– Lipids are a large and varied group of biological molecules. Lipids are made mostly from carbon and hydrogen atoms and are generally not soluble in water. – The common categories of lipids are fats, oils, and waxes. – Lipids can be used to store energy. Some lipids are important parts of biological membranes and waterproof coverings. – Steroids synthesized by the body are lipids as well. Many steroids, such as hormones, serve as chemical messengers.