- **Lipids** are a class of nutrients that do not dissolve in water. - They will dissolve in organic solvents - Oil is less dense than water, so it will rise to the top of a solution - Major functions of lipids in the body include - Providing and storing energy - forming and maintaining cell membranes - producing steroid hormones - insulating the body - cushioning the body against bumps and blows - forming body contours - **absorbing fat soluble vitamins and phytochemicals** ## Fatty Acids A fatty acid is a hydrocarbon chain found in lipids; one end of the chain forms a carboxylic acid, and one end forms a methyl group. - Short chain fatty acids have 2 to 4 carbons - Medium chain fatty acids have 6 to 12 acids - Long chan acids have 14 to 24 carbons - Fatty acids are identified by: - The number of carbon atoms - The type of bond between carbon atoms - **Saturated fatty acid (SFA)** Every single carbon atom is filled with hydrogen atoms - **Unsaturated fatty acid** is a fatty acid that is missing hydrogen atoms and has one or more double bonds within the carbon chain - **Monounsaturated** (MUFA) - Has **one** double bond within the carbon chain - Sources include: - **Canola oil** - **Olive oil** - **Avocados** - Nuts - Seeds - Peanut butter - **Polyunsaturated** (PUFA) - Fatty acid that has **two or more bonds** within the carbon chain - Sources include: - **Soybean oil** - **Fatty fish** - **Flax seed** - **Walnuts** - Corn oil - Sunflower oil - Most naturally occurring fatty acids are cis fatty acids - Hydrogen atoms of the double bonded carbon are on the same side of the hydrocarbon atom - **Trans fats** are unsaturated fatty acids that have a trans double bond. - Hydrogen atoms of the double bonded carbons are on the opposite side of the hydrocarbon chain - **Hydrogenation** is the food manufacturing process that adds hydrogen atoms to liquid vegetable oil, forming trans fats. - Can be stored for longer periods because they are less likely to undergo oxidation - Raise "bad" cholesterol levels in the blood - Increases risk of heart disease - **Essential fatty acids** are fatty acids that must be supplied by the diet - **Linoleic acid** - 18 carbon omega-6 fatty acid found in vegetable oils - **Alpha-linolenic acid** - 18 carbon omega-3 unsaturated fatty acid, found in flaxseed, walnuts - Precursor for - Eicosapentaonoic acid (EPA) - 20 carbons - Docosahexaenoic acid (DHA): 22 carbons - Both acids are found mainly in fatty fish - Essential fatty acids are needed for growth and healthy cell membranes, especially in the brain. # Triglycerides A lipid that has three fatty acids attached to a three-carbon compound called glycerol - Comprises 95% of lipids in food and body - **Glycerol** is a three carbon alcohol that forms the backbone of fatty acids - # Phospholipids A phospholipid is a type of lipid needed for the flexibility, structure, and makeup of the cell membranes and for proper functioning of the never cells. - Partially water soluble - Hydrophilic - Part that attracts water - Hydrophobic - Part that repels water and attracts fat - Can serve as an emulsifier - Helps water soluble and water insoluble compounds mix with each other # Sterols Sterols are lipids that have a more chemically complex structure than a triglyceride or fatty acid - -ol suffix: Attached to an alcohol **Cholesterol** is a lipid found in animal foods: precursor for steroid hormones, **bile**, and vitamin D. - Found in: - Egg yolk - Liver - Meat - Poultry - Dairy products # Lipases Lipases are enzymes that break down lipids - **Cholecystokinin** is a hormone that stimulates the gallbladder to release bile and the pancreas to secrete digestive juices - Bile helps with the emulsification of and digestion of fat. - Secretin is a hormone that stimulates the liver to produce bile and the pancreas to secrete bicarbonate rich pancreatic juice