The glycolipids do not contain phosphorus but are derived from carbohydrates, fatty acids, and nitrogen compounds. Sterols are composed of complicated molecules, each containing 20 or more carbon atoms in an interlocking or fused ring structure. The fats seem to provide a concentrated, efficient source of energy for the cells. The oxidation of a gram of typical fat releases 9300 calories of energy. In contrast, the oxidation of a gram of protein or carbohydrate yields only 4100 calories.
Fats also tend to stiffen the cells because they form a semisolid mixture with water.
Physiological Effects Research devoted to probing heart attacks and other circulatory disorders indicates that some forms of these diseases are caused in part by the excessive consumption of foods high in fats, including lipids and sterols. U.S. studies show that as much as 50 percent of the caloric intake in a modern diet is in the form of fats. Other studies demonstrate that the likelihood of heart attack decreases when the intake of saturated fats is reduced. High cholesterol levels in the blood appear to promote the deposition of hard, fatty materials in the arteries, causing the arteries eventually to clog. When the coronary artery around the heart becomes clogged in this manner, blood supply to the heart is interrupted and a heart attack occurs.