Fats: Types, Functions, and Digestion (PDF)

What are Fats? Fats are one type of lipid. Lipids: Diverse class of organic substances that are insoluble in water. Lipids (fats) do not dissolve in water. Types of lipids Three types of lipids are found in food...

What are Fats? Fats are one type of lipid. Lipids: Diverse class of organic substances that are insoluble in water. Lipids (fats) do not dissolve in water. Types of lipids Three types of lipids are found in foods Triglycerides Phospholipids Sterols  Triglycerides Composition of triglycerides  Triglycerides are composed of (see Figure 12)  Three fatty acid molecules Fatty acids: long chains of carbon atoms surrounded by hydrogen atoms One glycerol molecule Glycerol: A three-carbon alcohol that is the backbone of a triglyceride.  Fatty acids can differ in  Length of their carbon chain Short (13).  Level of saturation Saturation refers to "how many hydrogen atoms surround each carbon". Saturated fatty acids have hydrogen atoms surrounding every carbon in the chain; they have no double bonds. Monounsaturated fatty acids lack hydrogen atoms in one region; they have one double bond. Polyunsaturated fatty acids lack hydrogen atoms in multiple locations; they have two or more double bonds. Note: Each double bond causes the loss of two hydrogen atoms.  Shape The shape of a triglyceride is determined by the saturation of the carbon chains. - Saturated fatty acids can pack closely together and are solid at room temperature. For example, coconut oil, animal fats, butter are high in saturated fatty acids. - Unsaturated fatty acids do not stack together well and are liquid at room temperature. Unsaturated fatty acids are the predominant type in plants, two exceptions are coconut and palm kernel oil. The hydrogen atoms at the unsaturated region can be arranged in different positions; Cis: Same side of the carbon chain or Trans: Opposite sides of the chain  Hydrogenation It defines as "The addition of hydrogen atoms to unsaturated fatty acids." - Converts liquid fats (oils) into a semisolid (spreadable) or solid form. - Used to create margarine from plant oil. - Often creates trans fatty acids. - Listed on the food label as partially hydrogenated oil. Triglycerides and health Saturated and trans fats are harmful to health. Saturated and trans fats lower “good” cholesterol and raise the “bad” cholesterol. As of January 2006, trans fat content is required on the food label.  Provide essential fatty acids Two fatty acids cannot be synthesized in the body and must be obtained in the diet. Linoleic acid (omega-6 fatty acid) and alpha-linolenic acid (omega-3 fatty acid). Omega-6 and omega-3 fatty acids are precursors to biological compounds called eicosanoids, which regulate cellular function (see Figure 15). Linoleic acid (omega-6 fatty acid). Found in vegetable and nut oils. Converted by the body to arachidonic acid, which is involved in blood clotting and blood pressure.  Alpha-linolenic acid (ALA) (omega-3 fatty acid). Found in dark-green leafy vegetables, flaxseeds and flaxseed oil, soybeans and soybean oil, walnuts and walnut oil, canola oil, fish, and fish oils. Eicosatetraenoic acid (EPA) and docosahexaenoic acid (DHA) have important health benefits and are found in fish, shellfish, and fish oils. ALA Converted to EPA and DHA, which are important regulators of inflammation, blood clotting, and blood pressure.  Phospholipids Phospholipids composed of (see Figure 16) Glycerol backbone. Two fatty acids. Phosphate. Soluble in water. Manufactured in our bodies so they are not required in our diet. Important components of cell membranes.  Sterols Lipids containing multiple rings of carbon atoms, cholesterol is the major sterol found in the body (see Figure 17). Essential components of cell membranes and many hormones. Manufactured in our bodies and therefore are not essential components of our diet.  Why do we need lipids?  Energy source - Highly concentrated form of energy dense, containing 9 kcal/gram. - Much of the energy used during rest comes from fat. - Fat is used for energy during exercise, especially after glycogen is depleted. - Fat is also used for energy storage.  Fat soluble vitamins - Vitamins A, D, E, and K are soluble in fat; fat is required for their transport.  Essential to body functions - Cell membrane structure. - Nerve cell transmissions. - Protection of internal organs. - Insulation to retain body heat.  Provides flavor and texture to foods.  Contributes to making us feel satiated - Fats are more energy dense than carbohydrates or protein. - Fats take longer to digest.  Digestion, absorption, and metabolism of lipids. - Fats are insoluble in water. - Not digested and absorbed easily. - No digestion of fats occurs in the watery environment of the mouth. - Minimal digestion occurs in the stomach from gastric lipase. - Digestion and absorption of fats occurs primarily in the small intestine. In mouth (Little digesting by lingual lipase) - Triglycerides and phospholipids begin the first digestion step in the mouth as lipids encounter saliva. - The physical action of chewing mixes the food with saliva. The salivary glands produce the enzyme lingual lipase which initiates the process of digestion.  In stomach - Mixed and broken into droplets. - Gastric lipase continues the digestive process when the food reaches the stomach. Collectively the effects of these enzymes on fat digestion are small (No chemical digestion in stomach). In small intestine - As stomach contents enter the small intestine, the fatty material in our food must mix (by emulsification) with the water and fluids of the digestive system. Phospholipids are present in our foods can contribute to the emulsification process. Bile is produced in the liver and stored in the gallbladder until needed, it is the key emulsifier in the small intestine. Bile contains phospholipids which means it has both hydrophilic and hydrophobic properties. It is secreted from the gall bladder into the small intestine to disperses fat into smaller fat droplets - Pancreatic enzymes break triglycerides into two fatty acids and a monoglyceride. - The small droplets of fat surrounded by bile are called micelles. - Fat enters the mucosal cell as a micelles (fatty acids, monoglycerides, phospholipids, and sterols).  How does our body process lipids? Lipoprotein Lipids require handling to travel in the bloodstream. The carriers of triglycerides and cholesterol are called lipoproteins. Lipoproteins are made of phospholipids and proteins (see Figure 19). In the intestinal mucosal cell : - Fatty acids are reattached to the monoglyceride to re-form triglycerides. - A small amount of protein is added to the lipids, forming a chylomicron. - Short- and medium-chain fatty acids absorbed more quickly because they are not arranged into chylomicrons. - Cholesterol does not require any chemical digestion to be absorbed.  Chylomicrons - A lipoprotein produced by cells lining the small intestine. - Composed of triglycerides surrounded by phospholipids and proteins. - Soluble in water. - Transport tool that removes absorbed lipids from the small intestine. Travel through the lymphatic system and transferred to the bloodstream. Cells in the body - Lipoprotein lipase breaks chylomicrons before entering the cell membrane into: Two fatty acids Monoglyceride - After entering the cell, the triglycerides are reformed, which used in:  Used immediately for energy.  Used to make lipid-containing compounds.  Stored in liver and muscle cells.  The liver also produces lipoproteins, but they are different in size and composition than the chylomicron. The lipoproteins that primarily originate from the liver are very low-density lipoproteins (VLDL) and high-density lipoproteins (HDL). Low-density lipoproteins (LDL) are formed from VLDL after it is released from the liver. These lipoproteins are the ones often discussed when assessing a person’s risk for cardiovascular disease  How much lipids should we eat?  The Acceptable Macronutrient Distribution Range (AMDR) for fat 20%–35% of calories should be from fat.  The type of fat consumed is important - Intake of saturated and trans fatty acids should be minimized as much as possible (Saturated fats: no more than 7% of total calories and Trans fatty acids should reduce to the absolute minimum). - Get enough linoleic acid in the diets from vegetable oils. - To ensure an adequate amount of omega-3 fatty acids, we need to consume more dark-green leafy vegetables, walnuts, flaxseeds, and fish or fish oils. - Most fat should be from monounsaturated fats (e.g., olive oil) and polyunsaturated fats (e.g., plant oils).  Recognize the lipids in foods Visible fats are those we can see in foods or can easily have been added to foods, such as dressing or chicken skin. Hidden fats are those occur naturally in foods or added to processed or prepared foods to improve texture or taste, which we may not be aware of such as mixed foods like soups, cookies, or ice cream.  How to reduce lipids in the diet - Reduce your intake of saturated fats. Be conscious of the saturated fat content of meats, baked goods, and snack goods. - Avoid trans fatty acids. - Limit your intake of dietary cholesterol, which will also help limit your intake of saturated fats - Shop and cook smarter. - Select beneficial fats such as omega-3 fatty acids. Consume and cook with vegetables oil as soybean and flaxseed oil. Add walnuts, almonds, and flaxseeds seeds to your diet, consider including fish in your diet at least twice a week or consider taking a fish oil supplement. - Limit fats while eating out.  Fat replacers - Snack foods are frequent targets for fat replacers, substances that can reduce the fat content. - Fat replacers such as olestra have not proved because of potential gastrointestinal side effects. Role of lipids in chronic disease - Cardiovascular disease (CVD) is most closely associated with diets high in saturated fat. - Some cancers are associated with diets high in saturated fats, such as prostate cancer and breast cancer.