Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

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compensating for high levels of heat production in

other, thyroid-sensitive tissues.

0019 Glucocorticoids exert little or no direct effects on

BAT, even though the tissue has glucocorticoid recep-

tors. However, these adrenocorticoids have central

inhibitory actions on the sympathetic outflow to

BAT, which are particularly noticeable in genetically

obese rodents. Adrenalectomy in these rodents com-

pletely restores sympathetic activity, BAT thermogen-

esis, and DIT to levels seen in lean animals. Only very

low replacement doses of glucocorticoids are required

to reverse the effects of adrenalectomy, suggesting

that these obese animals are hypersensitive to the

inhibitory actions of glucocorticoids. The gluco-

corticoids are thought to inhibit thermogenesis via

feedback inhibition of hypothalamic corticotrophin-

releasing factor (CRF). In addition to its effects on

the pituitary, CRF is a potent stimulus for the sympa-

thetic activation of BAT. Insulin exerts direct, meta-

bolic effects on BAT that are essentially similar to

those that it exerts on white adipose tissue, but it

also influences the tissue indirectly via its actions on

the glucoreceptors of the VMH.

0020 A recent and exciting discovery has been the iden-

tification of the lipostatic hormone, leptin. In add-

ition to influencing energy balance (i.e., fat stores) via

the hypothalamic control of food intake, leptin also

causes sympathetic activation of BAT thermogenesis.

This is likely to prove a complex relationship because

increased sympathetic activity decreases the expres-

sion and release of leptin from both WAT and BAT.

Pharmacological

0021 For many years, the b-adrenergic receptor subtype

responsible for activation of BAT lipolysis and

thermogenesis was thought to be the b

-adrenoceptor.

However, there is much recent evidence to suggest

that the receptor is atypical (neither b

nor b

), and

it is now classified as the b

-adrenoceptor. Much of

this evidence came from experiments using novel

thermogenic drugs developed for the treatment of

obesity, and which were designed to be highly select-

ive agonists of BAT thermogenesis, with little or no

effect on b

-or b

-mediated functions. Subsequent to

the pharmacological identification, the gene sequence

for the b

-adrenoceptor was identified in the human

genome. Treatment with novel b

-adrenoceptor

agonists results in significant weight loss (mainly as

fat) without affecting food intake in both genetic and

dietary obese rodents. However, because the rodent

b-adrenoceptor is different, these agonists are not

effective in humans, and trials with human b

adrenoceptor agonists have yet to be undertaken.

BAT also contains a-adrenergic receptors, which are

known to be important for activating the conversion

of T

to T

by the 5

-deiodinase, and may also play a

minor, facilitatory role in thermogenesis. (See

Obesity: Treatment.)

See also: Exercise: Muscle; Hormones: Thyroid

Hormones; Obesity: Etiology and Diagnosis; Treatment;

Thermogenesis

Further Reading

Cinti S (1999) The Adipose Organ. Milan: Editrice Kurtis.

Himms-Hagen J (1990) Brown adipose tissue thermo-

genesis. In: Schonbaum E and Lomax P (eds) Thermo-

regulation and Biochemistry, pp. 327–414. New York:

Pergamon Press.

Rothwell NJ and Stock MJ (1997) Classics in obesity: A

role for brown adipose tissue in diet-induced thermo-

genesis. Obesity Research 5: 650–656.

Trayhurn P and Nicholls DG (eds) (1986) Brown Adipose

Tissue. London: Edward Arnold.

ADOLESCENTS

J J B Anderson, University of North Carolina,

Chapel Hill, NC, USA

Introduction

0001 Adequate amounts of energy from carbohydrates,

fats, and high-quality protein are considered the crit-

ical nutrients for the hormone-driven processes of

growth and development of the skeleton and the

other organ systems of the body. Developmental se-

quences vary by gender; Tanner staging is frequently

used to assess skeletal development. The needs for

nutrients other than those that provide energy and

essential amino acids (and N) continue to undergo

evaluation as new data are published, and several

micronutrients have new recommendations (see

below). It has become clear in recent years that ado-

lescents in the USA are not consuming the recom-

mended numbers of servings of foods each day from

the basic food groups, which suggests that a very

34 ADOLESCENTS

high percentage are not meeting daily nutrient

requirements.

0002 Because of the wide availability of healthful foods

but limited physical activities, overweight and obesity

have reached epidemic proportions in the US and

many technologically advanced nations. The energy

imbalance in children as well as in adolescents results

from changing societies that value time, speed, and

technological advances in their daily lives over phys-

ical activities and sports, e.g., physical work, walking,

climbing stairs, and other physically demanding

chores. It has been estimated in the 1990s that

between 30 and 50% of North American adults are

overweight (body mass index or BMI > 25). Lower

percentages of adolescents are overweight, but they

represent a much greater prevalence than is desirable

because of the tracking of body weight into adult-

hood and the potential risks for diabetes mellitus

type 2, hypertension, and cardiovascular diseases.

Obesity in children favors the development of

elevated blood pressure and total cholesterol. This

trend toward more overweight and obesity in adoles-

cents is facing many nations, especially those in Asia,

which have plentiful food available for their youth

and declining levels of physical activity.

0003 This review covers the nutritional needs for adoles-

cents, and it also highlights the problem nutrients

that are either too little consumed or ingested in

excess. Other issues of adolescent nutrition are also

addressed.

Nutrient Requirements

0004 Nutrient requirements are divided into macronutri-

ents and micronutrients. Phytomolecules, which are

technically not classified as nutrients and which

are consumed only in plant foods, may have signifi-

cant, but under-appreciated, health benefits.

Energy-providing Nutrients

0005 Fats and carbohydrates, when metabolized, generate

approximately 85% of the energy used by cells; the

other 15% is obtained from the metabolic degrad-

ation of the organic backbone of amino acids. Fats

also provide the essential fatty acids that exist in plant

foods and in fish, but only very minimally in other

animal products.

0006 The current adolescent Recommended Dietary

Allowances (RDAs) for energy, as kilocalories or

kilojoules, are listed in Table 1. As these RDAs are

currently under review, it is likely that they will be

altered, especially because of the problem of over-

consumption of food energy relative to daily energy-

expending activities (see above).

Proteins

0007Proteins supply the essential amino acids, as well as

nonessential amino acids; all the amino acids also

generate N that is used in the cellular synthesis of

many organic molecules, such as nucleic acids.

0008Table 1 lists the recommended intakes of protein,

assuming high-quality protein food sources (protein

digestibility and absorption of approximately 75%).

Micronutrients

0009More than 20 essential micronutrients have been es-

tablished for humankind, and RDAs exist for most of

them. A few micronutrients have become classified as

having less scientific basis for establishing RDAs;

these micronutrients have therefore been given

Adequate Intakes (AIs), even though they may previ-

ously have had RDAs. Calcium is a good example. In

the 10th edition of the RDAs, calcium RDAs for

adolescent girls and boys were 1200 mg per day

from 13 to 19 years of age. In the 1997 edition, the

calcium AIs have been increased to 1300 mg per day

for the same age range.

0010Other micronutrients with AIs include vitamin D,

fluoride, and choline.

0011Table 2 lists the recommended intakes of the micro-

nutrients.

Water

0012Often a forgotten nutrient, water carries no specific

recommendation. Aside from thirst, a general guide

to water consumption is the drinking of 1–1.5 l of

water and/or juices, but not counting caffeinated or

alcoholic beverages because they have mild diuretic

effects. Athletes and those with physically demanding

work will need more than the amounts given. The

goal is to maintain water balance and, therefore, to

avoid dehydration.

Dietary Fiber

0013No specific recommendation has been made for diet-

ary fiber, but food-labeling guidelines in the US sug-

gest that 25 g of fiber (total of both soluble and

insoluble fibers) per day should be consumed with a

2000-kcal diet and 30 g of fiber with a 2500-kcal diet.

It is generally assumed that the vast majority of

adolescents in the USA consume only 10–15 g of

fiber per day.

Phytochemicals

0014The broad group of phytochemicals, which are not

nutrients per se, have become increasingly recognized

as being important components of our diets because

of their numerous roles, such as antioxidants, in

ADOLESCENTS 35

promoting health. Because these nonnutrient mol-

ecules come exclusively from plant foods, adolescents

who avoid fruits and vegetables will consume little of

these molecules and not receive their beneficial

effects. Genistein, a soy-derived isoflavone, has been

shown to have several possible benefits on health.

Nutrition and Skeletal Growth

0015 Growth of the skeleton (height) is typically completed

during adolescence by both girls and boys, and bone

mass is practically maximized at this same time. For a

large majority of girls in the USA, the bone mass

achieved during this adolescent period is considered

to be less than optimal because of limited selections of

nutrient-dense foods and preferences for low nutri-

ent-dense foods. Figure 1 illustrates the declining

consumption of milk and the increasing intake of

soft-drink beverages over the last two decades in the

USA. Concern has arisen that girls, and possibly boys,

are not getting sufficient calcium and other essential

nutrients from milk and related dairy products,

because so many of these nutrients are essential for

the growth of skeletal tissue, and also that adolescent

females may be consuming excessive amounts of

phosphorus, which alters the calcium:phosphorus

ratio in a deleterious way (see Calcium and Phos-

phorus sections).

0016Although not the only nutrient required for the

extracellular mineral phase of bone, calcium may be

the limiting nutrient for mineralization. This divalent

cation is provided in the diet by only a few foods that

are commonly used and available in most countries.

In the USA, dairy foods (exclusive of butter) and

calcium-fortified foods provide the bulk of the cation,

i.e., approximately 60–70%, in the diets of adoles-

cents. Dark green leafy vegetables, such as broccoli,

provide modest, but important, amounts of calcium.

0017The problem of a shortfall in calcium in the pres-

ence of adequate, or possibly, excessive phosphorus

consumption is that the low calcium:phosphorus

ratio potentially produces a persistent elevation in

parathyroid hormone (PTH) that in turn prevents

adequate mineralization of the skeleton during the

tbl0001 Table 1 Food and Nutrition Board, National Academy of Sciences – National Research Council Recommended Dietary Allowances

revised 1989 (abridged), designed for the maintenance of good nutrition of practically all healthy people in the USA

Category Age (year)

or condition

Weight

Height

Protein

(g)

Vitamin A

(mgRE)

Vitamin E

(mg a -TE)

Vitamin K

(mg)

Vitamin C

(mg)

Iron (mg) Zinc

(mg)

Iodine

(mg)

Selenium

(mg)

(kg) (lb) (cm) (in)

Infants 0.0–0.5 6 13 60 24 13 375 3 5 30 6 5 40 10

0.5–1.0 9 20 71 28 14 375 4 10 35 10 5 50 15

Children 1–3 13 29 90 35 16 400 6 15 40 10 10 70 20

4–6 20 44 112 44 24 500 7 20 45 10 10 90 20

7–10 28 62 132 52 28 700 7 30 45 10 10 120 30

Males 11–14 45 99 157 62 45 1000 10 45 50 12 15 150 40

15–18 66 145 176 69 59 1000 10 65 60 12 15 150 50

19–24 72 160 177 70 58 1000 10 70 60 10 15 150 70

25–50 79 174 176 70 63 1000 10 80 60 10 15 150 70

51þ 77 170 173 68 63 1000 10 80 60 10 15 150 70

Females 11–14 46 101 157 62 46 800 8 45 50 15 12 150 45

15–18 55 120 163 64 44 800 8 55 60 15 12 150 50

19–24 58 128 164 65 46 800 8 60 60 15 12 150 55

25–50 63 138 163 64 50 800 8 65 60 15 12 150 55

51þ 65 143 160 63 50 800 8 65 60 10 12 150 55

Pregnant 60 800 10 65 70 30 15 175 65

Lactating 1st 6 months 65 1300 12 65 95 15 19 200 75

2nd 6 months 62 1200 11 65 90 15 16 200 75

The allowances, expressed as average daily intakes over time, are intended to provide for individual variations among most normal persons as they live

in the USA under usual environmental stresses. Diets should be based on a variety of common foods in order to provide other nutrients for which human

requirements have been less well defined. See text for a detailed discussion of allowances and of nutrients not tabulated.

Weights and heights of Reference Adults are actual medians for the USA population of the designated age, as reported by NHANES II. The median

weights and heights of those under 19 years of age were taken from Hamill et al. (1979) (see pp. 16–17). The use of these figures does not imply that the

height-to-weight ratios are ideal.

Retinol equivalents. 1 retinol equivalent ¼ 1 mg of retinol or 6 mgofb-carotene. See text for calculation of vitamin A activity of diets as retinol equivalents.

a-Tocopherol equivalents. 1 mg of d-a tocopherol ¼ 1 a-TE. See text for variation in allowances and calculation of vitamin E activity of the diet as

a-tocopherol equivalents.

This table does not include nutrients for which Dietary Reference Intakes have recently been established [see Dietary Reference Intakes for Calcium,

Phosphorus, Magnesium,Vitamin D, and Fluoride, 1997 and Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B

, Folate, Vitamin B

, Pantothenic

Acid, Biotin, and Choline, 1998].

36 ADOLESCENTS

tbl0002 Table 2 Food and Nutrition Board, Institute of Medicine – National Academy of Sciences Dietary Reference Intakes: recommended levels for individual intake

Life-stage group Calcium

(mg

per day)

Phosphorus

(mg

per day)

Magnesium

(mg

per day)

(mg

per day)

a,b

Fluoride

(mg

per day)

Thiamin

(mg

per day)

Riboflavin

(mg

per day)

Niacin

(mg

per day)

(mg

per day)

Folate

(mg

per day)

(mg

per day)

Pantothenic

acid

(mgper day)

Biotin

(mg

per day)

Choline

(mg

per day)

Infants

0–5 months 210* 110* 30* 5* 0.01* 0.2* 0.3* 2* 0.1* 65* 0.4* 1.7* 5* 125*

6–11 months 270* 275* 75* 5* 0.5* 0.3* 0.4* 3* 0.3* 80* 0.5* 1.8* 6* 150*

Children

1–3 years 500* 460 80 5* 0.7* 0.5 0.5 6 0.5 150 0.9 2* 8* 200*

4–8 years 800* 500 130 5* 1* 0.6 0.6 8 0.6 200 1.2 3* 12* 250*

Males

9–13 years 1300* 1250 240 5* 2* 0.9 0.9 12 1.0 300 1.8 4* 20* 375*

14–18 years 1300* 1250 410 5* 3* 1.2 1.3 16 1.3 400 2.4 5* 25* 550*

19–30 years 1000* 700 400 5* 4* 1.2 1.3 16 1.3 400 2.4 5* 30* 550*

31–50 years 1000* 700 420 5* 4* 1.2 1.3 16 1.3 400 2.4 5* 30* 550*

51–70 years 1200* 700 420 10* 4* 1.2 1.3 16 1.7 400 2.4

5* 30* 550*

>70 years 1200* 700 420 15* 4* 1.2 1.3 16 1.7 400 2.4

5* 30* 550*

Females

9–13 years 1300* 1250 240 5* 2* 0.9 0.9 12 1.0 300 1.8 4* 20* 375*

14–18 years 1300* 1250 360 5* 3* 1.0 1.0 14 1.2 400

2.4 5* 25* 400*

19–30 years 1000* 700 310 5* 3* 1.1 1.1 14 1.3 400

2.4 5* 30* 425*

31–50 years 1000* 700 320 5* 3* 1.1 1.1 14 1.3 400

2.4 5* 30* 425*

51–70 years 1200* 700 320 10* 3* 1.1 1.1 14 1.5 400

2.4

5* 30* 425*

>70 years 1200* 700 320 15* 3* 1.1 1.1 14 1.5 400

2.4

5* 30* 425*

Pregnancy

18 years 1300* 1250 400 5* 3* 1.4 1.4 18 1.9 600

2.6 6* 30* 450*

19–30 years 1000* 700 350 5* 3* 1.4 1.4 18 1.9 600

2.6 6* 30* 450*

31–50 years 1000* 700 360 5* 3* 1.4 1.4 18 1.9 600

2.6 6* 30* 450*

Lactation

18 years 1300* 1250 360 5* 3* 1.5 1.6 17 2.0 500 2.8 7* 35* 550*

19–30 years 1000* 700 310 5* 3* 1.5 1.6 17 2.0 500 2.8 7* 35* 550*

31–50 years 1000* 700 320 5* 3* 1.5 1.6 17 2.0 500 2.8 7* 35* 550*

As cholecalciferol. 1 mg of cholecalciferol ¼ 40 IU vitamin D.

In the absence of adequate exposure to sunlight.

As niacin equivalents. 1 mg of niacin ¼ 60 mg of tryptophan.

As dietary folate equivalents (DFE). 1 DFE ¼ 1 mg of food folate ¼ 0.6 mg of folic acid (from fortified food or supplement) consumed with food ¼ 0.5 mg of synthetic (supplemental) folic acid taken on an empty stomach.

Although AIs have been set for choline, there are few data to assess whether a dietary supply of choline is needed at all stages of the life cycle, and it may be that the choline requirement can be met by endogenous

synthesis at some of these stages.

Since 10–30% of older people may malabsorb food-bound B

, it is advisable for those older than 50 years to meet their RDA mainly by consuming foods fortified with B

or a B

-containing supplement.

In view of evidence linking folate intake with neural tube defects in the fetus, it is recommended that all women capable of becoming pregnant consume 400 mg of synthetic folic acid from fortified foods and/or

supplements in addition to intake of food folate from a varied diet.

It is assumed that women will continue consuming 400 mg of folic acid until their pregnancy is confirmed and they enter prenatal care, which ordinarily occurs after the end of the periconceptional period – the critical

time for formation of the neural tube.

This table presents Recommended Dietary Allowances (RDAs) in bold type and Adequate Intakes (AIs) in ordinary type followed by an asterisk (*). RDAs and AIs may both be used as goals for individual intake. RDAs

are set to meet the needs of almost all (97–98%) individuals in a group. For healthy breastfed infants, the AI is the mean intake. The AI for other life stage groups is believed to cover their needs, but lack of data or

uncertainty in the data prevent clear specification of this coverage.

adolescent growth phase, and also earlier during

prepuberty. The net result is suboptimal skeletal

development and peak bone mass accrual by the end

of adolescence that is less than maximal. So, low

dietary calcium intakes, especially in relation to ele-

vated phosphorus intakes, may be disadvantageous

for young girls and also for young boys. The problem

may be more widespread than previously thought

because of the possibility that the fracture rate in

adolescent girls may be underestimated.

Specific Problem Micronutrients: Deficits

and Excesses

0018Most of the mineral micronutrients reviewed below

exist in the body in solutions as cations (positively

charged) or anions (negatively charged). The vita-

mins, however, exist as organic molecules that may

carry a slight electrical charge that permits their bind-

ing, usually for only brief times, to other molecules.

Calcium

0019Inadequate consumption of calcium in the diets of

adolescents, especially females, in the USA has gained

them the label, ‘the lost generation.’ Calcium intakes

have reached an all-time low, and it has been pre-

dicted that the present generation of girls, and per-

haps boys, are placing themselves at increased risk for

skeletal fractures late in life, as longevity is increasing

in the USA and most other nations. The concern

about increased age-adjusted rates of osteoporosis

assumes that tracking, or following the same relative

path as age increases, of bone mass and density occur,

similar to the tracking of high blood pressure with

increasing age. Therefore, an individual who has less

bone at peak bone development is, during aging,

assumed to follow a path, i.e., track, at the relatively

lower level of bone mass to reach critically low bone

values sooner, e.g., after the menopause, than an

individual who develops a greater peak bone at the

end of the skeletal growth phase (Figure 2).

Iron

0020Low iron consumption by females is one of the most

common nutrient problems throughout the world.

Peak bone mineral density

Menopause

Normal

Low PBM

Fracture

risk range

Age (years)

Bone mineral density (g cm

−2

)

030 40 50 60 70

fig0002 Figure 2 Tracking of bone mass of females from early adulthood to postmenopausal life. Adapted from Anderson JJB (2000)

Nutrition in osteoporosis, in Mahan K and Escott-Stump S (eds) Krause’sFood,Nutrition,andDietTherapy, 10th edn. Philadelphia, PA:

Saunders with permission. PBM ¼peak bone mass.

1977−1978

NFCS

1989−1991

CSF II

1994−1996

CFS II

Percentage

fig0001 Figure 1 Percentages of US individuals in USDA National Food

Consumption Surveys (NFCS and CSF) consuming milk

and

soft drinks

between 1977–1978 and 1994–1996. Note the decline

in milk consumption while soft-drink consumption increased,

according to percentage of consumers.

38 ADOLESCENTS

Adolescent females are particularly likely to develop

iron deficiency, and even the more severe iron-

deficiency anemia, if they have little red meat in

their diets. In the USA, iron-fortified foods, especially

ready-to-eat breakfast cereals, have reduced the

severity of the two forms of iron deficits.

Zinc

0021 Too little zinc consumption by adolescents results

from poor intakes of plant foods. Red meats have

good amounts of zinc, as well as iron, but these

would not be consumed by many adolescents who

avoid red meats.

Magnesium

0022 Insufficient magnesium typically signifies poor selec-

tion of plant foods, especially dark green leafy vege-

tables. Although magnesium intakes by adolescents

are lower than recommended, it has been difficult to

pinpoint real physiologic problems, except possibly

that optimal heart function may be compromised.

Potassium

0023 Too little potassium consumption reflects a limited

selection of fruits and vegetables, the highest potas-

sium-containing sources of this monovalent cation.

Both potassium and magnesium have intracellular

roles, and in part, adequate intakes of potassium

are needed to counter the high intakes of sodium.

Therefore, a dietary balance between potassium and

sodium is needed to maintain efficient cellular func-

tions that require potassium ions. Renal mechanisms

tend to conserve sodium at the expense of potassium

and magnesium, which are excreted in increased

amounts when sodium intakes are higher than recom-

mended.

Sodium

0024 Excessive amounts of sodium in the diet may contrib-

ute to higher blood pressure levels, but still within the

normal range, even in adolescents. Sodium consump-

tion by adolescents is a concern, because the taste for

this mineral, or perhaps sodium sensitivity, becomes

established early in life and continues into adoles-

cence. Higher blood pressure is typically associated

with excessive intakes of sodium throughout adoles-

cence tracks with age.

Phosphorus

0025 Excessive consumption of phosphorus from foods

and soft drinks that contain phosphoric acid reduces

the calcium:phosphorus ratio in the total diet and,

thereby, may increase the circulating level of PTH,

though the elevated PTH concentration usually

remains within the upper range of normality. The

net effect is increased calcium losses, i.e., a negative

calcium balance. In the USA, food-labeling regula-

tions do not require that information on the phos-

phorus content of foods be included. This omission

means that consumers cannot estimate their daily

phosphorus consumption or calculate a calcium:

phosphorus ratio of a food or their entire daily intake.

In addition, a food may include hidden amounts of

phosphorus because of the wide use of phosphate

additives in food processing. The magnitude of this

potential problem of excessive phosphorus has not

been investigated by governmental agencies.

Folic Acid

0026Recent advances in understanding this nutrient have

focused on obtaining sufficient intakes of folic acid to

prevent neural tube defects in offspring, but other

important roles of this B vitamin exist in cell div-

isions, e.g., in red blood cell formation, and gut epi-

thelial turnover of cells. In addition, adequate intakes

of folate also maintain lower circulating levels of

homocysteine, which is now considered a risk factor

for coronary heart disease.

Vitamin D

0027The hormonal form of vitamin enhances intestinal

calcium absorption, when calcium intakes are low,

and also it increases osteoblastic bone-forming activ-

ities. This hormonal metabolite of vitamin D also

stimulates osteoblast cells in bone to make new or-

ganic matrix (osteoid) and therefore new bone tissue.

This metabolite, along with PTH, also contributes to

calcium homeostasis, i.e., regulation of blood calcium

concentration. Too little intake of vitamin D from the

few foods that contain it, and too little sun exposure

for skin biosynthesis of this vitamin, puts individuals

at risk for reduced functions in the gut and bone

tissues. Adolescent intakes of vitamin D are low in

the USA because the consumption of milk that is

fortified with this vitamin has declined (see above).

Vitamin K

0028An established requirement for vitamin K exists for

both blood clotting and bone health. The daily

amount needed for the production of mature osteo-

calcin may be higher than that needed for the blood-

clotting factors, but insufficient information has been

generated to be certain. Vitamin K intakes may be

insufficient in adolescents because of limited con-

sumption of dark green leafy vegetables and legumes.

Problem Areas

0029A few problem areas involving meeting nutrient

requirements by adolescents need special attention

ADOLESCENTS 39

because of their potentially adverse effects on nutri-

tional status.

Adolescent Athletes

0030 The female athlete triad of disordered eating, amen-

orrhea or oligomenorrhea, and osteopenia or low

bone mass, but generally not osteoporosis, has a

marked adverse effect on skeletal mass that has been

shown to increase the risk of stress fractures of ath-

letes, especially those participating in cross-country

running and other endurance events involving run-

ning or repetitive jumping as in volleyball. The risk

of fracture, however, is reduced if estrogen is replaced

in these athletes.

0031 However, Dutch investigators have suggested that

physical activity during adolescence may be even

more important for bone development than calcium

intake, so long as dietary calcium is in the adequate

range, i.e., approximately 1000 mg per day. This con-

clusion has also been reached for female gymnasts,

even amenorrheic gymnasts, because of the positive

effects of weight-loading on the skeleton.

Consumption of Alcoholic Beverages

0032 Over-consumption of alcoholic beverages by adoles-

cents in the USA has become a big problem. The

adverse effects of excessive alcohol consumption on

the nutritional status of adolescents may result from

insufficient food consumption, too many empty cal-

ories from low-nutrient dense alcoholic beverages,

and unwise food choices.

Strict Vegetarians

0033 Vegans or strict vegetarians place themselves at risk

for deficits of several micronutrients if supplements

are not taken. Fortunately, most vegans know about

the pitfalls of this practice of eating, and they do not

develop serious deficiencies. However, a few prob-

lems, such as iron, zinc, and cobalamin deficiencies,

may arise because of the avoidance of all animal

foods. Vegans may also not be able to consume suffi-

cient amounts of calcium or of omega-3 polyunsatur-

ated fatty acids. One of the potential disadvantages of

a vegetarian diet is a low estrogen status across the

life cycle in females. The lower estrogen status may

have an adverse effect on the skeleton, although it

may be protective against estrogen-dependent cancers

and other chronic diseases.

Nutrition Education

0034 Despite the fairly high level of knowledge about nu-

trition by youth in the US, health practices, including

food selection, are too often detrimental to the

support of continued skeletal growth. Part of the

reason for insufficient calcium consumption by ado-

lescent girls is their limited knowledge about daily

calcium allowances and the amounts of calcium in

foods. Adolescents, especially females, clearly do not

eat the way they should and even, perhaps, know how

to eat. These unhealthy eating practices result primar-

ily from bad attitudes toward specific foods, negative

reactions to parental influences, and peer pressure.

0035The serious problem in skeletal development in the

more technologically advanced nations relates to the

unwise food and drink choices being made by our

children, especially after about 10 years of age. In

the USA, adolescent females are not only not getting

sufficient amounts of calcium, but consuming too

little of the nutrient-dense foods in general. The prac-

tices of meal-skipping, grazing, snack/convenience

food selection, and soft-drink consumption insure

suboptimal intakes of several micronutrients in

addition to calcium. Surveys of food-consumption

patterns of girls demonstrate that inadequate mean

consumption exists for the following micronutrients:

calcium, magnesium, iron, zinc, and both fat-soluble

and water-soluble vitamins, especially E, folate, coba-

lamin, and other B vitamins. Vitamins D and K typic-

ally have not been assessed in these surveys. Mean

sodium and phosphorus intakes were higher than

recommended.

0036Avoidance of dairy products by young girls has

become widespread, at least in the USA, for fear of

weight gain, despite the fact that low-fat milks and

no-fat yogurts are widely available. Thus, dairy foods

can be consumed with little or no fat. Education of

the appropriate fats and amounts of daily fat intake

for these females is either lacking or not appropriately

highlighted. Some fat is clearly needed for skeletal

growth, so that extremely low intakes may be dele-

terious. Of course, some mono- and polyunsaturated

fats found in salad dressings and cooking oils are now

being recommended for overall balance within the

types of fatty acids and also for optimal health out-

comes, but young females are barely aware of these

important needs.

0037Finally, nutrition education messages about the

consumption of soft drinks should target both parents

and children to limit the number of servings because

they displace nutritious beverages, such as milk and

fruit juices (see Figure 1), especially when two or

more 400-ml (12-ounce) soft drinks are consumed in

a day (more than 22% of one adolescent population

in the USA). Since many of the soft drinks contain

phosphoric acid as the acidulant, the calcium:phos-

phorus ratio becomes even further skewed away from

a recommended ratio of 0.70–0.75. The widespread

use of soft drinks, in place of milk, has contributed to

40 ADOLESCENTS

the increase in phosphorus consumption and the low

calcium:phosphorus dietary ratio of USA adolescents.

How serious this trend of increased phosphorus con-

sumption is cannot be resolved without a better

understanding of the overall phosphorus intake

from processed foods, lowly processed foods, and

soft drinks that contain phosphoric acid.

See also: Alcohol: Alcohol Consumption; Calcium:

Properties and Determination; Dietary Fiber: Properties

and Sources; Exercise: Metabolic Requirements; Folic

Acid: Properties and Determination; Iron: Physiology;

Functional Foods; Magnesium; Phosphorus:

Properties and Determination; Obesity: Epidemiology;

Plant Antinutritional Factors: Characteristics; Protein:

Requirements; Sodium: Properties and Determination;

Vegetarian Diets; Vitamin K: Properties and

Determination

Further Reading

Alaimo K, McDowell MA, Briefel R et al. (1994) Dietary

Intakes of Vitamins, Minerals, and Fiber of Persons Ages

2 Months and Over in the United States: Third National

Health and Examination Survey, Phase 1, 1988–91. Ad-

vance Data No. 258 (November 3, 1994). Washington,

DC: National Center for Health Statistics, CDC, PHS,

USHHS.

Anderson JJB (1999) Plant-based diets and bone health:

nutritional implications. American Journal of Clinical

Nutrition 70 (supplement): 539S–542S.

Anderson JJB (2000) Nutrition in osteoporosis. In: Mahan

K and Escott-Stump S (eds) Krause’s Food, Nutrition,

and Diet Therapy, 10th edn. Philadelphia, PA: Saunders.

Anderson JJB, Anthony M, Messina M and Garner SC

(1999) Effects of phytooestrogens on tissues. Nutrition

Research Reviews 12: 75–116.

Anderson JJB and Garner SC (eds) (1995) Calcium and

Phosphorus in Health and Disease. Boca Raton, FL:

CRC Press.

Anderson JJB and Miller CP (1998) Lower lifetime estrogen

exposure among vegetarians as a possible risk factor

for osteoporosis: a hypothesis. Vegetarian Nutrition 2:

4–12.

Calvo M and Park YK (1995) Changing phosphorus con-

tent of the US diet: Potential for adverse effects on bone.

Journal of Nutrition 126: 1168S–1180S (1996).

Goulding A, Cannan R, Williams SM et al. (1998) Bone

mineral density in girls with forearm fractures. Journal

of Bone and Mineral Research 13: 143–148.

Harel Z, Riggs S, Vaz R, White L and Menzies G (1998)

Adolescents and calcium: what they do and do not know

and how much they consume. Journal of Adolescent

Health 22: 225–228.

Harnack L, Stang J and Story M (1999) Soft drink con-

sumption among US children and adolescents: nutri-

tional consequences. Journal of the American Dietetic

Association 99: 436–441.

Hetzel BS and Berenson GS (1987) Cardiovascular Risk

Factors in Childhood: Epidemiology and Prevention.

Amsterdam: Elsevier Science.

Institute of Medicine, Food and Nutrition Board (1997)

Dietary Reference Intakes for Calcium, Phosphorus,

Magnesium, Vitamin D, and Fluoride. Washington,

DC: National Academy Press.

Institute of Medicine, Food and Nutrition Board (1998)

Dietary Reference Intakes for Thiamin, Riboflavin,

Niacin, Vitamin B

, Folate, Vitamin B

, Pantothenic

Acid, Biotin, and Choline. Washington, DC: National

Academy Press.

McMurray RG, Harrell JS, Levine AA and Gansky SA

(1995) Childhood obesity elevates blood pressure and

total cholesterol independent of physical activity.

International Journal of Obesity 19: 881–886.

Munoz KA, Krebs-Smith SM, Bvallards-Barbash R and

Cleveland LE (1998) Food intakes of US children and

adolescents compared with recommendations. Pediat-

rics 100 (3 Pt 1): 323–329.

National Research Council, Food and Nutrition

Board(1989) Recommended Dietary Allowances, 10th

edn. Washington, DC: National Academy Press.

Simopoulos A (1999) Essential fatty acids in health and

disease. American Journal of Clinical Nutrition 70 (sup-

plement): 560S–569S.

Tanner JM (1962) Growth in Adolescence, 2nd edn.

Oxford: Blackwell Scientific.

Thrash L and Anderson JJB (2000) The female athlete triad.

Nutrition Today 35: 168–174.

Weaver CM, Peacock M and Johnston CC Jr. (1999) Ado-

lescent nutrition in the prevention of postmenopausal

osteoporosis. Journal of Clinical Endocrinology and

Metabolism 84: 1939–1843.

Weaver CM, Proulx WR and Heaney R (1999) Choices for

achieving adequate dietary calcium with a vegetarian

diet. American Journal of Clinical Nutrition 70 (supple-

ment): 543S–548S.

Welten DC, Kemper HCG, Post GB et al. (1994) Weight-

bearing activity during youth is a more important factor

for peak bone mass than calcium intake. Journal of Bone

and Mineral Research 9: 1089–1095.

Adrenal Hormones See Hormones: Adrenal Hormones; Thyroid Hormones; Gut Hormones; Pancreatic

Hormones; Pituitary Hormones; Steroid Hormones

ADOLESCENTS 41

ADULTERATION OF FOODS

Contents

History and Occurrence

Detection

History and Occurrence

M Tsimidou and D Boskou, Aristotle University of

Thessaloniki, Thessaloniki, Greece

Introduction

0001 Food is a basic prerequisite for human survival and

also for social and economic welfare and progress.

Problems related to food have varied from one period

of history to another, from continent to continent,

and from country to country. The problem of food

adulteration has been a major one and the protection

of the consumer has occupied the attention of civil

authorities from ancient times.

0002 Food is considered adulterated if it contains poisons

or other substances which may render it injurious to

the health of the consumer, or if it contains filth or it is

decomposed; if it contains a coloring agent or other

food additive, that is not approved or contains mater-

ials that disguise inferior quality; if any important

constituent has been wholly or in part abstracted or

any specified ingredient has been substituted by a

nonspecified ingredient; if it contains any substance

that increases its weight and bulk or changes its

strength to improve appearance. A food is misbranded

if it is illicitly labeled or it is a food for which stand-

ards of identity have been written and it fails to

comply with these standards.

History

0003 Food has been liable to adulteration to a greater or

lesser extent since very early times. Mosaic and Egyp-

tian laws made provision for preventing contamin-

ation of meat, while several centuries before the time

of Christ India had regulations prohibiting the adul-

teration of grain and edible fats. Athens had its public

inspector of wines. Adulteration was also common

during the Roman period. Evidence for this is given

in Apicius’ famous cookbook (De Re Coquinaria).

During the Middle Ages in England, pepper and

other costly spices imported from the east were

adulterated by mixing with ground nutshells, local

seeds, and olive pits.

0004Between the 13th and 16th centuries, bread, wine,

beer, spices, and valuable natural coloring materials

were often adulterated. In England in 1319, a meat-

market overseer succeeded in putting a butcher in the

pillory for selling unsound beef. Wines were ‘sophis-

ticated’ (adulterated) with burnt sugar, juices, starch

and gums, and other substances. Such practices may

have reduced the quality of the wine but they were

not injurious to health. After the 18th century, how-

ever, food adulteration became dangerous. Vinegar

was often adulterated with sulfuric acid, wine with

preservatives containing lead salts, green vegetables

in vinegar with copper (to improve color), essential

oils with oil of turpentine, confectionery products

with colorings containing lead and arsenic, choc-

olate with Venetian red (ferric oxide), and red pepper

with vermilion (mercury sulfide). ‘Black extract’,

obtained by boiling poisonous berries of Cocculus

indicus in water and concentrating the fluid, was

used in beer. This extract imparted flavor, but also

narcotic properties and intoxicating qualities to the

beverage.

0005Bread was not only the basic item of diet for many

centuries but also the one most subjected to adulter-

ation. The incorporation of sieved boiled potatoes,

chalk, or bone ashes in the flour was a common

fraudulent practice, but the most serious example

was the addition of alum, which whitened flour of

inferior quality.

0006Recipe books of the 18th century contain instruc-

tions, which today would cause alarm. The recipe

for preserving green color in pickles is character-

istic: ‘To render pickles green, boil them with a half-

penny or allow them to stand for 24 hours in copper

brass pans.’ It is not surprising that records of

that period list a number of deaths from copper

poisoning.

0007Frederic Accum, writing from London in 1820,

gives a vivid description of the adulteration of bread,

alcoholic drinks, tea, coffee, and many other foods.

Accum claimed that: ‘Indeed, it would be difficult to

mention a single article of food which is not to be met

42 ADULTERATION OF FOODS/History and Occurrence

with in an adulterated state; and there are some sub-

stances which are scarcely ever to be genuine.’ Even

if these accusations are somewhat overstated, the

seriousness of intentional adulteration of food,

which prevailed between 1800 and the early 1900s,

is undisputed.

0008 The second decade of the 19th century marks the

beginning of the second period in the history of food

adulteration. In the first period (ancient times to

about 1820) food was procured from small enter-

prises and individuals who were, to a certain extent,

responsible for their own transactions. In the second

period (early 1800s to 1900s), the methods of food

production changed significantly. Large-scale food

production became necessary because of the indus-

trial revolution, which led to a move of population

from country to city. This created conditions that

were conducive to large-scale adulteration of food.

In the second half of the 19th century the first pub-

licly supported analytical laboratories for food in-

spection were established in Germany and the USA.

Intentional adulteration of food remained a serious

problem until the beginning of the 20th century.

Regulatory pressures and the effectiveness of ana-

lytical methods reduced the frequency and magnitude

of food adulteration. Further improvements have

been achieved up to the present time and, owing to

strict legal standards and also to the growth of an

increasingly critical public, deliberate adulteration in

industrialized countries has become less serious. Of

course, fraudulent practices still continue in most

countries, especially those which lack adequate

means to insure that laws and regulations are en-

forced.

Food Additives

0009 The excessive use of additives and the use of nonper-

mitted ones present a serious threat to food safety. It

could be argued that a fourth phase of food adulter-

ation began some 40 years ago, when foods contain-

ing chemicals became prevalent in the diet. Since

then, we have moved gradually from an outrage

over fraud, sometimes practiced with dangerous sub-

stances, to a growing concern over the more subtle

toxic effects of common chemicals added to food to

assist manufacture and storage. As a result, there has

been a shift in focus from food adulteration to safety

of food, and to a different approach which empha-

sizes not only evaluation of the food in its entirety, but

also evaluation of individual components. Current

legislation relating to food additives provides statu-

tory lists of all permitted additives which may be used

and, where appropriate, the maximum levels for their

use. Nevertheless, as the food industry becomes in-

creasingly sophisticated and relies more and more on

the use of additives, many consumers believe that

governments are unable to control the situation and

that preservatives, antioxidants, colorings, flavor or

texture modifiers, and other chemicals are and always

will remain a potential hazard. (See Food Additives:

Safety.)

Food Legislation

0010The use of government regulatory powers to control

the purity and safety of foods is very old but the first

serious efforts to regulate malpractice took place only

in the 19th century. The first general food laws were

passed in the UK in 1860. Accum’s book, A Treatise

on Adulteration of Food and Culinary Poisons

(1820), aroused the indignation of the British public.

In 1850, Thomas Wakley, editor of the Lancet, estab-

lished an Analytical Sanitary Commission under the

direction of Arthur Hill Hassal, the first man to in-

vestigate food adulteration from a scientific point of

view. He turned the microscope into a weapon in the

detection of adulterants. The Commission’s reports,

published in the Lancet from 1851 to 1854, led to the

formation of a parliamentary committee to investi-

gate food adulteration and, in 1860, to the passage of

the world’s first Food and Drink Act. This law made it

a criminal offence to sell adulterated food and drink.

It also established the appointment of public analysts

to examine foodstuffs produced throughout the coun-

try. In 1866, a second country, New Zealand, passed

pure food legislation and, in 1874, Canada passed the

Food and Drug Law.

0011In the 20th century, new regulations were de-

veloped in industrialized countries, and old regula-

tions were repeatedly updated, taking into account

the advice of governmental and international com-

mittees. Modern food law establishes and maintains

standards for the composition of food, controls the

use of additives and extent of contamination, controls

packaging materials and unsanitary practices in the

production of food, and restrains unwarranted and

misleading claims and advertisements. Effective food

surveillance systems have also been developed which

insure that there is a constant supply of the right kind

of food to keep people properly fed and that the food

we eat is wholesome as a result of strict adherence to

national and international law. The current world-

wide access to data and information through the

internet may soon reveal that administrative trace-

ability can be successfully used to monitor the sale

of fraudulent food products in the global market of

the 21st century.

ADULTERATION OF FOODS/History and Occurrence 43