Although C. elegans is being recognized as a potent genetic tool to study the relationship of nutrition to growth and aging, surprisingly little is known about how worms utilize dietary molecules. Therefore, we have established a stable isotope enrichment strategy to characterize the ingestion and metabolism of dietary nutrients in developing and aging animals. Here, we present a study using 13C labeled bacteria to determine the relative abundance of dietary and de novo synthesized fatty acids in worm lipids using mass spectrometry. Quantitative analysis of 13C enrichment in feeding worms revealed that most lipid species; e.g., triglycerides, phospholipids, sphingolipids, etc., are primarily composed of fatty acids directly absorbed from the bacterial food source. Therefore, it is clear that direct incorporation of dietary fats plays a significant role in the formation of fat stores and lipid membranes. Because our labeling approach is effective at quantifying both dietary and synthesized fatty acids, we are now exploiting this strategy to identify genetic factors that impact de novo fat synthesis, dietary fat absorption, and/or fat expenditure. Thus far, we have surveyed genes known to significantly affect overall fat storage in nematodes to specifically identify factors that affect fatty acid synthesis. We found that mutations in the
daf-2 gene result in a dramatic increase in the de novo synthesis of fatty acids, which likely explains the high fat phenotype of these mutants. In contrast, mutations in
eat-2, which cause caloric restriction, lead to a significant decrease in de novo fat synthesis. We are continuing this approach to examine other genes known to affect overall fat storage. We expect our novel labeling strategy to generate new insights into how worms incorporate and process their dietary fats and other nutrients.