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.
A 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
FIGURE 12-2 An overview of metabolism.
a. Insoluble fiber—substance (e.g., cellulose, hemi-cellulose, and lignin) that gives structure to plant cell walls; adds bulk and softness to stools; reduces contact with possible carcinogens by decreasing transit time through the colon; foods high in insoluble fiber include wheat bran, raw fruits, and vegetables
b. Soluble fibers—substances (e.g., gums, mucilages, pectin, and oat bran) that dissolve to become gummy or viscous; lower blood cholesterol; regulate the use of sugars and slow down gastric emptying; foods high in soluble fiber include legumes, raw apples, and whole oats
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)
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.
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
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
(1) Sugar alcohols (xylitol, sorbitol, and mannitol) are noncariogenic nutritive sweeteners that are slowly fermented through anaerobic metabolism by oral bacteria; excessive intake of these polyols can cause diarrhea because of the osmotic transfer of water into the bowel
(2) Xylitol is found naturally in plants and is equal to or sweeter than sucrose. Consumption of xylitol-containing products following consumption of food has been shown to interfere with the metabolism of S. mutans and decrease the demineralization of enamel
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
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
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
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)
d. Dietary monosaccharides and disaccharides enhance supragingival bacterial growth and plaque formation; these bacteria set the stage for the growth and development of subgingival bacteria and plaque, which are responsible for the destructive effects of periodontitis
1. 130 g/day of digestible carbohydrate is the recommended daily allowance (RDA) for adults and children. Minimum adult intake (50 to 100 g of digestible carbohydrate) prevents use of body protein as an energy source; pregnant and lactating women need additional carbohydrates to prevent ketosis
†Recommended dietary allowance values meet the needs of 97% of individuals in a group. Daily reference intake values are groups of values that provide quantitative estimates of nutrient intake for planning and assessing diets for all healthy individuals.
‡The lower number represents the adequate intake for infants and children, and the higher range of numbers will vary depending on life stage and gender group. Refer to the National Academy Press Web site (nap.edu/) for more in-depth information. The therapeutic range, also referred to as adequate intake, is the dose at which physiologic benefits for healthy individuals and decreased risk for toxicity may exist.
§The lower number represents the upper limits for infants and children, and the higher number represents upper limits for males and females (pregnant and lactating). The tolerable upper limit is the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects.
A 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
(2) Nonessential amino acids can be synthesized by the body and need not be provided by the diet but are necessary for normal metabolic reactions; include alanine, arginine, aparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine
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)
(1) In a “vegan” (or strict vegetarian) diet, the complementing of plant proteins can be accomplished by combining appropriate incomplete proteins; the amino acids in different foods can complement one another, even when eaten at different meals; persons on a strict vegetarian diet are at the greatest risk for developing deficiencies in calcium, iron, zinc, and vitamin B12 because the major food sources of these nutrients come from animal products
(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
a. The pancreas secretes bicarbonate into the duodenum to neutralize the acidic products from the stomach and proteolytic enzymes into an inactive form; enzymes activated by trypsin through a hormonal feedback mechanism are chymotrypsin, aminopeptidase, and carboxypeptidase; each hydrolyzes peptide bonds formed by different classes of amino acids
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
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
(1) Ketogenic amino acids are those whose carbon skeleton, after deamination, yields acetyl-CoA or acetoacetyl-CoA, which then yields ketone bodies; high concentrations of ketone bodies lead to some of the undesirable side effects of high-protein, low-carbohydrate diets, for example, ketoacidosis
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
a. Positive balance—intake is greater than output; indicates net protein synthesis and is the normal situation for anyone building protein-containing tissue, such as during childhood, pregnancy, and recovery from undernutrition, surgery, or illness
b. Negative balance—intake is less than output; indicates net protein breakdown, when the body must break down its own protein to meet energy or metabolic needs; can result from insufficient protein (or essential amino acids) or energy intake or from fever, infection, anxiety, or prolonged stress
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
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
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
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
(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)
a. Olestra—a zero-kilocalorie (0-kcal) artificial fat made from an indigestible combination of sucrose and fatty acids; may help serum cholesterol levels by directly interfering with cholesterol absorption; may increase the requirement for vitamin E; approved for use in snack foods
b. Simplesse—has approximately 15% of the kilocalorie of the fat it replaces; made by microparticulation of protein; the small protein particles have the feel of fat; not suitable for use in cooking but used in fat-free dairy products and salad dressings
a. Lipogenesis—synthesis of triglycerides for long-term storage of energy; starting material is acetyl-CoA, which can come from glucogenic amino acids, carbohydrates, or breakdown of dietary lipids; lipogenesis takes place in nearly all cells but is most active in adipose cells
a. β-Oxidation—fatty acids are broken down in a stepwise manner to yield one molecule of acetyl-CoA for every two carbon atoms; acetyl-CoA can be catabolized further by means of the TCA and oxidative phosphorylation
b. Ketone production—when the body’s supply of carbohydrates is low, the TCA is depressed and acetyl-CoA from β-oxidation accumulates; alternative route for acetyl-CoA is ketone production; acetoacetone, acetone, and β-hydroxybutyrate are the ketone bodies; excess ketone production can cause ketosis, ketonuria, and ketoacidosis (which is sometimes fatal)
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
b. Deficiency symptoms—seen in infants on low polyunsaturated fatty acid (PUFA) diets and in adults receiving total parenteral nutrition feedings without lipids; the deficiency is characterized by slow growth, reproductive failure, and skin lesions