How Do Lipids Move Through Body?

Lipids in your diet include phospholipids, sterols and triglycerides. The primary component of dietary lipid is triglyceride or triacylglycerol, which is composed of a single glycerol molecule and three fatty acid molecules. Your body must break down the triglyceride into two fatty acids and one monoacylglycerol molecule for absorption to occur. Following digestion and absorption, lipids are then either stored in adipose or utilized as an energy source.

Digestion

Lipid digestion, like carbohydrate digestion, begins in your mouth. You secrete enzymes, known as lipases, in your mouth, stomach and small intestine that work to digest dietary triglycerides. Although you have lipases working in the mouth and stomach, the vast majority of triglyceride digestion occurs in the small intestine. Digestion of triglycerides, and other lipids, is a long process. For you to completely digest and absorb dietary fat, your body will require up to 24 hours.

Absorption

Lipid absorption occurs in the duodenum and jejunum of the small intestine. Lipids are not absorbed in the ileum or in the large intestine. Bile salts, a critical component of lipid absorption from the intestine, are absorbed in the ileum. Once the fatty acids and monoacylglycerol are absorbed in the intestine, they re-form triglycerides prior to their secretion into the blood circulation. Lipids secreted into the circulation are primarily used to deliver the lipids to muscle and adipose. Lipids taken up by adipose are used to store excess energy, while lipids taken up by skeletal muscle are used for energy production and to a lesser extent, storage.

Storage

Lipid storage is largely handled by adipose tissue, although lipids are stored in other tissues to a much lesser extent. Triglycerides stored in adipose are constantly being broken down for energy utilization in other tissues and re-formation of triglycerides for storage. In the period following a meal, insulin increases the ability of adipose to take up and store lipids as needed.

Utilization

During fasting, or when caloric intake is less than the calories expended, lipids from adipose are needed to provide energy for the body. During this time, insulin levels drop and fatty acids are released from adipose into the circulation. Fatty acids released into circulation are transported throughout the body for uptake, mainly by the liver and muscle. Once taken up into the muscle or liver cell, oxidation of the fatty acids occurs for energy production needed to maintain the cells.