Hey everyone, welcome to the Drive

podcast. I'm your host, Peter Aia.

[music]

Peter, welcome to another AMA. How you

doing?

>> I'm doing well. Thank you once again for

having me.

>> Living life happy, healthy. All is good.

>> Very much so.

>> That's good. People will be sad to learn

who listen to our last full AMA. I do

not think as of now you are the proud

owner of an 87 Caprice Ghostbuster car.

Is that correct?

>> Correct. Uh the uh CFO vetoed the

purchase.

>> Yeah. Which is it's a shame. Um but

maybe with enough outcry one day you can

accomplish something where you deserve

that car. I don't know if you can,

>> but the hope is one day you can treat

yourself to something nice like a 87

Ghostbuster Caprice

>> or just an 87 Caprice. But yeah,

>> you could say could be a dream of yours.

You know, maybe that's your dream. On

that, we're going to talk about fiber,

which has nothing to do with anything we

just covered. Um, but it's a subject we

get asked about a lot and we've never

really talked about on the podcast

before. And if you think about usually

what we cover on AMAs or podcasts,

there's some tie in. We've looked at it

some way before, but I think fiber is

one of those topics we've never really

dove deep into, and we get a lot of

questions on it. And so, we're going to

cover what fiber is, where it can, can't

be beneficial, how to think about using

it. We'll look at all the various claims

that people talk about which is satiety

weight management, glycemic control,

cardiovascular health, colon cancer

prevention, all things from the outside

would be very important and very nice to

have. And so we're going to look at all

those and then close on some practical

takeaways of how people can apply all

this as they think about fiber in their

life. So, with that said, anything on

fiber you want to add before we get

rolling?

>> Nope.

>> Why do we want to talk about fiber? Why

do we think it's worth spending an AMA

on? You know, I think it's it really

comes down to the importance of

occasionally checking things that we

view as aiomatic or dogma, right? So,

the general consensus is that fiber is

good. The more you eat, the better. End

of story. Case closed. But if we're

going to be critical of our beliefs, we

have to acknowledge that the recommended

uh daily allowance for fiber is almost

entirely based on epidemiologic studies.

And we know that epidemiologic studies

have left us uh on the wrong track with

many of their recommendations, not all.

Um and of course, just because

epidemiologic studies point to something

being the way to do it doesn't mean it's

wrong either. Um but basically we just

don't have um as much clear causal

evidence as we would like to make the

type of recommendations that we're

making now. I would say historically I

have it's not that I haven't known this.

I've just let it slide because my view

has been what is the harm, right? So so

what if the epidemiology says you should

be eating you know whatever 50 grams or

30 grams a day? What's the downside in

that? Um but you know, look, there's

been some polarizing discussions on this

topic lately. Um and you seem to have

people uh accumulating on either sides

of this debate, right? You've got the

you need zero fiber crowd uh obviously

more on the sort of carnivore side of

the diet landscape. And then you've got

the if you're not getting 50 grams a

day, uh you know, you're you're you're

probably going to die like in the next

week or so. Obviously I'm being

facicious but that's that's basically

the the way the discussion is is sort of

shaping out. So I think with that said

we we need to take a closer look at the

data um so that an individual uh who you

know is in the 97% of the population who

chooses not to be completely dogmatic

and extreme can make a well-informed

decision and and frankly that starts

with me like I actually care deeply

about this topic on a personal level

because I you know I'm actually not sure

how much fiber I should be eating. And

we've talked about epidemiology in the

past, but I think it's worth just kind

of double clicking is when you look at

epidemiology around fiber nutrition, do

you just kind of want to walk through

how you think about that and what

sometimes the limitations are?

>> Yes. And apologies in advance to the to

the to the to the veteran listener who's

heard me talk about this at length, but

I think it's it's always worth, you

know, spending a moment on this because

I also realize there are people that

might be new to this. So epidemiology,

in particular, nutritional epidemiology,

um, tends to be heavily confounded by

healthy user bias. Um, and that means

that people who are doing one healthy

thing, for example, like eating a

high-fiber diet, tend to be doing many

other healthy things. They might be

exercising more. They're much less

likely to smoke. They're probably

getting more sleep. And while a number

of these things can be statistically

modeled and corrected for in what is

referred to as an adjusted analysis, it

is essentially impossible to capture

every one of these things and

statistically correct for them. In other

words, you are very likely to be

capturing other healthy habits when

you're trying to simply measure one

thing. And of course that's the hallmark

of doing experiments, right? The reason

an experiment, particularly a randomized

experiment and ideally a blinded

randomized experiment as the gold

standard, uh is so important is because

it allows you to isolate one variable at

a time and epidemiology does not allow

you to do that. Um I think the other

reason that epidemiology is challenging

here and this is uh again not not unique

to epidemiology. This is a a common

phenomenon in all nutrition research is

it is difficult to disentangle the

potential impacts of fiber itself from

the potential impacts of things that

traffic with fiber. the other

micronutrients and phyitochemicals

specifically because of course fiber is

found in plants and plants are

presumably known to contain many things

that provide some benefit um and

therefore it's difficult to disentangle

them. So I would say those are the two

main reasons why it has been uh not easy

to to come up with I think some um more

concrete points of view on this uh

particular nutrient. And before we get

further following that I think it's

always just helpful to even define fiber

and how we're talking about it because I

think a lot of times people have heard

it. I don't know if everyone knows

exactly what we're referring to. So, as

we look at what we're going to cover, do

you just want to define how we're

talking about fiber?

>> Yeah, I I and I'm I think this is

actually a very important point and I I

I you know, this is and this is an AMA

where I found myself learning a lot in

the preparation for it with the research

team. Um, so in nutrition, dietary fiber

refers to a diverse group of compounds

that make their way to the large

intestine. [snorts] Um, so why is that

relevant? Well, if you think about how

your digestion works, you've got, you

know, you put things in your mouth.

Digestion actually begins in the mouth,

right? You've got these enzymes in the

mouth that are already starting to break

things down. Um, but but mostly the

mouth is for mechanical breakdown. The

stomach then undergoes uh more of a

breakdown, right? So now you've got this

high acid environment and other enzymes

in the stomach that break things down

further. The stomach then exits the the

the food stuff into the proximal part of

the small intestine called the dadum and

then ultimately ilium jigunum and that's

where the bulk of uh nutritional

absorption takes place. Um but of course

this is what separates fiber from many

of the other things we consume which is

the enzymes um can't break down fiber so

they actually make their way all the way

to the large intestine. Um, now these

these these compounds that make their

way to the large intestine are virtually

always carbohydrate-based.

Um, and that's why, you know, if you

look at a nutrition label, you'll

usually see fiber as kind of a subset of

carbohydrates. Um, but it usually

doesn't count towards the caloric

content because you're not really using

them for energy. So, the common thread

across fiber types is that we can't

digest them. But that's really where the

similarities end and where the chemical

composition of fibers vary widely. This

is where you start to get into at least

for me kind of a nomenclature that uh

and a and a set of uh explanations that

that actually is quite complicated and

and you know probably worth getting into

a bit more.

>> Yeah. And based on that kind of the

difference there and even the last

comment on how they can't really be

digested based on that can we treat them

all the same and how they affect the

body or are there going to be

differences there?

>> Yeah. No, there are differences. So we

we you know not all fibers are created

equal and this is where unfortunately we

do need to get a into a little bit of

semantics uh to be able to to really

make progress uh in this topic. So um

there are lots of things that are

classified as fiber. wide range of

physical properties that a particular

fiber might have. Um, but these

different properties produce different

effects on the body. So, some fibers

provide primarily microbiome support

because they're actually fermented by

gut microbiomes. Okay? Uh, some fibers

can improve blood sugar and we'll talk

about how that happens. and others

simply bulk up stool and again the

absence of those fibers would lead to

altered uh bowel habits. Um but

importantly not all fibers do the same

things and they don't all do them

equally well. So in the end fiber is a

function sorry the function of fiber uh

comes down to a bunch of properties of

that specific fiber. So I think then

let's double click on those. What are

the properties of fiber that determine

the different functions it can do in our

body?

>> Okay, so the single most important one

and the one that I think most people

will be familiar with is what's called

solubility. Everybody's heard the term.

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. Um 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, right? Something that remains

largely intact as it moves through your

digestive system. Uh these are the ones

that I talked about earlier. They're

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. Okay. Um so

um most insoluble fibers are also not

fermented by gut bacteria. So we

contrast that of course with soluble

fibers. So a viscous fiber is able to

absorb water and create a gel, a viscous

gel in the gut. And um 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, um, 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. Um, so some examples of

these would be pectin, which you'd find

in apples and other fruits. uh beta

glucan found in oats um and the psyllium

husk which I think is probably the most

common one that we would look at right

so that's actually um a plant um that

you can most commonly consume as a

supplement

um so again these are all viscous but

there's some variability in how viscous

they are and we we'll get to that later

okay so the other category of soluble

fibers are the fermentable fibers which

are broken down by gut bacteria to

produce short- chain fatty acids such as

butyrate. These are also known as

prebiotic fibers which um you know the

most common examples of this would be

inulin and pectin. Uh while most

prebiotic fibers are soluble, there are

some exceptions. Uh so for example

resistant starches found in cooked and

cooled starchy foods, oats, potatoes and

rice uh or in beans. We're going to talk

more about these later but I just kind

of want to start high level. Um,

important to be aware that these two

properties uh, viscosity and

fermentability are not mutually

exclusive. You'll notice that because I

just use pectin as an example in both.

So, some soluble fibers are fermentable

but don't form gels. Others are gel

forming forming but poorly fermentable.

And some can do both and some may do

neither. All of this is to say this is a

bit of a mess and sometimes can be a

little hard to wrap your head around.

for uh for the sake of my lack of brain

damage and anybody else's listening, we

have included a table in the show notes

of common fibers along with all their

properties and the food sources you can

find them in. So, if at the end of this

podcast you're thinking to yourself, all

right, I kind of want to beef up my

intake of this fiber and this fiber and

I frankly care a lot less about this

type of fiber. We want to be able to

help you do that in terms of

understanding what sorts of foods you'd

find that in and of course what

supplements. not to cause you to incur

more brain damage and not to go through

the full table, but I think sometimes it

is helpful just to highlight one or two

examples of what you just said so people

can kind of put an understanding to what

you just talked about and where they

might find it in their day-to-day diet.

So, can you just go through just a few

examples to kind of paint the picture

for people as they're listening or

watching?

>> Yeah. So, when you take fiber from a

whole food source, um, which I think is

what we mostly want to be able to do,

you're typically going to get a mix of

different fiber types and therefore

they're going to have different

properties. So, cellulose and lignen,

which are insoluble fiber, um, are

structural components of plant cell

walls. So, that means that any whole

[snorts] plant-based food you consume

will have some amount of insoluble

fiber, but the exact quantity is going

to vary across plants. Um though

vegetables will typically contain more

and uh fruits and like within fruits,

peels and skins uh would also contain

more than the you know the meat of the

fruit so to speak. When it comes to

soluble fibers, some foods are

especially high in certain types. So for

example, oats are packed with beta

glucan which is a soluble gel forming

fiber that's also fermentable by the gut

biome. So when you eat oats, you're

getting insoluble fiber from cellulose.

and then the betalucan and you're

getting both gel formation and the

fermentation driven prebiotic effects

that make those short- chain fatty acids

which also have a positive and favorable

effect on blood glucose. Now beans on

the other hand don't contain any single

dominant fiber. They're high in fiber

overall because they provide a diverse

mix including resistant starches which I

I want to come back and talk about

insoluble fiber and soluble fibers with

varying degrees of fermentability. So

when you get fiber from whole food

sources, just remember you're getting a

mixture of fiber types um as opposed to

just one.

>> You mentioned their resistance starch. I

think it's worth just kind of doubling

down on that right now. Can you just

walk through what a resistant starch is

and how cooking relates to that? Cooking

or cooling. I think you mentioned

earlier.

>> Yeah. Yeah. This is actually something

that I I learned in the prep for this

podcast. I didn't appreciate the the the

temperature component of this. So, a

resistant starch is a type of insoluble

fiber where the word resistant is

referring specifically to the fact that

they resist digestion. Now, they're

subdivided into five types. RS1 to RS5,

which actually I think would really be a

better car name. You know, the Audi RS1

or the Audi RS5, but uh we'll put that

aside for now. Um, but the most common

types we encounter are RS1, RS2, and

RS3. So, RS1 are the starches that are

physically inaccessible to digestive

enzymes in the GI tract. um they're

typically found in whole grains, seeds,

legumes,

um and other minimally processed foods,

uh that are high in fiber. RS2 are

naturally resistant starch uh granules.

So, they're present in raw potato

starch, unripe green bananas, if you

anybody's up for that. Um and some high

uh amalos maize starches. That's just a

type of corn. Um, this is the type

you're most likely to find in supplement

form, right? So, if you're if you're

looking to double down on RS2,

um, you're you're going to be buying an

RS2 supplement. [snorts]

RS3s are known as retrograde starches

because these are starches that have

been cooked, which disrupts the starch

structure, but then cooled, which causes

the starch to retrograde into a

crystalline form that resists digestion.

In practice, and by the way, again, I

this is not something I knew until a few

weeks ago. In practice, this looks like

cooking your starchy food like your

potatoes or rice and cooling them in the

refrigerator overnight. Now, it can be

warmed up, but if it gets too hot, the

resistant starch will break down. So,

what's really interesting here is I'm

the only person in my family, Nick, that

loves eating cold starchy food. So if we

have leftover m mashed potatoes, if we

have leftover potatoes of any kind, if

we have leftover rice, I am simply too

lazy to heat that stuff up. So I'm

always eating it cold, much to my wife's

chagrin. And I finally realized like I'm

doing one thing right here, which is I

am actually getting the maximum amount

of RS3 resistant starch. Um, so anyway,

we'll we'll note this in the table. Um,

and and again, remember RS2 you're going

to buy in supplement form. Uh, whereas

RS1 you you're going you're going to get

in in a in a whole uh oat. U by the way,

you're not going to get that in an

instant oatmeal. So, I just um worth

making that point here. If you process

the heck out of oats, you you sort of

lose this capacity. Um, but okay.

Anyway, hopefully that helps with odor

resistant starch juice.

>> Perfect. With that background laid out,

I think now we can kind of move to what

people want to know next, which is how

fiber relates to their health. So, do

you want to just kind of go through

quickly which claims that we see most

often around fiber and then how you want

to talk about them, how you want to

cover them for the rest of the show.

>> Yes. Uh you mentioned them at the

outset, but I'll restate them. Right. So

satiety and weight management uh

glycemic control cardiovascular health

and colarctal cancer prevention. Um so

so these are the big ones and this being

the drive we do everything in structure

and therefore we have a framework and so

the way we want to do this is we want to

for each of these claims ask the

question do we know the mechanism or

mechanisms that would account for it? Do

we have a sense of the effect size? um

do we have a better tool to accomplish

this? Uh in other words, should we

consider fiber as an adjunct? Um

versus is this sort of the primary tool

and the one that we should rely on

mostly as our um you know as our as our

quiver in the uh or arrow in the quiver.

So after we go through each of these,

we'll we'll you know try to wrap it up

with hey, what's what's a recommendation

on how much fiber and what type of fiber

you should prioritize? And you know

effectively it's just going to come down

to how much data do we have to

understand this and go through this

framework.

>> Perfect. Let's start with weight loss.

What do we know about the mechanism of

which fiber can help with weight loss?

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