Basic Chemical Structure amongst Fats

Most dietary fat takes the form of triglycerides. A triglyceride has a glycerol ‘backbone’ to which is attached three fatty acids. Triglycerides can vary considerably in the type of fatty acids, which are attached.

C - Fatty acid 1

C - Fatty acid 2

C - Fatty acid 3

There are 3 types of fatty acids: 1) Saturates 2) Monounsaturates and 3) Polyunsaturates. The type depends on the number of

‘double bonds’ in the molecule. Polyunsaturates are further divided into Omega-6 polyunsaturates or Omega-3 polyunsaturates. The difference lies in the position of the double bonds in the molecule. Omega-6 fatty acids have the first double bond after the sixth carbon and Omega-3 fatty acids have the first double bond after the third carbon.

Classification:

Saturated

Monounsaturated

Polyunsaturated

All fatty acids are made up of two parts, which gives them oil and water soluble properties. They have a fatty chain at one end, which is made up of carbon and hydrogen atoms and is oil soluble and an acid group at the other, which is water-soluble. Within the fatty chain, atoms are bonded or linked together by sharing electrons.

The more double bonds a fatty acid contains, the more beneficial it is because it increases oxidation, metabolic rate and energy production.. Two carbon atoms sharing two pairs of electrons form a double bond. A single bond is formed when two carbon atoms share one pair of electrons. In addition, the more double bonds a fatty acid contains, the more fluid they are and the less likely they are to stick together.

Double bonds change the shape of fatty acids by making them bend. Fatty acids with multiple double bonds have multiple bends, whereas fatty acids with no double bonds are straight and stiff. The more double bonds a fatty acid has the less likely they are to stick together, like straight fats which tend to solidify. These properties are critical for optimum cell membrane function.

The Chemistry of Fats Determines their Function for our Health

The extent of saturation or unsaturation has practical importance for the use of fats for our health and also in food applications. The more saturated a fat mixture is, the more likely it is to be solid at room temperature. For example, lard, butter and palm oil contain mainly saturated fats. However, butter and palm oil are softer at room temperature compared to lard. This is because butter and palm oil contain a proportion of unsaturated fats mixed with the saturates.

Melting point is an important characteristic of fats:

- The fats which are more solid at room temperature have a higher level of saturates in them.

- Saturated fat content decreases in the following oils as:

lard > butter > palm oil > other vegetable oils > fish oil > marine mammal oil

As the proportion of saturated fats decrease and the proportion of unsaturated fats increase, the melting point of a fat is lowered. Thus, polyunsaturated fats are liquid at room temperature and generally they remain liquid in the refrigerator. Monounsaturated fats also are liquid at room temperature, but they begin to solidify in the refrigerator. Saturated fats are solid at room temperature and in the refrigerator.

Fats, which are liquid at room temperature, are called "oils." Because the monounsaturated and polyunsaturated fats are generally liquids at room temperature, they are called oils. Oils can be vegetable, fish, or mammal in origin. Thus, fats derived from olive, canola, sunflower, soybean, cottonseed, and peanut are all oils. In addition, fats derived from fish and seal are also oils. However, some vegetable derived fats are semi-solids at room temperature because they have a significant proportion of saturated fats. Such an example is palm oil.

In addition to being a determinant of melting point, the extent of unsaturation is also a determinant of the stability of a fatty acid. Instability refers to the chemical degradation of fatty acids by oxidative breakdown. If all fats were kept in the refrigerator in the absence of air, they would all be stable to a similar extent. However, in the real world the methods we use to prepare and store food, allow the fats to be exposed to oxygen and to heat. The oxygen in air can react with the double bonds in a fatty acid to initiate its destruction. This process is increased by heat. In addition to losing the fatty acid in this process, the by-products of the reaction are free radical compounds, which can initiate chain reactions leading to destruction of other molecules. This leads to unsuitability for consumption. The final result is known as rancidity.

Fatty Acid Stability

-Oxygen from the air and heat combine to degrade fatty acids

-Saturates and monounsaturates are more stable than polyunsaturates

-The degradation can produce destructive free radicals and off-flavours

-The end-point is rancidity

In most cases, the problem is not as serious as it seems. This is due to the presence of natural anti-oxidants such as Vitamin E in the monounsaturated and polyunsaturated vegetable oils and also in seal oil. Anti-oxidants protect against oxidative reactions, which may be destructive. In normal applications, these agents keep the oils stable and sometimes extra anti-oxidants are added. However, in the high temperatures such as in frying, natural anti-oxidants are overwhelmed and breakdown occurs.

The Fate of Dietary Fats

Dietary fat is necessary for energy and all fats, regardless of their chemical structure, contain the same amount of energy (37 kilojoules/gram or 4 calories/gram). However, fats also have biological functions, which vary with their chemical structures, and this variety in their functions is essential for maintenance of good health. Hence, when examining the relationship between dietary fat and health, it is important to distinguish between the different types of dietary fat and their balance in the diet.

Chemical Structure of Fats:

Does not alter their energy content

Does alter their function in the body

The excess of Omega-6 fat intake compared with Omega-3 fat intake has practical consequences because the Omega-3 and Omega-6 fatty acids are homologues of each other (very similar - except for the position of one double bond. Therefore, they compete for the same enzymes, which metabolise them.

Incorporation into Cell Membranes

Fatty acids do not stay as free fatty acids in cells. They are rapidly incorporated into the phospholipids of the cell membrane. There are a number of different types of phospholipids, and all of them contain two fatty-acids linked to a back-bone molecule. Lecithin is one of the most common phospholipids.

The unique chemistries of the different types of fatty acids have unique physical effects on cell membranes. While the outer membrane of the cell is like a wall in some respects, and like a selective sieve in other respects, it is not rigid like a wall nor a sieve. Rather, it is dynamic and fluid. The more unsaturated and the longer are the fatty acids, the more fluid the membrane is, which in turn affects the function of membrane enzymes and other membrane proteins. Therefore, it is significant that the long-chain omega-3 fatty acids (DPA-C22: 5w3 and DHA-C22: 6w3) in membranes are generally more unsaturated and longer than the Omega-6 fatty acids AA. (C20 :4w6)

From Dietary Fat to Prostaglandins

Functionally, prostaglandins are short-lived, hormone-like chemicals that regulate cellular activities on a moment to moment basis. The membranes of your nerves, blood cells, blood vessels, and muscles are made of trillions of fatty acid molecules. The balance of these fatty acids within the membranes is determined largely by our diet. When our diet is balanced in omega-6 and omega-3 fatty acids, your cells are balanced in these fatty acids as well. When our diet has too little omega-3 fatty acids our cell membranes have too little omega-3 fatty acids.

Fatty acids that form the structure of your cell membranes become messengers when a call to action is sent out. This call can be in the form of trauma, a virus, bacteria, a free radical, a toxic chemical, a heavy metal, or some other trigger. Once the call to action has been sent, our cell’s fatty acids are released from the membrane and are chemically transformed into highly active hormone-like substances. Once the hormone-like substances are released they exert powerful and profound effects on a vast array of functions within our body.

These substances are called prostaglandins because they were originally discovered in the prostate gland. They are produced throughout the body and are formed directly through a series of steps from dietary fatty acids. Those of importance are called PGE1, PGE2 and PGE3.

PGE1 is formed from dietary linoleic acid. This is the fatty acid found mainly in corn oil, sunflower oil, sesame oil and safflower oil. PGE1 is important in the nervous system as it affects the release of compounds from nerve cells that transmit nerve impulses. It tends to have anti-inflammatory properties and is immune-enhancing. It can reduce fluid accumulation and has a significant effect on the nervous system. Some doctors have manipulated the PGE1 pathway to improve depression, multiple sclerosis, PMS (premenstrual syndrome) related mood changes, schizophrenia, ADHD (attention deficit hyperactivity disorder), and other conditions.

PGE2 is formed from the fatty acid - arachidonic acid. This fatty acid is found only rarely in plants and is most common in animal meat. PGE2 is a highly inflammatory substance. It can cause swelling, increased pain sensitivity, and increased blood viscosity. Some of the other compounds associated with PGE2 can cause blood platelet clumping, spasm of blood vessels, and accumulation of inflammatory cells in an area, and over the long term can change the way in which nerve cells communicate. These compounds can also cause an overactive immune system within the nervous system, chiding the immune cells to attack the host. Elevated PGE2 has been found in a number of problems affecting mood, behavior, and nervous system function.

Substances called leukotrienes are related to PGE2 in that they are made from the fatty acid arachidonic acid. However, leukotrienes are even more potent inflammatory substances. They have been estimated to be 1,000 to 10,000 times more inflammatory than histamine, the substance associated with the runny nose and watery eyes of allergy and hay fever. They signal white blood cells to travel to an area. This is good when you need them, but white cells can do a lot of damage when present in excess.

The PGE2 family is sometimes viewed as a ‘bad guy’ because of the powerful inflammatory potential it possesses. In reality, we need this family for many vital functions. The problem arises when the system is out of balance, when there is too much activity in this family. This balance is tied to fatty acid balance.

PGE3 is formed from the fatty acid EPA (eicosapentaenoic acid), found in salmon, mackerel, herring, sardines, and other fish. Another form of PG3 is formed from the fatty acid DHA (docosahexaenoic acid). PGE3 tends to be mildly anti-inflammatory and immune enhancing. It is thought to counter the affects of the powerfully inflammatory PGE2 substances. It prevents blood platelets from clumping and helps prevent blood vessel spasm. Fatty acids important in PGE3 formation, like EPA and DHA, can also reduce arachidonic acid in the cells. This reduces the chance of producing messengers from arachidonic acid and is one way that these fatty acids can alter the production of highly inflammatory messengers.

	Room Temperature	Refridgerator
Saturates	Solid	Solid
Monunsaturates	Liquid	Semi-solid
Polyunsaturates	Liquid	Liquid