Understanding Essential Fatty Acids: The Fats Your Body Cannot Synthesize and Must Be Acquired by the Diet

November 16, 2025 •

3 min read

Humans lack the specific desaturase enzymes necessary to insert double bonds at certain positions on a fatty acid chain, making certain fats impossible to produce internally. This guide explains which fatty acids are unable to be synthesized in the body and therefore must be acquired by the diet, focusing on the crucial omega-3 and omega-6 types.

Quick Summary

This article identifies the essential omega-3 (alpha-linolenic acid) and omega-6 (linoleic acid) fatty acids that the body cannot produce and explains why they are critical for maintaining human health.

Key Points

Essentiality: Alpha-linolenic acid (omega-3) and linoleic acid (omega-6) are the only two fatty acids that the human body cannot synthesize on its own.
Enzymatic Deficiency: Humans lack the specific delta-12 and delta-15 desaturase enzymes required to create these fatty acids.
Dietary Necessity: ALA and LA must be obtained directly from dietary sources or supplements to support normal physiological function.
Precursor Role: These essential fats serve as precursors for producing other important polyunsaturated fatty acids, including EPA and DHA from ALA.
Health Impact: EFAs are crucial for cell membrane integrity, brain health, and regulating the body's inflammatory and immune responses.
Omega Balance: A proper balance of omega-3 to omega-6 fatty acids is vital for health, as they produce opposing inflammatory signaling molecules.

What are Essential Fatty Acids?

Essential fatty acids (EFAs) are polyunsaturated fatty acids (PUFAs) that are vital for normal physiological function but cannot be synthesized by the human body. The two main families are omega-3 and omega-6. Humans lack the enzymes to insert double bonds at the omega-3 and omega-6 positions, making dietary intake essential. A non-essential omega-9 fatty acid called Mead acid can indicate EFA deficiency. EFAs are integrated into cell membranes, affecting fluidity and integrity, and serve as precursors for signaling molecules that regulate inflammation, blood clotting, and immune responses.

The Two Key Essential Fatty Acids

The two primary fatty acids that must be consumed are linoleic acid (LA) and alpha-linolenic acid (ALA). The body can synthesize other omega-3 and omega-6 fatty acids from these two, though with varying efficiency.

Linoleic Acid (LA) - The Parent Omega-6

Linoleic acid is an 18-carbon, omega-6 fatty acid found in plant oils like corn, sunflower, and soybean, as well as nuts, seeds, meat, and eggs. It is a precursor to other omega-6s, including arachidonic acid (AA), important for cell membranes. A high omega-6 to omega-3 ratio, common in Western diets, can contribute to inflammation.

Alpha-Linolenic Acid (ALA) - The Parent Omega-3

Alpha-linolenic acid is an 18-carbon, omega-3 fatty acid present in flaxseed, walnuts, chia seeds, and canola oil. It is the precursor to EPA and DHA. Conversion of ALA to EPA and DHA is inefficient, especially in men, making marine sources of EPA and DHA beneficial. ALA and its derivatives have anti-inflammatory effects and support cardiovascular and cognitive health.

The Importance of the Omega-3 to Omega-6 Balance

Maintaining a healthy balance between omega-3 and omega-6 fatty acids is crucial. They have distinct metabolic pathways and produce opposing signaling molecules: omega-6 derivatives are often pro-inflammatory, while omega-3 derivatives are typically anti-inflammatory. An imbalanced ratio, with excess omega-6s, is common in Western diets and can contribute to chronic inflammation, highlighting the need to increase omega-3 intake.

How Essential Fatty Acid Deficiency Manifests

EFA deficiency is uncommon but can occur with malabsorption or lack of fat in total parenteral nutrition. Symptoms may include rough, scaly skin, dermatitis, poor wound healing, and impaired growth. The triene-to-tetraene ratio in blood can indicate deficiency.

Rich Dietary Sources of Essential Fatty Acids

Here is a list of foods that are particularly rich sources of ALA and LA:

Alpha-Linolenic Acid (ALA) Sources:

Flaxseed and flaxseed oil
Chia seeds
Walnuts
Hemp seeds
Canola oil
Soybean oil
Green leafy vegetables

Linoleic Acid (LA) Sources:

Sunflower seeds and sunflower oil
Safflower oil
Corn oil
Soybean oil
Walnuts
Almonds
Poultry and eggs

Comparison of Omega-3 and Omega-6 Fatty Acids


Feature	Omega-3 Fatty Acids (ALA)	Omega-6 Fatty Acids (LA)
Classification	Essential fatty acid	Essential fatty acid
Dietary Source	Flaxseed, walnuts, chia seeds, hemp seeds	Corn, safflower, soybean oil, nuts, seeds, poultry
Metabolic Precursors	Precursor for EPA and DHA	Precursor for arachidonic acid (AA)
Inflammatory Effect	Generally anti-inflammatory	Generally pro-inflammatory
Enzyme Requirement	Humans lack necessary desaturase enzymes	Humans lack necessary desaturase enzymes
Conversion Efficiency	Inefficiently converted to longer chains (EPA, DHA)	Converted to longer chains (e.g., AA)

Conclusion: Prioritizing Dietary Intake

In conclusion, the body’s inability to synthesize alpha-linolenic acid (ALA) and linoleic acid (LA) makes them essential dietary components. Both fatty acid families, omega-3 and omega-6, are vital for health, from cell structure to regulating inflammation. A healthy diet requires a balance, often needing increased omega-3 intake to counter high omega-6 levels in processed foods. Including rich plant sources like flaxseed and walnuts, plus fatty fish for pre-formed EPA and DHA, helps meet essential fatty acid needs. For more information, the Linus Pauling Institute is a reputable resource: Linus Pauling Institute: Essential Fatty Acids.

Frequently Asked Questions

The two primary fatty acids that the body cannot synthesize and must be acquired from the diet are alpha-linolenic acid (ALA), an omega-3 fatty acid, and linoleic acid (LA), an omega-6 fatty acid.

The human body lacks the necessary enzymes, specifically delta-12 and delta-15 desaturases, which are required to insert double bonds at the proper positions in the fatty acid chain to synthesize ALA and LA.

Essential fatty acids must be consumed through the diet because the body cannot make them, while non-essential fatty acids can be synthesized by the body from other food components.

Essential fatty acids are important for numerous bodily functions, including maintaining cell membrane structure, supporting brain function, and serving as precursors for signaling molecules that regulate inflammation and immunity.

Rich plant-based sources of ALA include flaxseed oil, walnuts, chia seeds, hemp seeds, and canola oil.

Linoleic acid is found in many common plant oils, such as sunflower, corn, and safflower oil, and is also present in nuts, seeds, poultry, and eggs.

Yes, maintaining a healthy balance is important. While both are essential, a disproportionately high intake of omega-6s, common in many Western diets, can contribute to chronic inflammation.