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. We would love it if you could
share with us your stories about reinventing your health
through evidence-based nutrition. Go to nutritionfacts.org/testimonials. We may share it on our social media
to help inspire others. 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. For a vital, timely text on the
pathogens that cause pandemics you can order the e-book, audio book, or hard copy of my latest book
“How to Survive a Pandemic.” For recipes, check out my even newer
“How Not to Diet Cookbook”.

It’s beautifully designed, with more than 100
recipes for delicious and nutritious meals. All the proceeds I receive from
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