The cheese and steak are glistening with fat.You may have never been to Philadelphia, but you're probably familiar with its renowned gastronomic delight, the Philly cheesesteak, pictured here.This sandwich would not be recommended for those who are on a low-fat diet, since cheese and steak are typically high-fat foods.Getting too much fat in our diet can be harmful to our health, no matter how good it tastes.Defining fats


Types of Lipids

There are a variety of lipids, ranging from fatty acids to proteins.A lipid can contain alcohol or phosphate groups, for instance.Triglycerides, phospholipids, and steroids are types of lipids.They all play different roles in the body.


Triglycerides are made by combining glycerol with three fatty acids.(Glycerine) is a sugar alcohol, also known as glycerol.The liquid is colorless and odorless, sweet tasting, and nontoxic.Body fat consists primarily of triglycerides, which are present in humans and animals alike.There are also traces of them in plant fats.Among the many types of triglycerides, two main groups are those comprised of saturated fatty acids and those composed of unsaturated fatty acids.

The triglycerides in the bloodstream are important as energy sources and carrier molecules for dietary fats.The other major source of energy in the diet is carbohydrates, which contain twice as much energy as fats.The body transforms any calories that aren't used right away into triglycerides, which are stored in fat cells. When you need more energy between meals, hormones start releasing some of these triglycerides back into the bloodstream.



All living things possess phospholipids, which are a major component of their cell membranes.In phospholipid molecules, two long fatty acids make up the "tail." The phospholipid molecules have a phosphate group and glycerol molecules make up the "head." (See diagram below).A phosphate group is a negatively charged molecule.Phobic or water-attractive, it is present on phospholipid heads.The phospholipid's tail is hydrophobic or repels water.They possess these properties, which enable phospholipids to form a two-layered, or bilayer, cell membrane.

In the figure below, phospholipid bilayers are formed when many molecules of phospholipid line up tail to tail, resulting in an inner and outer surface formed by hydrophilic particles.Both the hydrophilic heads point towards the watery extracellular space and the watery intracellular space (lumen) in the cell.