NUTRITION CHPT 5
Functions of Cholesterol
Essential component of cell membrane Produced by the liver Found only in animal products Forms important hormones estrogen testosterone vitamin D Precursor to bile acids
Functions of Phospholipids
Emulsifier -Bile acids -Lecithins Improves food products Found in wheat germ, peanuts, yolks, soy beans, organ meat
Triglycerides
Most common form of fats and oils 3 fatty acids attached to a glycerol diglyceride breakdown product of triglyceride consisting of two fatty acids bonded to a glycerol backbone monoglyceride breakdown product of a triglyceride consisting of one fatty acid attached to a glycerol backbone
Types of Lipids and Fats
Types of lipids Triglycerides Phospholipids Sterols (Cholesterol) Fats (solid) and oils (liquid) 9 kcal /gm
Health-Related Effects
DHA, EPA (Omega-3) -Decrease blood clotting -Reduce heart attack -Decrease inflammation -Excess may cause hemorrhagic stroke -Other possible uses: lower triglycerides, rheumatoid arthritis, behavioral disorders
ALL CONCEPTS CHECKS
Concept Check 5.1 1. What is the common property that all lipid compounds share? They do not readily dissolve in water. Concept Check 5.2 1. What are the four possible structural forms of lipid? Lipids are a group of compounds that do not dissolve readily in water. Included in this group are fatty acids, triglycerides, phospholipids, and sterols. 2. In what ways do fatty acids differ from one another? Fatty acids can be distinguished from one another by the length of the carbon skeleton and the number and position of double bonds along that skeleton. 3. What is the difference between a saturated and unsaturated fatty acid, and between an omega-3 and an omega-6 fatty acid? Saturated fatty acids contain no double bonds within their carbon skeleton; that is, they are fully saturated with hydrogens. Monounsaturated fatty acids contain one carbon-carbon double bond, and polyunsaturated fatty acids contain two or more of double bonds. The location of the first double bond on an unsaturated fatty acid is an important feature and will be either 3, 6, or 9 carbons from the methyl end. If the first double bond starts three carbons from the methyl (omega) end of the fatty acid, it is an omega-3 fatty acid. If the first double bond is located six carbons from the omega end, it is an omega-6 fatty acid. 4. Which fatty acids are essential? The essential fats start with the dietary omega-3 and omega-6 parents. Linoleic acid (an omega-6 fatty acid) and alpha-linolenic acid (an omega-3 fatty acid) are called essential fatty acids because we must obtain them from foods to maintain health. 5. How do triglycerides differ from phospholipids? Triglycerides are the major form of fat in the body and in foods. These consist of three fatty acids bonded to a glycerol backbone. Phospholipids are similar to triglycerides in structure, but at least one fatty acid is replaced by another compound containing phosphorus. Phospholipids play an important structural role in cell membranes. 6. What are the main functions of cholesterol in the body? Sterols, another class of lipids, do not resemble either triglycerides or phospholipids, but instead have a multi-ringed structure. Cholesterol, one example of a sterol, forms parts of cells, some hormones, and bile acids. Whereas certain essential fatty acids (as components of triglycerides) are needed in the diet, the body produces all the triglycerides, phospholipids, and cholesterol it needs. Concept Check 5.3 1. Which foods are the most fat-dense (>60% total calories as fat)? Fat-dense foods—those with more than 60% of total calories as fat—include plant oils, butter, margarine, mayonnaise, nuts, bacon, avocados, peanut butter, cheddar cheese, steak, and hamburger. 2. Where is cholesterol found in the food supply? Of the foods we typically eat, cholesterol is found in significant amounts only in those of animal origin, with eggs being a primary source. 3. Which types of fats are used as emulsifiers, and what is their function in food? Phospholipids function as emulsifiers - they are soluble in both fat and water, so they can suspend fats in water. One example of a phospholipid in foods is lecithin. Emulsifiers are added to salad dressings and other fat-rich products to keep the vegetable oils and other fats suspended in the water. 4. What are some strategies used to produce reduced-fat foods? To lower the fat in foods, manufacturers may replace some of the fat with water, protein, or forms of carbohydrates such as starch derivatives, fiber, and gums. Manufacturers also may use engineered fats, such as olestra, that are made with fat and sucrose (table sugar) but that provide few or no calories because they cannot be digested and/or absorbed well. 5. How do fats become rancid and how can this be prevented? The carbon-carbon double bonds in polyunsaturated fatty acids are easily broken, yielding products responsible for rancidity. The presence of antioxidants, such as vitamin E in oils, naturally protects unsaturated fatty acids against oxidative destruction. Manufacturers can use hydrogenated fats and add natural or synthetic antioxidants to reduce the likelihood of rancidity. 6. What happens to unsaturated fats during the process of hydrogenation? Hydrogenation of unsaturated fatty acids is the process of adding hydrogen to carbon-carbon double bonds to produce single bonds. This results in the creation of some trans fatty acids. Hydrogenation changes vegetable oil to solid fat. 7. What regulations are in place to educate and protect the public from the presence of trans fats in foods? The FDA now requires the trans fat content of foods on food labels. The food labels in Canada also must list trans fat content. FDA hopes to make consumers more aware of the amounts of trans fat in foods as well as the negative health consequences associated with their excessive consumption. North American companies are already responding to this issue by creating products free of trans fat. Concept Check 5.4 1. What enzyme is responsible for digestion of triglycerides? In the small intestine, a lipase enzyme released from the pancreas digests dietary triglycerides. 2. What are the end products of fat digestion? Lipase digests dietary triglycerides into monoglycerides (glycerol backbones with single fatty acids attached) and fatty acids. These end products of fat digestion then diffuse into the absorptive cells of the small intestine. 3. What are the differences between the absorption of long- versus short-chain fatty acids? Long-chain fatty acids are transported through the lymphatic system, whereas fatty acids with shorter carbon chains are absorbed directly into the portal vein that connects directly to the liver. Concept Check 5.5 1. How do lipids move through the bloodstream? Lipids generally move through the bloodstream as part of lipoproteins. 2. How are dietary fats packaged in the small intestine and transported? Dietary fats absorbed from the small intestine are packaged and transported as chylomicrons. 3. Where are VLDLs made and what do they contain? Lipids synthesized in the liver are packaged as very-low-density lipoproteins (VLDL). VLDLs contain mostly triglycerides with a smaller proportion of cholesterol and protein. 4. Where do the LDLs originate and what is their destination? Lipoprotein lipase removes triglycerides from the interiors of both chylomicrons and VLDL, breaking the triglycerides down into glycerol and fatty acids, which are taken up by tissues for energy needs or storage. What remains after the action of lipoprotein lipase are chylomicron remnants (from chylomicrons), the components of which are recycled by the liver, or low-density lipoproteins (LDL, from VLDL), rich in cholesterol. LDL is picked up by receptors on body cells, especially liver cells. Scavenger cells in the arteries may do the same, speeding the development of atherosclerosis. 5. Why are HDLs considered "good" cholesterol? High-density lipoproteins (HDLs), also produced in part by the liver, pick up cholesterol from cells and transport it primarily to other lipoproteins for eventual transport back to the liver. Risk factors for cardiovascular disease include an elevated level of LDL and/or low amounts of HDL in the blood. Concept Check 5.6 1. What are the functions of triglycerides in the body? Triglycerides are the major form of fat in the body. They are used for energy and stored in adipose tissue, they insulate and protect body organs, and they transport fat-soluble vitamins. 2. Where are phospholipids found in the body? Phospholipids are emulsifiers—compounds that can suspend fat in water. They are found in cell membranes and lipoproteins. They are also a component of bile, which emulsifies fats in the small intestine. 3. What are some compounds that are made from cholesterol in the body? Cholesterol, a sterol, forms part of cell membranes, hormones, and bile acids. If sufficient amounts are not consumed, the body makes what phospholipids and cholesterol it needs. Concept Check 5.7 1. How does the percent of calories as fat in the North American diet compare to recommendations? There is no RDA for fat. We need about 5% of total calorie intake from plant oils to obtain adequate essential fatty acids. Eating fatty fish at least twice a week is also advised to supply omega-3 fatty acids. Many health-related agencies recommend a diet containing no more than 35% of calorie intake as fat, with no more than 7% to 10% of calorie intake as a combination of saturated fat and trans fat for the general public. 2. What is the limit for cholesterol intake? Cholesterol intake should be limited to 300 milligrams per day. 3. What are the characteristics of the Mediterranean diet? The major sources of fat in the Mediterranean diet include liberal amounts of olive oil compared to a small amount of animal fat (from animal flesh and dairy products). The diet is rich in foods of plant origin, including whole grains, legumes, fruits, vegetables, and herbs. The Mediterranean diet also allows for moderate alcohol consumption (usually in the form of red wine, which contains many antioxidants).
Fatty Acids and Triglycerides
Found in our body and foods In triglycerides, composed of three fatty acids bonded to glycerol, an alcohol Saturated fatty acids, higher in animal fats Solid form Unsaturated fatty acids, higher in plant foods Liquid form Cis and trans Fats are composed of both saturated and unsaturated
Omega-6 Fatty Acid
Found in vegetable oils Need is about 2-4 tablespoons a day
Excessive Trans Fatty Acid Intake
Increases risk for cardiovascular disease Required to be listed on food labels
Omega-3 Fatty Acid
Primarily from nuts, seeds, fish oil, flax seed oil Also found in canola, walnuts, mussels, crab, shrimp, and soybean oil Recommended intake of ~2 servings of fish per week
Omega-3 Fatty Acid pt2
Primarily from nuts, seeds, fish oil, flax seed oil Also found in canola, walnuts, mussels, crab, shrimp, and soybean oil Recommended intake of ~2 servings of fish per week
Functions of Fatty Acids
Provide energy Efficient storage of energy Insulating and protecting body Transport fat-soluble vitamins A, D, E, and K Phospholipids, become part of cell membrane Cholesterol, becomes part of hormones, estrogen, testosterone, and precursor of active vitamin D hormone Structural component in cells and lipoproteins
Goal of Healthy People 2020
Reduce consumption of saturated fat in population ages 2 years and older to 9.5% of total calorie intake Total fat intake may exceed 35% of total kcal as long as saturated and trans fat intakes are minimal Eat plenty of fruits and vegetables Cut down on red meats Cut down on simple sugars and refined carbohydrates Promote healthy weight Be active
Phospholipids
Built on a glycerol backbone Contains phosphorus compound(s) Found in body Synthesized by the body as needed Component of cell membranes
Cardiovascular Disease
Leading cause of death in North America 600,000 people die each year Annual cost is $108.9 billion each year Myocardial infarction death of part of heart muscle also termed a heart attack Cerebrovascular accident death of part of brain tissue due typically to a blood clot also termed a stroke
Fat Is Hidden in Some Foods
Look on the Nutrition Facts labels Look on the lists of ingredients Control portion size
sterols
Multi-ringed structure Do not have a glycerol backbone Cholesterol is a sterol Waxy substance Do not readily dissolve in water Found in animal foods
Essential Fatty Acids
Must be supplied by the diet to maintain health Omega-3 fatty acid (alpha-linolenic acid) Omega-6 fatty acid (linoleic acid) immune system function and vision help form cell membranes produce eicosanoids, which are involved in practically all important functions in the body
Recommendations for Fat Intake
No RDA AMDR: 20% to 35% of total kilocalories (44 to 78 g/d) 2015 - 2020 Dietary Guidelines Limit saturated fats to <10% of total kcal Shift from using solid fats to oils AHA Diet and Lifestyle Recommendations for Cardiovascular Disease Risk Reduction (2006) Limit saturated fats to <7% of total kcal Limit trans fats to <1% of total kcal Limit cholesterol to <300 mg/d Average U.S. intake: 33% of total kcal from fat 13% of kcal from saturated fat 180-320 mg cholesterol/day
Hydrogenation of Fatty Acids
Process used to solidify an oil Addition of H to C=C double bonds Increases shelf life of food product Formation of trans fatty acid (similar to shape of saturated fatty acid) Presents health risk like saturated fats
Benefits of a High HDL level
Removes cholesterol from the bloodstream HDL may block oxidation of LDL Reduces risk of cardiovascular disease Pre-menopausal women have higher HDL
High-Density Lipoprotein (HDL)
Synthesized by liver and intestine High proportion of protein Picks up cholesterol from dying cells and other sources Transfers cholesterol to other lipoproteins Transfers cholesterol directly back to the liver
