Position of double bond (C=C) in fatty acids.

The position of the first double bond (starting from the CH 3-end) in unsaturated fatty acids largely determines its physiological properties.

Notation:

Omega notation: Indicates the first double bond counting from the CH3 end.

Delta notation: Indicates the exact positions of all double bond(s)

counting from the carboxylate (COOH) group

ω-3 or n-3

Notation: C20:5 (n-3) OR C20:5-Δ5,8,11,14,17

ω−3 fatty acids that are important in human nutrition are: α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). ω−3 fatty acids are associated with health benefits e.g. reduced risk of heart disease. Foods that contain ω−3 fatty acids are e.g. fish and soybean oil.

ω-6 or n-6:

Notation: C18:3 (n-6) OR C18:3-Δ6,9,12

It is suggested that an excess intake of ω-6 fats interfere with the health benefits of ω-3 fats. Dietary sources of ω−6 fatty acids include: diet margarines, nuts, cereals, eggs and poultry.

ω-9 or n-9:

Notation: C18:1 (n-9) OR C18:1-Δ9

Some ω-9 fats are common components of animal fat and vegetable oil such as olive oil.