Lipids, Fats and Oils • A category of compounds that include: triglycerides (fats and oils), phospholipids, and sterols. • Fats: lipids in foods or the body; composed mostly of triglycerides. • Oils: Lipids that are liquid (at room temperature) • Fatty acid: an organic compound composed of a carbon chain with many hydrogen atoms bonded with an acid group bonded at the molecule's end. “Lecture 4: Lipds, Fats and Oils PowerPoint" by Dr. Michael Kobre, Achieving the Dream OER Degree Initiative, Tompkins Cortland Community College is licensed under CC BY 4.0
Lipids • Like cabohydrates, lipids are made up of carbon (C), hydrogen (H), and oxygen (O) atoms. Triglyceride lipids have many more carbon and hydrogen molecules in proportion to their oxygen, because of this; they can supply over twice the energy per gram (9Kcal/gm) compared to CHO. • Of all the lipids found in the body, 99% are triglycerides.
Lipid Structure • Every triglyceride is constructed of one molecule of glycerol and three fatty acid molecules. • Fatty acids vary in length from 4 to 24 (even numbers) of carbons atoms long, the 18-carbon fatty acids are the most common in foods and the most important to body function. • Fatty acids can be saturated or unsaturated (mono or polyunsaturated)
Lipid Structure "Triglycerides-01.jpg" by OpenStax College is licensed under CC BY 4.0
Lipid Structure • Certain lipids are of special importance to nutrition. These lipids are the polyunsaturated fatty acids known as omega-3 linolenic acid and omega-6 linoleic acid. • Each is a member of a family of longer chain fatty acids that are involved in regulating blood Pressure, blood clotting, and other important body regulation functions.
Common Lipid Structures "Other Important Lipids-01.jpg" by OpenStax College is licensed under CC BY 4.0
Lipid Saturation Properties • What is the difference between saturated and unsaturated fats that we find in foods we eat? • Saturated fats are solid at room temperature, while unsaturated fats are liquid at room temperature. This is becausesaturated and Unsaturated fats differ in their chemical bond structures. Saturated fats have no double bond between molecules, which means they are more stable and the fat has more hydrogen molecules.
Lipid Saturation Terms • Unsaturated fatty acid: a fatty acid that lacks some hydrogen atoms and has at least one double bond between carbons making it more flexible and liquid at room temperature.
Lipid Saturation Terms • Monounsaturated Fatty acid: is a fatty acid that has only one double bond between carbon atoms. They are still liquid at room temperature. If you put a monounsaturated fat like olive oil in the refrigerator, it will start to get cloudy as it cools down because it is becoming slightly solid as it cools. When you remove it warms up it becomes clear again.
Lipid Saturation Terms • Polyunsaturated Fatty acid: is a fatty acid that has two or more double bond between carbon atoms. These fats are very much liquid at room temperature and don’t become cloudy when placed in the refrigerator. The multiple double bonds keep made a polyunsaturated fat molecule very flexible (liquid) at most temperatures.
Location Of The Double Bonds • Fatty acids differ not only in the length of their carbon chains and their degree of saturation, but also in the locations of their double bonds. • Chemists identify polyunsaturated fatty acids by the position of the double bond nearest to the methyl (CH3) end of the carbon chain. Fatty acids are named based on these double bond positions.
Firmness Of Fats • The degree of unsaturation (number of double bonds) influences the firmness (how solid) of the fat at room temperature. Generally speaking, polyunsaturated vegetable oils are liquid at room temperature, and the saturated animal fats are solid. • The more double bonds between carbons, the softer (more fluid) the fat is.
Triglycerides • Very few fatty acids occur free in food or in the body. Most often, they are incorporated into Triglyceride molecules. These are lipids composed of three fatty acids attached to a molecule of glycerol. Triglycerides are the major storage form of lipid fuel for most of the cells of the human body. Our adipose (fat storage) cells can store an unlimited amount of triglyceride. Once these fat storage cells fill up, they can divide to make additional fat storage cells in our body.
Commonly Consumed Lipids • Olive oil and peanut oil are monounsaturated fats • Canola oil is polyunsaturated • Coconut oil is a saturated plant fat • Lard is a saturated animal fat • Flaxseed oil contains omega-6 and omega-9 essential fatty acids
Stability Of Fats • Saturation also influences fat stability. All fats can become rancid when exposed to oxygen. The oxidation of unsaturated fats produces a variety of compounds that smell and taste rancid. The more double bonds in a fat the more easily it will spoil. The double bonds in fatty acids are very unstable. Both heat and oxygen exposure are bad for fats.
Fat Stability Protection • We can protect fat containing products from becoming rancid in three ways: • Antioxidants: These are compounds that protect fats from oxidation by being sacrificially being oxidized themselves. (examples are BHA, BHT, Vits C and D).
Fat Stability Protection • Hydrogenation: a chemical process by which hydrogen molecules are added (bonded) to mono or polyunsaturated fats to reduce the number of double bonds. This turns them into more saturated fats. • Sealed Air-tight containers: the best and most expensive way. If you keep oxygen away, it can’t react with the double bonds…… e.g. vacuum sealing.
Fat Stability • There is a major downside to using the hydrogenation process on polyunsaturated fats: • Hydrogenation makes polyunsaturated fats more saturated, thus, the health benefits are lost.
Trans-Fatty Acids • Another disadvantage of hydrogenation is that some of the molecules that remain unsaturated after processing change physical shape from a cis (normal) to the trans bond configuration. • This transformation moves the hydrogen molecules to the opposite sides of the carbon chain next to the double bond and results in a different (unhealthy nutritionally speaking) configuration for the fatty acid.
Trans-Fatty Acids "Isomers of oleic acid.png" by Edgar181 is licensed under CC BY 4.0
Trans-Fatty Acids • This “trans”structural change affects function: in the body, trans-fatty acids behave more like saturated fats. The relationship between trans-fatty acids, heart disease and cancer has been the subject of current research.
Trans-Fatty Acids • Major sources of trans-fatty acids: • Margarine: all types • Imitation cheese. • Cakes, cookies, doughnuts, pastry, crackers. • Snack chips • Peanut butter • Deep-fried foods.
Phospholipids • These are compounds similar to a triglycerides but have a phosphate group (a phosphorus containing salt) and choline (or another nitrogen containing compound) in place of one of the three fatty acids. • The fatty acid par makes the phospholipids soluble in fat; the phosphate group mixes/dissolves in water. This makes the molecule “polar”
Phospholipids in Food • The versatility of phospholipids enables the food industry to use them as emulsifiers to mix fats with water in such products as mayonnaise and candy bars. • Lecithin (the major food phospholipid) is also found in some foods naturally, the richest foods sources of lecithin are eggs, liver, soybeans, wheat germ, and peanuts.
Phospholipids In The Body • The lecithin and other phospholipids are important components of cell membranes. • Because phospholipids are bi-polar, (both water and fat loving) they help lipids move back and forth across cell membranes into the watery compartments both inside and outside of the cells.
Phospholipids In The Body "Phospholipid Bilayer.jpg" by OpenStax is licensed under CC BY 4.0
Sterols Sterols: Are lipid compounds composed of C, H, and O atoms arranged in connected ring structures. Similar to cholesterol and with any of a variety of side chains attached. The four ring core structure identifies a steroid; sterols are alcohol derivatives with a steroid ring.
Sterols In Foods • Foods harvested from both plants and animals contain sterols, but only those from animals contain cholesterol. • Meats, eggs, fish, poultry, and dairy products are the main food sources that contain cholesterol.
Sterol In The Body • Many vitally important body components are sterols. Among them are bile acids, sex hormones, adrenal hormones, vitamin D, and cholesterol. • Cholesterol in the body serves as the starting material for the synthesis of these compounds or as structural components of membranes in cells.
Cholesterol • Cholesterol is made in the liver from fragments of carbohydrates, protein, and fat. The liver makes about 800 to 1500mg of cholesterol per day. • Cholesterol causes problems in the body when it deposits in the artery walls. These deposits lead to Atherosclerosis, a disease that causes heart disease and strokes. Consuming too much cholesterol is one of the main causes of this condition.
Cholesterol "Cholesterol (chemical structure).svg" by Wesalius is licensed under CC BY 4.0
Digestion of lipids • The goal of fat digestion is to dismantle triglycerides into molecules small enough for the body to absorb and utilize, mostly monoglyceride molecules. • Monoglycerides: are a molecule of glycerol with one fatty acid bonded.
Digestion of lipids • Starting in the Mouth: Some saturated fats begin to melt as they reach body temperature. Our sublingual salivary gland at the base of the tongue secretes the digestive enzyme lingual lipase. • In the stomach: the acid-stable lingual lipase starts lipid digestion by breaking bonds of triglycerides to produce diglycerides and fatty acids.
Digestion of lipids • Stomach: The stomach’s muscular action mixes fat with secretions and acid. Gastric lipase (made in the stomach) helps to hydrolyze fat. • Small intestine: most breakdown of lipids takes place in the small intestine. Fat triggers the release of the hormone cholecystokinin (CCK), which signals the gallbladder to release bile (bile acid) to emulsify fat for absorption.
Bile’s role • Bile is needed to disguise fat ad make it more water soluble. Fat doe not mix with water unless bile is present. Each bile acid contains side chains of amino acids (protein) that are attracted to water. On the opposite, end a sterol that is attracted to fat is attached. Bile’s structure allows it to act as an emulsifier, bringing fat molecules into small intestine’s watery digestive fluids.
Bile’s role "Lipid and bile salts.svg" by Frank Boumphrey, MD is licensed under CC BY 4.0
Digestion of lipids • Most of the hydrolysis of triglycerides occurs in the small intestine. The major fat-digesting enzymes are pancreatic lipases. Some intestinal lipases are also active. These enzymes remove two of the fatty acids leaving a mono-glyceride.
Digestion of lipids "Catabolic Reactions.jpg" by OpenStax College is licensed under CC BY 4.0 "Lipid Absorption.jpg" by OpenStax is licensed under CC BY 4.0
Digestion of lipids • Phospholipids that are consumed are digested similarly. Their fatty acids are removed by hydrolysis, and then the parts of the complex are absorbed. • Sterols can be absorbed as is however, if any fatty acids are attached they must be hydrolyzed off before absorption takes place.
Digestion of lipids "Absorptive State" by Openstax is licensed under CC BY 4.0
What Happens to Bile? • After bile enters the small intestine and emulsifies fat, it has two possible fates. Most of the bile is reabsorbed from the intestine and recycled in the liver. The other possibility, some of the bile will be bound to dietary fibers and carried out of the body with the feces. This excretion of bile can help reduce blood cholesterol levels which is a good thing for our cardiovascular system.
Lipid Absorption • Small molecules of digested triglycerides (glycerol, short and medium chain fatty acids) can diffuse easily into the intestinal cells, they are absorbed directly into the bloodstream. • Large molecules (monoglycerides and long chain fatty acids) merge with bile into spherical complexes, known as micelles.
Lipid Absorption • Micelles molecules are emulsified fat droplets formed by molecules of bile surrounding monoglycerides and fatty acids. This configuration permits solubility and transport into intestinal cells. Once inside, the monoglycerides and long-chain fatty acids are broken down and reassembled into new triglyceride molecules.
Lipid Absorption • Inside the intestinal cells newly reassembled triglycerides and other large lipids (cholesterol, and phosphlipids) are packaged into transport molecules called chylomicrons. The intestinal cells will release the chylomicrons into the lymphatic system, and from the lymph into the bloodstream and eventually to the liver for processing.
Lipid Absorption and Transport "MetabolismoLipidiE.png" by Peter Forster is licensed under CC BY 4.0
Lipid Transport • Lipoproteins: There are four types of lipids associated with proteins that serve as transporter molecules for lipids in the lymph and blood. • Chylomicrons: the biggest and least dense lipoprotein that transports lipid from the intestine to the rest of the body.
Lipid Transport • VLDL (very low-density lipoproteins): the type of lipoprotein made by the liver cells to transport lipids to other cells and tissues around the body. These are mainly composed of triglyceride molecules . • LDL (low-density lipoprotein): is derived from VLDL as triglyceride are removed and delivered to cells. They are composed mainly of cholesterol. This is the molecule that is bad for our cardiovascular system.
Lipid Transport • HDL (high-density lipoprotein): This is the type of lipoprotein that transports products such as glycerol, fatty acids, phospholipids, and cholesterol back to the liver from blood for recycling or disposal. These are composed mainly of protein (are like recycling containers).HDL is the good type of cholesterol. It helps clean our blood vessels.
Health Implications • LDL and HDL have implications for the health of the heart and blood vessels. • The blood cholesterol linked to heart disease is LDL (the bad stuff) cholesterol. • HDL (the good stuff) represents cholesterol returning from the bloodstream to the liver.
Lipids Roles In The Body • As blood carries lipids to various sites around the body, the lipids can start providing energy, insulating against temperature extremes, and protecting cells and tissue shock damage, lipids are also used to help build cell structures.