Part 2: How Essential Fatty Acids (EFAs) Work in Your Body

Introduction

In Part 1, we discovered that your body cannot make two essential fatty acids: linoleic acid (omega-6) and alpha-linolenic acid (omega-3). But what does your body actually do with these building blocks once you consume them? The answer reveals why these nutrients are so critical for every cell in your body.

EFAs are essential for two main roles: as membrane components and as precursors for biologically active metabolites, the eicosanoids. Lets first look at the cell membrane. 

Cell Membrane Structure & Function.

The cell membrane, also called the plasma membrane, is an intricate assembly of lipids, proteins, cholesterol, and other components. The membrane structure consists of a phospholipid bilayer. 

A phospholipid is two fatty acids (these could be omega 3 or 6 or something else) attached to a phosphate head. In Figure 1 the phospholipid looks like a head with two legs. As you can see one leg is bent and one is straight. The kink is where a double bond has been inserted into the chain making it unsaturated and would be termed monounsaturated. Omega-3 fatty acids contain three double bonds, while omega-6 fatty acids have two double bonds. Saturated fatty acids, which are characterized by a straight hydrocarbon chain, lack any double bonds.

Figure 1 Phospholipid bilayer & individual phospholipid

The cell membrane is in a constant state of dynamic flux, continually monitoring its external environment and changing in response to events taking place inside the cell and its surroundings. Critical to its structural and functional integrity are the essential fatty acids (EFA’s) omega 3 and 6.

These essential fatty acids not only provide structural support but also help maintain the ideal balance between fluidity and integrity of the membrane. This balance is crucial for optimal cell communication and the efficient movement of molecules in and out of the cell.

What does ‘fluidity’ mean?

Fluidity refers to how objects within the membrane can move around relative to one another. The nature of the fatty acid (legs) attached to the head dictates whether they are rigid (solid) or fluid (liquid). If there are long chain saturated fatty acids (no double bonds) attached, the phospholipids will be less fluid at body temperature. With each increase in double bonds – monounsaturated one double bond, polyunsaturated – two or more double bonds, membrane fluidity increases

Think of fluidity in terms of being a passenger on a commuter train. If there is space in the carriage passengers can move around. If, however, people are packed in like sardines then it becomes very difficult to move even within the carriage.

Essential fatty acids provide this ‘space’ for objects embedded within the membrane to move around relative to one another (see figure 2).  This is a critical function if the cell is to work at its optimal capacity.

Figure 2 How phospholipids move within the cell membrane

Eicosanoid Production.

Eicosanoids are a diverse group of lipid signaling molecules derived from polyunsaturated fatty acids (PUFAs). They play a crucial role in various physiological processes, including inflammation, blood clotting, immune response, and cell signaling.

The two primary fatty acid precursors of eicosanoids, are the essential fatty acids (EFA’s) arachidonic acid (AA) from omega-6 and eicosapentaenoic acid (EPA) from omega-3.  For AA or EPA to produce eicosanoids they must be modified. This modification is performed by three enzymes. Cyclooxygenases (COX), lipoxygenases (LOX), and cytochrome P450 enzymes, leading to the formation of different classes of eicosanoids (see figure 1). 

There are many different eicosanoids each with unique effects on the body. Once AA or EPA are released from the cell membrane, enzymes like LOX, COX, or cytochrome P450 modify them inside the cell (see figure 3). This happens in specific cells as a response to physiological events. For instance, when you cut your finger, platelets produce the eicosanoid thromboxane, causing blood platelets to stick together, to clot and smooth muscle to constrict. Once bleeding has been stemmed, local endothelial cells (they line the interior surface of blood vessels and lymphatic vessels) produce prostacyclin inhibiting blood clotting and stimulating smooth muscle to dilate. Thus, maintaining circulatory homeostasis.

Figure 3 Overall pathway for conversion of essential fatty acids into eicosanoids

This is why aspirin an anti-inflammatory agent works – it blocks eicosanoid production from AA which is a pro-inflammatory agent.

Having an understanding of how these powerful local hormones work reminds us that balance is key - you need both omega-6 and omega-3 derived eicosanoids working together.

Cardiovascular Health.

It wasn’t until the middle of the last century that we started to investigate a link between our diet and heart disease. Early studies such as the Seven Countries Study and the Framingham Heart Study started tracking this relationship between diet and health.

In 1980 the Nurse’s Health study tracked 80,082 women for 14 years. This study looked at how different types of fat in our diet affect the risk of getting heart disease. They found that for every 5% increase in saturated fat, there was a 17% increase in the risk of getting heart disease. Trans fats, which are found in some processed foods, were even worse - every 2% increase in trans fats led to a nearly twofold increase in the risk of heart disease.

On the other hand, monounsaturated and polyunsaturated fats, found in foods like nuts (hempseeds are technically a nut) and fish, were associated with a lower risk of heart disease. Overall, the total amount of fat in the diet did not significantly affect the risk of heart disease. The study estimated that replacing some saturated or trans fats with unsaturated fats could significantly reduce the risk of heart disease. (Hu, 1997). 

By incorporating healthy fats such as monounsaturated fats (MUFAs) and polyunsaturated fats (PUFAs omega 6 & 3), into your diet and avoiding unhealthy saturated ones can help to reduce harmful LDL cholesterol levels and increase the beneficial HDL cholesterol levels. This can lead to a lower risk of heart disease and stroke. (Willett, 2017) 

Prof. Walter Willett from Harvard University suggests that the most compelling evidence for the benefits of omega-3 fat is its ability to prevent or treat heart disease and stroke. (Willett, 2017). Omega-3 fats aid in maintaining a regular heartbeat, which is essential for good cardiovascular health. If the heart's electrical rhythm is significantly disrupted, it can lead to serious complications such as ventricular fibrillation (also known as arrhythmia) or cardiac arrest.

This cardiovascular benefit applies to the whole family as prevention, not just treatment. By ensuring adequate intake of essential fatty acids from childhood onward, families can build a foundation for lifelong heart health.

What’s Next?

You now understand how essential fatty acids work at the cellular level – building flexible, functional cell membranes and creating powerful signalling molecules that regulate everything from healing to heartbeat. But a critical question remains: are New Zealand families actually getting enough of these essential nutrients? 

Next month in Part 3, we'll explore the modern dietary challenge: why most families get enough omega-6 but fall short on omega-3, and what's changed in our food environment to create this imbalance.

References

Hu, F. B. (1997). Dietary Fat Intake and the Risk of Coronary Heart Disease in Women. New England Journal of Medicine, 1491–9.

Willett, W. C. (2017). Eat, Drink and be Healthy. The Harvard Medical School Guide to Healthy Eating. New York: Simon & Schuster.

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