12: Biochemistry, Nutrition, and Nutritional Counseling

Biochemistry, Nutrition, and Nutritional Counseling

Humans, as multicellular organisms, require specific chemicals or nutrients from food to grow, maintain homeostasis, and achieve optimal health. An understanding of cellular biochemistry and nutrition is essential for preventing and treating disease and for promoting health. Nutrition science includes the intake of food and the processes involved in digestion, absorption, transportation, metabolism of nutrients, and excretion. As an applied science, it involves counseling people to adapt food patterns to nutritional needs within the cultural, economic, and psychosocial environment. Nutritional assessment counseling, when performed effectively, motivates individuals to modify eating behaviors so that optimal health can be achieved.

This chapter reviews the six major nutrient groups and their metabolic activities in mammalian cells, dietary modifications for diseases, nutritional diseases and disorders, and oral manifestations of nutritional deficiencies and toxicities. The effects of nutrients on oral tissues and the dietary assessment tools and techniques available for counseling individuals with various types of oral diseases are also described. Because nutritional problems in the developed countries are a result of overeating and undereating, a review of energy balance and weight control is included. Cellular biochemistry is fundamental to the study of nutrition; therefore, the reader is referred to the “General Histology” section in Chapter 2 for a review of structural and functional similarities in cells.

Six Major Classes of Essential Nutrients


Definition—polyhydroxy aldehydes or ketones that serve as the body’s primary sources of quick energy; carbohydrates (CHO) are composed of monosaccharides, basic units that contain carbon, hydrogen, and oxygen

Basic chemical structure


1. Simple carbohydrates

a. Monosaccharides

b. Disaccharides—composed of two monosaccharide units

c. Oligosaccharides—composed of two to six monosaccharide units

2. Complex carbohydrates

a. Homopolysaccharides—made up of more than six identical monosaccharide units

b. Heteropolysaccharides—carbohydrates associated with noncarbohydrates or carbohydrate derivatives

Digestion, absorption, and transport

1. Digestion (Table 12-1)

a. Mouth

b. Stomach—no digestive enzymes for carbohydrates; initial enzymatic hydrolysis of starch by salivary amylase may continue

c. Small intestine

d. Large intestine—bacterial “fermentation” of some undigested carbohydrates

2. Absorption (Figure 12-1)

Metabolism—glucose is the main immediate source of energy for the body; a glucose level of 70 to 120 mg/100 mL blood is maintained by most healthy persons (Figure 12-2)

1. Sources of blood glucose

2. Reactions of blood glucose—”burned” (oxidized) for energy

3. Storage for reserve use

4. Conversion to other molecules, such as:

Metabolic regulators


1. Definition—substance, usually nonstarch polysaccharide, found in plants; not broken down by human digestive enzymes; some of it is digested by bacteria in the gastrointestinal (GI) tract

2. Epidemiologic studies indicate that individuals whose diets include a significant amount of fiber have a low incidence of chronic “Western” diseases, for example, coronary heart disease, diabetes, atherosclerosis

3. Specific fibers are believed to play roles in decreasing the incidence of obesity, irregularity, hemorrhoids, appendicitis, diverticulosis, colon cancer, hyperlipidemia, and fluctuations in blood glucose (Table 12-2)

TABLE 12-2

Dietary Sweeteners


NA, not applicable.

*Sucrose = 1.

Adapted from Hubrich B, Nabors LO. Glycemic Response. In Formulating Glycemic Strategies, a supplement to Food Product Design. July 2006, pp 3–17. July 2006, pp. 3–17.

4. Excessive dietary fiber

5. Recommended fiber intake—for adults, 20 to 30 grams per day (g/day); an upper limit of 35 to 40 g/day is recommended for individuals with a family history of diet-implicated cancer; a limit of 50 g/day is recommended for diabetics

Biologic role and functions of carbohydrates

Role in oral biology

1. Pre-eruptive effect on teeth

2. Post-eruptive effect on teeth

a. Energy source for oral cariogenic bacteria (e.g., Streptococcus mutans)

b. Acidogenic bacteria metabolize monosaccharides and disaccharides, particularly sucrose, for the production of energy through glycolysis that results in the formation of lactic acid, pyruvate, and other acetyl–CoA–dependent on the conditions

c. S. mutans synthesizes polysaccharides (glucans, levans, and glycogen) from sucrose

d. The firm texture of some complex carbohydrates, as found in raw fruits and vegetables, can help to remove food debris retained between teeth; the chewing action can also stimulate salivary flow

3. Dietary sweeteners (see Table 12-2)

a. Nutritive sweeteners are used by the body as an energy source; they provide calories

b. Nonnutritive sweeteners are calorie free and have no nutritive value; aspartame, saccharin, and acesulfame-K are nonnutritive sweeteners approved by the U.S. Food and Drug Administration (FDA); are noncariogenic

c. Aspartame should be avoided by patients who have phetylketonuria, a genetic disorder characterized by an inability to metabolize the amino acid phenylalanine

d. Food labels often list sugar content in its various forms (e.g., invert sugars, dextrose, fructose, corn sweeteners) to give an appearance of lower sugar content

4. Cariogenicity factors of diet habits (from most to least important)

a. Intake frequency of simple sugars—the more frequent the exposure to sugar, the more cariogenic is the diet; six candy bars eaten at six different times during the day are more harmful in terms of acid and bacterial plaque formation than six candy bars consumed at the same time

b. Form of simple sugars (liquid or retentive)—liquid sweets clear the oral cavity faster than solid or retentive sweets do and therefore are less cariogenic

c. Time of ingestion of simple sugars—combining sweets with liquids and other noncariogenic foods during a meal is less cariogenic than a concentrated exposure to sweets between meals as a snack

d. Total intake of simple sugars—average daily intake of sugar is 22 teaspoons; the majority of our simple sugar intake comes from soft drinks, fruit drinks, desserts, candies, and ready-to-eat cereals. The American Heart Association (AHA) recommends 6 teaspoons per day for women and 9 teaspoons for men1

e. Starch-rich foods that are retained on the teeth for prolonged periods are ultimately degraded to organic acids and can contribute to the production of dental caries

f. Combining cariogenic foods with noncariogenic foods—recent studies indicate that certain cariogenic foods (e.g., canned pears in syrup) are less cariogenic when combined with a particular noncariogenic food (e.g., cheese)

5. Importance of carbohydrates in periodontal health


Dietary modifications for persons with disease conditions

1. Obesity—reduce total calories and percentage of simple carbohydrates (concentrated sweets) to increase the nutrient density of a lower-calorie diet

2. Genetic defects

a. Lactose intolerance (inability to hydrolyze lactose)—eat fewer milk products, use fermented products, or add a commercial lactose enzyme (lactase) to milk

b. Galactosemia—congenital inability to metabolize galactose; lactose and milk products should be removed from the diet

c. Fructose intolerance—congenital inability to metabolize fructose; fructose and sucrose should be removed from the diet; individuals with fructose intolerance have significantly fewer dental caries

3. Dental caries and periodontal disease—a protective diet should be implemented

a. A diet that is low in retentive carbohydrates

b. Avoidance of cariogenic snacks

c. A diet that is adequate in all nutrients (Table 12-3)

d. Inclusion of foods of firm or hard texture

4. Diabetes (inability to regulate glucose because of insufficiency or relative ineffectiveness of insulin)—dietary treatment (see the section on “Diabetes Mellitus” in Chapter 19)

a. Two major forms

b. Signs and symptoms of diabetes mellitus

c. Dietary recommendations

5. Reactive hypoglycemia—rare; symptoms of dizziness, hunger, and heart palpitations are lessened with a low-carbohydrate diet

6. Dumping syndrome—occurs after gastric surgery; postprandial symptoms of nausea, dizziness, cramping, and diarrhea are lessened by a low-monosaccharide, low-disaccharide diet

7. Alcoholism—overconsumption of alcohol may cause malnutrition (see the section on “Chronic Alcohol Abuse and Dependence” in Chapter 19)

8. Alcohol consumption during pregnancy—has a direct teratogenic effect on the developing fetus: fetal alcohol syndrome (see the section on “Fetal Alcohol Spectrum Disorders” in Chapter 19)

9. Carbohydrate regulation in some hyperlipoproteinemias—total carbohydrate and alcohol intake is controlled; concentrated sweets are restricted


Definition—complex biologic compounds of high molecular weight that contain nitrogen, hydrogen, oxygen, carbon, and small amounts of sulfur; each protein has a specific size and is made up of amino acid building blocks linked through peptide bonds in a specific arrangement


1. Chemical

2. Biologic

a. Complete proteins contain sufficient amounts of the essential amino acids for normal metabolic reactions; found in foods of animal origin

b. Incomplete proteins have insufficient quantities of one or more essential amino acids to support protein synthesis in humans; plant proteins are often incomplete (e.g., corn protein is low in lysine; legume protein is low in methionine)

c. Complementary proteins are proteins that are incomplete when ingested singly but, when combined, provide sufficient essential amino acids

d. Protein quality is a measure of a protein’s ability to support protein synthesis; it is measured by comparing the test protein with a reference protein, usually egg protein

(1) Amino acid or protein chemical score (CS)—compares the essential amino acid content in a dietary protein to that of a reference protein

(2) Protein efficiency ratio (PER)—measures a protein’s ability to support growth

(3) Biologic value (BV)—expression of the percentage of nitrogen retained for maintenance and growth compared with the amount absorbed

(4) Net protein utilization (NPU)—expression of the percentage of retained nitrogen compared with the amount ingested; differs from BV because it takes into account the protein’s digestibility

(5) Protein-digestibility-corrected amino acid score (PDCAAS)—compares the amino acid balance of a food protein with the amino acid requirements of preschool-aged children and then corrects for digestibility; used by the FDA for labeling


Digestion, absorption, and transport (see Table 12-1 and Figure 12-1)

1. Mouth—mechanical breakdown and moistening

2. Stomach

3. Small intestine

4. Absorption—at the brush border of the microvilli of the small intestine, absorption occurs both by simple diffusion along a concentration gradient and by active transport at specific amino acid sites involving carrier enzymes, a sodium–ATP pump, and vitamin B6

5. Transport—absorbed amino acids collected by the portal blood system and transported to the liver

Metabolism (see Figure 12-2)

1. Amino acid pool—a collection of amino acids in a dynamic equilibrium in the liver, blood, and other cells that provides the raw material for the body’s protein and amino acid needs

2. Anabolism

a. De novo synthesis—requires deoxyribonucleic acid (DNA), messenger ribonucleic acid (mRNA), and ribosomal ribonucleic acid (rRNA)

b. Transamination

3. Catabolism—amino acids in excess of those needed for the synthesis of proteins and other biomolecules cannot be stored or excreted; they may, however, be deaminated and the α-keto acid used as a metabolic fuel for immediate energy needs or for long-term energy storage as fat

a. Amino group

b. α-Keto acid

4. Nitrogen balance—comparison measurement of the amount of nitrogen ingested with the amount excreted (e.g., urinary nitrogen plus approximately 1 g/day for nail, hair, skin, and perspiration losses) made to determine whether net protein catabolism, anabolism, or equilibrium exists

Metabolic regulation


1. Structural—formation of:

2. Dynamic

3. Energy source (4 kilocalories [kcal]/g)

4. Role of proteins in oral biology


1. Determination and estimates of protein requirements

2. Recommended dietary allowances—developed by the National Research Council; based on 1985 World Health Organization recommendations, which use nitrogen balance data; these allowances assume ingestion of good-quality protein in a mixed diet; adjustments are made for growth, pregnancy, and lactation

3. Food sources—protein needs of an average adult can be met by choosing two or more servings per day of meats, poultry, fish, eggs, dried beans, and nuts

Dietary modifications for disease

1. Genetic disorders

a. Phenylketonuria (PKU)—inherited enzyme defect in which individuals cannot metabolize the phenylalanine found in nearly all proteins; the prescribed diet provides only enough phenylalanine to meet growth and maintenance needs; dietary protein is restricted, but amino acids are provided by a synthetic formula from which the phenylalanine has been removed

b. Other genetic disorders—maple syrup urine disease, homocystinuria, tyrosinemia, methylmalonic aciduria, propionic acidemia, and isovaleric acidemia are genetic disorders in which amino acid metabolism is altered; treated with low-protein diets and synthetic amino acid formulas

c. Gout—characterized by excessive uric acid production leading to the formation of urate crystals deposited in the joints; treatment often includes restriction of protein to limit purine and uric acid production

2. Protein needs are increased during fever, after severe injury and surgery, and by intestinal malabsorption, increased protein loss from the kidneys, or diminished protein synthesis by the liver

3. Dietary protein must be restricted when the kidneys can no longer remove nitrogenous wastes from the body or in severe liver disease when the nitrogenous byproducts of protein catabolism can no longer be synthesized

4. Protein-energy (calorie) malnutrition (PEM or PCM)

Lipids (Fats)

Definition—biochemical compounds composed of carbon, hydrogen, oxygen, and small amounts of phosphorus; insoluble in water and soluble in fatty substances and organic solvents


1. Simple lipids

a. True fats—contain fatty acids attached to glycerol (a trihydroxy alcohol) through an ester linkage; these may be monoglycerides, diglycerides, or triglycerides, depending on the number of glycerol–hydroxyl groups esterified; chemical and biochemical characteristics of glycerides depend on the number, order, and kinds of fatty acids attached

(1) Saturated fatty acids—contain no double bonds and are found in lipids from animal sources; are solids at room temperature (high melting point)

(2) Unsaturated fatty acids—contain one or more double bonds and come from plant sources; are usually liquids at room temperature (low melting point)

(3) Hydrogenation—addition of hydrogen to some or all of the double bonds; used in the manufacture of margarine or butter substitutes from vegetable oils; in partial hydrogenation, some trans bonds are formed and may present a health risk

(4) Rancidity—addition of oxygen to some of the double bonds of fatty acids that contributes to spoilage; occurs spontaneously in foods and can be reduced by the addition of antioxidants, such as butylated hydroxytoluene (BHT)

(5) Iodine number—chemical indication of the degree of unsaturation of a fatty acid; the more molecules of iodine bound by the fatty acid, the more unsaturated and the higher is the iodine number

b. Waxes—esters of a fatty acid and an alcohol other than glycerol; the body is unable to use waxes because digestive enzymes do not hydrolyze their ester linkage

2. Compound lipids contain compounds added to the glycerol and fatty acids

a. Phospholipids (glycerol + 2 fatty acids + phosphate group = R group)

b. Glycolipids—contain a carbohydrate component and are found in the brain and nervous tissue (e.g., cerebrosides)

c. Lipoproteins—are water soluble and responsible for carrying lipids throughout the body

3. Derived lipids are compounds whose synthesis begins like fatty acid synthesis, with acetyl groups added on one at a time

4. Artificial fats—substances developed for use in foods; have the flavor, appearance, and feel of dietary fats without their physiologic effects

Digestion, absorption, and transportation (see Table 12-1 and Figure 12-1)

1. Digestion

2. Absorption and transport

Metabolism (see Figure 12-2)

1. Anabolism

2. Catabolism

Metabolic regulators

Biologic role and functions of lipids

Nutritional requirements

1. Essential fatty acids (EFAs)—cannot be synthesized in sufficient amounts to meet the body’s needs; must be supplied in the diet; for humans the only EFAs are linoleic (ω-6) and linolenic (ω-3); requirement is approximately 3% of total kilocalories

2. Recommendations (dietary goals as recommended by the AHA)

3. The seventh edition of Dietary Guidelines for Americans makes similar recommendations for healthy persons ages 2 years and older

Dietary modifications for disease

Jan 1, 2015 | Posted by in Dental Hygiene | Comments Off on 12: Biochemistry, Nutrition, and Nutritional Counseling
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