The Encyclopedia Of Nutrition And Good Health - J pps

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