The use of sucrose polyester containing behenate fatty acid chains as a non-absorbable fat marker to determine total dietary fat absorption by the digestive tract of a subject. A test food for use in measuring fat absorption contains a non-absorbable fat and a dietary fat. The method is useful for diagnostic testing for diagnosing malabsorption of dietary fat by the digestive tract of the subject, and impairment of dietary fat digestion in the subject.