fats and lipids : fats are concentrated sources of energy because they give twice as much energy as either carbohydrates or protein on a weight basis. the functions of fats are to: make up park of the structure of cells, from a protective cushion and heat insulation around vital organs, carry fat soluble vitamins, and provide a reserve storage for energy. three unsaturated fatty acids which are essential include: linoleic, linolinic, and arachidonic and have 2,3 and 4 douple bonds respectively. saturated fats, along with cholesterol, have been implicated in arteriosclerosis, "hardening of the arteries". for this reason, the diet should be decreased in saturates fats (animal) and increased in unsaturated fat (vegetable).