Why are linoleic acid and alpha-linolenic acid considered essential fatty acids?

• A. They are stored in adipose tissue.
• B. They must be supplied exogenously via the diet.
• C. They can be synthesized in the body.
• D. They are not required in the human diet.

Answer: (B)

Essential fatty acids are fats that must come from the diet because humans cannot synthesize them. Linoleic acid and alpha-linolenic acid are essential for this reason: we lack the desaturase enzymes needed to introduce the necessary double bonds beyond certain points, so we cannot produce these fatty acids endogenously. Without dietary intake of these, the body would miss important structural components for cell membranes and cannot reliably generate longer-chain precursors like arachidonic acid, EPA, and DHA. So their status as essential rests on the inability to synthesize them, not on where they’re stored or on any ability to make them from other fats.