Recall the chemical elements present in carbohydrates, proteins and lipids (fats and oils).
The elements present in a carbohydrate is Carbon, Hydrogen and Oxygen (CHO). The simple molecule in carbohydrates are sugars and the larger molecules are the polysaccharites e.g. starch.
The elements present in a protein is Carbon, Hydrogen, Oxygen and Nitrogen (CHON). The simple molecules of proteins are amino acids and the larger molecules are proteins itself.
The elements present in lipids are Carbon, Hydrogen, Oxygen (CHO). Lipids can be split into two categories - the fats and the oils.
Even though lipid and carbohydrates consists of the same elements, the structure is very different from one another.