Introduction Fatty acid synthesis plays a vital role in the homeostasis of the human body. The process of fatty acid synthesis regulates energy metabolism and provides fuel in case of hunger1. This process also synthesizes biomolecules important for life during embryonic development and lactation in the mammary glands2. Overproduction of synthesized fatty acids is implicated in disease states such as obesity, liver disease and cancer3. The fatty acid synthase (FAS) complex plays a vital role in the synthesis of fatty acids. Although two FAS complexes are known, FAS I is the complex present in higher eukaryotes and prokaryotes4. Despite the difference in the complexes used, the steps of fatty acid synthesis are, for the most part, conserved throughout life4. FAS I is a homodimer of ~272-kd subunits and contains three N-terminal active domains, each comprising a number of catalytic sites2,5. Seven catalytic sites are known in the FAS I complex, linked together by a polypeptide chain2,5. These include β-ketoacyl synthase (KS), malonyl/acetyltransferase (MAT), dehydrogenase (DH), enoyl reductase (ER), β-ketoacyl reductase (KR), acyl transporter protein (ACP) and thioesterase (TE)6. These sites facilitate the reactions necessary for fatty acid synthesis to occur (see figure 1). Figure 1. Diagram of the FAS I complex showing each of the seven catalytic sites6 Overexpression of FAS I is common in some cancers. Therefore, inhibition of FAS I is of considerable importance because anticancer therapies aimed at inhibiting FAS I have the potential to be an effective anticancer treatment. This review will discuss the regulation of fatty acid synthesis, examine the biochemical reactions involved in fatty acid synthesis...... middle of the article ......Iwaya K. Prognostic impact of fatty acid synthase expression in the upper urothelial tract of the urinary tract carcinoma. Journal of Clinical Oncology, 2014; 44 (4): 1093Swierczynski J. Hebanowska A. Sledzinski T. Role of abnormal lipid metabolism in the development, progression, diagnosis and therapy of pancreatic cancer. World Journal of Gastroenterology, 2014; 20(9): 2279–2303. Ito T. Sato K. Maekawa H. Sakurada M. Orita H. Shimada K. Daida H. Wada R. Abe M. Hino O. Kajiyama Y. Elevated serum fatty acid synthase levels in patients with gastric cancer. Oncology Letters, 2014; 7(3):616-620Uddin S. Siraj AK. Al-Rasheed M. Ahmed M. Bu R. Myers JN. Al-Nuaim A. Al-Sobhi S. Al-Dayel F. Bavi P. Hussain AR. Al-Kuraya KS. Fatty acid synthase and AKT pathway signaling in a subset of papillary thyroid tumors. Journal of Clinical Endocrinological Metabolism, 2008; 93(10):4088-97