Chap. 5: Lipids

Properties of Lipids Do not readily dissolve in water Fats are solid at room temperature Oils are liquid at room temperature Triglycerides are the main form of lipids in food and body (storage) Energy dense (9 kcal /gm)

Fatty Acids Basic Form of Fats Form together to make use for the body and for food Saturated Unsaturated Polyunsaturated

Fatty Acid Structure (Fig. 5-1-A) omega endalpha end degree of saturation H H H H H H H H H H H H H H H H H O H-C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C-C-OH H H H H H H H H H H H H H H H H H

Saturated Fatty Acid Structure (Fig. 5-1-A) omega endalpha end degree of saturation: single carbon bond H H H H H H H H H H H H H H H H H O H-C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C-C-OH H H H H H H H H H H H H H H H H H

Monounsaturated Fatty Acid Structure (Fig. 5-1-B) omega endalpha end One double bond H H H H H H H H H H H H H H H O H-C--C--C--C--C--C--C--C--C=C--C--C--C--C--C--C--C--C-OH H H H H H H H H H H H H H H H H H

Polyunsaturated Fatty Acid Structure (Fig. 5-1-C) omega endalpha end > 2 double bonds H H H H H H H H H H H H H O H-C--C--C--C--C--C=C--C--C=C--C--C--C--C--C--C--C--C-OH H H H H H H H H H H H H H H H H H

Essential Fatty Acids Body can only make double bonds after the 9th carbon from the omega end Primarily need Omega-3 and Omega-6

Essential Fatty Acid- Omega-3 (alpha-linolenic acid) omega endalpha end 1st double bond is located on the 3rd carbon from the omega end H H H H H H H H H H H H H H H H H O H-C--C--C=C--C--C =C--C--C=C--C--C--C--C--C--C--C--C-OH H H H H H H H H H H H

Omega-3 Fatty Acid Primarily from fish oil Also found in canola or soybean oil Recommend intake of ~2 servings of fish per week

(Omega-3) Alpha-linolenic acid decrease blood clotting reduces heart attack excess may cause hemorrhagic stroke large amounts may decrease inflammation pain with rheumatoid arthritis

Essential Fatty Acid- Omega-6 (alpha-linoleic acid) omega endalpha end 1st double bond is located on the 6th carbon from the omega end H H H H H H H H H H H H H O H-C--C--C--C-- C--C =C--C--C=C--C--C--C--C--C--C--C--C-OH H H H H H H H H H H H H H H H H H

Omega-6 Fatty Acid Found in vegetable oils Only need ~ 1 tablespoon a day

Linoleic acid (Omega-6) Arachidonic acid increase blood cot increase inflammatory responses

Fats in the body/food Triglycerides Main form of fats in the body and in food Phosolipids Manufactured by the liver (not essential) Sterols Manufactured by the liver and in food Differ based upon structure & function

Triglycerides Structure: 3 fatty acids connected to a glycerol backbone Function: Main form of fats in food and body Taken up my muscles for energy Taken up by adipose tissue for storage

Triglycerides (Ester bond) Glycerol + 3 FA’s Triglyceride + 3 H 2 0 H H--C--OH H--C--OH H--C--OH H O HO-C-R O HO-C-R O HO-C-R + H O H--C--O--C-- O H--C--O--C-- O H--C--O--C-- H R + H2O R + H20

Phospholipid Structure: Built on a glycerol backbone Has at least one fatty acid replaced with phosphorus compound Function: EMULSIFICATION Needed for transport of triglycerides and sterols Needed for breakdown of triglycerides inside the cell Part of the cell membrane

Functions of Phospholipids cont. Emulsifier Bile acids Lecithins Improves food products

Emulsifier Hydrophilic end (attracts water) Hydrophobic end (attracts lipid)

Emulsification

Sterol--Cholesterol Structure: A multi-ringed structure Do not have a glycerol backbone Waxy substance Function: Needed for cell structure Needed for bile and hormone production

Digestion

Digestion of Fat in the Stomach Gastric lipase works only on triglycerides containing short & medium chain fatty acid Minimal digestion in the stomach

Digestion of Fat in the Small Intestine Primary site of fat digestion CCK stimulates pancreas to release pancreatic lipase Bile acid emulsifies digested fat Fat is broken down to monoglycerides and fatty acids

Absorption of Fat Short and medium chain (<12 C) fatty acids are water soluble Enters the portal system Long chain fatty acids reforms into TG Enters the lymphatic system

Carrying Fat in the Bloodstream Water (blood) and oil (fat) are incompatible Unique system of fat transportation is needed Fat

Transportation of Digested Fat Re-formed triglycerides are packaged into a lipoprotein called chylomicrons Enters Lymphatic System Enzymes in the chylomicrons break down triglycerides Fatty acids are absorbed by cells (i.e. muscles or adipose)

Lipoproteins

Transportation of Synthesized Fat LIVER: takes up lipids from blood Manufactures fats (lipids) and cholesterol Synthesizes new lipoproteins and releases them into the blood stream

LIPOPROTEINS produced by the liver VLDL becomes more dense as it releases lipid to cells; turns into LDL carries and releases fat LDL carries and releases cholesterol and protein HDL Cleans up loose cholesterol in the blood High proportion of protein

Benefits of HDL Remove cholesterol from the blood stream HDL may block oxidation of LDL Reduce risk of heart disease Pre-menopausal women have higher HDL

Good vs Bad Cholesterol CVD increases with low HDL If LDL not cleared from bloodstream, WBC’s take it to the arteries Eventual build up of cholesterol in BV Leads to CVD

Functions of Lipids (a recap) Provide energy (muscles) Efficient storage of energy (in adipose) Insulation/Protection Transport fat-soluble vitamins Satiety Flavor and mouth feel

Lipids in Foods

Hidden Fat Look on the Nutrition Facts Look on the lists of ingredients Control portion size

Reduce-Fat Foods Total energy is about the same Sugar is commonly added in place of fat

Hydrogenation of Fatty Acids Process used to solidify an oil Addition of H to C=C double bonds Increases shelf life Decreases rancidity Formation of trans fatty acid (similar to shape of saturated fatty acid)

Health Dangers of Excessive Trans Fatty Acid Raises LDL Lowers HDL Increases risk for heart disease Current intake is~3% of total kcals Soon to be on food labels

Where do we get Trans Fatty Acids? hydrogenated fats deep-fried foods baked goods non-dairy creamers

Rancidity Decomposed oils Breakdown of the C=C double bonds by ultraviolet rays, &/or O 2 Yields unpleasant odor and flavor PUFA more susceptible Limits shelf life

Recommendation Essential fatty acids: 2 servings of fatty fish/wk 2-4 Tbls. of plant oil ~ 20-35% of total caloric intake Current diet supplies ~33% of total kcal from fat much from animal, whole milk, pastries, cheese, margarine, and mayo

The American Heart Association For high risk individuals <20-30% of total kcal from fat/day <7-10% from saturated fat (includes trans fatty acid) < mg cholesterol a day