Linoleic Acid

What Is Linoleic Acid?

Linoleic acid (LA) is an 18-carbon polyunsaturated omega-6 fatty acid with two cis double bonds at positions 9 and 12 (18:2, n-6). It is a strictly essential fatty acid — the human body lacks the delta-12 desaturase enzyme needed to insert the second double bond — and therefore must be obtained entirely from food. Linoleic acid serves as the metabolic precursor for all omega-6 fatty acids, including gamma-linolenic acid (GLA) and arachidonic acid (AA).

Linoleic acid is one of the most abundant fatty acids in the modern Western diet, primarily from refined vegetable oils. Its adequate intake (AI) is set at 17 g/day for adult men aged 19–50 and 12 g/day for adult women aged 19–50 by the Institute of Medicine. Most people in developed countries consume well above these levels.

Key Functions and Health Implications

• Cell membrane integrity: LA is a critical structural component of phospholipids in all cell membranes, maintaining fluidity and supporting membrane protein function.
• Skin barrier: Linoleic acid is essential for synthesis of ceramides in the skin. Deficiency leads to a scaly skin condition called essential fatty acid deficiency dermatitis. Topically, LA-rich oils (rosehip, sunflower) support wound healing and barrier repair.
• Cardiovascular effects: Replacing saturated fat with linoleic acid reduces total and LDL cholesterol. Large-scale analyses associate LA intake with reduced cardiovascular disease risk.
• Eicosanoid precursor: LA is converted to arachidonic acid, which serves as the substrate for pro-inflammatory prostaglandins and leukotrienes. While this pathway has raised concerns, context-dependent regulation means dietary LA does not linearly increase systemic inflammation in most healthy individuals at normal intakes.
• Omega-6:omega-3 ratio: Modern diets often have ratios of 15:1 to 20:1 (omega-6:omega-3), far above the estimated ancestral ratio of 4:1 or lower. Excessive LA relative to ALA and EPA can competitively suppress omega-3 conversion and modestly skew eicosanoid balance toward pro-inflammatory pathways.

Food Sources