Dr. Paul Mason – ‘From fibre to the microbiome: low carb gut health’
So thanks for having me back here again.
In this talk, I’m going to take you on a tour of gut health and low carbohydrate diets and by the end of it
I hope to have convinced you of a few things.
Firstly that fiber is not a necessity for a healthy diet.
there are some low carbohydrate foods which commonly cause bloating and other symptoms,
and we can identify these,
and improve gut symptoms on a low carbohydrate diet,
I want to demonstrate that
at the moment there’s simply
not enough evidence that altering
our gut bacteria can lead to weight loss.
So let’s start with fiber.
This is defined as the
carbohydrate portion of plant foods
which we can’t digest.
And remember fiber only comes from plant foods.
It can be divided into two types:
we have a soluble fiber and this is readily able to be fermented by the bacteria in our colons,
and this produces gases
and something called short chain fatty-acids,
and then we have insoluble fiber,
that’s much more resistant to being broken down by the bacteria in our colon
and this is the type of fiber that adds bulk to our stools.
Now, there’s been a lot of suggested benefits to the ingestion of fiber.
This includes preventing bowel cancer,
lowering blood sugar levels,
and, of course, treating constipation.
In fact, it is now conventional wisdom
that fiber is a necessary component of a healthy diet.
Understandably, many of my patients are concerned about the potential impacts of removing
high carbohydrate cereals and breads from their diet.
So in the Australian diet, these represent 45% of the fiber that the average Australian gets,
and when we have a look at the the current governmental advice,
they consider that fiber is the best available treatment for constipation (surpassed) by none.
But this opinion doesn’t bear a scientific scrutiny.
Now, for such a widely accepted believed claim you’d think there would be compelling evidence to back it up.
Except there’s not.
I could not locate one randomized control trial expressly looking at symptoms of constipation.
Sure, there’s trials looking at bulky and transit rate and a few other things like that,
but when we look at the symptoms of constipation,
the research just isn’t there.
So, I’d like to present to you the best trial
that I could find.
This was a case control study.
So in this study,
63 patients who presented with constipation
and high and low fiber diets were compared in these patients,
and this also included a zero fiber diet
that required the complete
cessation of all vegetables, cereals, fruits,
wholemeal breads and rice.
So this graph here represents the percentage of study participants before the study
suffering from each of the symptoms
listed on the right side.
So you can see,
before the study started all of them had constipation,
and strain opening their bowels,
and a number also experienced bloating,
bleeding, and pain.
And when the study participants, those who
went on a high-fiber diet,
we can see that the proportion
and suffering symptoms actually increased,
So, then there was a reduced fiber arm,
and what you can see here is that,
those on the reduced fiber diet actually
demonstrated a modest reduction in symptoms.
So, the question is what happened
the majority of those in the study
who had zero fiber in their diet?
This is not a mistake.
I didn’t just forget to put something in the side there.
Now, not one patient on the zero fiber diet
had any symptoms.
That’s quite astonishing really,
and these findings were highly statistically significant.
They weren’t due to random chance.
Now just out of interest,
every single person in the zero fiber group,
ended up having one bowel action per day, every day.
How did this compare to those in the high-fiber group?
One bowel action on average every 6.83 days.
Still think that fiber is good for constipation?
So, to understand why fiber reduces constipation
gives such striking results,
let’s look at the diagnostic criteria that we as doctors use to diagnose functional constipation,
and you’ll note that each one of these criterion
relates to ease of passage of stool
through the anal sphincter,
which is quite logical, really.
Now fiber, especially insoluble fiber,
the kind you have in wheat bran has long been heralded for its ability to bulb the stool,
to make it bigger,
but when you think about it logically,
is it making something bigger really the solution,
when you’re trying to pass it through a small hole?
Packing the rectum with feces actually
makes it harder to expel the fecal matter,
so using fiber to help constipation is analogous to adding more cars to fix a traffic jam,
but that’s not the only argument.
People say: “well, it also moistens the stool”.
Except it doesn’t.
It’s been long known
and well understood
that stool moisture does not vary,
regardless of how much fiber or
how much water you consume.
Fiber does not moisten the stool,
and while it’s not technically a diagnostic feature,
bloating is a known issue that
many people understand is related to excess consumption of fiber,
and the reason for this is because
it doesn’t get digested in the small bowel,
remember that’s a definition of fiber,
it’s not able to be digested.
So it passes down to the large bowel,
which has a large bacterial population,
and then these bacteria can ferment the fiber,
especially the soluble fiber,
and they produce something called
short chain fatty-acids,
which is heralded as being one of the things which it provides health benefits through,
but in the process of this they also produce gases,
such as hydrogen and given that the volume of the whole gastrointestinal tract is only about one liter
it only takes a relatively modest amount of gas production before you start feeling bloated,
and start having an element of abdominal pain,
and anybody who lived through the 1980s,
anybody remember the bran craze?
You can probably attest to that.
So what we’re left with is that,
when we look at their best evidence available,
fiber worsens constipation
It causes bloating and does absolutely nothing to moisten our feces.
So, how does this relate to low carbohydrate diets?
Well, there’s a lot of low carb foods
that are actually high in fiber.
So even though 45% of the fiber in the average Australian diet comes from breads and cereals,
a lot of the food we replace it with when we go on a low carbohydrate diet are also high in fiber,
and some of the staples that we love,
Like berries cauliflower and almonds.
They’re in that high fiber group,
and if you understand that when they get metabolized in the colon by the bacteria,
they can produce gas and bloating,
you can understand why
if you have a whole bag of nuts,
you might feel a degree of discomfort down there.
So, some of you are probably looking at that going:
“you know what?
I did have a big plate of cauliflower mash the other night and I did feel a bit funny overnight”.
So let’s turn our attention to something called the short chain fatty acids.
So you’ll remember when
once the fiber is fermented by bacteria,
it produces these fatty acids,
and they’re thought to offer some health benefits.
So these bacteria allow the body to salvage energy from an otherwise unusable source,
and provided in the form of fats,
and estimates vary widely,
but it’s commonly considered that
about 5% of the energy
we actually get from our diet,
when we’re eating an average diet,
actually comes from these short chain fatty acids
which are produced from fiber,
and it said that these short chain fatty acids
nourish the cells that line our colon
they’re called colonocytes,
and this is thought to help improve conditions
like inflammatory bowel disease (IBD),
and while it’s true this is a representation of some of the cells that line the colon,
while these cells can use
short chain fatty acids for energy,
they only do so,
by after converting them to ketones first.
So if ketones are produced from short chain fatty-acids
and that’s beneficial,
then isn’t it logical that ketones in the
circulation from being in nutritional ketosis,
or in a ketogenic diet would also be beneficial
to these cells, they can still get to them,
and in fact, the ketones in the circulation are probably even more effective
because they’re delivered to every colonocyte,
not just those in which they’re in direct contact with,
and this is actually being demonstrated in studies comparing enemas
given short chain fatty acids,
and ketones given into the circulation,
and it’s been shown that the ketones given in the circulation
are more effective at treating
the inflammation of IBD,
which might mean the short chain fatty-acids
aren’t so magical after all,
and even if they were, fiber isn’t the only source of
short chain fatty acids from gut bacteria.
This is a graph here and it shows a short chain fatty acid production
between a plant-based diet, with lots of fiber, and an animal-based diet, with lots of amino acids.
Here in red, you can see that the short chain fatty acid production is actually higher on the animal-based diet
than it is on the plant-based diet.
So it would seem there’s nothing uniquely beneficial
about the production of short chain fatty acids
from fiber at all.
So let’s turn our attention to one of the other putative benefits of fiber in the diet,
that you can control your blood sugar levels,
and when you take that in isolation,
that’s actually correct
So this graph here compares blood sugar levels between
a diet recommended by the
American Diabetes Association,
yes with all that spike in blood sugar,
diabetic association recommended diet
and below that, a diet that’s higher in fiber.
So you can actually see that
the high fiber diet actually does
moderate the spikes in insulin to a degree.
But the point that should probably be made that,
if you didn’t eat all the carbohydrates in the first place,
Then you wouldn’t need to worry about
controlling the sugars with fiber
and even with the fiber, if we convert it to our units,
the blood sugar level still goes over 10,
and additionally if a diet that I was recommending for diabetes had blood sugar control like that,
I’d probably start looking for another job
So, let’s have a look at this graph.
This study was also published in the
American Diabetes Association Journal,
and on the top you can see a control diet with significant spikes in blood sugar level,
and on the bottom you can see that
height looks massively better,
and you know, far better than the diet that you just saw with extra fiber added to it.
Now the diet on the bottom is what’s called a low bagged diet, this stands for
low biologically available glucose diet.
I guess he can’t use the term low carb
in a diabetes journal, huh?
Now for a final thought on whether fiber
is a necessary part of a healthy diet,
let’s just look at a herbivore gut which
has a really large cecum,
which is where fermentation of fiber occurs
and compare it to a human gut.
So clearly, you can see that our gastrointestinal tract
just isn’t set up to metabolize or process fiber
in the way that herbivores are.
I’d like to now move on to the
next section of my presentation,
and have a look at something else that can cause gastric problems on a low-carb diet,
and that’s something called FODMAPs.
So FODMAPs, are again carbohydrates,
are a group of short-chain carbohydrates
with some common features.
So firstly, they’re poorly absorbed in the intestine
and because of that they get down
to the colon where they can be
fermented by the bacteria, again causing gas.
Much in the same way that happens with soluble fiber
and also (the issue of) these FODMAPs is
particular carbohydrates attract fluid
due to a high level of osmotic activity
and that can lead to watery stools,
and both of these symptoms are seen in a condition that we call irritable bowel syndrome (IBS),
and as well, (besides) causing those stools,
FODMAPs can also cause constipation,
something else which is seen in IBS,
and the way it does that is,
when the bacteria metabolized them,
they produced methane and methane gas has
actually been shown to cause constipation,
and when people with this IBS,
repeated in lots of different studies,
when they’re put on a diet that’s low in these FODMAPs,
about three-quarters of them have significant improvements,
and I’d like to illustrate that point with a very interesting study published earlier this year,
So there’s a condition called
non-celiac gluten sensitivity
So these patients they get gut symptoms
when they eat foods that contain gluten.
But when we test them for celiac disease,
it all looks normal.
Now the thing to understand is that
foods that contain gluten,
also often contain something called fructans,
and and this is one of the FODMAPs.
So, this study recruited patients
with this non-gluten celiac sensitivity,
and gave them specially made bars,
some of them had fructan in them, some had gluten and some had neither,
and what you can see on the right,
is that their symptoms were far worse when they’re given the fructans than when they’re getting gluten.
So it appears the diagnosis of non-celiac gluten sensitivity is in fact a problem with FODMAPs.
So how does this relate to the low-carb diet?
Because we don’t tend to eat much wheat, right?
True but FODMAPs are found in a number of other foods some of which are seen on a low carbohydrate diet.
and unfortunately, this includes cauliflower.
Again, one of the staples
which we also saw was high in fiber.
So if you’ve ever wondered why you feel bloated
or constipated after cauliflower mash,
you may have just found the answer.
Now let’s have a look at the P in FODMAPs
and this stands for Polyols,
which represents artificial sweeteners
called sugar alcohols.
Now because they essentially provide calorie free sweetness,
polyols are used widely in a lot of
low carb bars and sweets.
The problem is they’re poorly absorbed,
they attract water, they produce gas,
they give you loose stools,
and many people on low carb diets have suffered diarrhea as a consequence of
having one too many Atkins bar.
Now I’d like to touch on what we call the microbiome.
Now this reflects the colonies of bacteria
or microbes that exist within the human body.
But in particular we’re going to focus on those
in the colon, in the large bowel.
It’s often been said that we’ve got 10 times more bacteria than we do human cells.
That’s an exaggeration,
when we actually look at the science,
they do outnumber us by about 1.3 to 1
but not quite 10 times.
So we’re going to focus on the microbes right down at the bottom of this arrow here
and the question I want to specifically address is,
can these bacteria make us fat?
Because that’s what we’ve been hearing
a lot about recently.
Now we’ve got more than a thousand
different types of bacteria
within our gut, but 90% of these come from
one of two main groups:
the firmicutes phyla or the bacteroidetes,
and the firmicutes phyla has actually been associated
in a number of studies with obesity,
while the bacteroidetes has been
associated with weight loss,
and the graph here demonstrates
how when you lose weight,
the bacteroidetes actually increases
But the thing to understand about bacteria is that,
they have very specific conditions for their growth.
Some prefer oxygen, some don’t
some like fiber, some don’t,
and so on.
And the bacteria, if they like the conditions
you give them,
if they like the nutrition you provide them,
they will proliferate.
So simply by providing a different source of nutrition,
we can change the bacterial colonies in our gut.
And these changes occur rapidly.
Within a single day,
it’s been documented that you can get major changes in the bacteria within your gut.
But the big question is,
can we deliberately change the balance of bacteria
to lose weight?
Now a key point here is that the bacteroidetes phyla,
which is associated with weight loss,
also happens to be associated with high-fat ketogenic diets.
This has been found in studies
of children on this kind of diet
when they’ve been having their epilepsy managed.
So it becomes the case of the chicken or the egg.
Is it a change in bacterial population?
Or the change in the diet that leads to the weight loss?
So back in 2006, is this famous paper that was published that showed that an obese
microbiota could make mice fat.
So they had some germ-free mice,
and they gave these germ-free mice
some bacteria from some fat mice
and from some skinny mice,
and they actually found that
the bacteria from the fat mice
made these germ-free mice fatter.
And this is why this graph here demonstrates
short chain fatty acid production
comparing the two groups,
and what you can see is that the obese bacteria led to an increased energy harvest
by way of producing more short chain fatty acids.
But that doesn’t mean that you can simply transplant bacteria in our colons to lose weight.
Firstly, the bacteria were transplanted
into germ-free mice.
There was no competition from other bacteria.
It’s highly unlikely that if you transplanted bacteria
into a gut that had an existing colony,
that it would do as well.
Secondly, the extra energy was derived from fiber.
So if you’re on a low fiber diet
then there would have been no finding,
and the fact that there short chain fatty-acids
are then converted into ketones,
which as we know, is an appetite suppressant,
means that in the real world
when we’re not on calorie controlled diets,
when we’re not just in a cage
with a limited amount of food
that our volitional food intake becomes important.
So the ketones that are produced
from the short chain fatty-acids
probably would have had
an appetite suppressant effect,
and those mice would be predicted to then eat less.
So it’s not clearly apparent that we can simply change our gut bacteria to lose weight.
Far more likely
is that changing a diet permits weight loss,
and that’s associated with the
changing gut bacteria, not the cause.
It’s the age-old conundrum.
Is it causation or is it correlation?
So as a final demonstration that what we eat
does influence a gut bacteria
and not always in a good way,
let’s have a look at this study.
So trehalose is a sugar composed of
two glucose molecules.
But it’s fairly recent and that it’s been in our food supply.
It was only approved for use in Australia in 2003,
and that was after some Japanese scientists discovered a way to mass-produce it back in about 2000.
And it’s not very sweet
but it is very effective at lowering the freezing point of food.
And because of that it’s used in a lot of
things like ice cream.
Now the problem is
that a particularly harmful bacteria called Clostridium difficile is very fond of trehalose and
The increased consumption since
the early 2000s has been associated
with an increase in a dangerous condition called pseudomembranous colitis
associated with this bug.
So what we eat changes our gut bacteria.
So to conclude, I’d like to leave you with three key messages:
fiber is not a necessity for a healthy diet;
Secondly, even on a low carbohydrate diet,
certain foods contain high levels of fiber
or FODMAPs that can cause stomach upset,
and you need to be aware of this;
and finally the whole concept of altering
our microbiome for weight loss
is a bridge too far with
the current understanding of science.