What are lipids in the human body and what are they for?

Lipids, along with carbohydrates, proteins and nucleic acids, are one of the four main classes of biologically important organic molecules found in all living organisms; their quantity and quality in the diet can influence the physiology of cells, tissues and body. Unlike carbohydrates, proteins and nucleic acids, they are not polymers, but small molecules with molecular weights ranging from 100 to 5000, and also differ significantly in polarity, including hydrophobic molecules such as triglycerides or sterol esters, while others are more water soluble such as phospholipids or very short chain fatty acids.