Dissimilar fatty acid composition of standard rat chow

The lower incidence of coronary heart disease in populations consuming polyunsaturated fatty acids has spurred interest in the possible cardioprotective nature of these fatty acids. Furthermore, the source of dietary fats may modify the natural history of some chronic inflammatory disorders such as rheumatoid arthritis and systemic lupus erythematosus. Some studies examining these issues have involved animals fed a standard chow diet to which the desired fatty acids were added. Our observation that two lots of standard rat chow varied considerably in fatty acid composition, prompted us to analyze two additional standard rat chow lots for fatty acid composition. Each lot was extracted and fatty acid chain length determined by gas chromatography with the percentage of total fatty acids determined by integration. A wide variation in the total saturated (27.4-42.1%), monounsaturated (8.3-30.9%), omega 6 (17.2-44.2%), and omega 3 (3.8-11.2%) fatty acids was observed. By one-way analysis of variance, significant differences (p less than 0.025) between the various lots were observed for total saturated, monounsaturated, and omega 6 fatty acid groups. These findings suggest that fatty acid composition of standard rat chow is not similar. If the baseline fatty acid composition is critical to the experimental design, custom chow diets should be used.