Trans fats
Shown below are two fatty acids. The fatty acid on the top is saturated and the fatty acid on the bottom
is unsaturated. Note the bend in the unsaturated fatty acid.
In lecture you learned that triglycerides that are rich
in saturated fatty acids are solid at room temperature
(many animal fats), and triglycerides that are rich in
unsaturated fatty acids (many plant fats, oils) are liquid
at room temperature. Triglycerides that have lots of
saturated, straight tails can pack tightly together and
thus not move around much, while triglycerides that
have lots of unsaturated, kinked tails cannot pack tightly.
In the 1890’s a process called hydrogenation was developed. Hydrogenation of an unsaturated fatty
acid refers to the addition of hydrogen atoms to the acid, causing double bonds to become single ones,
as carbon atoms form bonds with hydrogen (in a molecule, carbon will maintain four covalent bonds)
Full hydrogenation results in a molecule becoming “saturated” with hydrogen, i.e. becoming a saturated
fatty acid. Why partial hydrogenation of vegetable oils? There
are many reasons. Liquid fats are not stable for
The process of partial hydrogenation, results in the addition of hydrogen long term at room temperature – they become
rancid. As plant fats are generally less expensive to
atoms at some of the empty positions, with a corresponding reduction
produce, it seemed reasonable to convert a liquid
in the number of double bonds. Typical commercial hydrogenation is fat to a solid fat for longer shelf life. This process
partial in order to obtain a malleable mixture of fats that is solid at room got a boost during WWII, as there were butter
shortages, and much vegetable oil was converted to
temperature, but melts upon baking. margarine by partial hydrogenation. In the 1950s
and 1960s more was becoming known about the
But there is another thing that occurs during partial dehydrogenation. negative effects of saturated fat on human health,
so it seemed reasonable to convert plant oils into
Partial hydrogenation reconfigures most of the double bonds that do solid fats. These solid fats, which we now know as
not become saturated with hydrogen, converting them from a cis to a trans fats, were deemed to be a healthy alternative
to saturated fats.
trans configuration where the hydrogen atoms end up on opposite sides
of the chain (trans from Latin meaning "across"). For any chemistry buffs, the trans configuration is the
lower energy form, so it is favored as a side reaction in hydrogenation. The figure below shows the
result of the partial dehydration of linoleic acid; note the production of the trans double bond. Also
note the trans configuration is straighter and that
when this type of fatty acid is present in a triglyceride
it will pack more tightly and be solid.
So what’s all the fuss these days about trans fats?
They are not, in fact, the healthy alternative to sat- Eliminates some double bonds
Partial hydrogenation
urated fats as was once thought. Like saturated fats,
trans fats RAISE levels of LDL cholesterol and increase
the risk of heart disease. But unlike saturated fats,
trans fats LOWER levels of HDL cholesterol!
In addition, consumption of trans fats leads to an increased level of visceral fat in individuals. The
accompanying article, Killer Fat, provides details into the problems with visceral fat.
As we learn more about the ill effects of trans fats, we should realize that we need to avoid them as
much as possible. Small amounts of trans fat occur naturally in beef, lamb, and dairy products. But
most trans fats come from the processing of liquid vegetable oil to become a solid fat (partial
hydrogenation). Trans fats have traditionally been found in restaurant foods (although they have been
banned in some cities) and in processed foods. Make sure you read nutrition labels on any pre-
packaged items you purchase. If you see “partially hydrogenated oil” in the ingredients, you can be
assured that some trans fats are present. Several semesters ago, this statement was declared in Zoology
101 lecture. The next class period, a student arrived with the nutrition label from her hot cocoa mix.
The product ingredients listed partially hydrogenated plant fats, but the nutrition facts showed there
Product Ingredients was not trans fat! Could it be possible that the instructor
SUGAR, CORN SYRUP SOLIDS, VEGETABLE OIL (PARTIALLY
HYDROGENATED COCONUT OR PALM KERNEL AND
HYDROGENATED SOYBEAN), DAIRY PRODUCT SOLIDS, COCOA
was wrong? Not this time! Federal regulations for food
PROCESSED WITH ALKALI, AND LESS THAN 2% OF CELLULOSE
GUM, NONFAT MILK, SALT, SODIUM CASEINATE, SODIUM labeling state that if trans fat is present in an amount of less
CITRATE, DIPOTASSIUM PHOSPHATE, SODIUM
ALUMINOSILICATE, MONO- AND DIGLYCERIDES, GUAR GUM, than 0.5g (per a single serving, which is often less than a
ARTIFICIAL FLAVORS. MADE ON EQUIPMENT THAT ALSO
PROCESSES SOY AND WHEAT.
person eats), it can be listed as zero.
So, if you are trying to be a good consumer, and reach for
that product that says ZERO TRANS FATS, you may not be
getting zero trans fats. If you are not looking for the
presence of partially hydrogenated oil in the product
ingredients, you could be ingesting a significant amount of
trans fats.
How much trans fat can you eat? The American Heart
Association suggests limiting the total trans fat that is
consumed by an individual to 1% of daily calories. For a
typical person, that is less than 2 g.
The figures of fatty acids used were taken from http://www.fda.gov/FDAC/features/2003/503_fats.html.
