Heteroatom-substituted fatty acids have been observed to modulate the extension and desaturating of fatty acids, and to influence their distribution within phospholipids pools. 10-Thiastearic acid inhibits desaturation of radiolabeled stearate to oleate in rat hepatocytes and hepatoma cells by more than 80% at a concentration of 25 µM. This activity is associated with a hypolipidemic effect, making this 10-thiastearic acid a useful tool for evaluating new anti-obesity therapeutics.