The final type of macromolecule that we ingest into our bodies are lipids, also known as fats. Lipids are not water-soluble and are not polymers. They can come in many different forms such as steroids, fatty acids, phospholipids, triglycerides, etc. Each of these types serves its own purpose. Since lipids are not water soluble, they cannot dissolve in our blood and must be carried by special protein carriers.