Trying to stay healthy can seem like a full-time job sometimes.
Especially during a pandemic.
But I’m here to make that goal a little easier.
Welcome to the Nutrition Facts Podcast.
I’m your host Dr. Michael Greger.
Fermented foods have been getting a lot of attention recently,
but some of these options work better than others.
In our first story, we look at which foods appear more protective,
fermented or unfermented soy foods.
There is an enormous variation in the rates of prostate cancer
around the globe, with among the highest rates in the U.S.
and lowest rates in Asia, though that may be changing.
The largest increase in prostate cancer rates in the world
in recent decades has been in South Korea, for example.
A 13-fold increase in prostate cancer deaths nationwide.
They suggested the increase in animal foods may have played a role,
since that was the biggest change in their diet over that period,
nearly an 850% increase.
This is consistent with what we know in general about foods
and the prevention and management of prostate cancer.
Tomatoes, broccoli family vegetables, and soy foods decrease risk,
no clear benefit from fish,
and an increased risk from meat and dairy.
This may be because a diet based around whole plant foods
effectively reduces inflammation in the body.
There is a genetic factor.
If you have a first-degree relative with prostate cancer,
you may be at 3-fold higher risk.
But non-genetic factors may increase your risk 300-fold.
How do we know the low rates in Asia aren’t genetic?
Because when they move to the United States,
their rates shoot up,
and by the second generation, they’re almost caught up.
This may be because of more Burger Kings and Dairy Queens,
but could also be because of eating fewer protective foods,
such as soy.
A systematic review of all soy and prostate cancer population studies
to date confirmed soy foods could lower the risk.
But, that’s kind of a broad category.
There’s all sorts of soy foods.
There’s fermented soy foods, like miso and tempeh,
and unfermented foods, like tofu and soymilk.
Which is more protective?
Researchers sifted through the studies.
And, it turns out that only the unfermented soy seemed to help.
Tofu and soy milk consumption were associated
with about a 30% reduction in risk,
whereas there didn’t appear to be any protection
linked to fermented soy foods.
In our next story we discover how, with certain medical conditions,
probiotic supplements may actually make things worse.
When you make sauerkraut at home,
you don’t have to add any kind of starter bacteria
to get it to ferment,
because the lactic acid producing bacteria
are already present on the cabbage leaves themselves
out in the field.
This suggests raw fruits and vegetables may not
only be a source of prebiotics—fiber—
but also a source of novel probiotics.
Researchers have since worked on characterizing
these bacterial communities and found two interesting things.
First, that the communities on each produce type
were significantly distinct from one another.
So, the tree fruits harbor different bacteria
than veggies on the ground, and grapes and mushrooms seem
to be off in their own little world.
So, if indeed these bugs turn out to be good for us,
that would underscore the importance of eating
not just a greater quantity, but greater variety
of fruits and veggies every day.
And second, they found that there were significant differences
in microbial community composition
between conventional and organic produce.
This highlights the potential for differences
in the bacteria between conventionally and organically
farmed produce items to impact human health;
but, we don’t know in what direction.
They certainly found different bacteria on organic versus conventional,
but we don’t know enough about fruit and veggie bugs
to make a determination as to which
bacterial communities are healthier.
What about probiotic supplements?
I’ve talked about the potential benefits,
but there appears to be publication bias
in the scientific literature about probiotics.
This is something you see a lot with drug companies,
where the sponsor, the supplement company
paying for their own probiotic research,
may not report negative results, not publish it,
as if the study ever happened.
And so, then, we doctors just see the positive studies.
Using fancy statistical techniques, they estimated
that as many as 20 unflattering studies were simply MIA.
And, even in the studies that were published,
even when the authors were directly sponsored by like some yogurt company,
the conflicts of interest were very commonly not reported.
There’s also been concerns about safety.
A review for the government’s Agency for Healthcare Research and Quality concluded
that there’s a lack of assessment and systematic reporting
of adverse events in probiotic intervention studies;
so, while the available evidence in randomized controlled trials
does not indicate an increased risk for the general public,
the current literature is not well equipped
to answer questions on the safety of probiotics with confidence.
This is the study that freaked people out a bit.
Acute pancreatitis, sudden inflammation of the pancreas,
is on the rise, which can become life threatening in some cases,
as bacteria break through our gut barrier
and infect our internal organs.
Antibiotics don’t seem to work, so how about probiotics?
Seemed to work on rats.
If you cause inflammation by cutting them open
and mechanically damaging their pancreas,
not only do probiotics show strong evidence for efficacy,
but there were no indications of harmful effects—
So, half the people with pancreatitis got probiotics,
half got sugar pills, and, within 10 days,
the mortality rates shot up in the probiotics group
compared to placebo.
More than twice as many people died on the probiotics.
Thus, probiotics for acute pancreatitis probably is not a good idea.
But, further, probiotics can no longer
be considered to be just completely harmless.
The researchers were criticized for not telling patients,
not cautioning patients about the risk
before signing up for the study.
(The study subjects were told probiotics had a long history
of safe use with no known side effects).
In response to the criticism, the researchers replied
there were no known side effects—until their study.
Finally today, we look at how probiotics
may reduce the risk of upper respiratory tract infections.
Babies delivered via caesarean section
appear to be at increased risk for various allergic diseases.
The thought is that vaginal delivery leads to the first colonization
of the gut with maternal vaginal bacteria,
while c-section babies are deprived of this natural exposure,
and exhibit a different gut flora.
This is supported by research noting that disturbance
in maternal vaginal flora during pregnancy
may be associated with early asthma in their children.
This all suggests our natural gut flora
can affect the development of our immune system for better or for worse.
In adulthood, two studies published back in 2001
suggested that probiotics could have systemic immunity enhancing effects.
Subjects were given a probiotic regimen between weeks 3 to 6,
and saw a significant boost in the ability of their white blood cells
to chomp down on potential invaders.
And what's interesting is that even after the probiotics were stopped
there was still enhanced immune function a few weeks later compared to baseline.
The same boost was found
in the ability of their natural killer cells to kill cancer cells.
And similar results were also found using a different probiotic strain.
Improving immune cell function in a petri dish is nice,
but does this actually translate into people having fewer infections?
For that, we had to wait another 10 years,
but now we have randomized, double- blind, placebo-controlled studies
showing that those taking probiotics may have significantly fewer colds,
fewer sick days, and fewer symptoms.
The latest review of the best studies to date found that probiotics,
such as those in yogurt, soy yogurt, or supplements,
may indeed reduce one's risk of upper respiratory tract infection,
but the totality of evidence is still considered weak,
so it's probably too early to make a blanket recommendation.
Unless one has suffered a major disruption of gut flora
by antibiotics or an intestinal infection—
unless one is symptomatic, with like diarrhea or bloating--
I would suggest focusing on feeding the good bacteria we already have,
by eating so-called prebiotics, such as fiber.
After all, as we saw before,
who knows what you're getting when you buy probiotics?
They may not even even be alive by the time you buy them.
They also have to survive the journey down to the large intestines.
Altogether, these points suggest
that the advantages of prebiotics— found in plant foods--
outweigh those of probiotics.
And by eating raw fruits and vegetables we may be getting both.
Fruits and vegetables are covered with millions of lactic acid bacteria,
some of which are the same type used as probiotics.
So when studies show eating more fruits and vegetables boosts immunity,
prebiotics and probiotics may both be playing a role.
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To see any graphs, charts, graphics, images, or studies mentioned here,
please go to the Nutrition Facts Podcast landing page.
There you’ll find all the detailed information you need –
plus links to all of the sources we cite for each of these topics.
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you can order the e-book, audio book,
or hard copy of my latest book “How to Survive a Pandemic.”
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