One of the benefits of plant-based diets that has been particularly well-documented recently
is the connection between animal products, trimethylamine N-oxide abbreviated as TMAO
and atherogenesis.
Briefly, consuming animal products fosters the growth of intestinal bacteria that can
convert the choline and carnitine found mostly in animal products into trimethylamine, or
TMA.
This is then absorbed and oxidised by the liver to the molecule TMAO, which increases
our risk of atherosclerosis and it's devastating consequences.
As I have covered in videos previously, whole plant foods promote the growth of a healthy
intestinal microbiome in many ways.
But relevant to our current discussion, a plant-based diet selects against these TMA-producing
bacteria, such that the smaller amount of choline and carnitine present in plants is
irrelevant, since it will never go on to become TMAO.
It is not that we simply produce less TMAO - we produce none at all since the responsible
bacteria are not present in the first place thanks to our diet.
And not only that, but excessive choline itself may be a problem and is linked with cancer,
possibly at least partly via this TMAO mechanism, another win for basing our diet on foods naturally
lower in choline - plants.
But one thing that is less-often discussed is just how much lower are plants in choline?
Carnitine is not an essential nutrient and we can synthesize all that we need, but the
same cannot be said for choline - our capacity for synthesis seems to be insufficient in
the circumstances that have been studied and it is recommended that we obtain some from our
diet.
We may get benefits from lower intake, but are there any potential risks from not getting
enough?
I'd like to start off our exploration of this topic with an examination of adequate intake
in the general adult population to keep things simple, then move on to vegans specifically.
The daily adequate intake level is set by the National Academy of Medicine at 550 mg
for men and 425 mg for women.
To put this in context, these numbers are actually quite high and can be difficult to
hit regardless of diet.
This is seen repeatedly in studies surveying choline intake across various populations
- people are consistently not hitting these numbers.
There are a number of ways of approaching this finding.
The first is favoured by websites and individuals trying to sell you on supplements or unhealthy
foods, speaking of the "crisis" of under-recognised choline deficiency.
The second way is to dig a little deeper, look at the actual number of cases of inadequate
choline intakes in these same studies, where it becomes clear that they are practically
non-existent.
So what's the deal?
How can so many people be consuming less than the daily adequate intake and yet not end
up being deficient?
Well first of all, where did they actually get these numbers from in the first place?
The Institute of Medicine set the numbers back in 1998, based off one metabolic ward
experiment done on 16 men in 1991.
Essentially, they compared an intake of 500 mg with an intake of 13 mg, and found that
13 led to deficiency whilst 500 did not.
They then added a margin of error to the 500, adjusted down a little bit for women, and
that's where we get the adequate intake from to this day.
In fact, it's so long since these numbers were set that the Institute of Medicine as
it was known back then has actually changed it's name in the interim.
But this definition is important - what does "adequate intake," or "AI" actually mean?
The level of evidence we have on what a healthy intake of choline should be is obviously lacking
even to a lay person, and that is reflected in this definition.
An adequate intake is set when there is insufficient data to determine the estimated average requirement,
and hence recommended daily allowance.
The AI cannot be used to estimate the probability of nutrient inadequacy, yet perhpas unknowingly,
this is exactly what these articles that capitalise on fear and lack of awareness do.
It is acknowledged that the RDA would likely be lower than the AI, but due to the paucity
of data and uncertainty this cannot be officially set, so we are stuck with AIs for now.
All this AI number tells us is that the RDA is somewhere between 13 and 550 mg, but we
can't resolve the number any more closely than that since we simply don't have the data
to tell us.
We must also always bear in mind that the human body and the intricacies of metabolism
and a real-life diet are far more complex than the hypothetical all-or-nothing situations
set up in artificial diets on a metabolic ward.
There are many other factors that influence the requirement for a nutrient as I will touch
on later on.
However, this is gradually starting to become reflected in guidelines.
Whilst the National Academy of Medicine's AI is based largely on that sole metabolic
ward experiment, we now have the large population studies looking at intake and rate of deficiency
that I alluded to earlier in addition to the benefit of two more decades of research.
Based on these studies, in 2016 the European Food Safety Authority has set their AI a little
lower at 400 mg for the general adult population, which is a lot more manageable.
Perhaps more importantly, this intake level may also be safer due to the cancer and TMAO
concerns we have already discussed, in addition to other potential negative health consequences
of high choline intake.
This relative lack of academic and public health attention to choline reflects the fact
that deficiency of this nutrient simply isn't a big concern.
It isn't even mentioned in large studies examining micronutrient intake in general in the population
at large, and you might not even have heard about it as being an essential nutrient until
now.
But what about vegans specifically?
Like the large population studies, smaller studies looking at micronutrient intake and
status in vegetarians and vegans specifically again do not mention choline.
And we must remember that despite the fact that we have an even lower chance of hitting
the optimistic 550/425 mg, this isn't to say that the nutrient is not still ubiquitous
in vegan diets, and actual choline deficiency is simply not seen outside of research settings,
unlike other nutrients.
In the plant kingdom, choline is found particularly in greens, certain legumes and whole grains
- all staples in a whole foods, plant-based diet.
Additionally, many more whole plant foods are rich in betaine, which seems to spare
some of the requirement for choline.
In a recurring theme in vegan nutrition like what we see with calcium and EPA/DHA, it appears
vegans require less choline than those consuming a standard Western pattern diet because of
this.
Sources of betaine include beets, spinach, sweet potatoes and whole grains.
Furthermore, it has been shown that cruciferous vegetables actually inhibit the enzyme that
oxidises TMA to TMAO.
This sounds good, but more importantly we must remember that the reason we are concerned
with TMAO in the first place is because of the increased risk of cardiovascular disease
and cancer, and of course cruciferous vegetables lower our risk of cardiovascular disease and
help fight cancer in addition to all the other amazing health benefits.
So with cruciferous vegetables we get the benefit of a good source of choline, without
the downsides of this nutrient.
Returning to the intestinal microbiota which I began the video with, I'd like to mention
one more potential benefit of how eating healthier ties into all of this.
It has been shown that resveratrol, found in grapes, berries, peanuts and pistachios
amongst other healthy foods, appears to decrease TMAO levels and resultant atherosclerosis
in mice by remodelling their intestinal microbiota.
One more reason to focus on healthy fruits and nuts!
So to summarise all of this, there is a paucity of research into healthy intake of choline,
and a common theme accross the literature going right back to the 1998 recommendations
through the last 20+ years since is the call for more research in this area, in particular
looking at graded intakes and to determine an EAR and RDA so we can stop relying on the
out-of-date AI.
Until this is done, there will be no easy way of knowing whether or not the ubiquitous
choline intake of much less than 550/425 in the general population and in vegans is a
problem.
But for now, some comfort can be taken in the knowledge that choline deficiency appears
to be rare in the general population and amongst vegans.
However, to make sure you are getting enough, shoot for the EFSA's conservative recommendations
by eating plenty of cruciferous vegetables and other greens, legumes and whole grains
in addition to betaine- and resveratrol-rich foods, and you should get the best of both
Worlds - enough choline, but not so much that you convert some to that disease-causing TMAO.
That's it guys, hope you found the video informative!
Let me know in the comments if you've thought about choline in your diet before or if this
was the first time, if it was a nutrient you were worried about or if this video helped
assuage your concerns!
Also if there's anything you'd like clarification on or you have any questions or comments,
let me know and I'll get back to you.
I have more videos coming up on perceived and actual nutrients of concern, so make sure
you subscribe if you haven't already so you don't miss out on them!
That's it for now though, talk to ye soon.
Sláinte!