Lipids; Fats and Oils
Lipids
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| Fats and Oils |
Recommended Fat Intakes:
Fats are an essential part of a healthful diet but, for optimal health, the total amount and type of fat consumed need careful attention. There is no RDA for fat, but there is an adequate intake for infants. The institute of Medicine's Acceptable Macronutrient Distribution Range for total fat is 20-35% of calories for most age groups. A total fat intake that exceeds 35% of calories often means saturated fat intake is too high. A low intake of total fat (less than 20% of calories) increases the chances of getting too little vitamin E and essential fatty acids and may adversely affect blood levels of triglycerides and a type of cholesterol called high-density lipoprotein (HDL) cholesterol, which is sometimes called good cholesterol.
Infants and children younger than 2 years need to get about half their total calories from fat to meet calorie needs and to obtain sufficient fat for normal brain development. For children 2 to 3 years of age, keep total fat intake between 30 and 35% of calories. Between the ages of 4 and 18 years, keep fat intake between 25 and 35% of calories.
Fat Digestion & Absorption:
The body is very efficient at digesting and absorbing dietary fat. Lipid digestion and absorption take place in the small intestine. Enzymes made by the mouth, stomach, pancreas, and small intestine, as well as bile from the liver, participate in the process of digestion.
Digestion Steps:
1. Mouth:
Lingual lipase is secreted. Little or no fat is digested.
2. Stomach:
Gastric lipase is secreted. Little fat is digested.
3. Liver:
The liver produces bile, which is stored and released by the gallbladder into the common bile duct, which empties into the small intestine. Bile emulsifies fat.
4. Pancreas:
The pancreas secretes pancreatic lipase, phospholipase, and cholesterol esterase into the common bile duct, which empties into the small intestine. Pancreatic lipase digests triglycerides. Phospholipase digests phospholipids. Cholesterol esterase digests cholesterol.
5. Small Intestine:
Fat is digested Fat is digested and absorbed in the duodenum and jejunum. Bile is reabsorbed in the ileum.
6. Large Intestine:
Less than 5% of fat passes through the large intestine and is excreted.
Absorption Steps:
1. Large fat droplets enter small intestine after meal.
2. Bile (mostly) and lecithin emulsify fats into smaller particles.
3. Lipase breaks down fat into fatty acids and monoglycerides.
4. Monoglycerides and fatty acids are absorbed as micelles through the brush border and then reformed into triglycerides.
5. Short- and medium- chain fatty acids enter the bloodstream.
6. Triglycerides combine with cholesterol, protein, and phospholipids to form chylomicrons, which enter the lymphatic system.
Health Concerns Related to Fat Intake:
Dietary fat is essential for good health. However, high intakes can adversely affect health status.
High Polyunsaturated Fat Intake:
Intakes of polyunsaturated fats greater than 10% of total calorie intake seem to increase the amount of cholesterol deposited in arteries, which raises the chances of developing cardiovascular disease. High intakes also may impair the immune system's ability to fight disease.
Excessive Omega-3 Fatty Acid Intake:
Diets that include fish rich in omega-3 fatty acids twice a week can reduce blood clotting abilities and may favorably affect heart rhythm in some people _both of these effects help lower the chances of having a heart attack. Larger intakes of fish further reduce the risk of heart disease by lowering blood triglyceride levels in those whose levels are high. However, an excessive intake of omega-3 fatty acids may impair the functions of the immune system, allow uncontrolled bleeding, and cause hemorrhagic stroke. Excessive levels of omega-3's are usually the result of supplement use.
Imbalances in Omega-3 and Omega-6 Fatty Acids:
On average, Americans consume 20 times more omega-6 fatty acids than omega-3's. Both fatty acids use the same metabolic pathways; as a result, they compete with each other. Thus, the body may not have enough of some compounds and too much of others. For example, omega-6 fatty acid can be converted to arachidonic acid, which then can be used to make inflammation-causing eicosanoids called prostaglandins. In contrast, the omega-3 fatty acids EPA and DHA can be made into substances that help decrease inflammation , pain, and blood triglycerides. Low intakes of omega-3's may worsen inflammatory diseases, such as arthritis.
Intake of Rancid Fats:
Rancid fats smell and taste bad. They also contain compounds that can damage cells. Polyunsaturated fats go rancid fairly easily because their double bonds are easily damaged by oxygen, heat, metals, or light. The broken double bonds cause the polyunsaturated fats to decompose. Saturated and trans fats are less susceptible to rancidity because they have no or few double bonds in their carbon chains.
The foods most likely to become rancid are those high in polyunsaturated fats (e.g., fish and vegetable oils), packaged fried foods (e.g., potato chips), and fatty acid with a large surface area (e.g., powdered egg yolks). To prevent rancidity, food manufactures can break the double bonds and add hydrogen. Or they can protect the double bonds in fats by sealing foods in airtight packages or adding antioxidants, such as nutrients, or additives.
Diets High in Trans Fat:
Trans fatty acids from hydrogenated fats have harmful health effects. Hydrogenated fats were popular for many years because they helped food manufactures produce high quality baked and fried products. For example, some foods are more pleasing when made with solid fats. Pastries and pies made with oil tend to be oily and mealy, whereas those made with solid fats are flaky and crispy. Although solid fat from animals, such as butter or lard, could be used instead of hydrogenated fat, hydrogenated fat is cholesterol free. Another advantage of hydrogenation is that it delays fat decomposition and spoilage in packaged foods.
Despite any advantages of hydrogenation, consuming trans fatty acids raises blood cholesterol levels, which increases the risk of heart disease. In addition, trans fats lower HDL cholesterol and increase inflammation in the body. The diets that rich in trans fats raises body weight and the amount of body fat stored in the abdomen, even when calories are at levels that should only maintain weight. Much of the stored abdominal fat is visceral fat, which increases the risk of type 2 diabetes.
To help people control trans fat intake, the FDA now requires trans fats to be on Nutritional Facts labels. To lower the trans fat levels in foods, food manufactures have reformulated many products to make them trans fat free. The reformulated products often use interesterified fats, which are made by interchanging the fatty acids in solid fats and liquid oils. This interchange creates a fat with properties similar to trans fats __that is, it is solid at room temperature, stands up to high temperature cooking methods, and stays fresh a long time. Interesterified fats appear to be healthier than trans fats, but more research is needed.
Both trans and interesterified fat intake can be kept to a minimum when eating out by limiting fried foods, pastries, flaky bread products (e.g., pie crusts, crackers, croissants, and biscuits), and cookies. At home, keep intake of these fats under control by using little or no stick margarine or shortening. Instead, substitute vegetable oils and squeeze margarine. Applesauce and fruit purees can be substituted for shortening in many baked goods. Also, to avoid deep-fat frying in shortening, try baking, pan-frying, broiling, steaming, grilling, or stir frying. Most nondairy creamers are rich in hydrogenated vegetable oils, so replace them with reduced fat milk or nonfat dry milk.
Diets High in Total Fat:
Diets high in total fat increases the risk of obesity, certain types of cancer and cardiovascular disease. Diets high in fat, especially saturated fat, may increase the risk of colon, prostate, and breast cancer. Although it is not known how high fat diets increase risk, 1 theory related to colon cancer is that bile, which is secreted into the intestine to emulsify dietary fat, may irritate colon cells. As fat intake rises, more bile is secreted, which then irritates the cells more intensely and frequently, perhaps damaging them and causing them to become cancerous. In the case of breast and prostate cancer, the risk of both climbs as blood levels of estrogen hormones rise. High fat diets elevate blood lipid levels, which in turn raise blood estrogen levels. In contrast, low fat diets seem to lower blood estrogen levels. Another possible explanation of the relationship between fat diets and cancer is that high fat diets usually are low in fiber and other phytonutrients __thus, high fat diets may lack the protective plant compounds that help prevent certain cancers.
Lowering the intake of dietary diets is way to help control calorie intake and avoid being overfat. Obesity is linked with a greater risk of cancer of the colon, breast and uterus.
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