Answer: What is dietary fiber?

 It seems obvious...  

.. but as I said, I suddenly realized that I didn't really understand what "fiber in my diet" really meant.  

This happens all the time. There's a kind of skill of recognizing that something isn't lining up--of knowing that you don't quite know what something really is. 

As you might have noticed, a lot of these posts start with "I didn't know..."  

In this particular case, I thought I knew was "dietary fiber" was.  Isn't fiber just the indigestible part of your food--you know, the little threads, husks, hulls, and tiny fragments that just pass straight through without much digestion seeming to take place?  

But as I noticed when I let my cereal sit for too long in the milk, things that say they have fiber in them (like my whole grain cereal) often don't look like there's anything fibrous within.  There's nothing like the kernels of corn or bits of apple skin that (as far as I can tell) are untouched by my digestive juices.  How could there be any "fiber" there?    

So... what is fiber really?  It's obviously not just undigested bits of food.  

Can you help me understand what's going on here?  Today's Challenges are: 

1. So what, really, is dietary fiber?  Is it something more than indigestible bits like wheat bran, corn kernels, and rice husks?  

I wanted to start with the basics.  First query: 

   

     [ define fiber ] 

This starts to untangle part of my confusion. I was thinking of dietary fiber as a kind of textile-like fiber.  That is, my mental model of "fiber in food" was based on what I thought of as a fiber that I might see in clothing or the husk of a seed.  This is very much along the lines of that word you see at the bottom of the definition, "roughage."  

But reading carefully, I learned that "fiber" (or "fibre") is also a "dietary material containing substances such as cellulose, lignin, and pectin that are resistant to the action of digestive enzymes." 

And THAT is a surprise. It means that the fiber in my diet can be pretty non-fibrous.  

Just a few weeks ago I had way too many plums on the tree at my house, so I spent a few happy hours making jelly and jam.  One of the steps in the process is to put pectin into the mix.  But when I do that, I can see that the pectin dissolves into a clear liquid... there aren't any obvious fibers that look like roughage.  

I was curious about lignin and cellulose, so I looked up those terms as well.  Are they fibrous in the way I'd expected? 

Answer: NO!  If you look at images of lignin, cellulose, or pectin, it's pretty clear that all of those come in powdered form--and if you look for [ liquid cellulose ] or [ liquid pectin ] it's pretty obvious that those don't have any roughage in them. 

So dietary fiber must mean something other than the roughage you get from (say) celery.  

My next query was for: 

     [ fiber in food ] 

and I quickly learned that fiber is, indeed, not just the rough indigestible bits, but is actually all the long-chain molecules that make up those indigestible bits!  

As the Wikipedia entry on dietary fiber tells us "Dietary fiber consists of non-starch polysaccharides and other plant components such as cellulose, resistant starch, resistant dextrins, inulin, lignins, chitins (in fungi), pectins, beta-glucans, and oligosaccharides."  

Okay.  I now know that "dietary fiber" is really all of those complex (long-chain) molecules in the food I eat.  So, "high fiber foods" have a lot of those chemicals AND roughage. 

But wait... there's more!  

I also learned by reading some of the links from the SERP that there are two kinds of dietary fiber!  There's "soluble" and "insoluble," that is, fiber that dissolves, and fiber that doesn't.  

     [ soluble insoluble fiber ] 

The first result is to the Medline page about dietary fiber, which includes this: 

"There are 2 different types of fiber -- soluble and insoluble. Both are important for health, digestion, and preventing diseases.

Soluble fiber attracts water and turns to gel during digestion. This slows digestion. Soluble fiber is found in oat bran, barley, nuts, seeds, beans, lentils, peas, and some fruits and vegetables. It is also found in psyllium, a common fiber supplement. Some types of soluble fiber may help lower risk of heart disease.

Insoluble fiber is found in foods such as wheat bran, vegetables, and whole grains. It adds bulk to the stool and appears to help food pass more quickly through the stomach and intestines." 

Ah ha!  So there really are two kinds of fibers in our food.  The soluble kind and the insoluble kind.  

Insoluble fiber:  This type of fiber does not get dissolved in the body and is also known as “roughage”, helping to clear out the intestinal tract. Since it's not broken down in the body, insoluble fiber has effectively zero calories. This is why a high fiber diet is recommended for weight loss as insoluble fiber will fill you up and pass through your body unchanged. 

Soluble fiber: By contrast, this kind of fiber is a bit more complex than the other. Unlike insoluble fiber, soluble fiber dissolves making a gel like substance, which is incredibly handy for slip/sliding your gut contents along.  

2. What is the current recommendation for dietary fiber in my diet?  Is 5 grams of fiber in a serving a lot?  Or is it a little?  

A quick search for: 

     [ dietary fiber recommendations ] 

generated a lot of hits.  Interestingly, when you compare the top 5 reputable sources, you see this: 

Mayo Clinic – Women:  21 to 25 grams / day; men: 30 to 38 grams / day

UCSF – everyone: 25 to 30 grams / day from food, not supplements 

NIH -everyone:  25-29 grams / day (more than 30 grams would be better) 

Harvard – people < 50 years, 25 grams for women and 38 grams for men. 

                For people > 49, Women and men should have 21 and 30 daily grams

Oddly, none of the sources break down the amount of fiber by soluble vs. insoluble.  But it's clear that "fiber from food" solves a lot of the soluble/insoluble question by providing both in roughly equal quantities.  

Basically, if you can dissolve the food in water, it's got soluble fiber.  If it doesn't dissolve, it's insoluble fiber.  You need both.  

Bottom line: Women need slightly less fiber than men, but everyone needs roughly 30 grams / day.  

If you look up various foods (after doing a query like [ data set food fiber amount ]), you'll probably end up on the USDA's list of foods with the amount of fiber listed for each.  In that list you'll see a lot of high fiber foods that you probably won't eat in large amounts (who eats 100 grams of cinnamon?), but you'll be able to look up your favorite foods and estimate the amount of fiber you're getting.  

US folks: Note that the table is given in "amount of fiber in 100 grams of food."   So you'll have a vivid image--100 grams is around 3.5 ounces, or to make it visually memorable, small cans of cat food are 3.5 ounces (100 grams). 

And you'll see that my favorite cereal has 10 grams of fiber in 100 grams of cereal.  But take note--most people I know don't eat 100 grams of cereal in a serving at breakfast.  My bowl of morning cereal usually has 36 grams of cereal, which means I'm getting 4 grams of fiber in each bowl. 

Apple with 2.8 grams of fiber

That's okay, I guess, but an average apple has 2.8 grams of fiber, and a regular serving of plain old oatmeal has 4 grams of fiber and 6 grams of protein.  (And it's about half the cost per serving.)  

SearchResearch Lessons 

1. Search out the things you don't understand, even sometimes fairly obvious things.  This was just one of those little things that struck me while reading: I couldn't actually define dietary fiber.  I make it a practice to question what I'm reading at a very basic level.  This is deeply important when you're reading something that's complicated or has an intricate back story.  Do you really understand all of the parts and pieces that are involved?  

Being a skilled searcher is, in large part, having enough background knowledge to know when something you just read (or heard) doesn't fit in with the other things you've read.  In this case, it was a small observation about my breakfast cereal.  For you, it might be something else.  Follow up those small questions--they could be deeply important.  

2. Look for multiple sources.  As I did with searching for multiple sources of fiber recommendations, it's easy to find them.  Be aware of differences between measurements! 

Keep Searching!  

SearchResearch Challenge (9/20/23): What IS dietary fiber?

 I realized I don't know what "fiber" really is!  

I was at a farmer's market buying a few veggies for the week ahead, and while standing in line I was browsing my news feed, and came across an article about the amount of dietary fiber in different foods.  I was impressed to read that my favorite breakfast cereal, a "high fiber" food, delivered a "whopping" 3.57 grams of fiber in each serving.  

Years of SRS have taught me to be very wary of anything I read, especially when it's surrounded by such superlative adjectives. 

So I found myself wondering my SearchResearch type of questions:  "Is that a lot of fiber?"  And "so how much fiber should I be getting?"  

When I got home I did a little searching around and found that... I really don't understand what fiber is! 

In particular, I thought that fiber was the indigestible part of your food--you know, the little threads, husks, hulls, and tiny fragments that just pass straight through without much digestion seeming to take place. 

But when I let my cereal sit for too long in the milk, I know it turns into a pure paste.  There's nothing like the kernels of corn or bits of apple skin that (as far as I can tell) are untouched by my digestive juices.  How could there be any "fiber" in that glop?  

Later, I saw a bottled drink for sale in my grocery store that promised a solid 6 grams of fiber in a single drink.  So far as I could tell, the drink looked pretty much like some kind of exotic juice--not the pulpy slurry I would have expected.  

Can you help me understand what's going on here?  Today's Challenges are: 

1. So what, really, is dietary fiber?  Is it something more than indigestible bits like wheat bran, corn kernels, and rice husks?  

2. What is the current recommendation for dietary fiber in my diet?  Is 5 grams of fiber in a serving a lot?  Or is it a little?  

These don't look like difficult questions--BUT--when I did my research, I found the story much more interesting and complicated than I'd originally thought.  

Among other things, I've started looking at the listed amount of fiber in a food product with a huge grain of salt.  (Which will then upset my sodium intake, but so be it.)  

What IS the story with fiber?   It seems there's more here than meets the eye, the tooth, and the entire alimentary canal.  

Can you find out? 

Let us know what you discovered, and what you did to find out about it.  

Keep Searching!  

Answer: A mysterious octopus? And the woman who understood.

  An octopus has eight arms... 

Gloomy octopus. P/C John Turnbull.

... and, even though it's a mollusk, it doesn't have a shell.  They do have a hard beak, but there's no shell in the ordinary sense of a mollusk.    

As I've mentioned before, there are exceptions to just about every generalization (even this one). A friend mentioned an octopus that DOES have a shell.  How can we find out about this?   Is that true?  Here are the Challenge questions for the week:  

1. Is my friend right?  Is there an octopus that has a shell?  Really? 

Let's start with the obvious: 

     [ octopus has shell ] 

and we quickly learn that it's complicated...  The short answer is "yes..but..."    

It's not hard to find that there are actually two octopus creatures (that is, they have 8-legs, in the Order of Octopoda).  One is the Cirrina sub-order of Octopoda--they have a small, internal shell and two fins on their head, and NO ink sack.  Here's a deep-water Cirrinothauma, often called the "Dumbo Octopus" for its resemblance to the Disney character.  

This dumbo octopus (Cirrothauma murrayi) is often called the blind octopod due to the lack of a lens and reduced retina in its eyes. Its eyes can really only detect light and cannot form images P/C NOAA

Then there's the other one--the Argonaut (Argonauta argo), a fabulous creature that also creates a very thin, papery shell that it uses to move up and down in the water column... but only the females do so. They are not attached to the body of the female.  But, oddly, they make the shell by extruding it from their body and then holding onto it for the rest of their lives.  

So the shell is of the Argonaut, but not part of the Argonaut.  They make shells for use as egg-cases.   By searching for [ argonaut shell ] I was able to find this lovely image of just the shell.  

Argonauta argonaut eggcase / shell. P/C James St. John (Flickr) CC by attribution 2.0

For our purposes, if the Argonaut creates it, we'll call it her shell.  This is what one looks like in the wild: 

The white shell is on the left, with the octopus eye and
tentacles sticking out on the right.

But then there's the more delicate issue of whether or not an Argonaut is an octopus or not.  It behaves a lot like a regular nautilus (it's got that nautilus-looking shell that it hangs onto), but the Argonauta argo is a genuine octopus that just seems like a nautiloid.  By comparison, a regular nautilus (e.g., Nautilus belauensis) has a very different body plan.  In this image you can see the outside and the inside of an "ordinary" nautilus shell.  

Exterior and interior of a nautilus shell showing the chambered interior construction

As we've talked about before, these distinctions are important when you're doing your online research.  

Early illustrations of the Argonauta. P/C Wikimedia. Original from Natural History: Mollusca (1854), p. 22 - "Paper nautilus" [Argonauta]

For a wonderful paper about the Argonauta (in particular, with great details about its shell), I highly recommend the paper Recognising variability in the shells of argonauts (Cephalopoda: Argonautidae): the key to resolving the taxonomy of the family Memoirs of Museum Victoria 77: 63–104 (2018).  

2. As I read more, I learned a couple of fascinating details about the life of this particular octopus.  Can you find two really unexpected things about this animal? 

There are many remarkable things to notice about the Argonauta argo, but perhaps the two most remarkable things I picked up just by reading. 

A. The Argonauta argo controls its buoyancy by scooping air into its shell while on the surface. With this little bubble of air, it can hover easily in the water column.  By contrast, other octopuses linger at the bottom of the sea.  They can swim around, but they prefer to hide out on the bottom.  The Argonauta defies this with its mid-water behaviors.    

B. The little octopus can repair its shell!  The shell is large, but has thin walls with just one chamber (not like the chambered nautiluses above).  The material of the shell is high in magnesium, but is primarily a kind of calcium carbonate. The biggest surprise to me was learning that if the shell of the paper nautilus is damaged, a female can repair it or can completely rebuild it as needed. 

C. Males have a modified sex arm called the hectocotylus.  When mating, the hectocotylus detaches from the male and is left inside the body of the female.  Sometimes, mature female Argonauts are often found with multiple male hectocotyli (each from a different male) wrapped around the gills inside their mantle cavities. When this was first observed by naturalist Georges Cuvier, it was thought that the hectocotyli were actually a kind of worm.  Seems like a strange mistake to make, but the hectocotyli are small and, lets face it, kind of worm-like.  If you see several of them wiggling around inside of a female Argonaut's mantle cavity, you too might think they were worms.  

I could go on... but I'll let discover more about these strange and wonderful creatures on your own. 

3. Who was the woman who first did serious research on this octopus?  What essential piece of research gear did she invent?  

Since the argonaut octopus is such a wonderful animal, I was curious about who did the first research on the topic.  My query was: 

     [ first researcher argonaut octopus ] 

Note that I added the term "octopus" in order to get better, more focused results. But once I did that, the results were great.  

Who was Jeanne Villepreux-Power? 

Jeanne Villepreux-Power  P/C Wikimedia

She has a remarkable story.  Orphaned at 11, began working as a seamstress in Paris, married an English merchant and moved to Sicily where she began an intensive study of geology, archaeology, and natural history.  While walking on the beaches near Messina she came across the washed-up shell of the Argonauta and started studying them.  In the process, she invented glass-sided aquariums for research purposes, devising clever ways to work with the difficult Argonauts.  

Just as importantly, she published her work as a member of the Zoological Society of London.  Unfortunately, much of her work was lost in a shipwreck.  

But she was the first to show that the Argonaut can create its shell.  At the time, some thought that they stole the shells from other mollusks.  But Villepreux-Power showed that the paper nautilus actually secretes its own shell material. The ability to generate the shell also lets the creature add onto its shell to make it ever larger, and then repair the shell if it breaks (or if a malicious scientist comes along and breaks off a bit).  

SearchResearch Lessons 

1. You may find more than you bargained for!  When I started this research, I thought there was only one such octopus. I was very surprised to learn of the Cirrina sub-order of Octopoda.  I then found myself in a rathole making sure the results I was finding were about the Argonauta argo, and not the "classic" nautilus.  Be careful when you find a lot of results--be sure the thing you're reading is actually about the target of your search.  

2. Reading matters.  One thing I notice about young searchers is a remarkable ability to NOT read the articles they find. Reading in detail (or syntopical reading) is a real skill that you should practice.  That's how you find the most remarkable observations.  (Such as learning about hectocotyli that look like worms...)  

Keep searching.  

 🐙

  

SearchResearch Challenge (9/6/23): A mysterious octopus? And the woman who understood.

 I thought I knew what an octopus was... 

Gloomy octopus. P/C John Turnbull.

... they're the ultimate shape-shifter with an amazing ability to solve puzzles, slip through tiny holes, and possessed of a fascinating kind of intelligence.  I've watched them for hours while scuba diving, and I have to admit--they're probably my favorite undersea animal.  (Full disclosure: they're SO interesting that I can't eat them any longer--it would be like eating a very smart pet house cat.)  

But my understanding of them was as a shell-less mollusk.  Their bodies are as close to fluid as you can imagine--they flow rather than walk.  Even so, as they move across the ocean floor, they seem to move as an ensemble, rather than just as a single animal.  That's NOT what I think of as an octopus.  This video of a mimic octopus moving around, shifting shapes and colors--that's an octopus.  

https://www.youtube.com/watch?v=Wos8kouz810 

But when I was talking with a scuba-diving friend, they mentioned that there's a kind of octopus that actually DOES have a shell.  This claim, naturally, leads to today's Challenges--one about the surprising octopus, and the woman who did the first serious research on this remarkable beast.  

1. Is my friend right?  Is there an octopus that has a shell?  Really? 

2. As I read more, I learned a couple of fascinating details about the life of this particular octopus.  Can you find two really unexpected things about this animal? 

3. Who was the woman who first did serious research on this octopus?  What essential piece of research gear did she invent?  

I love Challenges like this.  It's not hard to find the answer, but once you know, it's hard to stop from reading more about this particular octopus and about the researcher who understood more than anyone else.  Trust me, there are many more than 2 "fascinating details" about this very surprising octopus.  

Let us know what you've found by leaving a comment here.  Enjoy the SearchResearch!  

Keep searching.