This chapter outlines the nutritional and metabolic function of fat within the human body. Compared to the two other macronutrients, fat is the highest energy-dense macronutrient, allowing it to provide enhanced taste, texture, and palatability to foods, as well as promote temperature regulation. The main dietary form of fat is triglycerides, consisting of three fatty acids, found mainly in dairy products, animal products, and fish/cooking oils. Fatty acids have around three different chain length variations of short, medium, and long: all with varying roles within the body. Two of the long-chain fatty acids are considered essential, indicating the need for them in the diet as the body cannot synthesize them. Deficiencies in essential fatty acids can result from inadequate dietary intake, malabsorptive disorders, or during times of increased demands, leading to several issues. Fat digestion and absorption involve complex processes including emulsification by bile salts, enzymatic breakdown by pancreatic lipase, and transport via chylomicrons. Malabsorption disorders hinder this process, leading to fat malabsorption and nutritional deficiencies. Specific genetic disorders such as lipase deficiency or abetalipoproteinemia also contribute to fat malabsorption, requiring enzyme replacement therapy and dietary modifications.