Interactive Summaries

Chapter 5: Lipids

Fatty Acids are Key Building Blocks

Lipids are a broad range of molecules that dissolve easily in organic solvents, but are much less soluble in . They are generally hydrophobic and lipophilic. The three main types of lipids are triglycerides, phospholipids, and sterols. are the largest category of lipids and are stored in the body in . are major building blocks of cell membranes. They keep fats suspended in watery fluids. The most famous sterol, cholesterol, is manufactured in the body and is a precursor to the synthesis of sex hormones, and vitamin D. Lipids share many of the same functional properties and transport mechanisms.

are common components of triglycerides and phospholipids. There are many types of these substances, which are basically chains of atoms with a carboxyl group on one end and a methyl group at the other end. Short chain fatty acids have less than carbons; medium chains have 6-10; and long chains have or more. The water-soluble property of shorter fatty acids affects their absorption.

A triglyceride is made of fatty acids attached to a glycerol molecule. Triglycerides are esters which form when a hydrogen and an oxygen from the carboxyl group combine with a hydrogen atom from the alcohol’s hydroxyl group. A molecule of water is produced which makes this a reaction.

Lipids in the Body and the Diet

Lipoprotein carriers transport lipids through the bloodstream. Chylomicrons are formed in the . They eventually reach the bloodstream through the in the neck. As they travel through the bloodstream they gradually give up triglycerides to capillary walls. Lipoprotein lipase breaks them down. After hours little is left of the chylomicron except cholesterol-rich remnants.

HDL are scavenger lipoproteins, picking up excess released by dying cells and arterial plaques. These plaques are created by LDL degrading over a long period of time. that have embedded themselves in arterial walls damaged by smoking or diabetes have scavenger receptors which bind to LDL and cause it to release its cholesterol. If HDL levels are low there is an increased risk for atherosclerotic heart disease.

The Daily Value on food labels recommend consuming of fat based on a 2000 kcalorie diet. To fulfill the need for omega-6 fatty acids, linoleic acid should provide 2% of our calories.

When protein is used as part of a fat substitute, the product cannot be used in cooking because high temperatures cause denaturation. Many products use carbohydrates as fat replacements and bind to further dilute calories. Olestra is a very controversial fat substitute. Because olestra is not absorbed it may cause symptoms of fat malabsorption such as .

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