Fats and fatty acids

Fatty acids

Most of the fat in our food is in the form of triglyc­erides. Each mol­e­cule of triglyc­eride con­sists of a mol­e­cule of glyc­erol bound to three mol­e­cules of fat­ty acid. The rea­son that the fat from choco­late stays sol­id at room tem­per­a­ture but melts in your mouth, while the fat in olive oil stays liq­uid at room tem­per­a­ture, has to do with which fat­ty acids the fat con­tains.

The fat­ty acids are a large group of chem­i­cals. They are all made up of a long string of car­bon atoms, stud­ded with hydro­gen atoms. This hydro­car­bon string is what makes them “fat­ty.” All fat­ty acids also have a car­boxyl group at one end. That’s what makes them “acid.”

Length matters

The small­est car­boxylic acid is formic acid, which puts the sting in a fire ant’s ven­om. It’s a car­boxyl group (-COOH) with just a hydro­gen attached. If you replace that hydro­gen with a methyl group (one car­bon and three hydro­gens), you end up with acetic acid, which puts the bite in vine­gar. Pro­pi­onic acid is a car­boxylic acid with a three car­bon chain. Butyric acid has a four-car­bon chain.


The longer the car­bon chain, the more the car­boxylic acid behave like a fat and the less it behaves like an acid. Formic acid and acetic acid are com­plete­ly sol­u­ble in water. Butyric acid can mix with water, but it is some­what oily. The fat­ty acids with a longer car­bon chain, such as the ole­ic acid you find in olive oil or the stearic acid you find in choco­late, do not mix with water.

Fats versus oils

An oil is sim­ply a fat that is liq­uid at room tem­per­a­ture. In oth­er words, its melt­ing point is low­er than room tem­per­a­ture.

The longer the car­bon chain in a fat­ty acid, the high­er its melt­ing point will be. That’s why the stearic acid (18 car­bons) in choco­late stays sol­id at room tem­per­a­ture while butyric acid (four car­bons) is a liq­uid at room tem­per­a­ture.

The more hydro­gen atoms a fat­ty acid has, the high­er its melt­ing point will be. when a fat­ty acid is hold­ing as many hydro­gen atoms as it pos­si­bly can, it’s said to be “sat­u­rat­ed.” Sat­u­rat­ed fat­ty acids have no dou­ble bonds between any of the car­bons in its car­bon chain. A fat­ty acid with one dou­ble bond is said to be “monoun­sat­u­rat­ed.” Fat­ty acids with more than one dou­ble bond in the car­bon chain are said to be “polyun­sat­u­rat­ed.”

You can see the effects of sat­u­ra­tion when you com­pare four dif­fer­ent fat­ty acids that each have 18 car­bons: stearic acid, ole­ic acid, linole­ic acid, and alpha-linolenic acid. Choco­late stays sol­id at room tem­per­a­ture because it con­tains a lot of stearic acid. Olive oil, on the oth­er hand, stays liq­uid because it con­tains the monoun­sat­u­rat­ed fat­ty acid ole­ic acid. Linole­ic acid is a major con­stituent of corn oil, and alpha-linole­ic acid is found in flaxseed oil.



Sat­u­rat­ed fats have desir­able traits. They stay sol­id at room tem­per­a­ture and have a bet­ter shelf life. You can con­vert unsat­u­rat­ed fats to sat­u­rat­ed fats through a process called hydro­gena­tion.



Triglycerides and fatty acids

If you’ve ever got­ten soap in your eye, you know that fat­ty acids are irri­tat­ing. That’s because the car­boxylic acid tail of the free fat­ty acid is caus­tic. So you can under­stand why our cells like to bind up the sharp car­boxylic acid end of a fat­ty acid with glyc­erol. A glyc­erol mol­e­cule can bind up to three mol­e­cules of fat­ty acid in this way.



Are some fats “healthy”?

Fat is extreme­ly high in calo­ries. As you can see from these illus­tra­tions, a fat mol­e­cule con­tains very lit­tle oxy­gen. It will take a lot of oxy­gen, and a lot of oxi­da­tion (burn­ing) to con­vert them to car­bon diox­ide and water. That means that they will release a lot of ener­gy. If you are strug­gling to get enough calo­ries to sur­vive, fat­ty foods are a real advan­tage. That’s why peo­ple instinc­tive­ly like fat­ty foods.

Unfor­tu­nate­ly, peo­ple in West­ern soci­ety have too much access to fat­ty foods. As a result, we suf­fer from obe­si­ty and heart dis­ease. When sci­en­tists first noticed that heart dis­ease and obe­si­ty were much more com­mon in North­ern Europe and the Unit­ed States than in South­ern Europe or in Asia, they fig­ured that the prob­lem was sat­u­rat­ed fat. So the rec­om­men­da­tion came for peo­ple to switch from but­ter to mar­garine, which was low­er in sat­u­rat­ed fat. Then peo­ple real­ized that mar­garine, being made by hydro­gena­tion of polyun­sat­u­rat­ed oils, could con­tain a lot of trans fat. So then peo­ple were told to switch to olive oil, which con­tains monoun­sat­u­rat­ed fat. Some sci­en­tists noticed that the Native Green­lan­ders didn’t have quite as many heart attacks as you might expect, giv­en their high-fat diet. So then peo­ple told us to eat fish and fish oil. Late­ly, peo­ple have been telling us to eat a “Mediter­ranean diet,” which is described as fea­tur­ing fish and olive oil. In real­i­ty, what made the Mediter­ranean diet healthy is all the veg­eta­bles. Peo­ple who avoid all ani­mal foods, includ­ing fish, and all oils can be even health­i­er than peo­ple eat­ing a Mediter­ranean diet.

All of these shift­ing rec­om­men­da­tions are con­fus­ing, but the sim­ple truth has been obvi­ous all along, to those who read the sci­en­tif­ic arti­cles care­ful­ly. The peo­ple who are the health­i­est and least like­ly to die of heart attacks are the ones who eat very lit­tle fat of any kind. The peo­ple with the low­est blood cho­les­terol lev­els are not only heart-attack-proof, they have a low risk for can­cer and oth­er “dis­eases of afflu­ence.” The health­i­est diet con­sists of low-fat unre­fined plant foods and gets less than 10% of its calo­ries from fat. Peo­ple who eat a low-fat diet that includes lots of fresh veg­eta­bles will get enough fat from their food, and they’ll get a good bal­ance of the omega-6 and omega-3 essen­tial fat­ty acids. Adding a spoon­ful of ground flaxseed or a few wal­nuts can ensure a plen­ti­ful intake of omega 3 fat­ty acid.

Often, you will see peo­ple rec­om­mend­ing that tod­dlers be fed whole cow’s milk instead of 2% or skim milk. In real­i­ty, there’s no need for chil­dren to receive any cow’s milk at all.

Can you get sick from eating too little fat?

Although your body does need small amounts of two “essen­tial” fat­ty acids: linole­ic acid and alpha-linolenic acid, it’s prac­ti­cal­ly impos­si­ble to find peo­ple who get sick from eat­ing a low-fat diet. The typ­i­cal cas­es of essen­tial fat­ty acid defi­cien­cy occur in peo­ple who have been fed noth­ing but sug­ar intra­venous­ly for an extend­ed peri­od. They are get­ting no fat from their diet, and the high insulin lev­els make it hard for them to release the essen­tial fat­ty acids from their fat stores. These people’s require­ment for essen­tial fat­ty acids can be met by rub­bing some veg­etable oil on the skin.

Some peo­ple wor­ry that they won’t be able to absorb the fat-sol­u­ble vit­a­mins (vit­a­mins A, D, E, and K) if they don’t get enough fat in the diet. In real­i­ty, ordi­nary unprocessed plant foods con­tain enough traces of fat to enable peo­ple to absorb vit­a­min A, E, and K. You don’t need to put oily sal­ad dress­ing on your sal­ad in order to absorb vit­a­mins from the sal­ad! Vit­a­min D is made in our own skin when it is exposed to sun­light and doesn’t have to come from the food.

There are, of course, some peo­ple who have trou­ble absorb­ing fat from their food. Fat mal­ab­sorp­tion can result from many dis­eases, includ­ing cys­tic fibro­sis. Peo­ple who have trou­ble absorb­ing fat from their food should be get­ting nutri­tion­al advice from a reg­is­tered dietit­ian, along with med­ical care from a doc­tor, nurse prac­ti­tion­er, or physi­cian assis­tant.