Lipids are a group of structurally and functionally diverse organic compounds that are insoluble in water. Lipids are mainly composed of hydrocarbons and contain the same elements as carbohydrates: carbon, hydrogen, and oxygen (C, H, and O). However, lipids contain fewer polar hydroxyl groups (-OH). Lipids include fats and oils (triglycerides), phospholipids, waxes, and steroids.