Dogs, more than cats, are naturally attracted to foods rich in lipids, but they must be limited when the animal does not get a lot of physical exercise. In the absence of very strict rationing an excess of lipids can lead to obesity. Cats and dogs however cannot survive without them, as they provide energy and essential fatty acids necessary for life.
Lipids constitute a family of organic substances more commonly known as fats. Fatty acids and glycerol, which together form the triglycerides, are the main elements. Lipids may be simple (triglycerides, waxes) or complex (containing many other elements). Cell membranes for example are composed of phospholipids (which are considered complex).
Fats are the benchmark energy source for dogs and cats. One gram of lipid represents approximately 9 kcal of metabolisable energy, two and a half times more than what one gram of carbohydrate or protein provides.
Some fatty acids are termed essential and have structural roles for the cell or act as precursors for specific hormones. Dietary lipid sources are all foods rich in animal fats (butter, tallow, lard, eggs, fowl fat, fish oil) and vegetable fats (oils, oilseeds).