The Encyclopedia Of Nutrition And Good Health - G ppt

G 302 galactose A simple SUGAR found in the diet in milk sugar (lactose). Galactose is a six-carbon sugar, as is the more common GLUCOSE (BLOOD SUGAR). Unlike glucose, however, it does not occur by itself in foods. DIGESTION of lactose by the intestinal enzyme LACTASE yields equal amounts of galactose and glucose. Before galactose can be used by the body for energy, it must first be transformed into glucose by the LIVER. Certain people have a genetic susceptibility to galactose accumulation. (See also CARBOHYDRATE METABOLISM; GALACTOSEMIA.) galactosemia A rare genetic disease due to an inability to degrade the sugar GALACTOSE normally. The most common defect is the inability to convert galactose to GLUCOSE, an essential preliminary step for galactose to be used for energy production. Because galactose cannot be extensively degraded when the path to glucose is blocked, it accumulates in the blood of galactosemic patients. This leads to severe mental retardation unless special galactose- free (milk-free) diets are administered shortly after birth. The prevalence of galactosemia is about one in 50,000. (See also CARBOHYDRATE METABOLISM.) gallbladder A dark green organ that concentrates and stores BILE from the LIVER. Bile is a mixture of powerful emulsifiers needed to digest and absorb FAT and oils and fat-soluble vitamins. When the INTESTINE detects food and fat released by the stomach, the intestine releases the hormone CHOLECYS- TOKININ into the bloodstream, which causes the gallbladder to release bile into the DUODENUM, the upper section of the small intestine. (See also DIGESTIVE TRACT.) gallstones Gravel-like deposits in the gallbladder in which BILE is stored; the gallbladder releases bile during meals to aid fat digestion and absorption. Many people consuming Western diets develop gallstones, although the causes of gallstones are unknown. Risk factors include high- FAT, low-FIBER diets, female gender, obesity, aging, CROHN’S DIS- EASE, cystic fibrosis, and alcoholic cirrhosis of the liver. The more refined and processed the foods in the diet, the greater the risk of developing gallstones. High-fiber diets may increase bile flow, thus preventing stone formation. For example, pre-1950s northern Canadian Inuit populations consuming a traditional diet had no record of gallstones. As a Western diet became more popular, the incidence of gallbladder disease increased dramatically. Food allergies are also a contributing factor, especially allergies to egg, pork, and onion. Hypo- chlorhydria (low stomach acid) may underlie maldigestion and food allergies, thus contributing to symptoms such as abdominal pain, bloating, and gas. The composition of gallstones ranges from almost pure CHOLESTEROL to mixtures of bile salts, cholesterol, calcium carbonate, and BILE PIGMENT (bilirubin). In the United States, most stones are of the mixed variety. Frequently, stones are small enough to pass through the duct leading to the intestine. Other stones often remain in the gallbladder without causing discomfort. When large stones become lodged in the common bile duct, this triggers a painful gallbladder attack called choledocholithiasis. It is clear that materials normally dissolved in bile create stones, and that stone formation begins with bile saturation. Bile contains cholesterol emulsified by bile salts and LECITHIN for digestion. Cholesterol will precipitate when there is a decrease in bile acids, water, or lecithin content in bile. For example, less bile salt is made as one ages, making cholesterol more insoluble. gamma globulins A family of specialized proteins (antibodies) that are the first line of defense against foreign invaders such as BACTERIA and viruses in the bloodstream. Unlike most serum proteins that are made by the LIVER, gamma globulins are products of B cells and related plasma cells of the IMMUNE SYSTEM . Most antibodies in the blood belong to the IgG class. Together with circulating white blood cells, they constitute “humoral immunity.” Gamma globulin shots temporarily boost immunity for protection against diseases such as HEPATITIS . (See also ALLERGEN; ALLERGY, FOOD; ANTI- BODIES.) gamma hydroxybutyric acid A compound that has been promoted by some body builders as a muscle-enhancing agent. It occurs naturally in the central nervous system, and it has been used as a general anesthetic and hypnotic or tranquilizing substance. However, gamma hydroxybutyric acid has caused comas and convulsions in susceptible individuals, and the U.S. FDA has warned con- sumers against its use because of possible serious adverse side effects. gamma linolenic acid (GLA) A polyunsaturated FATTY ACID found in seed oils such as borage, evening primrose, and blackcurrant. GLA is the raw material for a family of PROSTAGLANDINS, HOR- MONE -like lipids that regulate many physiologic processes. GLA forms the PGE 1 class of prostaglandins that counterbalance the effects of other prostaglandins (PGE 2 ) by decreasing inflammation, expanding blood vessels (vasodilation), lowering blood pressure and reducing the tendency to form blood clots. This may be the basis for the observa- tion that GLA may help reduce pain associated with rheumatoid arthritis. GLA is derived from LINOLEIC ACID, the ESSENTIAL FATTY ACID , and belongs to the omega-6 family of fatty acids. GLA possesses 18 carbons. Its three double bonds are located at different points along the chain. The structure of GLA differs from ALPHA LINOLENIC ACID , an omega-3 essential fatty acid. Therefore GLA and alpha linolenic acid are not interchangeable and serve different functions in the body. Specific nutrients NIACIN, VITAMIN B 6 , VITAMIN C, and ZINC participate in the formation of PGE 1 . The ability to produce GLA from linoleic acid seems to diminish with age, diabetes, high ALCOHOL consumption and high blood CHOLESTEROL. Therefore, supplementation may be helpful in certain situa- tions. GLA is one of the polyunsaturated fatty acids of BREAST MILK, suggestive of its importance in development and growth. gamma-oryzanol (ferulate; ferulic acid) A plant extract derived from rice bran oil. It is also found in other grains and in some fruits, vegetable, and herbs. Gamma-oryzanol has been used in Japan for decades as a treatment for anxiety, digestive disorders, menopause, and elevated cholesterol, LDL cholesterol, and triglyceride levels. Some studies done in Japan support use of gamma-oryzanol for these conditions. However, the results are ques- tionable because either the subjects studied were laboratory animals or the number of humans studied was too small to produce conclusive evidence of efficacy. In the United States gamma-oryzanol is available as a dietary supplement. It has gained popu- larity among some athletes and bodybuilders who believe it can increase muscle mass and enhance strength and endurance. However, a study of male weightlifters who took supplements for nine weeks showed that gamma-oryzanol had no effect on exercise performance. Other studies indicated the substance retards production of growth hormones. Gamma-oryzanol may have a positive effect on the body’s production of endorphins, chemicals that produce a feeling of well-being. Although this claim has not been proven, many athletes claim taking supplements can reduce fatigue and pain associated with hard physical training. Because gamma-oryzanol is sold as a dietary supplement and not a drug, its safety and efficacy have not been tested by any government agency. Because there is inadequate safety information, pregnant and breast-feeding women should not use this product. gamma-oryzanol 303 Fry, A. C. “The Effects of Gamma-Oryzanol Supplemen- tation During Resistance Exercise Training,” Interna- tional Journal of Sport Nutrition 7 (1997): 318–329. garbanzo bean See CHICKPEA . garlic (Allium sativum) This bulbous plant is closely related to ONIONS, leeks, and chives. The ancestor of modern garlic grows in Central Asia, and garlic has been cultivated for at least 5,000 years. The underground compound bulb is made up of cloves or sections. Garlic is strongly scented and strongly flavored, and has many culinary applications. Most of the garlic produced in the United States comes from California. Much of the commercially grown garlic is processed to garlic powder. The healing power of garlic has been recognized by Chinese folk traditions dating back thousands of years. Research has shown that garlic can lower blood CHOLESTEROL, especially the undesirable frac- tion of serum cholesterol LOW-DENSITY LIPOPROTEIN (LDL) and serum fat in animals and humans. Gar- lic also can significantly lower high blood pressure. Eating half a clove of garlic a day may lower blood cholesterol by 9 percent. Garlic reduces the tendency to form blood clots, although the conjecture that garlic decreases the risk of CARDIOVASCULAR DISEASE has been challenged. The suggestion has also been made that eating garlic and onions (not supplements) on a regular basis may lower the risk of stomach CANCER because materials isolated from garlic inhibit cancer production in experimental animals. Garlic can prevent dietary nitrites, used as a preservative in processed meat, from forming nitrosoamines, which can cause cancer, or can block their action. Garlic boosts the IMMUNE SYSTEM by increasing natural killer cells and phagocytic activity of white cells, and this may explain its anti- cancer activity. Garlic contains 0.4 percent volatile oil containing a variety of unusual organo-sulfur compounds, believed to be responsible for most of the pharma- cologic and antimicrobial actions. “Allylsulfides” increase the production of so-called phase 2 liver detoxification enzymes (glutathione transferases) that increase the water solubility of cancer-causing compounds and toxins, speeding their excretion. Diallylsulfide may protect against lung cancer and stomach cancer. Other compounds in garlic seem to limit tumor cell growth. However, garlic yields different active ingredients depending on the way it is prepared. Garlic juice possesses antibacterial activity, antifungal activity, and antiviral activity. Allicin causes the pungent odor of raw garlic and seems to be partly responsible for antimicrobial activity. Garlic has been reported to lower blood pressure in experimental animals and in humans and to inhibit blood platelet clumping, a necessary step in clot formation in vessels. Garlic reduces inflammation by blocking the formation of agents that induce it, including PROSTAGLANDINS, thrombox- anes, and LEUKOTRIENES. Steam distillation of garlic juice produces a sulfur product called ajoene, which inhibits a prostaglandin, PGE 2 , which in- duces pain. Garlic sauteed in oil produces still other sulfur compounds, vinyldithiins, which are bronchial relaxers (they open air passageways in the lungs). Garlic supplements have yielded mixed results. Although odoriferous, fresh garlic seems to be generally more effective than garlic powders and oils. Certain products carefully prepared from freeze- dried garlic appear to be effective. Garlic usually does not cause side effects, but in sensitive people garlic can cause allergic symptoms. Gastrointestinal upsets can be diminished by mixing crushed fresh garlic in oil and mixing this with food. Researchers have found garlic supplements can interfere with the beneficial effects of a type of medication to treat HIV/AIDS. Investigators from the National Institutes of Health (NIH) found that garlic supplements sharply reduced blood levels of the anti-HIV drug saquinavir. Piscatelli, S. C. et al. “The Effects of Garlic Supplements on the Pharmacokinetics of Saquinavir,” Clinical Infec- tious Diseases 34 (January 15, 2001): 234–238. gas See FLATULENCE. gastric acid See STOMACH ACID. gastric juice Secretions from glands lining the stomach. Up to 700 ml of gastric juice are secreted daily. Different types of secretory cells produce gas- 304 garbanzo bean tric juice. “Chief cells” produce pepsinogen, the inactive form of the stomach’s protein-digesting enzyme, PEPSIN. “Parietal cells” produce hydrochloric acid ( STOMACH ACID). This very strong acid creates a pH of 1.2 to 3.0, equivalent to 10 to 50 ml of dilute hydrochloric acid. The acid unfolds food PRO- TEINS , making them more accessible to attack by digestive enzymes. To further aid digestion, acid activates pepsin to initiate protein DIGESTION. The strong acid also helps sterilize ingested food and destroy bacterial toxins. Gastric juice contains a LIPASE or fat-degrading enzyme that, when secreted, can liberate BUTYRIC ACID from BUTTER-FAT ; as well as INTRINSIC FACTOR,a protein that binds VITAMIN B 12 and aids VITAMIN B 12 absorption by the small intestine. Chloride in gastric juice is efficiently absorbed by the intestine and is recycled. (See also ACHLORHYDRIA.) gastric ulcer An open sore (also known as peptic ulcer) in the lining of the stomach. There are two major forms of ulcers: duodenal ulcer in the upper region of the small intestine, and gastric or stomach ulcer. Gastric ulcers are somewhat less common. Most patients with gastric ulcers report abdominal discomfort about an hour after a meal, or during the night. Acid secretion is normal or reduced, rather than excessive. Eating or using ANTACIDS relieves the pain. There are several causes of gastric ulcer. ASPIRIN, phenylbutazone, indomethacin, and other non- steroidal anti-inflammatory agents can cause stomach bleeding and ulcer formation. ALCOHOL, smoking, and COFFEE (whether decaffeinated or not) decrease tissue resistance and may play a causative role. ACHLORHYDRIA (the absence of stomach acid) is associated with gastric ulcers. Heredity is a factor. The bacterium HELICOBACTER PYLORI (H. pylori) is associated with chronic gastric inflammation and ulcers. Infection increases the risk of stomach cancer. High levels of antibodies against H. pylori can often be detected in the blood of gastric ulcer patients, and long-term eradication of H. pylori often clears up stomach ulcers and inflammation and prevents ulcer recurrence. Researchers have discovered that BROCCOLI and broccoli sprouts contain a chemical, SULFORAFANE, that kills H. pylori in mice. Similar studies on humans are ongoing. Ulcer patients have a tendency to suppress emo- tions. Whether stress is involved in the development of ulcers is controversial. Conventional medical treatment involves the use of drugs that block stomach acid secretion (cimetidine, ranitidine) or agents that coat ulcers and bowel. Cimetidine (Tagamet) is the second most commonly prescribed drug in the United States. Food sensitivities are implicated in experimental and clinical studies of gastric ulcer, and ELIMINATION DIETS have been used in preventing recurrent ulcers. Calcium carbonate antacids should not be used for gastric ulcer because they trigger excessive stomach acid secretion later (rebound effect). In botanical medicine, a licorice extract called deglycyrrhizinated has been used as an anti-ulcer agent, shown to be as effective as cimetidine and ranitidine. Eradication of H. pylori requires treatment with antibiotics and bismuth compounds. (See also ACID INDIGESTION.) Sepulveda, A. R., and L. G. Coelho. “Helicobacter pylori and gastric malignancies.” Helicobacter. 7 Suppl. 1 (2002): 37–42. gastrin A hormone formed by pyloric glands in the lower region of the stomach. In response to food, gastrin is released into the bloodstream where it stimulates the secretion of stomach acid by specific cells in the stomach lining called parietal cells. Gastrin also stimulates intestinal peristalsis. (See also DIGESTION.) gastritis Any inflammation of the stomach lining. Gastritis may be accompanied by nausea and vomiting, or by a sense of fullness after eating a small meal. Gastritis is one of the most common stomach ailments and it increases the risk of stomach cancer. A variety of causes have been implicated, including excessive consumption of ALCOHOL, rich food, COFFEE, tea, and other irritating foods. Among the most common causes of gastritis is ASPIRIN, which may cause stomach bleeding. Other drugs can cause acute symptoms: sulfonamide, certain antibiotics, and quinine. Viral and bacterial infections may be involved. Pernicious ANEMIA (due to gastritis 305 VITAMIN B 12 deficiency), gastric ulcer and polyps, diabetes and adrenal insufficiency often accom- pany chronic gastritis. Symptoms, which are intermittent and variable, include loss of appetite, mild nausea, a feeling of fullness or abdominal pain, recurrent heartburn or pain in the upper abdominal region, and vomiting. Eliminating the offending irritant and avoiding alcohol, caffeine, smoking, and foods that provoke a response may help reduce pain. Symptoms may be relieved by medications (such as cimetidine) that coat the lesions or reduce acid production. Deglycyrrhizinoted licorice has been used to help heal peptic ulcers. Recurrent, chronic gastritis can indicate an underlying problem. For example, food allergies can cause gastric inflammation and other gastrointestinal symptoms. The bacterium HELICOBACTER PYLORI is frequently associated with chronic stomach inflammation. Elimination of infection by antibiotics and bismuth compound treatments can eliminate recurrent episodes. (See also ACID INDI- GESTION.) Fay, M., M. B. Fennerty, J. Emerson, and M. Larez. “Dietary habits and the risk of stomach cancer: a com- parison study of patients with and without intestinal metaplasia,” Gastroenterology and Nursing 16, no. 4 (1994): 158–162. gastroenteritis An inflammation of the stomach and large and small intestines. It is most often caused by viruses like rotaviruses and aden- oviruses, but it can also be caused by bacteria or parasites in food and water. Bacterial causes include SALMONELLA and ESCHERICHIA COLI 0157. It can be easily passed on to others in bodily fluid. It can also be a reaction to LACTOSE INTOLERANCE. Symptoms include vomiting, diarrhea, stomach cramps, headaches, and fever. ANTIBIOTICS can help if the cause is bacterial. There are as many as 90 million cases of gastroenteritis each year in the United States. gastroenterology A specialized branch of medicine focusing on the structure, function, and pathology of the STOMACH, INTESTINES, ESOPHAGUS, and related organs like the LIVER and PANCREAS. (See also GASTROINTESTINAL DISORDERS.) gastrointestinal Concerning the stomach and intestines. (See also DIGESTION.) gastrointestinal disorders A wide variety of conditions affecting the gastrointestinal tract, including food sensitivities; structural defects; infections by VIRUSES and BACTERIA (such as Helicobacter pylori and Escherichia coli) and by organisms causing food poisoning; parasites such as giardia; fungal patho- gens such as YEAST; STRESS; and glandular imbal- ances, such as low stomach acid. Diet is directly related to problems due to nutritional deficiencies, food allergies, food sensitivities, and low fiber intake. LACTOSE INTOLERANCE is an example of a common food sensitivity. In the United States, overall rates of gastrointestinal illness range from 1.5 to 1.9 illnesses per person per year. Diarrheal illnesses are second only to CARDIOVASCULAR DISEASE as a cause of death worldwide, and they are the leading cause of child- hood death. The following is a listing of important gastrointestinal disorders: • GASTRITIS: Characterized by gastric pain due to a generalized inflammation of the stomach lining. • GASTRIC ULCERS and DUODENAL ULCERS: Open sores in the stomach or intestinal wall. The pitting may be severe enough to cause internal bleeding. • GASTROENTERITIS: An illness that can cause diarrhea, stomach cramps, vomiting, nausea, fever, and headache. • Chronic constipation. • Chronic DIARRHEA. • COLITIS: Inflammation and/or ulcer of the colon and rectum. • ILEITIS: An inflammation and ulceration of the small intestine that causes alternating diarrhea and constipation, occasionally with vomiting. • LIVER CIRRHOSIS: Scarring of the liver. • HEPATITIS: Inflammation of the liver, often due to viral infection. • Stomach cancer. • Hiatus hernia: The bulging of the stomach through the diaphragm. • MALABSORPTION: Maldigestion and infection by bacteria and parasites. • MALDIGESTION: This can lead to secondary nutrient deficiency states. Inadequate pancreatic 306 gastroenteritis gene 307 enzymes, low stomach acid (hypochlorhydria), and carbohydrate intolerance (such as lactose intolerance) may be involved. • DIVERTICULITIS. • Hemorrhoids. (See also CELIAC DISEASE; FLATULENCE ; INFLAMMA- TORY BOWEL DISEASE ; LACTOSE INTOLERANCE; SPRUE.) Chang, L. et al. “Perceptual Responses in Patients with Mild Inflammatory and Functional Bowel Disease,” Gut 47 (2000): 497–505. gastrointestinal tract That part of the DIGESTIVE TRACT represented by the stomach and the intestines and their ancillary glands, including the liver and pancreas. (See also DIGESTION.) gastroplasty A surgical procedure that reduces the functional size of the stomach by stapling a por- tion (sealing off). This is a drastic weight-reduction strategy used for severely obese individuals. Weight loss ensues because the capacity for food intake is reduced. (See also DIETING; OBESITY.) gastrostomy A surgical procedure introducing a passageway from the STOMACH cavity through the abdominal wall (fistula). When the ESOPHAGUS is closed off, for example due to tumors, or when swallowing reflexes are inhibited, as in some stroke patients, food may be introduced into the stomach through such an opening. (See also DIGESTION.) gavage Liquid feeding that occurs with a tube through the nasal passage to the ESOPHAGUS and the STOMACH (nasal gavage). Gavage also refers to feeding via a stomach tube (gastrogavage). gelatin A processed form of animal PROTEIN that dissolves when mixed with hot water and gels upon cooling. Gelatin absorbs 5 to 10 times its weight as water. It is commercially prepared by the breakdown of connective tissue protein, especially COLLAGEN, from the bones of slaughtered animals. Gelatin is a low-quality protein because it is defi- cient in many essential AMINO ACIDS, including TRYPTOPHAN and METHIONINE. Gelatin is used as a culinary thickening and sta- bilizing agent. It is used with flavorings in desserts and pudding mixes, and in candy, jellies, and ice cream. Commercial gelatin desserts usually contain high levels of SODIUM, SUCROSE, and artificial color- ing to make them look and taste like fruit desserts. Despite popular opinion, gelatin neither strength- ens nails nor helps cure ulcers. (See also BIOLOGI- CAL VALUE .) gemfibrozil A cholesterol-lowering drug that has been shown to raise HIGH-DENSITY LIPO- PROTEIN (HDL), the desirable CHOLESTEROL. (See also CHOLESTEROL-LOWERING DRUGS.) gene A unit of heredity that defines a trait or characteristic. A gene represents a region of DNA that codes for the sequence of AMINO ACIDS of a specific protein. Consequently DNA is said to be the “blueprint” of the cell’s proteins. The cell nucleus contains a set of chromosomes with many thousands of genes. MUTAGENS are agents that alter genes by attacking the DNA molecule, changing the genetic structure and causing mutations. Once a mutation has occurred, it is passed from one generation to the next. Mutagens are a diverse group of agents: Cer- tain endogenous chemicals in plants, as well as pol- lutants, certain PESTICIDES and some synthetic FOOD ADDITIVES , even ultraviolet light, can cause mutations. This is a major concern because most mutagens are cancer-causing agents ( CARCINOGENS). In the nucleus of a human cell, chromosomes occur in pairs. Each member of a pair of genes is called an allele, which may be dominant or recessive. In a simple scenario, one or both genes of a pair of alleles may be dominant; therefore the trait or characteristic determined by the gene is expressed. A recessive trait (autosomal recessive gene) will not be expressed if it is paired with a dominant gene, though it will nonetheless be car- ried along through inheritance. Individuals who carry the recessive trait possess one normal gene and one modified gene and are classified as het- erozygotes (hybrids). A gene coding for a defective protein would be expressed when two recessive genes are inherited (homozygotes), leading to the occurrence of certain rare genetic diseases at birth. Several genetic diseases are based upon altered metabolism due to mutant enzymes. About 5 percent of cases with highly elevated blood cholesterol are due to genetic alterations in proteins responsible for cholesterol metabolism or transport. Typical examples are PHENYLKETONURIA, which reflects a defect in the metabolism of the amino acid PHENY- LALANINE, and GALACTOSEMIA, the result of a defect in the metabolism of the SUGAR GALACTOSE. The severe effects of PKU can be avoided by strict dietary measures initiated soon after birth to avoid ingesting excessive amounts of phenylalanine. Early detection is the best strategy. Individuals who carry a recessive gene and a normal gene usually do not experience the genetic disease. For example, about one person in 100 carries the trait for phenyketonuria while those with PKU possess a pair of abnormal genes—a much rarer occurrence (one out of 10,000 births). Genetic polymorphism refers to the multiple genetic variants for a given protein, such as HEMO- GLOBIN, the oxygen carrier protein of red blood cells. Most of the protein variants function more or less normally and do not directly cause disease. On the other hand, it is the slight differences in proteins reflecting differences in genetic makeup that account for individual traits among people. As a consequence, there will be slightly different nutrient requirements for optimal health among different persons. Their levels of liver detoxication enzymes will also vary. This variation partially explains why different individuals vary in their susceptibility to toxins, medications, anesthetics, and even cigarette smoke. (See also BIOCHEMICAL INDIVIDUALITY ; GENETIC ENGINEERING.) generally recognized as safe (GRAS) Substances added to foods that are judged as safe because of their long history of usage without apparent harm- ful effects. Because of public concern for the safety of an increasing number of new food additives, in 1958 the Food Additive Amendment was appended to the federal Food, Drug and Cosmetic Act requiring pre-market approval of all food additives. Developers must demonstrate “reasonable certainty of no harm” of a new food additive. Oth- erwise, foods containing the additive may be con- sidered adulterated under the original act. The amendment, however, contains an important exception: If an additive is “generally regarded as safe” (GRAS), then the additive is exempt from formal premarket safety review. The intent of this exception was to prevent common food additives such as salt and pepper from having to undergo unnecessary safety testing. The determination of GRAS status is not a formal process, and the devel- oper may presume an additive to be GRAS, only to be contradicted later by the FDA. The 1958 law regulating food additives exempted about 700 apparently safe chemicals and materials, which were approved by the U.S. FDA as food additives without further study. Subsequently developed food additives have had to meet requirements for premarket clearance in the FDA. The GRAS “grandfather” clause is controversial because the safety of some have been questioned. As a result, the FDA has reevaluated the GRAS list- ings and banned or restricted some substances on the basis of new data indicating potential health problems. The process by which an additive is cleared for use is complex. The responsibility for proving a substance belongs on the list is borne by the manufacturer, who must first prove to the FDA that the proposed additive is effective and that the additive can be detected and measured in the final product. The next step requires the manufacturer to study the effects of the substance on animals who ingest large amounts of the additive to make sure that the substance does not cause cancer, birth defects, or other injury. If the additive meets these requirements, the FDA validates the research and then schedules a public hearing to discuss expert testimony for and against the substance. A ruling is then issued by the FDA. Once the substance is approved for the GRAS list, the FDA determines in what amounts and for what purposes the substance may be used. (See also FOOD, DRUG AND COS- METIC ACT.) genetically modified foods The chemical modifi- cation of genes of plants, animals, and microorgan- isms. Typically, additional genetic messages are removed from one organism and inserted into chromosomes of another type to create the ability to synthesize new proteins in the recipient. For 308 generally recognized as safe example, a genetically engineered BOVINE GROWTH HORMONE being sold in the United States can boost milk production in cows by 10 percent. Genetic engineering also may improve the protein quality of plant foods and feed for livestock. A renewed interest in the disease-prevention and the health- enhancing properties of foods has sparked other efforts to improve these characteristics in foods; for example, breeding carrots with increased levels of the antioxidant BETA-CAROTENE. Technology is producing plants resistant to insects to viral diseases and to HERBICIDES . Some of the first experiments with genetically engineered crops have yielded tomato plants that produce animal antibodies against viral infections, conferring disease resistance. Alternatively, infection-resistant genes from other plant species have been inserted into tomatoes, making them resistant to bacterial infection. Planting crops that have herbicide- tolerant genes may help farmers control weeds in crops that would otherwise be damaged. One method is to insert an altered gene for a specific plant enzyme normally targeted or inactivated by a given herbicide. The change can make the enzyme insensitive to the herbicide. Another approach is to insert a gene for a new enzyme that detoxifies the herbicide. For example, a gene from petunia protects soybean plants from herbicides; and bacterial gene inserted into corn protects it against the Euro- pean corn borer. Genetic alteration may yield crops that can grow in cooler or warmer, wetter or drier climates. Plants may someday produce drugs such as vaccines and human hormones. Genes from other species can be incorporated in plants to develop products that are more nutritious or are sweeter; have a better flavor or more color for consumer appeal; and/or have a longer shelf life. Viruses affect many crops, ranging from wheat, corn and POTATOES to TOMATOES and CITRUS FRUIT. By inserting a gene coding for a protein of an attacking virus into a susceptible plant species, the recipient plants tolerate tobacco, alfalfa, and cu- cumber mosaic viruses as well as potato viruses. Virus-resistant potatoes and tomatoes have been field-tested. A number of concerns have been expressed by food scientists, consumer groups, and policymakers about genetic engineering. There is concern that plant geneticists may engineer crops to improve processing and yield at the expense of good nutrition. Cosmetic changes could be developed that might mask unripe or overripe foods. Safety is another concern. Genetically engineered plants could make higher levels of known toxic substances. Viral genes that can increase a plant’s resistance to a pest could produce altered plant viruses that may harm plants. Transferring genes could cause allergies. For example, genes from a peanut plant inserted into another plant could make the new variety able to trigger reactions in those with peanut allergies. The FDA does not require special labeling for genetically engineered foods, except to potential aller- gens. Another possibility is the production of plant toxins in genetically engineered food. One type of genetically modified corn became the subject of a class-action consumer lawsuit in the late 1990s. Starlink corn seed, developed by Aventis, contained the insecticidal protein Cry9C. Corn containing this protein was protected from attack by corn boring insects. Starlink corn was registered and annually renewed for domestic animal feed and nonfood industrial use in the United States in 1998, 1999, and 2000. In mid- 2000 fragments of Starlink corn began appearing in the food supply, specifically taco shells. Dozens of people claimed they became ill after eating food containing Starlink corn. By the end of 2000 Aventis had withdrawn its registration for Starlink corn. Three federal agencies regulate genetically engineered products in the United States. The Depart- ment of Agriculture (USDA) must first approve field tests of transgenic (genetically engineered) plants. The Environmental Protection Agency (EPA) establishes the tolerance levels of all synthetic pesticides in such food crops. The FDA eval- uates all genetically engineered plant foods to determine whether the new genetic trait consti- tutes a FOOD ADDITIVE or other major plant alteration. The FDA does not require special labeling or review unless alteration of a food changes its nutritional value or produces possible toxins or aller- gens. (See also DNA; FUNCTIONAL FOODS; GREEN REVOLUTION .) genetically modified foods 309 310 geophagia geophagia The consumption of inedible materials such as clay, dirt, and chalk. Famine has been associated with earth and clay eating, but clay eating is not limited to hardship. Clay is consumed around the world in spices, condiments, or relishes. The hypothesis that clay eating is a response to deficiencies of minerals like IRON or CALCIUM has not been supported by hard evidence, possibly because the minerals in clay may be readily absorbed. Another proposal is that clay eating is a detoxifying strategy allowing people to make wider use of plants as food. In certain cultures, pregnant women have traditionally eaten clay to settle their stomach. A common over-the-counter remedy for diarrhea is kaolinate, a major mineral in clay. germ The nutrient-rich embryo of seeds or ker- nels. This area is vitamin-rich and contains VITAMIN E plus THIAMIN, RIBOFLAVIN, NIACIN, and plant oils. Wheat germ is removed during the milling and refining process to obtain white flour. (See also BRAN, WHEAT; ENDOSPERM; GRAIN; WHEAT.) gestational diabetes See DIABETES, GESTATIONAL. ghee See BUTTER, CLARIFIED. giardiasis An intestinal infection caused by the protozoan parasite Giardia lamblia. This disease usually is associated with contaminated drinking WATER that may look clean. Water chlorination may not destroy giardia cysts, therefore water treatment may not remove this parasite. In the United States, giardiasis is the most frequent cause of waterborne diarrhea, and an estimated 2 percent to 5 percent of adults are infected. The numbers are higher for children; in some counties of the western United States, the percentage of infected adults may be as high as 13 percent. It can be transmitted by fecal contamination, and thus by infected food handlers. Children at day care centers, and individuals with low stomach acid and compromised IMMUNE SYSTEMS, are more likely to acquire giardia. Symptoms include DIARRHEA, stomachache, FLATULENCE, ANOREXIA, nausea, and vomiting. Giar- diasis promotes atrophy of the surface of the small intestine, which can result in LACTOSE INTOLERANCE and MALABSORPTION. However, chronic giardiasis may cause only mild symptoms and people without symptoms are reservoirs of this parasite. In order to minimize the risk of infection, campers are advised to boil water for 10 minutes, or use water purification tablets or a portable water filtration unit. (See also GASTROINTESTINAL DISORDERS; MICROVILLI.) ginger (Zingiber officinale) A spice originating in the East Indies, now cultivated in many tropical areas including Jamaica, and regions of Nigeria, India, and Japan. Ginger is a yellow or reddish- brown underground stem called a rhizome and belongs to a family of reedlike perennials. Several hundred varieties of ginger exist. The characteristic peppery taste of ginger is produced by a compound called gingerin. When harvested at the appropriate time, it is not fibrous, nor does it have a bitter after- taste. Ginger is used fresh or dried, powdered or crystallized, in pickling spices, ginger bread, cakes, puddings, stews and curry bases. Ginger, boiled and preserved in syrup, is known as Canton ginger and is used in desserts. Dried ginger has been used in folk medicine to treat complaints of the digestive tract, such as gas and bloating, nausea and vomiting, diarrhea and stomach cramps. Ginger also has a long history in treating rheumatism and reducing inflammation; clinical studies suggest it can help ease knee pain in osteoarthritis. gingivitis Inflammation of gums (gingiva), a chronic DEGENERATIVE DISEASE. Gingivitis affects 70 percent of Americans over the age of 65. Inflam- mation can lead to bleeding gums, recession of gums, destruction of the bony tooth matrix, and, eventually, to tooth loss. Gingivitis is associated with vitamin deficiencies and metal poisoning and can be caused by pathogenic organisms associated with dental plaque accumulation. Ill-fitting appli- ances and dentures can also cause gingivitis. Floss- ing and prophylactic cleaning by a dental hygienist are the best approaches to prevention. (See also FLUORIDE.) ginkgo (Ginkgo biloba) An ancient species of deciduous tree whose leaves have long been used in Asian medicine. Ginkgo is native to China, and extracts of ginkgo leaves have been used to support heart, brain, and lung function for nearly 5,000 years. Ginkgo leaf extracts are standardized in terms of their active components. The leaves contain substances called ginkgolides and bilobalide, complex organic compounds that help fight disease. Ginkgo also contain FLAVONOIDS that function as ANTIOXIDANTS, which limit damage due to reac- tive forms of oxygen and can help reduce inflammation. Furthermore, ginkgo extracts can help maintain normal blood flow in arteries, veins, and capillaries and maintain circulation. Ginkgo leaf extracts can increase and normalize blood flow by relaxing blood vessel walls. They can also improve blood flow to the brain, thereby improving brain function. Ginkgo extracts inhibit the action of a substance called platelet activating factor, which triggers inflammation through the production of oxidized lipids and the migration of attacking white blood cells. They therefore protect areas such as the lungs and intestine against inflammation and tissue damage. Clinical studies suggest that ginkgo leaf extracts can stabilize, slow the progression, and sometimes improve certain aspects of Alzheimer’s disease or mixed dementia. They may also improve cognitive function in older adults with mild to moderate age-dependent mem- ory deficits. Lower doses of 120 mg/day were as effective as 600 mg/day. Pain-free walking may improve in patients with intermittent claudication. Ginkgo may also benefit some patients with PMS, or those with age-related macular degeneration. In addition ginkgo leaf extract has been used to prevent altitude sickness. Side effects are rare and may include headaches and stomach upsets. Crude ginkgo preparations, but not the widely used leaf extracts, can cause severe allergies. Safety data on ginkgo extract is insufficient regarding its use by pregnant or lactat- ing women. (See also SENILITY.) ginseng (Panax ginseng; Chinese ginseng, Korean ginseng) A medicinal herb native to northern China and Korea. Ginseng is widely cultivated in Korea, China, and Japan. It is available as white ginseng, from the dried root, or as red ginseng, which has been steamed. (Siberian ginseng, Eleuthrococcus senticosus, is a distant relative to the more popular Panax ginseng. Its properties are similar to Panax ginseng. Most research on Siberian ginseng has been conducted in Russia and the former Soviet Union.) Ginseng is a famous herb of Chinese medicine, long used to restore “yang” energy, specifically to support normal healing processes during infections, to overcome fatigue, and to counter elevated blood pressure and high blood lipids (fat and cholesterol). Ginseng can stimulate the IMMUNE SYSTEM, especially natural killer cells and scavenger immune cells (macrophages) in the liver, spleen, and lymph nodes, and antibody- producing cells. In experimental animals, ginseng has prevented viral infection. However, excessive amounts of ginseng can inhibit the immune response during serious infections. Ginseng may lower the risk of some types of CANCER in experimental animals. Ginseng can also lower elevated BLOOD SUGAR levels and high blood pressure. Human studies performed in the former Soviet Union support ginseng’s role in increasing stamina. Animal studies indicate that it can improve metabolism of the central nervous system and nerves controlling muscles, and spare GLYCOGEN, the glucose reserve, in exercising muscle. A class of plant compounds called saponins appears to be the active ingredient. In terms of adapting to stress, ginseng saponins (ginsenosides) stimulate the adrenal glands by promoting the release of adrenocorti- cotropin (ACTH) and ENDORPHINS, the brain’s own opiates, from the PITUITARY GLAND. The adrenals are responsible for adapting the body to stress by producing hormones such as epinephrine (adrenaline) and cortisol. Ginseng can affect the body in many ways, and long-term consumption of excessive amounts may have negative consequences. It may depress the central nervous system, and cause vaginal bleeding and breast pain in postmenopausal women. Long- term use can lead to “ginseng abuse syndrome,” with possible high blood pressure, DIARRHEA, skin eruptions, loss of sleep, edema, nervousness, femi- nization of males, and masculinization of females. One of the problems with ginseng is the wide variation in quality of commercially available products, which range from chewing gum and teas to cap- sules. Preparations standardized for content of an ginseng 311 [...]... is the storage form of GLUCOSE in plants Both are large molecular weight chains composed of glucose building blocks Unlike starch, glycogen has a very highly branched structure Because of its high degree of branching, glycogen binds 3 to 5 g of water per gram of glycogen A normal adult weighing 150 pounds (68 kg) possesses approximately 800 g of glycogen, found predominantly in skeletal muscle and. .. secretes digestive enzymes, and the LIVER secretes BILE for digestion in the intestine through a duct leading to the small intestine Mucous glands produce protective materials to coat the surface of the digestive tract and other cavities Gastric glands in the lining of the stomach secrete GASTRIC JUICE for digestion The parotoid and salivary glands produce SALIVA Sudoriferous glands in the skin produce... “growth hormone releasing factor” from the HYPOTHALAMUS, the part of the brain that regulates the PITUITARY GLAND, the master gland of the ENDOCRINE SYSTEM (hormone secreting glands) (See also AGING; ANABOLISM; BOVINE GROWTH HORMONE.) growth promoters GTF See ANIMAL DRUGS IN MEAT See GLUCOSE TOLERANCE FACTOR guanine A nitrogen-containing base that is a building block of DNA and RNA Guanine in one DNA chain... DISODIUM GUANYLATE; GOUT; PURINE.) guar gum A vegetable GUM used as a thickening agent, Guar gum is obtained from the guar plant, Composia teragonolobus, grown in India and the United States Guar gum is a form of soluble FIBER and contains long chains composed of the sugars MANNOSE and GALACTOSE Guar gum dissolves in cold water, readily forms gels and is one of the most widely used gum stabilizers in... PANCREAS.) gliaden A protein found in wheat, rye, and other grains Together with glutenin, the other major type of GLUTEN protein, gliaden is responsible for the stickiness of dough The high gluten content of wheat FLOUR creates an elastic, versatile dough for baking Gliaden contains unusually large amounts of nonessential amino acids, GLUTAMINE and PROLINE On the other hand, wheat protein and gliaden... roots, pods, and seeds, as glucose, as other sugars or as STARCH, composed of long chains of glucose units DIGESTION converts starch back to glucose Glucose occurs naturally in food It is a major ingredient of HONEY and SUCROSE (table sugar) and consists of half-glucose and half-fructose, while milk sugar (lactose) contains half-glucose and halfGALACTOSE Free glucose occurs in fruit (grape sugar) Glucose... mussels, scallops, and clams contain a little glycogen when eaten (See also CARBOHYDRATE LOADING; CARBOHYDRATE METABOLISM; GLYCOGENOLYSIS.) glycogen loading See CARBOHYDRATE LOADING glycogenolysis The breakdown of glycogen in the LIVER and muscle to glucose EPINEPHRINE, a hormone of the adrenal glands, signals glycogenolysis in muscle for quick energy and, to a lesser extent, in the liver in response... digested slowly and cause a slower rise in blood sugar Factors influencing the rate of carbohydrate digestion include the type of food and methods of storage, processing, and cooking Furthermore, the presence of one food can affect digestion of another Before the development of the glycemic index in 1981, scientists assumed that the human body absorbed and digested simple sugars quickly, producing rapid increases... in the LIVER Muscle accounts for approximately two-thirds of the glycogen in the body Liver Glycogen Metabolism The liver helps regulate BLOOD SUGAR through the synthesis and degradation of glycogen After a carbohydrate meal, the liver absorbs glucose from the blood and incorporates it into glycogen in response to the pancreatic hormone INSULIN With low blood glucose, EPINEPHRINE (adrenaline) from the. .. adrenal glands and GLUCAGON from the pancreas signal 320 glycogen loading glycogen breakdown The liver, alone, can disengage glucose from cellular reactions and release it into the bloodstream Muscle Glycogen Metabolism Insulin, released in response to elevated blood sugar levels, stimulates glucose uptake by skeletal muscle, where it is deposited as glycogen Muscle glycogen does not form blood sugar To . for approximately two-thirds of the glycogen in the body. Liver Glycogen Metabolism The liver helps regulate BLOOD SUGAR through the synthesis and degradation of glycogen. After a carbohydrate meal, the liver. protective materials to coat the surface of the digestive tract and other cavities. Gastric glands in the lining of the stomach secrete GASTRIC JUICE for digestion. The parotoid and salivary glands. nucleus contains a set of chromosomes with many thousands of genes. MUTAGENS are agents that alter genes by attacking the DNA molecule, changing the genetic structure and causing mutations. Once

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