Why all the fuss about fat these days? All sorts of products are advertising that they are "low in trans and saturated fats" or "100% trans fat-free". What's the deal with that?
Actually, there are several different types of fats, and it's important for our health to get them straight. Fats must be distinguished because while some are necessary for survival, the negative health effects of others are serious. When it comes to fats, two teams exist:
Unsaturated fats: The good guys = Should eat Trans and saturated fats: The bad guys = Should avoid eating
"Facts" About Fat
Unsaturated fats are healthy because they are the main form of energy storage in the body and help to absorb important fat-soluble vitamins such as Vitamins A, D, E and K. Unsaturated fats are found in:
Vegetable oils Nuts Avocados Olives Eggs, fish and lean meat Milk products
Saturated and trans fat, which give fat its bad reputation, are found in:
Deep-fried foods Processed foods Baked goods Many animal products such as cream and butter Some margarines
Let's Talk Chemistry!
The chemical structure of fatty acids (i.e. the building blocks of fat) is what puts fats in two different teams. A fatty acid is an organic molecule that is made up of a carbon chain, in which 16-22 carbons are linked together. At one end of the chain is an acid group (COOH), which links with other molecules to make fat. To illustrate what this chemistry means to fat, let's look at an example:
Butter and vegetable oil are both fats, but they have different physical properties; at room temperature butter is a solid and vegetable oil is a liquid. This is because butter has a higher melting point than vegetable oil. A fat's melting point, the temperature at which it turns from solid to liquid, is determined by the structure of its fatty acids.
Did you know? Fat is an organic molecule with a carbon chain backbone and an acidic group on one end.
Saturated fats such as butter contain fatty acids with single bonds between the carbons, resulting in straight chains. When many saturated fatty acid chains come together to form fat, they are able to pack very close to each other. The resulting fat is more solid and has a higher melting point.
Unsaturated fats are graced with double bonds between adjacent carbon atoms in the backbone. These fats come in two "flavours": cis- and trans-; this refers to the TYPE of bonding between adjacent carbons on in a fatty acid chain. Unsaturated fats such as vegetable oil have lower melting points and are liquid at room temperature because their fatty acid chains cannot pack so close together. The double bonds within the chains of the unsaturated fatty acid of vegetable oil have a cis-orientation. In cis-bonding, the carbons of the fatty acid backbone are on the same side of the double bond, which give rise to a bent-up, kinky fatty acid chain (see figure).
Did you know? Saturated fats have single bonds between carbon atoms.
Although trans fats also fall under the "unsaturated" category, since they also have double bonds between carbons of the fatty acid chain, they have higher melting temperatures..."melt in your mouth" temperatures in fact! This is because trans-double bonds have the carbons of the backbone on opposite sides of the double bond. The trans bond allows fatty acid chains to pack very close together and yields a fat with a higher melting point (see figure). Food manufacturers often exploit this by adding trans fats to unsaturated fat products to make them more stiff.
Did you know? Unsaturated fats have double bonds; those with cis-bonding have a kinky, bent up carbon chain, while those with trans-bonds resemble the straight chain of an unsaturated fat.
Although now trans-fat free, everyone's favourite Oreo cookie filling was once stiffened in this manner: using trans double bond-containing fats. Solid or semi-solid products containing trans fats have other advantages in food production such as a longer shelf life (fewer double bonds means fewer reactions with air and less funky smells) and greater stability at high temperatures used for frying.
Did you know? Traditionally, trans fats are added to foods to increase shelf life, increase stiffness, and make foods "melt in your mouth" good. Trans fats are also used for frying.
So why all the fuss about cis and trans?
One little change from cis to trans makes a huge difference! Unlike unsaturated fats, which are recognized by the body's machinery and help it function, trans fats have no nutritional value. In fact, much like saturated fats, they affect cholesterol levels in the blood in a dangerous way. Researchers have found that diets high in saturated and trans fats increase the blood level of LDL (bad cholesterol that clumps in the arteries) and decrease that of HDL (good cholesterol that removes LDL), thus increasing the risk of serious medical conditions such as atherosclerosis and coronary heart disease...conditions that can make a person sick, sick, sick.
The whole "anti-trans fat trend" comes down to is this: fats that "melt in your mouths" tend to be the dangerous saturated and trans fats, while healthy unsaturated fats are important for survival...all because of the chemistry of a few double bonds!
So, keep the blood pumping smooth through your arteries by avoiding foods containing the bad guys, i.e. unhealthy saturated and trans fats. Instead, make sure your body has lots of stored energy and absorbs the vitamins it needs with foods containing the good guys...unsaturated fats.
For More Information:
Health Canada: "Fact sheet on trans fats."
Wood, P.A. 2006. How fat works. Cambridge, Massachusetts: Harvard University Press.
Alison Palmer has a BSc in Chemistry from the University of British Columbia and is currently completing an MSc in Chemical Biology at McGill University, where she modifies DNA to make it do tricks. She loves to talk and write about science, and hopes to pursue a career in science journalism.