[acb-hsp] Mind-Gut Connection

[peter altschul]

Mind-Gut Connection: Why Intestinal Bacteria May Have Important 
Effects on Your Brain
  Ari LeVaux, Alterationet April 29, 2011
  Most children seem determined to eat dirt.  It may be a 
coincidence, but what those little mud pie makers appear to 
intuit is now being supported by a growing body of scientific 
evidence that early exposure to diverse microorganisms results in 
healthier immune systems.  Now there's reason to think that 
intestinal bacteria have important effects on brain development 
as well.
  A study published in the March issue of Neurogastroenterology 
and Motility examined germ-free mice -- i.e.  mice deprived of 
contact with bacteria at a formative age.  The researchers 
observed changes in brain activity based on varying microbe 
levels.  They also found germ-free mice more likely to engage in 
risky behavior -- measured as time spent in areas where they 
could be seen -- than mice with normal levels of intestinal 
flora.  The study concludes that this constitutes evidence of 
bacteria in the loop between belly and brain, and influencing 
behavioral development.
  A separate study, published last November in Archives of 
General Psychiatry, surveyed the scientific literature for 
evidence of a connection between gut microbes and depression, and 
suggested that certain bacteria might be considered as treatment 
for depression.
  Discoveries such as these support the decades-old "Hygiene 
Hypothesis," which postulates that hyper-sterile environments, 
widespread use of antimicrobial soaps, and general paranoia about 
bacteria are responsible for many so-called "diseases of 
civilization," like asthma, allergies, and other autoimmune 
disorders.  The recently discovered importance of bacteria in 
brain function helps deepen understanding of our relationship 
with these ancient organisms.
  Anybody who's ever "listened to their gut" when making 
important decisions might be satisfied to learn of this 
biochemical evidence for the mind/belly connection.  The 
mechanism by which mouse-belly microbes might influence mice 
brains isn't known.  There is speculation that the vagus nerve is 
a likely conduit.
  The vagus nerve connects the brain to several parts of the 
digestive system.  It's what tells your brain how hungry you are, 
based on what it senses in your belly.  The vagus nerve has also 
been shown to carry signals initiated by bacteria.  
Staphylococcus can attack the vagus nerve and induce vomiting.  
Salmonella infections have been shown to affect brain activity, a 
connection lost when the vagus nerve is severed.
  However mouse gut bacteria exert their influence on the brain, 
the fact that they do so, on top of all of the other cooperative 
relationships we've been discovering with bacteria, is amazing.  
And it makes me wonder who's really in charge.  Are we simply 
hosting these creatures, or driving them around as well? When 
kids eat dirt, is it because the bacteria are telling them to?
  Although we have a clear size advantage on the bacteria we 
harbor, they dramatically outnumbered us.  And on the genetic 
level, bacteria bring far more to the table.  Of the 3 million 
different genes identifiable in our bodies, only 30,000 are human 
genes.  We share those additional millions of bacterial genes 
with thousands of different species.
  The species lines in bacteria can be fuzzier than with mammals.  
I'm a lot less likely to exchange DNA with my dog than are two 
bacterium with each other.  The genetic mixing is greatly 
assisted by bacteriophages: viruses that infect bacteria.  Some 
of the most numerous and widely distributed creatures in the 
biosphere, bacteriophages are viruses that attack bacteria.  They 
usually insert some of their own genetic information into the 
host, while helping themselves to what looks good in the host's 
genetic fridge.  Then they move on to the next bacteria and do it 
again, spreading genes as they go.  When we speak of bacterial 
populations it's a given that there is an associated 
bacteriophage population greasing the wheels of whatever's going 
on.
  A recent study found large amount of bacteriophage DNA in 
kimchi, suggesting a significant role of bacteriophages in the 
fermentation process.  Kimchi is just one of many bacteria-rich 
(and presumably phage-rich) foods, like yogurt and sauerkraut, 
that many people consider to be superfoods.  There are countless 
kinds of fermented foods in many diets, both old and new.
  The Paleo diet -- short for Paleolithic -- is a modern diet 
that's based on the foods humans would have had access to during 
our evolutionary formative years.  According to the Paleo diet, 
modern-day foods like sugar, grains, and processed carbohydrates 
shift the balance toward undesirable flora, while animal- and 
vegetable-based dishes, including fermented foods and vinegar, 
encourage good bacteria.  It's no wonder, according to the Paleo 
worldview, that foods that have been with us since the beginning 
are the ones that keep our bodies in proper balance-with the help 
of our old friends bacteria.
  The "Gut and Psychology Syndrome" (GAPS) diet (it's also the 
name of the related book) is built on the premise of a link 
between mental and intestinal health.  The diet mixes probiotic 
supplements with a regimen of foods designed to tilt the playing 
field so the good bacteria take over.  Probiotic supplements are 
essentially "good bacteria" by the millions, in pill form.  
Doctors often recommend them after a round of antibiotics, which 
can kill the good bacteria in your body along with the bad.
  Much of what we're learning in labs is validating ancient 
wisdom, like the importance of fermented foods.  And along these 
bacterial lines, science is also finding an important function 
for an organ it once dismissed as a useless evolutionary relic: 
the appendix.  Now they're realizing that the appendix probably 
has immunological functions related to the fact that it acts as a 
reservoir of spare bacteria in case your gut flora gets killed 
off or flushed out, say, in a nasty bout of diarrhea.
  We're still at the beginning of the bacterial learning curve.  
A research team recently determined that humans can be classified 
into three categories depending on the type of bacteria in their 
guts.  Such bacterial affiliation is found in all humans, and is 
unrelated to race or to the gut-bacteria type of one's parents.  
At this point we have no idea what this means, or where it will 
lead.
  But we can be sure that as we continue learning about our 
relationship with bacteria, kids will continue eating nature's 
probiotic wherever they can find it.  And the more we learn, the 
smarter they seem.
  Ari LeVaux writes a syndicated weekly food column, Flash in the 
Pan.
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