two of these pills (500 mg each) with a glass of water right before each meal, but that only comes out to 3 grams per day. Most studies used 10-15 grams per day (also divided and taken before meals), so for a research-backed dose you’ll probably want to mix the powdered form with water rather than taking 10 pills per meal.
Soluble fiber slows down or reduces absorption of drugs and supplements, so you should take drugs and other supplements 30-60 minutes before taking fiber supplements.
You will probably want to start with 1 gram at a time and work up from there to avoid gastointestinal discomfort. Also if you try the pill form, drink an entire glass of water with them since it’s not fun to have a clump of psyllium in your digestive tract (it will eventually hydrate and be fine but it’s uncomfortable).
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In retrospect, the American College of Gastroenterology specifically recommends “that soluble, but not insoluble, fiber be used to treat global IBS symptoms” and that “soluble, viscous, poorly fermentable fiber may provide benefits in IBS”.
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Trapping water softens hard stools by increasing their water content and improves soft stools/diarrhea by binding it together better.
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Improvements in cholesterol are not (just) caused by weight loss. Many of the studies involved controlled for weight and/or used non-obese subjects.
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The cholesterol benefits are also in addition to statins.
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Shockingly, even the FDA agrees that psyllium husk lowers LDL cholesterol.
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Psyllium stimulates the release of natural GLP-1, but semaglutide binds more tightly to GLP-1 receptors than GLP-1 does, and has a much longer half life (a week vs a couple minutes), so while they should do the same thing in one sense, we should expect semaglutide to be much more effective.
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Some meta-analyses say psyllium has no effect on weight loss, but these tend to be looking at studies that weren’t trying to cause weight loss[3].
So does the choice of which type of fiber to take boil down to the question of the importance of constipation vs microbiome and cholesterol? It’s seeming to me like if the former is more important you should take soluble non-fermentable fiber, if the latter is more important you should take soluble fermentable fiber (or eat it in a whole food), and that insoluble fiber is never/rarely the best option.
One important thing is that you don’t have to pick one or the other. I plan to take psyllium for IBS plus eat oats (high in soluble non-fermenting fiber) for the microbiome benefits and improved cholesterol benefits. Both should help with weight loss (in similar ways) and cholesterol (oats will help more because the fiber they contain ferments into substances that also reduce cholesterol, but both will reduce cholesterol via the bile removal method).
Insoluble fiber doesn’t help with any problems that I have, and excerbates my IBS, so I plan to (weakly) avoid it. So I will continue eating foods high in insoluble fiber if they’re good for me in other ways (oats) or tasty (pineapple), but I’ll avoid concentrated forms (wheat bran) and foods high in them that I don’t like anyway (whole wheat).
Oh I see, that makes sense. In retrospect that is a little obvious that you don’t have to choose one or the other :)
One other thing I didn’t think to mention in the post above is that I used to think of fiber as one category, so if I was eating something “high fiber” like vegetables or oats, I wouldn’t take psyllium since “I’m already getting fiber”, and then I’d feel worse. Since reading this, I’m taking psyllium with my oats and it improved the experience a lot (since the psyllium helps counteract the irritating effects of the insoluble fiber in oats).
Took Metamucil in water in glass form for about a year. Lost a lot of weight. Was great 98% of the time. However, sometimes I wouldn’t drink enough water. Would absolutely not recommend that experience.
I’ve had the same experience a few times and can confirm that it’s not great. At this point I drink a whole glass of water when I take it, and I usually take it with a meal (my theory is that this might mix it up more so even if there’s not enough water, it won’t be one solid clump).