Nutrition chapter 5

Differentiate between food cholesterol and blood cholesterol.

Food cholesterol is the waxy lipid substance found in animal foods. When we consume food cholesterol, the body digests the dietary cholesterol. The liver uses the components of the cholesterol and saturated fatty acids to formulate new lipids. Blood cholesterol includes cholesterol formed by the liver that is distributed throughout the body. Blood cholesterol also includes cholesterol that has been discarded by the cells and is traveling out of the body for either reuse or excretion.

Describe how a patient could be counseled to decrease fat consumption over time rather than all at once.

To decrease fat intake over time, these steps can be followed: (1) Record all food and beverages consumed for 1 week. At the end of the week, assess which foods are likely to be high in fat. Note which high-fat foods are eaten on a regular basis. (2) The following week, choose one of these foods, and either replace it with a lower-fat option or eat it less often. (3) The next week, do the same with another high-fat food. Continue to follow this pattern until fat intake is between 25% and 30% of the total kcal intake.

What is the function of bile in fat digestion? Which hormone signals bile release?

Bile emulsifies fats to facilitate digestion. Cholecystokinin (CCK) signals the release of bile from the gallbladder as fat enters the small intestine.

1. List three functions of fats (triglycerides) in food and three physiologic functions of fats (triglycerides).

Functions of fats in foods include (1) providing energy; (2) providing palatability of taste; (3) carrying vitamins A, D, E, and K and providing essential fatty acids; (4) providing satiety and preventing hunger between meals; and (5) performing functions in food processing. Physiologic functions include energy reserve, organ protection, body temperature regulation, and transmission of nerve impulses.

Summarize fat digestion.

In the mouth, mechanical digestion breaks food into smaller pieces. In the stomach, chemical digestion by enzymes hydrolyzes fatty acids and peristalsis continues. In the small intestine, chemical digestion continues as cholecystokinin (CCK) is released in response to fats entering the duodenum. CCK causes the release of bile, which emulsifies fats. The combination of chemical and mechanical digestion exposes the fats' surface area to pancreatic lipase, which breaks triglycerides into glycerol, monoglycerides, and fatty acids. Fat is absorbed in the small intestine. In the large intestine, some fats are partially digested, but the rest pass through unchanged into feces.

What is ketosis and what causes it?

Ketosis is the accumulation of ketone bodies in the blood. Ketone bodies are formed when fat is broken down quickly because of a lack of carbohydrate for energy. The liver cells form intermediate products from partially oxidation of fatty acids, called ketone bodies.

Describe the structures and functions of phospholipids and sterols.

Phospholipids contain two fatty acids with a phosphate group attached to a backbone of glycerol. They act as fat emulsifiers and are a component of cell walls. Because they are manufactured by the body, phospholipids are not essential nutrients. Sterols consist of carbon rings with side chains of carbon, hydrogen, and oxygen. Functions include being part of complex regulatory compounds and a constituent of bile, vitamin D, sex hormones and other hormones, and cells in the brain and nerve tissues. Cholesterol in particular is a vital part of all cell membranes and nerve tissues, and serves as a building block for hormones. As with phospholipids, sterols are not essential nutrients because they are manufactured by the body.

Name four synthetic fats or fat replacers.

Simplesse, carrageenan, salatrim, and olestra are synthetic fats or fat replacers.

What is the distinguishing characteristic between saturated, monounsaturated, and polyunsaturated fatty acids?

The distinguishing characteristic is the number of unsaturated double bonds. Saturated fatty acids have no double bonds, monounsaturated fats have one, and polyunsaturated fats have two or more.

Identify the essential fatty acids (EFAs). Why are they essential?

The essential fatty acids (EFAs) are linoleic and linolenic fatty acids. These fatty acids are essential because they cannot be manufactured by the body and must be consumed in the diet. EFAs are required components of compounds such as prostaglandins and cell membranes. Vegetable oils are a primary source of linoleic acid. Linolenic acid is associated with fish consumption.

How do fats aid in food preservation? Discuss the roles of hydrogenation and antioxidants.

Unsaturated fats in foods are more easily oxidized than saturated fats and can become rancid more quickly, which leads to decreased shelf life. Rancidity of fats changes the flavor of the food product and produces bad odors and may cause illness. To increase shelf life, the process of hydrogenation became popular. By adding hydrogen to unsaturated fats, they become more stable and are less likely to become rancid. However, hydrogenation results in the formation of trans fatty acids, which have adverse effects on the heart, leading to an increased risk of developing cardiovascular disease. Antioxidants also reduce oxidation and therefore rancidity in foods containing fat. Natural forms of antioxidants include vitamins E (tocopherol) and C (ascorbic acid). Synthetic forms include butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT).

Explain the functions of very low-density lipoprotein cholesterol (VLDL), low-density lipoprotein cholesterol (LDL), and high-density lipoprotein cholesterol (HDL) and their relationships to the development of plaque formation.

Very low-density lipoproteins (VLDLs) are the first to leave the liver and contain large quantities of fats and lipid components. As the lipids circulate within the blood, fats are deposited for use by the body's cells. As the density of the lipoproteins changes, they become low-density lipoproteins (LDLs). LDLs carry cholesterol throughout the body to tissue cells, but may also deposit cholesterol along the arterial walls as they circulate in the bloodstream. These deposits can lead to the buildup of plaques and atherosclerosis. High-density lipoproteins (HDLs) are formed within cells; HDLs remove cholesterol from the cells for disposal by the liver, and thus are considered "good cholesterol."