J 375 jam A preservative prepared from boiled SUGAR syrup and crushed or pureed FRUIT. Jams need a single cooking step. Fruits like ripe APPLES, QUINCES, currants, CRANBERRIES, GOOSEBERRIES, and PLUMS contain PECTIN, a complex carbohydrate that will gel upon cooling. Low-pectin fruit like BLUEBER- RIES, APRICOTS, CHERRIES, BLACKBERRIES, GRAPES, and PINEAPPLE or stalks of RHUBARB have to be mixed with pectin—or pectin-containing fruits—to obtain a thicker consistency. Jam flavor reflects the amount of sugar used in syrup. The less sugar, the more pronounced the fruity flavor. Jam, like jelly, is a high-calorie, refined CARBOHYDRATE food: A quart of jam typically contains 2 to 2.5 cups of sugar. (See also NATURAL SWEETENER .) jaundice A yellowing of skin, mucous mem- branes, and whites of the eyes due to the buildup of BILE PIGMENT (bilirubin) in the body. Jaundice itself is not a disease, but indicates an underlying problem. Three conditions promote jaundice (bilirubin accumulation). Prehepatic jaundice reflects the excessive breakdown of red blood cells. Bilirubin is produced during the degradation of the red pig- ment of the oxygen-carrying protein HEMOGLOBIN during disposal of aged red blood cells. Bilirubin travels to the LIVER, where it is processed for ex- cretion. In prehepatic jaundice the rate of bilirubin production exceeds the liver’s ability to process incoming bilirubin, for example in hemolytic ANE- MIA. Hepatic jaundice reflects abnormal liver func- tion. HEPATITIS, liver CIRRHOSIS, and certain liver dis- eases imbalance liver metabolism and decrease the liver’s ability to process bilirubin. Extrahepatic jaundice occurs when interference with BILE release from the GALLBLADDER forces bilirubin to back into the liver. Bile duct obstruc- tions commonly include GALLSTONES. (See also DIGESTION; HEME.) jejunum The middle segment of the small intes- tine. The jejunum is about 8 feet long and lies between the DUODENUM (the first 10 inches) and the ILEUM, the last 12 feet of small intestine. Like other regions of the small intestine, the jejunum possesses a large surface area due to its highly wrinkled surface. It is covered by numerous hair- like protrusions called VILLI. Furthermore, each vil- lus cell surface is covered with microscopic projections called MICROVILLI . These physiologic features dramatically increase the absorptive area and aid nutrient absorption and assimilation. (See also DIGESTION; DIGESTIVE TRACT.) jelly A sweet, thickened spread composed of boiled FRUIT juice. Jellies are used on toast and in biscuits and pastry. Commercial jelly contains at least 55 percent fruit. Home-prepared jellies can contain as much as 60 percent sugar. Jelly is there- fore a source of refined CARBOHYDRATE and a high- calorie food with few nutrients other than sugar. Jelly requires two cooking steps. In the first, JUICE is extracted from the fruit and filtered. The clear juice is then cooked with sugar until a gel forms. Often juices are extracted by pressure cooking. However, high temperatures destroy PECTIN, a form of fiber required for gel formation. Pectin is added back in this case. (See also EMPTY CALORIES; NAT- URAL SWEETENER.) joule The international scientific standard unit for ENERGY measurement used for all branches of science. Recommended by the International Orga- nization for Standardization, the joule was adopted by the U.S. Bureau of Standards in 1964. One joule is equal to 4.184 calories and is a measure of mechanical energy while the calorie is based on heat (thermal energy). Nutrition references still use KILOCALORIES as a measure of energy in foods. For example, caloric values (in kilocalories) of foods are published by the USDA; they can be converted to kilojoules (thousands of joules, abbreviated kJ.) by multiplying the listed calories by 4.184. juice The liquid extract of FRUITS and VEGETA- BLES. Juices typically contain only small amounts of FIBER and pulp, which are removed by filtration. Juices can be freshly prepared, concentrated, frozen, canned, or bottled. Juices contain sugars, soluble minerals, and vitamins that can be released when plant tissues are crushed or pulverized. Plant leaves yield green, chlorophyll-rich juices. Preparing juices at home with juicers is popular in the United States. On the other hand, consumers spend more than $9 billion on prepared fruit juices and fruit drinks annually. These preparations are subject to food labeling regulations. The U.S. FDA does not require manufacturers to specify the amount of fruit juice used in a given juice. Manu- facturers must list ingredients in order of predomi- nance, but not by percentages. Listing percentages of ingredients would indicate the actual ratios of the more expensive juices such as kiwi, strawberry, or peach. If the product label specifies “juice” only, then the product contains only pure fruit juice. Any other designation indicates a diluted juice. Apple juice and white grape juice are among the least expensive juices to produce and are fre- quently used in mixtures. Proposals by the FDA would require manufacturers to reveal how much juice is actually in “juice cocktail” or “juice drink.” A juicer/juice extractor is a popular mechanical device that extracts juices from vegetables and fruits. Juicers pulverize the vegetable or fruit by rotary blades. The pulp, seeds, and skin are sepa- rated from the juice by centrifugal filtration. In contrast, blenders combine pulp and juice. Fresh juices provide a convenient way of increasing consumption of vegetables and fruits while cutting back on SOFT DRINKS as part of a healthful diet that includes lower fat, more whole grains, vegetables, and fresh fruit. Eating whole fruits and vegetables can provide essential nutri- ents and lower the risk of cancer and help reduce the risk of diseases associated with deficiencies and aging. However, no juice is a panacea. Juicing removes most fiber and pulp, which retain signifi- cant amounts of vitamins, minerals, and perhaps as yet unknown materials that promote health. Fiber may have beneficial effects, including lowering the risk of colon cancer. There are few studies on the stability of vitamins in juices or on the efficacy of vitamins in the extracts. Fresh juices served immediately are better than those stored because oxidation begins to change the color, flavor, and nutritional quality after the juice is made. Juice combinations of vegetables may begin to separate soon after they are made. The juice is only as good as the produce used; therefore, using organically grown produce and cleaning produce before juicing make sense when whole produce is to be juiced. Ginger and mint can improve the flavor of many juice mixtures. (See also AGING; BALANCED DIET.) junk food A highly processed FOOD. Compared to unprocessed foods, junk foods generally contain less nutritive value beyond their caloric content due to added sugar, refined starch, fat or oils. Junk food therefore represents a major source of “empty calories” in the typical American diet. Junk food is often based on refined grains, such as white flour. Obvious examples include CHIPS, CRACKERS, dough- nuts, cookies, packaged sweet snacks, and sugar- laden BREAKFAST CEREALS. Gelatin desserts, soft ice cream, candy and soft drinks fit into this category as well. One-third of the average American’s diet is junk food, according to a recent study. Potential Problems with Junk Food Diets Individual foods are neither “good” nor “bad.” Whether a food is appropriate depends on how much and how often it is eaten, as well as on the health and nutritional status of the individual con- suming it. Reliance on junk food is often a direct cause of nutrient-deficient diets in the United States. Food manufacturing removes many nutri- ents; consequently, junk foods contain less FIBER; 376 juice less trace minerals such as ZINC, MANGANESE, SELE- NIUM, CALCIUM, CHROMIUM, COPPER, and IRON; and less vitamins like VITAMIN A, VITAMIN B 6 , VITAMIN C, and FOLIC ACID than usually found in unprocessed or minimally processed foods. Simultaneously, food manufacturing adds many materials not pre- sent in the original whole food, including: salt, SUGAR, SATURATED FAT and OIL, synthetic preserva- tives like BHA and BHT, artificial colorings, and fla- vors. To partially correct for nutrient losses in processing, FLOUR and grain products (such as processed breakfast cereals) are enriched with NIACIN, THIAMIN, and RIBOFLAVIN to bring them up to the levels found in whole grain. However, enrich- ment replaces few of the vitamins and trace miner- als, and none of the fiber lost during food manufacture. Overnutrition is a second consequence of diets relying on junk foods. Junk food is a major source of surplus calories and saturated fat in the typical U.S. diet, and a high fat intake is directly tied to a higher risk of CANCER and coronary heart disease. Excessive junk food is a major cause of OBESITY,a critical health problem in the United States. Satu- rated fats—such as HYDROGENATED VEGETABLE OIL, COCONUT OIL or palm kernel oil, LARD, and BUTTER— generally increase CHOLESTEROL levels, perhaps setting the stage for clogged arteries. Characteristi- cally, junk food contains large amounts of refined sweeteners such as high FRUCTOSE CORN SYRUP, DEX - TROSE , maltose malt sugar, corn sweetener and HONEY, as well as SUCROSE. On any given day 46 million Americans eat FAST FOOD , which now shapes many children’s eating habits. Studies suggest that children between the ages of six and 11 are more likely to eat cookies than fruit for snacks. Children between one and five are just as likely to drink powdered and carbonated soft drinks as they are to drink orange juice. (See also CONVENIENCE FOOD; FOOD PROCESSING.) Kant, Ashima. “Consumption of Energy-Dense, Nutri- ent-Poor Foods by Adult Americans; Nutritional and Health Implications. The Third National Health and Nutrition Examination Survey, 1988–1994,” American Journal of Clinical Nutrition 72 (2000): 929–936. juvenile diabetes See DIABETES MELLITUS. juvenile diabetes 377 . also DIGESTION; HEME.) jejunum The middle segment of the small intes- tine. The jejunum is about 8 feet long and lies between the DUODENUM (the first 10 inches) and the ILEUM, the last 12 feet of small intestine (thousands of joules, abbreviated kJ.) by multiplying the listed calories by 4.184. juice The liquid extract of FRUITS and VEGETA- BLES. Juices typically contain only small amounts of FIBER and. change the color, flavor, and nutritional quality after the juice is made. Juice combinations of vegetables may begin to separate soon after they are made. The juice is only as good as the produce