Fatty Acids

Fatty acids can be either saturated, monounsaturated, polyunsaturated, and in some cases, trans. As a rule of thumb, poly and monounsaturated fats are liquid at room temperature. Saturated and trans fats can range from soft to liquid to solid. Many sources of fat actually contain more than one type of fatty acid. In these cases the dominate fatty acid will define it. (E.g. olive oil holds saturated, polyunsaturated, and monounsaturated fats. Monounsaturated outweighs the others by volume, thus olive oil is known as a monounsaturated fat.)  You've no doubt seen these words on a food label, but what exactly do they mean?

Chemical Makeup

To understand "saturation" you need to recall some basic chemistry concepts, specifically about bonds. A carbon atom can form 4 chemical bonds, an oxygen atom can form 2 bonds and a hydrogen atom can form 1 bond. For those who have taken a chemistry class, you no doubt recognize the arrangement,

C-----H

That represents a carbon atom bonded to a hydrogen atom. The difference in the degree of saturation lies in the number and type of bonds that form.

1. Saturated Fatty Acid

• No carbon-carbon double bonds 
• Referred to as "stearic acid"

      2. Monounsaturated Fatty Acid

• One carbon-carbon double bond  (ex: C=C)
• Referred to as "oleic" acid

      3. Polyunsaturated Fatty Acid

• 2 or more carbon-carbon double bonds  (ex: C=C, C=C)
• Referred to as "linoleic acid"         

Effects on Health

The majority of fat in our diets should be monounsaturated and polyunsaturated. These provide several health benefits between them including: providing vitamin e, flooding our cells with nutrients, and lowering cholesterol levels. 

Now, there is almost always an antagonist in play seeking to undermine the protagonist. That antagonist here, is trans fatty acids. Trans fat is simply unsaturated fat that has undergone the process of hydrogenation. In order to make liquids more solid (ie: margarine, shortening), hydrogen is added to the carbon chain of unsaturated fat. One of the more noteworthy studies done on trans fatty acids and their affect on the human body was performed by Dr's Mensink and Katan. The study showed that not only does consuming trans fat increase low-density lipoprotein (LDL) levels, but it decreases high-density lipoprotein (HDL) levels. 

Saturated Fat

Recommendations from the American Heart Association include limiting saturated fats to 5-6 % of total calories consumed. On a 2000 calorie per day diet that translates to about 13 grams of saturated fat. Based on findings from the 2017-2018 National Health and Nutrition Examination Study, males and females consume around 13 grams of saturated fat on a 1000 calorie per day diet! 

There has been numerous studies and research done on the relationship between saturated fat and heart disease. One such review compared 15 randomized controlled trials with a total of over 59,000 volunteers. The purpose was to look at the effect of limiting saturated fat (minimum of two year period) on the health outcomes of individuals with and without cardiovascular disease. Findings showed a 21% decrease in the risk of cardiovascular disease. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) is a group that provides four levels of evidence quality ( from very low to high). Randomized studies (such as this one) start off as high level quality evidence and this particular one is currently deemed to be moderate quality evidence. The exact definition of moderate quality is "Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate." 

Essential

Similar to amino acids, our bodies are able to produce a number of fatty acids. Two fatty acids that our bodies do not produce, are Alpha-Linolenic acid (an omega 3 fatty acid) and Linoleic acid (an omega 6 fatty acid).  Both are polyunsaturated fatty acids and the numbers simply refer to the location of the acids in the carbon chain. Before we dive deeper into these essential fatty acids (EFA) lets discuss what it means to be "essential" from a nutrition standpoint. 

An essential nutrient has three defining features:

1. The absence of the nutrient from one's diet will lead to an adverse health outcome.
2. Replacing the nutrient back into the diet before permanent damage occurs will restore to normal one's health and physiological functions.
3. The nutrient has a specific biological function. 

Lets take a look at how this case here satisfies the requirements for linoleic acid as an essential nutrient. After being admitted to the hospital, the patient in the study was fed intravenously due to her gastrointestinal tract being impacted. After being discharged, the patient soon began experiencing complications including:  

• numbness 
• paresthesia 
• visual blurring
• weakness  
• pain

 Upon re-admittance to the hospital, the patient had a blood analysis done and doctors noted that her omega 3 levels were very low. After adjustment of the formula preparation to increase the amount of linolenic acid, the girl eventually became better.

Alpha-Linolenic Acid (Omega 3) & Linoleic Acid (Omega 6)

Omega 3	Omega 6
Alpha-linolenic acid	Linoleic acid
↓	↓
Eicosapentaenoic acd (EPA)	Dihomo-gamma-linolenic acid
↓	↓
Docosahexaenoic acid (DHA)	Arachidonic acid

As you can see from the table, alpha-linolenic and linoleic acids are used to make other fatty acids. Another important compound created by the essential fatty acids are eicosanoids. Together, the EFA's help control nerve transmissions, reduce inflammation, regulate blood pressure, and increase blood clotting among other benefits. 

Fatty fish such as salmon, mackerel, and tuna are generally the best source for omega 3's. Supplementing with a fish oil is a common practice, just make sure to check the EPA and DHA ratio (it should be relatively equal). The most rich source of omega 3 is found in flax seed, which boasts more than 50 percent of the acid. Vegetable oils are great sources of omega 6 along with seeds and nuts. Deficiency of either of the essential acids are few and far between, however a diet low in linoleic acid may have several consequences include:

• Dermatitis
• Scaly Rash
• Stunted growth in children
• Weakened Immune Response

References

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