This book is designed and formatted for an undergraduate student level and fits with the curriculum of biochemistry courses in all medical universities throughout the world. This book represents educational material which will provide students with a simple understanding of basic concepts of the macronutrient metabolism, biochemical events of macronutrients inside human cells, and cellular regulation of different metabolic pathways. This textbook provides insight into the nutritional biochemistry of macronutrients (carbohydrates, fat and protein) and their metabolic fate. The book covers basic concepts of digestion and absorption of three essential nutrients and their utilisation by human cells in anabolic and catabolic pathways. The book is designed to link basic biochemistry to metabolism with a specific reference to the enzymatic, hormonal regulation and integrated metabolic pathways. Special attention was given to the central role of glucose in controlling energy production and its relevance to enzyme activation and inhibition. The major pathways that regulate carbohydrates, fat and protein metabolites in different organs are discussed in correlation to the metabolic fate of each nutrient and the cellular responses to different hormones. The book provides a thorough understanding and lays the foundation for the metabolic basis of macronutrients and the biochemistry underlying disease pathogenesis. Finally, the main theme of this book is to address the macronutrient metabolism in terms of anabolic, catabolic and amphibolic pathways.