As the name suggests, fat blockers are substances that block
or at least reduce the body's ability to absorb dietary fat.
These are not to be confused with chemically modified fats like
Olestra that the body simply cannot ever digest. There is only
one true fat blocker on the market today and that is the
medication known as "Alli" or orlistat. Olistat is a drug called a
"panceatic lipase inhibitor" meaning that it interferes with the
body's normal fat digesting enzymes leaving about 30% of a
meal's fat undigestible. Orlistat really works and because it
cannot be absorbed into the blood stream it is generally safe,
but, as nearly every person who has ever tried Alli knows, it
does cause diarhea, gas and even trouble with bowel control.
These side effects are a direct result of the passage of
undigested fat into the colon where bacteria feed on it and
produce noxious gases as a by-product.

Still, many people have found orlistat helpful for weight loss. It
is worth noting that people who take orlistat for very long learn
to consume far less fat in order to reduce the drug's side
effects. With less fat in a meal, less fat is blocked and
therefore less passes into the colon to feed bacteria. If people
lower their fat intake enough while taking Alli, they can avoid
side effects altogether, but this begs the question: why not
just eat less fat to begin with and skip the drug?

Update on Labelling for Orlistat: May 26, 2010

Today the FDA announced that is will require the
manufacturers of the presciption strength of Orlistat (Xenial)
and the over-the-counter strength (Alli) to add to the package
labelling for the drugs a warning about the possibility of liver
damage that may be associated with orlistat. This action was
taken because of reports recieved by the FDA of twelve people
who developed severe liver damage while taking Xenical and
one case of severe liver damage in a person taking Alli. The
FDA says it that the liver damage may have been a coincidence
and not related to the drug, but they acted out of an
abundance of caution. People taking either Xenical or Alli should
consult with their physician and be mindful of symptoms of liver
damage like yellowing of the skin and eyes, severe itching, dark
urine, light stools or sudden and dramatic loss of appetite.
Fat Blockers: Xenical and Alli
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