Peter Attia

Let's just define it quickly.

Solubility means does something dissolve in water, yes or no?

So salt dissolves in water.

Glucose dissolves in water.

Fat does not dissolve in water.

So that's soluble, soluble, insoluble.

Similarly, we have soluble and insoluble fibers.

So let's talk about it.

Insoluble fibers obviously do not dissolve in water.

So think of an insoluble fiber as sort of roughage, something that remains largely intact as it moves through your digestive system.

These are the ones that I talked about earlier.

They are essentially there to bulk up stool, mechanically stimulating the gut lining to release water and mucus to dilute irritants and toxins in the colon and speed up intestinal transit.

So most insoluble fibers are also not fermented by gut bacteria.

So we contrast that, of course, with soluble fibers.

A viscous fiber is able to absorb water and create a gel, a viscous gel in the gut.

And we're going to talk about some of these.

And if anybody's ever played with these as supplements, it's actually kind of cool to watch how quickly something that is dry as a fiber, when mixed with water, will form a viscous gel that your kids would want to play with.

So this can lead to slower gastric emptying.

It can blunt blood sugar spikes, contributes to lower cholesterol, though I would argue not so meaningfully that we should rely on this for lipid management.

So some examples of these would be pectin, which you'd find in apples and other fruits, beta-glucan found in oats, and the psyllium husk, which I think is probably the most common one that we would look at.