Lipids are a group of naturally occurring hydrophobic molecules. Although used synonymously with fat they are actually a broad group with subgroups of steroids, fats, waxes, phospholipids, fat soluble vitamins, and more. Fat is just one of these groups. However, fat is one of the primary lipids used for energy storage in animals. Although plants tend to store starch, animals have adapted to storing fat in their systems. This is because one molecule of fat can store much more energy than one molecule of starch. This decreases unnecessary weight in organisms and allows them to move more efficiently. The fat is stored in an animal’s adipose tissues beneath the surface of the skin, around the organs, and even in bone marrow. The stick of butter in the picture above is pure fat. The butter, when ingested, will be used as a lipid for energy storage for the body.