Nonesterified Fatty Acids (NEFA)

Nonesterified fatty acids, or NEFA, are fatty-acid molecules that are not currently esterified to another molecule such as glycerol in a triglyceride. In blood they are often called free fatty acids, although that wording can be misleading because most circulating NEFA are not freely dissolved; they travel largely bound to albumin .¹

A major source of circulating NEFA is lipolysis in adipose tissue, where stored triglycerides are broken down and fatty acids are released. Tissues can take up these fatty acids and oxidize them for energy or use them as substrates for synthesis of other lipids. Their concentration changes with feeding, fasting, hormones, exercise, and metabolic state .¹

NEFA should be distinguished from triglycerides and from fatty acids carried within lipoproteins. Triglycerides contain three fatty acids esterified to glycerol and are transported or stored in that form. NEFA represent a different circulating pool that can move rapidly between adipose tissue and energy-consuming organs. The term describes chemical esterification status, not whether the fatty acid is saturated, monounsaturated, or polyunsaturated .¹