Fatty acids (FAs) are highly variable in structures, contributing greatly to the vast diversity in lipid structures. The fact that omega-3 FA supplements are a multi-billion dollar business indicates a strong belief about the impact of certain types of FAs on our health. However, despite sporadic reports linking FA variants with human diseases and development, their functional specificities are generally poorly studied, and we know little about the mechanism by which these variants contribute to the lipid composition in specific tissues for cellular events. Our lab has been addressing the above questions by combining complex genetics with biochemistry. Specifically, we have uncovered spectacular impacts of the rarely studied monomethyl branched-chain FAs (mmBCFAs) on cell signaling, development and behavior in C. elegans. mmBCFAs are synthesized in humans and richly present in our daily diet, but their physiological functions were unknown. We discovered that mmBCFAs are essential for postembryonic growth and development, as well as proper neuronal behaviors. We showed that this profound role is mediated by an mmBCFA-containing glucosylceramide and the TORC1 signaling pathway in the intestine. Strikingly, activation of TORC1, by either mutating the NPRL2/3 complexes or introducing hyperactive mutant transgenes of TORC1 components, can bypass the need of this lipid for this function. In another study, we revealed that ACS family enzymes critically regulate the incorporation of mmBCFAs into specific phospholipids (PL) in the somatic gonad so that proper phospholipid composition is achieved in the zygote. Imbalance of mmBCFA-containing PLs compromises IP3 signaling, leading to dramatic disruption of membrane dynamics and embryogenesis. We will report some of these findings with the emphasis on the physiological significance.