All dietary fats are not created equal. Some types of
fats have been linked to ailments like heart disease and diabetes, while
others, like those often found in plants and fish, have well documented health
benefits.
So why do our bodies respond so destructively to some
fats but not others?
A new hypothesis described in latest issue of The
Quarterly Review of Biology suggests the answer may lie in how different fats
interact with the microbes in our guts. According to researchers from the
University of New Mexico and Northwestern University, some fats may encourage
the growth of harmful bacteria in the digestive system. Our bodies have evolved
to recognize those fats and launch an immune response to preempt the impeding
changes in harmful bacteria. The result is low-level inflammation that, over
the long term, causes chronic disease.
"Although the inflammatory effects of [fats] are
well documented, it is less well appreciated that they also influence bacterial
survival and proliferation in the gastrointestinal tract," write the
researchers, led by Joe Alcock, of the University of New Mexico Department of
Emergency Medicine and VA Medical Center.
Some fats -- mostly unsaturated fats -- actually have
strong antimicrobial properties. They react chemically with bacterial cell
membranes, weakening them. "If you expose unsaturated fats on bacteria,
the bacteria have a tendency to lyse. The combination of long chain unsaturated
fats, especially omega-3 fatty acids, and innate host defenses like gastric
acid and antimicrobial peptides, is particularly lethal to pathogenic
bacteria," Alcock said. Saturated fats on the other hand generally lack
those antimicrobial properties, and in fact can provide a carbon source that
bacteria need to grow and flourish.
And it's these differing microbial effects, Alcock believes,
that are at the root of why some fats are inflammatory and some aren't. To test
that notion, the researchers poured through years of research on both the
microbial effects of fats and their inflammatory effects.
"We found a highly significant relationship between
those fats that had antimicrobial properties and those that had
anti-inflammatory properties," Alcock said. "Fats that lack
antimicrobial properties tended to be pro-inflammatory. It was a very, very
strong relationship."
In a sense, the researchers say, the presence of
saturated fats sets off an "early warning system" in the body. When
fats that encourage bacterial growth are present, the body prepares for
unwelcome microbial guests with an inflammatory immune response. And while that
response may help fend off infection in the short term, the constant presence
of such fats could cause the body to spiral into diseases related to
inflammation, like heart disease.
The researchers caution that while this hypothesis is
well supported by current data, there's much more research to be done.
"We have a pretty good idea that eating fatty foods
encourages the growth and invasiveness of harmful microbiota and we know that
certain fats kill off these potentially harmful species," Alcock said.
"But we're making a bit of a leap from the Petri dish to the whole
organism."
"We don't intend this to be the final word. Rather
it's a tool to generate additional hypotheses that can be tested."
Image Source: http://www.sxc.hu/photo/1412909
Image Source: http://www.sxc.hu/photo/1412909
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