Fact 1: The main sources of a body's energy are glucose, glycogen, and fat. Fact 2: Excess carbohydrates are converted to fat. Fact 3: Lipoproteins are different from cell membranes in that lipoproteins have a monolayer of phospholipids as their outer shell while cell membranes have a phospholipid bilayer instead. Fact 4: High-density lipoprotein is considered to be "good cholesterol."