What are essential fatty acids (EFAs) in nutrition?

Essential Fatty Acids (EFAs) in Nutrition

Essential fatty acids (EFAs) are two specific polyunsaturated fatty acids that humans cannot synthesize and must obtain through diet: linoleic acid (LA, an omega-6 fatty acid) and alpha-linolenic acid (ALA, an omega-3 fatty acid). 1

Core Definition and Classification

• LA (18:2n-6) and ALA (18:3n-3) are the only two truly essential fatty acids because the human body lacks the enzymes to produce them, making dietary intake mandatory for survival 1

• Conditionally essential fatty acids include arachidonic acid (AA, omega-6), docosahexaenoic acid (DHA, omega-3), and eicosapentaenoic acid (EPA, omega-3), which become essential under certain developmental or disease conditions 1

• The body can convert LA and ALA into their longer-chain derivatives (AA from LA; EPA and DHA from ALA), but this conversion is limited, especially during early life 2, 3

Dietary Sources and Requirements

Minimum Requirements to Prevent Deficiency

• Preterm infants require minimum LA intake of 0.25 g/kg/day to prevent EFA deficiency 1

• Term infants and children require minimum LA intake of 0.1 g/kg/day, which also provides adequate ALA when using standard lipid emulsions with an 8:1 LA:ALA ratio 1

• Adults with normal fat intake maintain adequate EFA status even with relatively low omega-6 consumption, making clinical deficiency extremely rare in healthy populations 4, 5

Primary Food Sources

• Vegetable oils (soybean, canola, flaxseed) provide both LA and ALA 1, 2
• Walnuts are rich sources of both omega-6 and omega-3 EFAs 1
• Seafood is the major source of long-chain omega-3 fatty acids (EPA and DHA) 1, 2

Metabolic Functions and Biological Roles

Structural Functions

• EFAs serve as critical structural components of cell membranes throughout the body, particularly in the central nervous system and retina 1, 3

• DHA is the predominant structural fatty acid in brain tissue and retina, making its availability crucial for neurodevelopment 3

Signaling and Regulatory Functions

• EFA metabolites serve as precursors for eicosanoids (prostaglandins, thromboxanes, leukotrienes), which are potent signaling molecules regulating inflammation, blood pressure, and immune function 1, 2

• Specialized pro-resolving mediators (SPMs) derived from EFAs actively resolve inflammation rather than simply suppressing it 1

• EFAs function as endogenous regulators of angiotensin-converting enzyme, cholesterol synthesis, and nitric oxide production 6

Clinical Consequences of Deficiency

Populations at Risk

Monitor for EFA deficiency in these specific groups:

• Patients with fat malabsorption syndromes (cystic fibrosis, cholestatic liver disease, short bowel syndrome) 1, 4
• Individuals on severely fat-restricted diets or fat-free medical foods 4
• Infants receiving parenteral nutrition without lipid emulsions can develop biochemical deficiency within days 1

Clinical Manifestations

• In cystic fibrosis patients, low LA levels correlate with poor pulmonary function and impaired growth in children 1, 4

• Low DHA combined with high AA:DHA ratio associates with impaired bone mineral density in children and young adults with CF 1, 4

• Classic deficiency signs include dermatitis, impaired wound healing, growth retardation, and learning disabilities, though these are uncommon in developed countries 1

Diagnostic Assessment

Measure EFA status using:

• Linoleic acid blood levels as the primary marker 1, 4
• Triene:tetraene (T3:T4) ratio as an alternative biochemical marker of deficiency 1, 4

Cardiovascular and Metabolic Effects

Omega-6 Fatty Acids (Linoleic Acid)

• LA consumption lowers LDL-cholesterol and triglyceride-rich lipoproteins while raising HDL-cholesterol 1

• LA demonstrates anti-inflammatory and insulin-sensitizing effects in humans, contrary to theoretical pro-inflammatory concerns based on rodent studies 1

• Higher biomarker levels of AA link to significantly lower CHD risk in prospective studies 1

• Vegetable oils rich in n-6 polyunsaturated fats reduce CHD events when replacing animal fats in controlled trials 1

Omega-3 Fatty Acids

• Seafood-derived EPA and DHA provide established cardiovascular benefits (see separate fish consumption guidelines) 1

• ALA evidence remains mixed and inconclusive for cardiovascular endpoints, with one Dutch trial showing nonsignificant reduction in major cardiovascular events (RR=0.91; 95% CI: 0.78-1.05) 1

Practical Clinical Management

When Supplementation Is NOT Needed

No intervention is required for healthy adults with low measured EFA levels if:

• They are asymptomatic 4
• No clinical signs of EFA deficiency are present 4
• They consume a varied diet with adequate fat intake 4

When to Consider Supplementation

Provide EFA supplementation only when:

• Diet contains inadequate sources of LA and ALA (extremely rare) 4
• Clinical signs of deficiency are present (dermatitis, poor growth, impaired wound healing) 1, 4
• Fat malabsorption syndromes exist (CF, cholestatic liver disease) requiring monitoring and potential supplementation 1, 4

Important Clinical Pitfall

Avoid the misconception that saturated fat is inherently harmful compared to EFAs. When compared with refined carbohydrates, saturated fat appears slightly beneficial, and the focus should be on increasing healthful polyunsaturated fats rather than simply reducing saturated fat 1. The key is replacing refined grains, starches, and added sugars with vegetable oils rich in polyunsaturated fats 1.