In sci.med.nutrition Dave <LowCarbHighFat-subscribe@yahoogroups.com> wrote:

Hydrogenation produces saturates, partial hydrogenation produces trans-fatty
acids.

The term hydrogenation stems from the chemical structure of lipids.
Every lipid molecule is simple a carbon chain with varying numbers of
hydrogen atoms attatched and varying numbers of double bonds.
"saturation" is the degree to which the maximum number of hydrogen
bonds are attatched....so unsaturated fats have fewer H atoms while
saturated fats are fully loaded with the maximum H atoms possible per
carbon atom.  Saturated fat has no double bonds to the structure is
flatter and the molecules pack together....hence its solid at room
temperature.  Unsaturated fats have some double bonds between carbon
atoms and so don't have the maximal amount of H atoms.  This results
in a less linear structure so the lipids don't pack together as
well....thus liquid at room temperature.  Mono-unsaturated fat has one
double bond while polyunsaturated can have three (the omega-3's), six
(the omega 6's) and on up.

so, trans-fat is produced commercially by forcing normally unsaturated
fats (vegetable oils) to give up some of their double bonds and accept
more H atoms.  Hence the fat is now partially hydrogenated...still has
some double bonds, but less than it naturally should.  Food companies
do this because the partially hydrogenated oils have different melting
points and other properties that they find desirable to make their
food last longer on the shelf.....oh and impair our health.  These
trans-fats have conformations unlike naturally saturated or naturally
unsaturated fats and, as I understand it, when the body trys to
encorporate these weird shapes into membranes, etc. things don't work
as well.

Hopefully this helps, I'm going off what I remember from nutritional
biochem so some details may be less than exact, but the general gist
is right.

Cheers!
Lisa

That's true.

If you don't have enough paint, yes.

No chain yanking, I promise.
A bit of background: Saturated fats have straight fatty acids, whereas
unsaturated fats have kinked fatty acids. This leads to saturated fat
being solid a room temperature, whereas unsaturated fat is liquid (oil).
To make margarine, which is solid, requires converting some of the
unsaturated (with hydrogen) oil to saturated fat. This is done by
pumping hydrogen gas through the oil in the presence of a catalyst.

The catalyst binds and distorts the unsaturated fatty acid making it
vunerable to attack by the hydrogen. If the hydrogen attacks and binds
the fatty acid it will no longer be unsaturated, it will have become
saturated (with hydrogen). If there is enough hydrogen and the process
is done for long enough you should end up with all the fatty acids fully
hydrogenated (saturated). If the hydrogenation is only partial - just
enough to make the oil more solid - not all of the unsaturated will be
turned into saturated.

If the unsaturated fatty acid is released from the catalyst without
picking up any hydrogen it will spring back to its original shape, OR,
it will spring back in a trans shape. The key thing is that this trans
shape, while still unsaturated is straight instead of kinked. This means
it appears to be a saturated fat and behaves like one physically, but as
soon as the body tries to burn it like saturated fat it finds it can't.

The result is that trans fats hang around in the body and are difficult
to get rid of without free radicals. Any unsaturated fats + free
radicals = damage to the body, so all in all trans fats are bad news.

MattLB