vents obesity and diabetes in mice, possibly
because they target bacteria that cause mice
to overeat. Genetically modified probiotics
can produce a hunger-suppressing compound
which signals the brain to want less food.
Other probiotics stimulate the release of a
hormone called GLP-1, which also causes a
reduction in food intake.
Another study, conducted at Washington
University in St. Louis, showed that slim people have different intestinal bacteria than overweight people do. Also, after obese people lost
weight, their microbiomes changed to more
closely look like those of thin people.
A balanced microbiome may also clear
acne. A study by scientists at the State University of New York Downstate College of
Medicine in Brooklyn showed a strong
connection between an unbalanced microbiome and acne.
Stress and a reliance on
food can slow digestion
and alter the ratio of
good and bad bacteria
in the gut. So, when
probiotics restored the
intestinal balance, most
acne cleared up.
Also, studies using probiotics
to treat allergies, asthma, inflammation, and even tooth decay have shown
promising results. Research has shown that
probiotics might even prevent colds.
Recent research has revealed that chemicals made by bacteria in the digestive
system can affect your brain—from
your mood to the way your brain
is structured. John Cryan and colleagues, at University College Cork
in Ireland, turned nervous mice
into mice that are, in the researchers’ words, “more chilled out,” by
feeding them strains of
They found barely
half the normal amount
of a stress hormone
called corticosterone in
the mouse brains. The
reduction was traced
to a neurotransmitter
known as gamma-ami-nobutyric acid (GABA),
which is secreted by
L. rhamnosus. In other words, the intestinal
bacteria produced an anti-stress compound
which took effect in the brain.
And how did the “anti-anxiety drug” get
from the gut to the head? A direct path,
called the vagus nerve, stretches
from the abdomen to the brain,
in people as well as in mice.
When researchers cut the
nerve in the mice, the calming effects of L. rhamnosus
Researchers at McMasters
University in Canada found evi-
dence that the mice’s mood was
influenced by other chemicals travel-
ing the vagus nerve. A French study found
that even healthy human
lower stress levels after
eating a combination of L. helveticus and B.
At the University of Oxford in the United
Kingdom, researchers engineered
an increase in mouse gut
Bifidobacteria, and they
found a matching increase
in a protein called brain-
factor. This protein
raises the production of
which is involved in mood
regulation, pain perception,
and perception of hunger and
satiety (feeling full).
So, for a healthier, happier,
better-looking you, probiotics
may offer a practical game
plan. Two weeks is a good
trial. Nothing is certain, but
there seem to be few, if any,
a bloated feeling or bad
breath—from adding probiot-
ics to your diet. And if cost is
an issue, homemade yogurt
and sauerkraut are especially recommended
by probiotics fans. The Internet abounds with
When the bad bacteria threaten, look for
help, courtesy of your favorite probiotics
team. When your brain is out of sorts, give
“live culture” reinforcements a try. Think probiotics for your stomach, or for allergies,
asthma, and anxieties. Bacteria might just
keep the peace in your gut and the rest of your
Specter, M. Germs Are Us. The New Yorker,
Oct 22, 2012: http://www.newyorker.com/
Williams, R. Bacterial Sentinels of Noses. The
Scientist, Sept 12, 2012: http://www.the-
NIH Human Microbiome Project Defines Normal
Bacterial Makeup of the Body. National
Institutes of Health, June 13, 2012: http://www.
[accessed July 2015].
Saey, T. H. Body Microbes Make Useful Molecules.
Science News, Oct 18, 2014; 186 ( 8), pp 8–9.
Gail Kay Haines is a science writer and book
author from Olympia, Wash. Her most recent
ChemMatters article, “Venoms: From Lethal to
Lifesaving,” appeared in the April/May 2015 issue. S H U
Recent research has
revealed that chemicals
made by bacteria in the
digestive system can
affect your brain.
PASTEURIZATION is a heat-treatment for uncooked food,
invented by the French chemist Louis Pasteur. Pasteur was
a problem-solver, and he was the first scientist to realize that
yeasts and bacteria cause fermentation. When panicked wine-makers came to him around 1860 to complain that their wines were
going sour, he traced the problem to post-fermentation action by
harmful bacteria, and he recommended killing them with gentle
heating. The process worked, and it is now used to keep milk and
other products safe from dangerous bacteria. Milk is usually pasteurized today by using relatively high temperatures for relatively short times (typically 72 °C, or 162 °F, for 15 seconds).
—Gail Kay Haines