SO, What is Fat? The good, the bad, and the ugly: A review of the biochemistry of fat.
(This is a very simplified description but designed to help you appreciate the role of fats in our diet.)
Diagram 1. The chemical structure of a typical long chain (>12 carbons) Triglyceride Fatty Acid.
Fats are one of the more important dietary components. They should make up between 15 to 25 percent of your diet. This intake should include long, medium, and short chain fatty acids (FA) as well as some cholesterol. Long chain FAs have 12 or more carbons in their tail, medium chain less than 12 and short chain FAs 6 or less. Unfortunately, in today's America 35 percent or better of daily calories come from fats. Since most people are sedentary this excess energy (fat) is stored in the body. The more we eat, the more we store and the larger we get.
But we cannot do without fats. Fats are an important component in the human diet. They serve as building blocks for hormones, energy sources, and insulation. We've all heard how women who become too thin and stop having their periods. For men excessive weight loss can cause testosterone deficiencies. This is because fatty acids and cholesterol are important for the production of hormones such as estrogen, testosterone, progesterone and other anabolic and mineral corticoids. So, fats are important for normal growth and energy production. But too much fat leads to obesity, increased fatty acids and cholesterol in the blood, hypertension, heart disease, atherosclerosis and musculoskeletal problems.
Diagram 2: Hormones dependent on presence of cholesterol and other FAs that have to be present to produce them. Without these hormones the person becomes unhealthy.
So how are fats eaten and what happens to them in the digestive system? Well, the diagram below demonstrates the digestive process and absorption of fats in our diet. Long chain FAs are absorbed into the blood stream, short chain and medium chain FAs are transported in the lymphatic system.
When the FAs reach the various cells in the body they are transported into the cells for further processing. They can be stored in muscle cells, liver cells, fat cells, adrenal glands, ovaries and testicles. Depending on which cell type absorbs them determines how they will be used (more later).
In Part Five we will discuss what happens to fats once they get into the body?