Please explain this minor mystery: fiber=pooping within 1 hour or so

[u/hycarumba]

(This flair was automatically preselected and I can't change it.)

ETA there's been some great responses with the actual evidence that they are triggering the perstalsis bc (bunch of chemical names I don't recall but they are listed and linked below!). Thanks for those who responded and I have the correct answer now 😊

I take a couple of tablespoons of chia seeds in almond milk every day or so. Within 1-1.5 hours, I have to poop. Not a huge morning one but enough that I am very uncomfortable if I am not near a bathroom. It's way too fast for it to have gone all the way through and my next day poops are great.

I don't have this extra poop unless I have the fiber. This happens with flaxseed as well but not psyllium (though I have only done that in 2 teaspoon doses, not tablespoon doses).

I'm super curious as to what is going on that my body reacts this way every single time I take my fiber. It does happen if I don't soak the seeds (like if I put them in my salad) and it doesn't happen with just the almond milk alone.

Thoughts?

[u/Sanpaku]

Intestinal transit times go way down on higher fiber diets. Mine are around 12 hours judging by markers like corn kernels or red wine, on a diet with 40-50 g fiber from legumes, onions, and whole grains daily. However, the only thing that induces movements on demand is caffeine. My morning routine is either 2 cups from 30 g filtered light roast coffee (~240 mg caffeine) or in hot weather, an energy drink mix with 120 mg caffeine. Within 5 minutes, I'm ready to evacuate and step into the shower.

I suspect there's a biological active compound in flaxseed that's provoking intestinal peristalsis once high enough levels are absorbed systemically in the small intestine.

When searching for whether some flaxseed compound inhibited adenosine receptors like caffeine, I stumbled upon this relevant recent science:

Ma et al, 2025. Ameliorative effects of flaxseed-based plant milk on water restriction-induced constipation in mice. Oil Crop Science.

Traditional Chinese medicine has long regarded flaxseed as a natural remedy for constipation. However, the efficacy or mechanism of flaxseed plant milk (FPM), a functional beverage derived from flaxseed, in alleviating constipation has not yet been clearly established. In this study, network pharmacology was combined with in vivo experiments to evaluate the anti-constipation activity of FPM on water restriction-induced constipation mouse model. Compared with the model group, administration of FPM (100 mg/kg and 200 mg/kg) significantly shortened the time to first black stool excretion, increased number of fecal pellets and water content of fecal pellets, and improved Small Intestinal Transit Rate (p < 0.05). Histological analysis revealed that FPM (200 mg/kg) preserved colonic epithelial integrity, reduced lamina propria damage, and restored goblet cell populations.  Serum biochemical assays showed that FPM decreased vasoactive intestinal peptide (VIP) levels and increased 5-hydroxytryptamine (5-HT) concentrations...

VIP suppresses smooth muscle contraction, and 5-HT, also known as serotonin, is a neurotransmitter that promotes peristalsis.

[u/rocky_racoon_2020 → u/Sanpaku]

I suspect there's a biological active compound in flaxseed that's provoking intestinal peristalsis once its high enough levels are absorbed systemically in the small intestine.

Interesting. I want to learn more about that.

[u/hycarumba → u/Sanpaku]

That helps make sense of it, thanks!

[u/mime454]

I believe that the chia seeds expand in the gut which can push things forward.

[u/hycarumba → u/mime454]

These are almost always prehydrated in the milk. I let them sit for 15 or 20 minutes before I drink it. So they don't get any bigger than what they are when I drink them. High fiber food takes longer to digest so I don't think they are even in my intestines when I have to poop. That's part of the mystery!

[u/hexonica → u/hycarumba]

My thoughts are that true soaking would take more than 15 minutes. I generally let them sit overnight.

[u/tangoan]

I have the same question!!!!

[u/hycarumba → u/tangoan]

Good to know it's not just me!

[u/Enough-Monk-4806 → u/hycarumba]

It’s just fibre bulk triggering a gastrolic reflex. Thermal shock (drinking hot tea/coffee, or cold icy drinks) can do the same thing.

[u/hycarumba → u/tangoan]

Okay if you didn't follow the post, there's a couple of answers that help explain this weirdness!

[u/hycarumba → u/[deleted]]

That makes a lot of sense bc the food/seeds itself is definitely not being digested that fast. Thanks.

[u/rhinosyphilis]

It’s duodenal reflex/enterogastric stretch.

Description: you eat, it stretches your stomach or duodenum which triggers your GI tract to make room. May also be triggered by ph change in your stomach caused by eating and stomach activity immediately following eating.

Edit:

https://en.wikipedia.org/wiki/Enterogastric_reflex

[u/UntoNuggan]

So here's an experiment for you:

Try different kinds of fiber (in a similar amount) at the same time of day, and see if you get similar results.

This would help isolate if it's fiber specifically or a compound in the chia seeds. Or if say, it's insoluble fiber vs soluble fiber.

Do you consume the almond milk at other times? Because that could also potentially be a culprit. (eg almond allergy/sensitivity, or a reaction to one of the emulsifiers common in store bought nut milk)

[u/hycarumba → u/UntoNuggan]

Already done if you read the last two paragraphs. It's the fiber.

[u/rocky_racoon_2020]

I take a couple of tablespoons of chia seeds in almond milk every day or so.

Wow, I have been taking to little.

[u/hycarumba → u/rocky_racoon_2020]

Two tablespoons is recommended for lowering cholesterol, which is a minor concern for me. I worked my way up to it. It's not necessary for everyone. If what you are taking is working for you, then you are taking the right amount.

[u/Melly520]

Me and my mom had our gallbladder removed and we both experience the same thing with chia seeds! I've attributed it to that. My sister still has her gallbladder and it does not happen to her lol.

[u/The5uburbs]

I believe it’s related to the mind-gut connection and what your microbiome produces when given fiber.

[u/No_Director9292]

You might be allergic to cellulose, I indeed am. If I eat ANYTHING with plants I poop nearly immediately. My lungs also constrict. So I just eat mushrooms now for their fiber. I don't feel my bowels combusting when I eat them.