Chapter 5: Lipids

Learning Outcomes

5.1 Define the term lipid and classify lipids according to their structure. 5.2 Describe how lipids are digested, absorbed, and transported in the body. 5.3 Describe the functions of lipids in the body. 5.4 Identify the dietary recommendations for total fat, saturated fat, trans fat, the essential fatty acids, and cholesterol. 5.5 Identify the best, worst, and alternative food sources of dietary fats 5.6 Describe the development of atherosclerosis and coronary heart disease, and explain how lifestyle factors can affect the risk.

Stability of Fatty Acids (1 of 2)

Rancidity: Spoiling of fats through oxidation • Double bonds are less stable than single bonds. • Foods with unsaturated fats become rancid faster than foods with saturated fats.

Dietary Cholesterol and Phospholipids Not Essential (1 of 2)

The liver synthesizes cholesterol needed by the body: -900 mg/day -the liver decreases synthesis based on dietary intake -total cholesterol levels in the blood are maintained by a feedback system -keep LDLs low (under 100, half, of total cholesterol) and HDL high

Fat Substitutes Lower Fat in Foods

• A research survey found that over 160 million Americans (79 percent of the adult population) chose lower-fat foods and beverages. - Health concerns are the major reason. • Lower-fat foods contain fat substitutes. - They are designed to provide the creamy properties of fat for fewer kilocalories and total fat grams. - There are three categories of fat substitutes.

Essential Fatty Acids Have Specific Recommendations

• AMDR for the essential fatty acids - Linoleic acid (omega 6, pro inflammatory, need some) ▪ 5 to 10 percent of total kilocalorie intake - Alpha-linolenic acid (omega 3, anti inflammatory) ▪ 0.6-1.2 percent of total kilocalorie intake (have problems getting this amount) - For people diagnosed with heart disease: ▪ Consume 1 gram of essential fatty acids each day ▪ 2-4 grams of EPA and DHA daily may reduce blood triglycerides.* *Currently Americans only consume about 0.1-0.2 grams/d of EPA and DHA.

A Word about the Protective Effects of Red Wine and Alcohol

• Alcohol, in moderate amounts, can reduce the risk of heart disease, but mainly in middle-aged adults. - Increases HDL levels - Decreases blood clotting • Moderate amounts are defined as no more than: - 1 serving of alcohol per day for females - 2 servings of alcohol per day for males

What Are the Recommendations for Daily Intake of Triglycerides and Cholesterol? (1 of 2)

• Americans' fat intake is within the guidelines at 33 percent of total kilocalories, but the type of fat consumed must be considered. (We eat too much saturated fat vs unsaturated) • AMDR recommendation - 20 to 35 percent of daily kilocalories should come from fat. • Excess fat consumption does not lead to weight gain unless excess kilocalories are eaten. • Because fat contains concentrated kilocalories, a diet high in fat is more likely to result in excessive kilocalorie intake.

Consume Antioxidants and Phytochemicals

• Antioxidants and phytochemicals neutralize free radicals, stimulate the immune system to repair tissue damage, and reduce heart disease risk. - Vitamin E, vitamin C, and beta-carotene (can be converted to vitamin A) - Garlic may help lower cholesterol. - Flavonoids may help prevent LDLs from oxidizing. (Oxidized easily -> want more reduction reactions vs oxidation reaction -> breaks down cholesterol -> excess in blood) - Nuts reduce LDL levels. -vitamin A comes from animals

Heart Disease Begins with Atheroscler

• Atherosclerosis in the arteries leading to the brain can cause a stroke. • Progression of atherosclerosis - Injury to the lining of the arteries promotes inflammation. - LDLs and other lipid substances accumulate at the injured site and become oxidized by reacting with free radicals and metal ions. - Macrophages are attracted to the oxidized LDLs and then form plaques.

What Are Lipids and How Do They Differ in Structure? (2 of 2)

• Basic functions in the body - Store and provide energy - Provide insulation - Help manufacture steroids and bile - Play a role in transporting fat-soluble nutrients in the blood - Used to manufacture major sex hormones - Key to the structure of cell membranes

Many Lipids Are Comprised of Fatty Acids (1 of 2)

• Building blocks for triglycerides and phospholipids • A chain of carbon and hydrogen atoms with a carboxyl group at the alpha end and a methyl group at the omega end

Carbohydrate-, Protein-, or Fat-Based Fat Substitutes (interferes with absorption of fat)

• Carbohydrate-based - Majority of fat substitutes - Use plant polysaccharides to help retain moisture and provide a fatlike texture • Protein-based - Created from the protein in eggs and milk - Provide a creamy texture in the mouth • Fat-based - Modified fats that provide the physical attributes of fat for fewer kilocalories than regular fat or interfere with the absorption of fat • Overconsumption of kilocalories from regular, low-fat, or fat-free products can lead to weight gain.

Length of Fatty Acids

• Carbon length of fatty acids is 2 to 80 carbons long. - The most common fatty acids contain 12 to 24 carbons. • Short-chain fatty acids - 2 to 4 carbons • Medium-chain fatty acids - 6 to 10 carbons • Long-chain fatty acids - 12 or more carbons • Long-chain fatty acids are the most common type in foods and take longer to digest than short- or medium-chain.

What is Heart Disease and What Factors Increase Risk?

• Cardiovascular disease (CVD) encompasses disorders of a vascular system, including the heart. • Heart disease is the number-one killer of adults in the United States. • Heart disease begins with atherosclerosis. -damaged arteries cause sticky cholesterol to stick -> place increases which create narrow pathways -> increases BP, decreases blood flow, decreases oxygen and nutrients to cells that the artery supplies

Eat More Fish and Plant Foods (2 of 2)

• Consume more plant foods. - Canola oil, soy, flaxseeds, and walnuts are rich in ALA. - Choose plant foods rich in soluble fiber. - Consume at least 2 grams of plant sterols a day. ▪ Shown to lower LDL levels by 10 percent ▪ Foods rich in plant sterols include soybean oil, many fruits, vegetables, legumes, nuts, and other plant foods as well as margarine made with plant sterols.

Consume Less Saturated and Trans Fats and Moderate Cholesterol Intake

• Diets high in saturated fats raise LDLs in the blood. • High-cholesterol diet does not affect LDLs. • The type of saturated fat may have a greater impact on LDL levels in the blood. (Plant saturated fat better than animal, doesn't raise LDLs as much) • Trans fats raise LDLs and blood triglycerides, and lower HDLs. - Myristic and palmitic acids raise LDLs. - Stearic acid doesn't raise LDLs. - It is difficult to isolate foods by saturated fatty acid type; recommend lowering overall saturated fatty acid intake.

Eat More Fish and Plant Foods (1 of 2)

• Eat at least two, 3.5 ounce servings of fatty fish rich in omega- 3 fatty acids per week. - Choose baked, broiled, or poached fish. - Limit consumption of EPA and DHA to 3 grams or less per day. ▪ Increases risk for excessive bleeding ▪ May raise both blood glucose and LDL levels ▪ Intakes >3 g only occur with supplementation. ▪ Omega-3 fatty acid supplements should be taken with medical supervision. • Pregnant women and children should consume no more than 12 oz of fatty fish per week.

Get Plenty of Exercise, Manage Your Weight, and Quit Smoking

• Exercise raises HDLs, lowers LDLs, and reduces high blood pressure and insulin resistance. • Aim for 30 minutes or more of moderate exercise a day. • Quit smoking. - Smoke damages the walls of the arteries and accelerates atherosclerosis. - Smokers are three times more likely to have a heart attack than nonsmokers.

How Are Lipids Digested, Absorbed, and Transported in the Body?

• Lipids from foods are primarily in the form of triglycerides. - Lesser extent as phospholipids and sterols • During digestion, fatty acids form a combination of free fatty acids, glycerol, and monoglycerides. • Lipases are the enzymes that digest lipids.

Most Triglycerides Are Digested and Their Components Absorbed in the Small Intestine (1 of 3)

• Fat globules in chyme tend to cluster together. • In the intestine, bile acid emulsifies larger fat droplets into smaller fat droplets. - This allows pancreatic lipase to digest the lipids easily. - The resulting lipid complex is a micelle. ▪ Micelles transport the lipid complex across the small intestinal wall. • Cholecystokinin (CCK) is the hormone that stimulates the gallbladder to release bile acid. - CCK is released by the cells of the duodenum in the presence of lipids

Many Lipids Are Comprised of Fatty Acids (2 of 2)

• Fat has more kilocalories than carbohydrates or proteins because of the higher ratio of carbon and hydrogen to oxygen. - Fat: 9 kilocalories per gram - Carbohydrate and protein: 4 kilocalories per gram - There are many different fatty acids, which vary by: ▪ Length of the carbon chain ▪ Degree of saturation ▪ Shape

Triglycerides Stored in Adipose Tissue Insulate the Body and Protect Vital Organs

• Fat in subcutaneous tissue - Insulates body - Maintains body temperature • Fat protects bones and vital organs from trauma. • Too much stored fat can be detrimental to health and increase risk for heart disease, hypertension, and diabetes.

Fats Are Used for Energy

• Fats are a powerful fuel source. - Preferred by the heart, liver, and resting muscle - Spares glucose so it is only used by the central nervous system and red blood cells - Provides a backup source of energy between meals - Cannot sustain life during prolonged starvation ▪ Glucose is needed to metabolize fat. ▪ The glycerol portion of fat can make small amounts of glucose.

Fatty Acids Are Used for Energy

• Fatty acids provide a concentrated source of kilocalories. - 9 kilocalories per gram • Readily available when the body needs energy. • Body's main source of energy throughout the day • Excess fat is stored. - The body has an unlimited ability to store excess energy as fat in adipocytes. ▪ Fat cells can grow up to 1,000 times their original size. ▪ Additional fat cells are made when fat stores are filled. - Some fat is stored in muscle cells.

What Are the Recommendations for Daily Intake of Triglycerides and Cholesterol? (2 of 2)

• For heart health: - Consume no more than 10 percent of total kilocalories from saturated fat (<7 percent of total kilocalories is ideal). - Replace saturated fats with monounsaturated and polyunsaturated fats. - Limit trans fats to <1 percent of total kilocalories.

Lipoproteins Transport Lipids

• Four lipoproteins carry lipids in the circulatory system. - Chylomicrons - Very-low-density lipoproteins (VLDLs) - Low-density lipoproteins (LDLs) - High-density lipoproteins (HDLs) • VLDLs, LDLs, and HDLs - Globular molecule with a lipid center surrounded by a plasma membrane - Density determines function. - More protein = higher density

Lipoproteins Transport Fat (2 of 2)

• HDL and LDL biomarkers are used to determine the health of arteries. • LDLs - Carry cholesterol from the liver to the tissues - "Bad cholesterol" - "Lousy" DLs • HDLs - Carry cholesterol from the cells to the liver - "Good cholesterol" - "Healthy" DLs

Foods with Trans Fats

• Hydrogenation: Replacing saturated fat with hydrogenated fat • During the hydrogenation process, some of the double bonds are reconfigured. (Trans fats) - The unstable cis fatty acids in the double bond form trans fatty acids. • Some trans fats are naturally occurring. • Trans fat may actually be worse for heart health than are saturated fats. - Raise LDL and lower HDL cholesterol • The FDA requires trans fat to be listed on food labels.

The Best Food Sources Are Low in Saturated Fat (2 of 4)

• Increase alpha-linolenic acid (Omega-3 fatty acids) by consuming: - Walnuts, flaxseeds, canola oil (mostly omega 6, some omega 3, but inactive form) - Fatty fish such as salmon, tuna, mackerel ▪ All fish contain EPA and DHA. (High in omega 3) • Avoid cod-liver oil, as it is very high in vitamin A, which can be detrimental. -grass fed beef, free range chickens/eggs, higher percentage of omega 3(active form) -grain fed animals create omega 6 and ALA (inactive omega 3)

The Best Food Sources Are Low in Saturated Fat (3 of 4)

• It is impossible to eliminate all saturated fat from the diet. (Found in plants and animals) • Primary saturated fat sources - Animal foods: Fatty cuts of meat, whole-milk dairy products, and the skin on poultry - Plant sources: Coconut, palm, and palm kernel oils (not as damaging as animal sources)

Phospholipids Differ from Triglycerides (2 of 2)

• Lecithin (aka phosphatidylcholine) is a type of phospholipid. • Synthesized by the liver • Functions - Used as an emulsifier in foods (e.g., salad dressing) - A major phospholipid in the cell membrane

Dietary Cholesterol and Phospholipids Are Not Essential (2 of 2)

• Lecithin is the most common dietary phospholipid in the diet. (Mostly used in cell membranes) - Liver makes all of the phospholipid, including lecithin, that the body needs. - Lecithin is digested in the GI tract and does not enter the small intestinal cell intact. • Lecithin supplements do not offer any health benefits as claimed by supplement companies. - Claims include weight loss, improving fat metabolism, cardiovascular health, and exercise performance.

Essential Fatty Acids Manufacture Eicosanoids and Cell Membranes

• Linoleic acid (omega 6, provides energy) - Converted to arachidonic acid • Alpha-linolenic acid (ALA) (omega 3, used directly by brain cells) - Converted to eicosapentanoic acid (EPA)* (controls inflammation) - Elongated to docosahexanoic acid (DHA)* -EPA and DHA active forms of omega 3, used most and heart healthy • EPA and arachidonic acid make eicosanoids. - Hormone-like substances that regulate blood clotting, immune system, inflammation, blood pressure • ALA is needed to make healthy cell membranes, particularly in the nerve tissues and retina.

Chylomicrons Facilitate Lipid Absorption

• Lipids are absorbed based on their structure. - Glycerol and short - to medium-chain fatty acids are absorbed directly into the bloodstream. - Long-chain fatty acids combine with phospholipids and cholesterol to form chylomicrons. • Chylomicrons are too large to be absorbed directly into the bloodstream. - Travel through lymph fluid first - Exit the lymph and enter bloodstream through thoracic duct next to the heart - Lipoprotein lipase (LPL) hydrolyzes triglycerides in the chylomicrons as they travel to the liver via the bloodstream.

What Are Lipids and How Do They Differ in Structure? (1 of 2)

• Lipids refer to a category of compounds that include: - Triglycerides - Phospholipids - Sterols • Contain carbon, oxygen, and hydrogen • Hydrophobic, which means they don't dissolve in water

What Are the Functions of Lipids in the Body?

• Lipids serve several critical roles in the body. - Used as a source of energy (triglyceride -fat) - Form body structures (including cell membranes) - Regulate metabolism - Enhance the absorption of fat-soluble vitamins (ADEK) - Provide a layer of insulation to help regulate body temperature - Help cushion the major organs

Phospholipids Differ from Triglycerides (1 of 2)

• Made of a glycerol backbone and two fatty acids, a phosphate group, and different nitrogen-containing compounds • Hydrophilic on one end; hydrophobic on the other • Make up the phospholipid bilayer in the cell membrane

Sterols Are More Complex Than Triglycerides

• Made of four connecting rings of carbon and hydrogen - They do not contain glycerol or fatty acids. - They do not provide energy. • Cholesterol is the best known sterol. - Found in every cell in the body - Helps with numerous body processes - Precursor to vitamin D, sex steroids, and adrenal corticoids • Phytosterols and phytostanols are major plant sterols.

Stability of Fatty Acids (2 of 2)

• Manufacturers have enhanced the stability of fatty acids by reducing rancidity. - Adding antioxidants (vitamins A, c, and E) - Limiting food exposure to oxygen, heat, and light - Hydrogenation (creates trans fat by shortening)

Triglycerides Are the Most Common Lipid

• Most common lipid in both foods and the body • Make up about 95 percent of lipids found in foods • A triglyceride molecule has three fatty acids connected to a glycerol backbone. • Functions - Add texture to baked goods - Make meats tender - Preserve freshness - Stored as adipose tissue for energy

Most Triglycerides Are Digested and Their Components Absorbed in the Small Intestine (2 of 3)

• Phospholipids - Emulsified by bile during digestion - Dismantled into two free fatty acids and the phospholipid remnant - Packaged as micelles - Transported through intestinal wall

Phospholipids and Cholesterol Make up Cell Membranes

• Phospholipids: Part of the phospholipid bilayer in cell membranes • Cholesterol: A structural component in cell membranes

Lowering Your Risk of Heart Disease

• Primary risk factor is elevated blood lipids. • Starting at age 20, have a blood lipid profile analysis every 5 years. • Measure cholesterol-to-HDL ratio. • Have a risk score calculated.

Reduce Foods That Contain Trans Fat and Cholesterol

• Saturated fats from animal and plant sources were used in home cooking and commercial food preparation to: - Provide a rich flaky texture to baked goods - Decrease the incidence of rancidity • Later, hydrogenated oils and trans fats were used because they performed a similar function without adding cholesterol to the diet.

Dietary Fat Aids the Absorption of Lipid Compounds

• Several essential nutrients require dietary fat for absorption. - Fat-soluble vitamins - Carotenoids (beta carotene, converts to vitamin A) - Cholesterol - Phospholipids • Twenty grams per day are needed to stimulate chylomicrons that transport fat-soluble vitamins.

Most Triglycerides Are Digested and Their Components Absorbed in the Small Intestine (3 of 3)

• Sterols - Not digested - Carried by the micelle and absorbed intact through intestinal wall - Bile emulsifies sterols. • If lipids are undigested and not absorbed in the small intestine, they: - Bind with fiber - Are eliminated in the feces

The Liver Uses Cholesterol to Make Hormones, Bile, and Vitamin D

• The body uses cholesterol as starting material for: - Vitamin D and sex hormones such as estrogen and testosterone - Bile acid

Saturation of Fatty Acids (1 of 2)

• The degree of saturation of a fatty acid is determined by whether the carbons are held together by a double or single bond. • Saturated Fatty Acids - All the carbons on the fatty acid are saturated with hydrogen. - There are no double bonds between carbons. - They are solid at room temperature. - They have a higher melting point. -tightly packed tougher, increases intermolecular force, means it is harder to break down Ex: butter

Triglyceride Digestion Begins in the Mouth and Stomach

• The digestion of fat begins in the mouth with chewing. - Food mixes with saliva and lingual lipase. - Lingual lipase hydrolyzes the medium-chain fatty acids. • The bolus of food travels through the esophagus into the stomach. - Gastrin is released from the gastric pits lining the stomach and stimulates the release of gastric juices, rich in gastric lipase. - Gastric lipase hydrolyzes one fatty acid from the triglyceride, which produces a free fatty acid and a diglyceride.

Location of the Double Bond

• The location of the first double bond from the methyl (or omega) end of unsaturated fatty acids affects the properties of fatty acids. (Essential fatty acids) • Omega-3 fatty acid - First double bond is between the third and fourth carbons from the omega end. - Example: Alpha-linolenic acid (EPA/DHA is what we need, can't get from plant sources of omega, need animal source ex: salmon) • Omega-6 fatty acid - First double bond is between the sixth and seventh carbons from the omega end. - Example: Linoleic acid

The Best Food Sources Are Low in Saturated Fat (4 of 4)

• Tips for lowering saturated fats - Limit intake of foods rich in saturated fat. - Consume lower fat versions of fat-containing foods. - Read the Nutrition Facts panel to help you choose foods that are low in fat.

The Best Food Sources Are Low in Saturated Fat (1 of 4)

• To replace or lower saturated fats with unsaturated fats, consume the following foods: - Vegetable oils: soybean, corn, canola oils - Soybeans - Walnuts, flaxseeds, wheat germ -good sources of unsaturated fat (poly, omega 3 and omega 6)

Saturation of Fatty Acids (2 of 2)

• Unsaturated Fatty Acids - Some carbons on fatty acid form a double bond with each other instead of binding to hydrogen. - Monounsaturated fatty acid (MUFA) ▪ Has one double bond - Polyunsaturated fatty acid (PUFA) ▪ Has two or more double bonds - They tend to be liquid at room temperature. - They have a lower melting point. -spread out more due to kinks created by double bond -Ex: oil, better for you

Lipoproteins Transport Fat (1 of 2)

• Very-low-density lipoproteins (VLDLs) - Transport triglycerides (TGs) and cholesterol from the live to the cells - Lipoprotein lipase located on the outside of adipocytes and muscle cells cleave fatty acids (FAs) from TGs. ▪ FAs move into the adipocyte and muscle cells and stored for later use. ▪ Increases the ratio of protein to lipids ▪ Process converts VLDLs to LDLs

Cholesterol and Plant Sterols (don't have cholesterol)

•Dietary cholesterol comes mainly from animal products. • The cholesterol produced in plant cell walls and oils is so minimal that they are considered cholesterol free. • Phytosterols and stanols (don't want to over-consume, interfere with normal hormone functions bc it mimics cholesterol) - Lower LDL levels by competing with cholesterol for absorption - Are found in soybean oil, many fruits, vegetables, legumes, sesame seeds, nuts, cereals, and other plant foods - Food manufacturers are fortifying foods with them to help lower cholesterol.