Chapter Summary, Questions Answers - Nutrition

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Chapter: Biochemistry : Nutrition

The Dietary Reference Intakes (DRIs) provide estimates of the amounts of nutrients required to prevent deficiencies and maintain optimal health and growth.


The Dietary Reference Intakes (DRIs) provide estimates of the amounts of nutrients required to prevent deficiencies and maintain optimal health and growth. It consists of the Estimated Average Requirement (EAR), the average daily nutrient intake level estimated to meet the requirement of 50% of the healthy individuals in a particular life stage (age) and gender group; the Recommended Dietary Allowance (RDA), the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97%–98%) individuals in a life stage and gender group; the Adequate Intake (AI), which is set instead of an RDA if sufficient scientific evidence is not available to calculate the RDA; and the Tolerable Upper Intake Level (UL), the highest average daily nutrient intake level that is likely to pose no risk of adverse health effects to almost all individuals in the general population. The energy generated by the metabolism of the macronutrients is used for three energy-requiring processes that occur in the body: resting metabolic rate, physical activity, and thermic effect of food. Acceptable Macronutrient Distribution Ranges (AMDR) are defined as the ranges of intake for a particular macronutrient that are associated with reduced risk of chronic disease while providing adequate amounts of essential nutrients. Adults should consume 45%–65% of their total calories from carbohydrates, 20%– 35% from fat, and 10%–35% from protein (Figure 27.23 ). Elevated levels of cholesterol in low-density lipoproteins (LDL-C) result in increased risk for cardiovascular disease. In contrast, high levels of cholesterol in high-density lipoproteins (HDL-C) have been associated with a decreased risk for heart disease. Dietary or drug treatment of hypercholesterolemia is effective in decreasing LDL-C, increasing HDL-C, and reducing the risk for cardiovascular events. Consumption of saturated fats is strongly associated with high levels of total plasma and LDL-C. When substituted for saturated fatty acids in the diet, monounsaturated fats lower both total plasma cholesterol and LDL-C but maintain or increase HDL-C. Consumption of fats containing w-6 polyunsaturated fatty acids lowers plasma LDL-C, but HDL-C, which protects against coronary heart disease, is also lowered. Dietary w-3 polyunsaturated fats suppress cardiac arrhythmias and reduce serum triacylglycerols, decrease the tendency for thrombosis, and substantially reduce the risk of cardiovascular mortality. Carbohydrates provide energy and fiber to the diet. When they are consumed as part of a diet in which caloric intake is equal to energy expenditure, they do not promote obesity. Dietary protein provides essential amino acids. The quality of a protein is a measure of its ability to provide the essential amino acids required for tissue maintenance. Proteins from animal sources, in general, have a higher-quality protein than that derived from plants. However, proteins from different plant sources may be combined in such a way that the result is equivalent in nutritional value to animal protein. Positive nitrogen balance occurs when nitrogen intake exceeds nitrogen excretion. It is observed in situations in which tissue growth occurs, for example, in childhood, pregnancy, or during recovery from an emaciating illness. Negative nitrogen balance occurs when nitrogen losses are greater than nitrogen intake. It is associated with inadequate dietary protein; lack of an essential amino acid; or during physiologic stresses such as trauma, burns, illness, or surgery. Kwashiorkor occurs when protein deprivation is relatively greater than the reduction in total calories. It is characterized by edema. Marasmus occurs when calorie deprivation is relatively greater than the reduction in protein. Both are extreme forms of protein-energy malnutrition (PEM).

Figure 27.23 Key concept map for the macronutrients. *Note: Trans fatty acids are chemically classified as unsaturated. PEM = protein energy malnutrition; LDL = low-density lipoprotein; C = cholesterol.

Study Questions
Choose the ONE best answer.


27.1 For the child shown at right, which of the statements is true and supports a diagnosis of kwashiorkor? The child:

A. appears plump due to increased deposition of fat in adipose tissue.

B. displays abdominal and peripheral edema.

C. has a serum albumin level above normal.

D. has markedly decreased weight for height.

The correct answer = B. Kwashiorkor is caused by inadequate protein intake in the presence of fair to good energy (calorie) intake. Typical findings in a patient with kwashiorkor include abdominal and peripheral edema (note the swollen belly and legs) caused largely by a decreased serum albumin concentration. Body fat stores are depleted, but weight for height can be normal. Treatment includes a diet adequate in calories and protein.


27.2 Which one of the following statements concerning dietary fat is correct?

A. Coconut oil is rich in monounsaturated fats, and olive oil is rich in saturated fats. B. Fatty acids containing trans double bonds, unlike the naturally occurring cis isomers, raise high-density lipoprotein cholesterol levels.

C. The polyunsaturated fatty acids linoleic and linolenic acids are required components.

D. Triacylglycerols obtained from plants generally contain less unsaturated fatty acids than those from animals.

Correct answer = C. We are unable to make linoleic and linolenic fatty acids. Consequently, these fatty acids are essential in the diet. Coconut oil is rich in saturated fats, and olive oil is rich in monounsaturated fats. Trans fatty acids raise plasma levels of low-density lipoprotein cholesterol, not high-density lipoprotein cholesterol. Triacylglycerols obtained from plants generally contain more unsaturated fatty acids than those from animals.


27.3 Given the information that a 70-kg man is consuming a daily average of 275 g of carbohydrate, 75 g of protein, and 65 g of fat, which one of the following conclusions can reasonably be drawn?

A. About 20% of calories are derived from fats.

B. The diet contains a sufficient amount of fiber.

C. The individual is in nitrogen balance.

D. The proportions of carbohydrate, protein, and fat in the diet conform to current recommendations.

E. The total energy intake per day is about 3,000 kcal.

Correct answer = D. The total energy intake is (275 g carbohydrate × 4 kcal/g) + (75 g protein × 4 kcal/g) + (65 g fat × 9 kcal/g) = 1,100 + 300 + 585 = 1,985 total kcal/day. The percentage calories from carbohydrate is 1,100/1,985 = 55, percentage calories from protein is 300/1,985 = 15, and percentage calories derived from fat is 585/1,985 = 30. These are very close to current recommendations. The amount of fiber or nitrogen balance cannot be deduced from the data presented. If the protein is of low biologic value, a negative nitrogen balance is possible.


For Questions 27.4 and 27.5:


A sedentary 50-year-old man weighing 80 kg (176 pounds) requests a physical. He denies any health problems. Routine blood analysis is unremarkable except for plasma total cholesterol of 295 mg/dl. (Reference value is less than 200 mg.) The man refuses drug therapy for his hypercholesterolemia. Analysis of a 1-day dietary recall showed the following:

Kilocalories 3,475 kcal

Protein 102 g

Carbohydrate 383 g

Fiber 6 g

Cholesterol 822 mg

Saturated fat 69 g

Total Fat 165 g


27.4 Decreasing which one of the following dietary components would have the greatest effect in lowering the patient’s plasma cholesterol?

A. Carbohydrate

B. Cholesterol

C. Fiber

D. Monounsaturated fat

E. Polyunsaturated fat

F. Saturated fat

Correct answer = F. The intake of saturated fat most strongly influences plasma cholesterol in this diet. The patient is consuming a high-calorie, high-fat diet with 40% of the fat as saturated fat. The most important dietary recommendations are lower total caloric intake, substitute monounsaturated and polyunsaturated fats for saturated fats, and increase dietary fiber. A decrease in dietary cholesterol would be helpful but is not a primary objective.


27.5 What would you need to know to estimate the total energy expenditure of the patient?

The daily basal energy expenditure (estimated resting metabolic rate/hour x 24 hours) and an activity factor (AF) based on the type and duration of physical activities are needed variables. An additional 10% would be added to account for the thermic effect of food. Note that if the patient were hospitalized, an injury factor (IF) would be included in the calculation, and the AF would be modified. Tables of AFs and IFs are available.

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