Lipids: Not Just Fat BIOL 103, Chapter 6

Today’s Topics What are Lipids? Fatty Acids are Key Building Blocks Triglycerides Phospholipids Sterols Lipids Digestion and Absorption Lipids in the Body Lipids in the Diet Lipids and Health

Lipids Essential nutrients Provide energy Help transport fat-soluble nutrients Contribute to flavor and texture of food

What are Lipids? Lipids include… Triglycerides (most abundant lipids) In body: stored in adipose tissue In food: “fats and oils” Phospholipids (~2% of dietary lipids) Plant and animal origin Body can make them Soluble in fat and water Sterols (very, very small % of lipids) Most well known: Cholesterol

Fatty Acids are Key Building Blocks Determine whether a fat is solid or liquid at room temperature Basic structure: (-COOH); (-CH3) Chain length 2-24 Carbon length

Fatty Acids are Key Building Blocks Saturation Saturated fatty acids All single bonds between carbons Unsaturated fatty acids One or more carbon bonds is a double bond Monounsaturated fatty acid (MUFA) Polyunsaturated fatty acid (PUFA) Fats with more double bonds are generally more liquidy

Saturated vs. Unsaturated Fatty Acids

Fatty Acids are Key Building Blocks Cis fatty acids Trans fatty acids Occurs naturally Chain is bent Produced by hydrogenation (adds hydrogen to an unsaturated fatty acids) A small portion of trans fat can occur naturally Chain is straighter

Trans Fat In health, trans fatty acids are known to raise LDL (“bad”) cholesterol, and lower HDL (“good cholesterol”), promote systemic inflammation, and increase triglycerides in your blood. History and how it is made: In Europe (1910) In US (1960s)

Fatty Acids are Key Building Blocks Nonessential and essential fatty acids Nonessential fatty acids Can be made in the body Not “essential” to have in your diet

Fatty Acids are Key Building Blocks Nonessential and essential fatty acids (cont.) Essential fatty acids Can’t be made in the body Must come from food Omega-3 (alpha-linolenic acid) and omega 6 (linoleic acid) Used to make eicosanoids

Triglycerides Structure Functions Glycerol + 3 Fatty Acids Energy source: 9 kcal/g Energy reserve: form of stored energy in adipose tissue (“fatty tissue”) Insulation and protection: Visceral fat (fat around organs) Subcutaneous fat (fat under skin to protect/insulate body) Carrier of fat-soluble nutrients Sensory qualities in food

Apple vs. Pear

Triglycerides in Food Found in a variety of fats and oils Classified by their most prevalent type Saturated fatty acids: animal foods and tropical oils Polyunsaturated fatty acids: plant or animal based Omega-3: soybean, flaxseed oils; salmon, tuna Omega-6: seeds, nuts, corn oil, meat, poultry, eggs

What are the positive and negative consequences of hydrogenating a fat What are the positive and negative consequences of hydrogenating a fat? (Problem Set 6, #3) Oxidation causes food to spoil and damage body tissues Pros Cons

Phospholipids Structure Functions: Glycerol + 2 fatty acids + phosphate group Functions: Emulsifiers Keep fat suspended in water Keep oil and water mixed Structural element for cell membranes

Phospholipids Cell membrane Double layer of phospholipids Store fatty acids temporarily and release them as needed  can regulate them closely Important role in nerve cells e.g. Ach

Phospholipids Lipid transport Stomach Intestine Blood Breaks fat into tiny particles for digestion (i.e. lingual lipase) Intestine Continues emulsifying fat (i.e. bile) Blood Coat the surface of the lipoproteins that carry lipid particles to their destinations in the body

Phospholipids Emulsifiers (Lecithin) In body In food Phospholipid with choline  phosphotidylcholine In food Blend of phospholipids with different nitrogen-containing components Used as emulsifiers (e.g. salad dressing, chili, sloppy-joe mixes, and chewing gum).

Phospholipids Phospholipids in food Occur naturally in plants and animals Examples: Egg yolks, liver, soybeans, peanuts Not dietary essential because the body can make it

Sterols A category of lipids that include cholesterol Structural characteristics: Multiple ring structure Contain no fatty acids Unlike TAG and PL, Sterols do not have glycerol backbone and fingerlike FA structures

Sterols Cholesterol functions: Cholesterol synthesis in liver Structural component of cell membranes Precursor to other substances Examples: Vitamin D, Sterol Hormones, Manufacture bile salts Cholesterol synthesis in liver Sterols in food Found only in animal foods

Lipid Digestion Digestion of triglycerides (TG), cholesterol, and phospholipids (PL) Mouth Chewing + lingual lipase Stomach 30% Triglycerides + gastric lipase  FFA and DG

Lipid Digestion (cont.) Small Intestine Emulsified by bile Rest of the “exposed” TG and DG are digested by pancreatic lipase Phospholipids digested by pancreatic phospholipase Cholesterol ester digested by cholesterol esterase Bile salts surround digested fat and form micelles

Lipid Absorption

Lipid Digestion (cont.) Micelles carry digested fat through the watery environment to microvilli/small intestine The lipid components are then absorbed into the intestinal cells at the microvilli Bile salts return to the liver to be used again Short-chain FA and glycerol are directly absorbed into your intestinal cells without the help of micelles.

Lipids Absorption To travel in the bloodstream, lipids are packaged into lipoprotein carriers How? In your intestinal cell: MG + FFA rejoin  TG Cholesterol esters and phospholipids form here also Then, TG, PL, cholesterol esters join protein carrier  lipoprotein. Lipoprotein leaves the intestinal cell  chylomicron  goes to lymph system  bloodstream.

Lipid Digestion and Absorption (Figure 6.21)

Chylomicron Transport In the blood stream, chylomicrons are large, fatty lipoproteins (90% fat)  circulate in the body while releasing TG When reaching capillaries, lipoprotein lipase “attacks” chylomicrons to remove TG  FFA and glycerol: FFA enter adipose cells  reassembled into TG OR FFA enter muscle cells  used for energy Glycerol  liver or kidney Your liver picks up “left-over” chylomicron and uses them to build VLDL

Lipids in the Body Very-low-density lipoproteins (VLDL): Deliver triglycerides to cells Intermediate-density lipoproteins (IDL) Returns to liver and is converted to LDL Low-density lipoproteins (LDL) Deliver cholesterol to cells, which body uses to synthesize membranes, hormones, etc. Returns to liver afterwards High-density lipoproteins (HDL) Pick up cholesterol for removal or recycling

Lipoprotein Pathway Summary

Lipoprotein density Lipoproteins differ by size, density, and composition of their lipid cores In general, larger the lipoprotein, the less dense it is. Size: HDL < LDL < IDL < VLDL < Chylomicron

Problem Set 6, Q#4: Describe the differences between LDL and HDL and protein composition

Lipids in the Diet Recommended intake: Reduce saturated fat and trans fat Total fat: 20-35% of calories Less than 10% of calories from saturated fat

Lipids in the Diet Essential FA requirements Linoleic acid/omega-6 FA should provide about 2% of calories Requirements for omega-3 FA is less well-known Omega-6 and omega-3 FA balance Ratio of 6:1 (omega-6 to omega-3 FA) While omega-3 FA is good for you, consuming too much of the omega-3 FA can suppress immune function and prolong bleeding time

Lipids and Health Following are examples are diseases associated to high intakes of saturated and trans fat. Obesity Determined by excessive accumulation of body fat leading to a body weight in relation to height that is significantly greater than some accepted standard. High-fat diets promote weight gain Heart Disease/Cardiovascular Disease Leading cause of death in US (1 death/minute) Major risk factors High blood cholesterol (High LDL, low HDL) Smoking High blood pressure

Lipids and Health Atherosclerosis Inflammation and atherosclerosis Slow, progressive hardening and narrowing of arteries Promoted by high blood cholesterol Inflammation and atherosclerosis How? Smoking, infection, or high blood pressure can speed up this process described above

Atherosclerosis

AHA diet and lifestyle recommendations: Reducing heart disease risk (pg. 222-226) Go over on your own Consume an overall healthy diet Aim for a healthy body weight Aim for a desirable lipid profile Aim for normal blood pressure Aim for normal blood glucose levels Be physically active Avoid use of and exposure to tobacco products I have listed them, but go over on your own. AHA: American Heart Association

AHA diet and lifestyle recommendations (cont.): Reducing heart disease risk (pg. 222-226) Balance calorie intake and physical activity to achieve or maintain a healthy body weight Consume a diet rich in fruits and vegetables Choose whole-grain, high fiber foods Consume fish, especially oily fish, at least 2/week Limit your intake of saturated and trans fat

AHA diet and lifestyle recommendations (cont.): Reducing heart disease risk (pg. 222-226) Minimize your intake of beverage foods with added sugars Choose and prepare foods with little or no salt If you consume alcohol, do so in moderation Follow the AHA recommendations when eating outside of the home

Metabolic Syndrome ¼ US adults has metabolic syndrome Has at least 3 of the following symptoms: Excess abdominal fat High blood glucose High serum triglycerides High blood pressure Low HDL cholesterol

Putting it all together Healthy People 2020 objectives target: Reducing deaths from heart disease and stroke Reducing the number of adults with high blood cholesterol levels

Cancer Stages of development: Initiation: a mutation in cell’s genetics  abnormal cell Promotion: when a chemical (e.g. carcinogen) encourages initiated cells to become active Reversible stage Progression: when promoted cells multiply and invade healthy tissues

Cancer (cont.) Dietary and lifestyle factors for reducing cancer risk: Maintain a healthful weight Adopt a physically active lifestyle Consume a healthy diet If you drink alcohol, limit consumption