Basically fats are a chain of carbon atoms (C).  Each carbon atom is linked to one or more hydrogen atoms (H), except the one at the extremity.  That one is linked to two oxygen atoms (O)

Fats are the form for storing energy, packing more calories per gram (9 calories per gram) than carbohydrates or proteins (4 calories per gram).


Saturated Fats
Saturated fat is with all carbon atoms “saturated” with as many hydrogen atoms it can hold.  Each carbon atom is linked to the next carbon in the chain by a single bond.  Usually each carbon atom must have 4 bonds.

Normally at room temperature saturated fats remain in solid form, except coconut oils.

Cheese, whole milk, butter, and high-fat cuts of meat are saturated fats.  Coconut and palm oils are also rich in saturated fats.


Unsaturated Fats
Unsaturated fats are liquids at room temperature.  They are good to “heart healthy”.  Unsaturated fats have at least one carbon atom not “saturated” with hydrogen atoms.  They consist of 2 types, MONOunsaturated fats and POLYunsaturated fats

MONOunsaturated fat
There are two carbon atoms with only one hydrogen atom (instead of two), and are linked together by a double bond.  They have only one double bond in the fat molecule therefore it is named “mono” unsaturated fat.

Monounsaturated fats are found in plant-based oils such as canola oil, olive oil and soybean oil.  Also they are found in foods such fish, nuts, seeds, and some vegetables (e.g. avocados).

POLYunsaturated fats
POLYunsaturated fats consists of multiple carbon atoms with only one hydrogen atom and more than one double bond between carbons.

polyunsaturated_fat_01There are two types of polyunsaturated fats – omega-3 and omega-6.  Vegetable-based oils like corn, soyabean and safflower oil are high in omega-6 polyunsaturated fats.  Canola oil, flaxseed, soybean oil, walnuts and fish such as salmon, trout, and herring are rich in omega-3 polyunsaturated fats

These double bonds between carbon atoms force the fat molecule to have a bent shape which is called the cis configuration of a fat.

Safflower oil      clickhere_orange25
红花     clickhere_red25

Cis–trans isomerism     clickhere_blue25
順反異構     clickhere_orange25

Trans fats
The natural form (the cis form) of unsaturated fats has both of the hydrogen atoms on the same side of the molecule (the yellow hydrogen atoms)


At room temperature unsaturated fats are in liquid form.  On account of this bend in the molecule, the fats can’t pack together very tightly while staying in a liquid form.

Some trans fats are naturally occurring in dairy products as well as some meat.  But most of the trans fats sold in markets are made by a chemical process – hydrogenation.  In hydrogenation process, a bunch of extra hydrogen atoms are added to polyunsaturated fats.  These extra hydrogen atoms break the double bonds between some of the carbons and then link to the “unsaturated” carbon atoms.  Technically, a trans fat is still an unsaturated fat but with the yellow hydrogen atoms are on different sides of the molecule.  This causes the trans fat molecule having more of a straight shape.

That straight shape indicates trans fats being solids at room temperature.  Actually this was the exact demand for developing trans fats – to make products such as margarine and spreads from vegetable-based oils.  At room temperature the products will become solid.  Trans fats are commonly used in bakery and frozen foods.


Nutrition Label
To check the processed foods and/or products whether containing Trans Fats:-

First – check the nutrition label on the packing.  If more than 0.5 gram of trans fats per serving, it must be declared in the nutrition facts panel.

Second – check the ingredients list.  Any ingredient named “partially hydrogenated oil” is a trans fat.   If less than 0.5 gram in a serving size, it does not need to be stated in the nutrition facts panel.  But it still needs to be listed in the ingredients.




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