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

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Yam

001 4 The yam (Dioscorea spp., family Dioscoreaceae) is a

carbohydrate-rich food crop grown in some tropical

areas, especially Africa, where its importance exceeds

that of sweet potato. In the USA, the term yam is

incorrectly applied to orange, moist-fleshed sweet

potatoes in the market place. Accordingly, there is

some confusion in popular terminology. True yams

are not grown commercially in the continental USA,

but are occasionally seen in ethnic markets.

Global Distribution, Commercial Importance, and

Varieties

001 5 About 96% of world yam production occurs in

Africa, principally West Africa (Table 4). Other pro-

duction centers include South America, the Carib-

bean islands, and Oceania. Nigeria alone produces

over two-thirds of the world yam crop. World pro-

duction has increased in recent years, due primarily to

increased area devoted to its production.

0016 International trade in yams is limited to small

markets in North America and Europe. For the most

part,yamsareused within thefamilyoraresoldlocally.

Where yams and other carbohydrate-rich root crops

such as cassava and sweet potato are available in the

same market, yams usually command a higher price.

Furthermore, yams are favored over other root crops

for special occasions and to serve to guests.

0017Five species of Dioscorea are grown commonly for

food (Table 5) and an additional five of about 60

known species are occasionally used for food.

Dioscorea alata, the greater yam, is widely distrib-

uted throughout the tropics, including South-east

Asia, Africa, and the Caribbean islands. The yellow

yam (D. cayenenis) is grown primarily in West Africa

and the Caribbean. D. esculenta, the lesser yam, is

distributed widely in the tropics, but production

is mostly in South-east Asia, the south Pacific

islands, and the Caribbean islands. The white yam

(D. rotundata) is the most important yam in West

Africa and is grown extensively in the Caribbean,

and to some extent in East Africa. Dioscorea trifida

is the only yam of New World origin, and its cultiva-

tion is mostly in the Caribbean. Distinct varieties

of some yam species are available, but different

names are used for the same yam in different parts

of the world so that variatal designations are not

particularly useful.

Morphology and Anatomy of the Edible Portion

0018The edible part of the yam plant is the tuber that

varies in shape according to species (Table 5) and

environment in which it was grown. Individual tubers

tbl0004 Table 4 Worldyamproduction

RegionAreaharvested(10

)Yield(kgha

1

)Production(10

1989^19911995^199620011989^19911995^199620011989^19911995^19962001

Africa 2153 3014 3908 9312 9773 9499 20 073 31 113 37 124

North and Central America 57 60 55 6915 8068 7825 396 490 431

South America 41 44 56 7897 9435 9863 317 414 549

Asia 15 17 14 14 314 14 406 16 017 208 237 224

Europe 7953 9955 16 154 1 1 2

Oceania 18 18 18 15 735 15 702 16 181 283 286 283

World 2283 3243 4051 9307 10 320 9532 21 278 32 541 38 614

DatafromFAO(2002)www.FAO.org.

tbl0005 Table 5 Descriptions of the most common Dioscorea species grown for food

Species Common name Origin Tuber number

and shape

Flesh color Leaf shape and

phyllotaxy

Stem

appearance

D. alat a L. Water or greater

yam

South-east Asia Single, cylindrical White to purple Ovate, opposite Winged

D. cayenensis

Lam.

Yellow or yellow

guinea yam

Western Africa Single, variable Yellow Pointed, opposite;

alternate

Spiny

D. esculenta

Burk.

Lesser yam Potato

yam

China 4–20 ovoid White Simple, alternate Spiny

D. rotund a t a

Poir.

White or white

guinea yam

Western Africa Single, cylindrical,

spherical

White to yellow Simple, opposite Circular,

smooth-spiny

D. trifida L. Cush-cush Tropical America Numerous, elongate White to purple Lobed, alternate;

opposite

Winged

Janick J (1990) Tropical root and tuber crops. Horticultural Reviews 12: 157–196. Reprinted by permission of Timber Press, Portland, OR, USA.

5968 VEGETABLES OF TROPICAL CLIMATES/Root Crops of Lowlands

may range from a few grams to over 50 kg in weight,

and tubers 2–3 m long have been produced under

special cultural conditions.

0019 Single or multiple tubers develop from a corm-like

structure at the base of the vine. The tubers are

covered by a thick layer of cork that often bears

many cracks caused by tuber expansion. Roots may

arise from the tuber, resulting in a somewhat hairy

appearance before the dried roots slough off. The

tuber has three general morphological sections – the

head, middle, and tail. Buds are initiated from

the head section after dormancy has been broken.

0020 The bulk of the tuber is composed of starch-filled,

thick-walled parenchyma cells in the central core.

Vascular bundles having both xylem and phloem are

scattered throughout the central core. A layer of meri-

stematic cells that give rise to the buds surround the

central core, and in turn is surrounded by a layer of

thin-walled cortical cells. Finally, the entire tuber is

surrounded by several layers of cork arranged in

radial rows that arise from cork cambia.

Nutritional Composition

0021 The principal nutritional component of yam is carbo-

hydrate (Table 2). Like sweet potato, yam is a good

source of ascorbic acid; however, it does not have the

advantage of the high pro Vitamin A found in sweet

potato. Yam is generally inferior to sweet potato in

terms of amino acid content (Table 3). Exceptions are

cystein, arginine, histidine, and glutamic acid, the

levels of which are slightly higher in yam. However,

other literature sources site yam as having a superior-

quality protein compared with sweet potato, and

being similar to potato in protein quality.

Handling and Storage

0022 Dormant yams of some species may be stored in the

ground for as long as 4 months. Harvested yams are

stored in ‘yam barns’ in West Africa; the tubers are

tied to vertical poles under a shelter to give the ap-

pearance of a barn with walls. Yams will remain in

good condition during the dry period with only loss of

weight from shrinkage and respiration, but loss from

rots occurs quickly with the return of the rainy

season. Postharvest applications of gibberellic acid

prolong harvest life, and fungicide treatments retard

rots, but these treatments are rarely practiced. Care

during harvest to prevent cuts and bruises is required

for long-term tuber storage. Yams can be cured like

sweet potatoes to assist healing of wounds and pro-

long storage life, but this practice is uncommon.

Yams can be stored under refrigeration, if available,

at 16



C and 70% RH, but are subject to chilling

injury at temperatures lower than 12



Industrial Uses

0023Currently, there is little processing of yams, but the

potential is great because the demand for yam as a

food is high since fresh yams are not available until

the next harvest season once tuber dormancy is

broken and sprouting occurs. Dehydrated products

such as chips or flour serve to fill the demand for

yams to a minor extent, but consumer acceptance of

these products is not universal.

Yam Bean

0024The yam bean (Pachyrrhizus erosus L., Family Faba-

ceae) is a minor tropical root crop known by many

common names throughout the world. Jicama or

some variation thereof is used most frequently.

Global Distribution, Commercial Importance, and

Varieties

0025Yam bean is native to Mexico and northern Central

America and is still cultivated there. In addition,

yam bean is produced in South-east Asia, China, the

Philippines, South America, the Caribbean islands,

and East Africa.

0026For the most part, yam bean is used locally and

does not enter into international trade. Production

data are not available, but Mexico is likely to be the

leading producer with an estimated 4000 ha under

cultivation. Experimental yields of 80–90 t ha

1

have

been reported from several countries. Traditionally,

creole types of yam bean have been grown in Mexico,

but they are being replaced by two new varieties –

Agreadulce and Cristalina.

Morphology of the Edible Portion

0027The brownish roots are mostly turnip-shaped, but

long and slender types are known. The preferred

market size is 10–15 cm in diameter, which is attained

in approximately 90 days from planting of seed.

However, the root will continue to grow and reach a

diameter of 30–45 cm and weight of 2–3 kg if not

harvested at market maturity. The thick, tough skin

is easily peeled to reveal the white flesh, which is crisp

and succulent. Thinly sliced roots are eaten raw with

a garnish or used in salads, and occasionally, it is

cooked or pickled. In the USA, yam bean is often

used as a substitute for water chestnut in oriental

cuisine.

Nutritional Composition

0028Yam bean root is more succulent than that of sweet

potato and yam and considerably less carbohydrate-

rich (Table 2). Of the vitamins, only ascorbic acid is

provided in significant amounts in yam bean. Except

VEGETABLES OF TROPICAL CLIMATES/Root Crops of Lowlands 5969

for histidine and aspartic acid, yam bean is inferior

to sweet potato and yam in amino acid content

(Table 3). Typically, yam bean does not play a major

role in the diet, in contrast to sweet potato and yam.

Handling and Storage

0029 Yam bean roots are usually harvested by hand,

washed, and stored in baskets or crates until sold.

Refrigerated storage at 13–18



C and 65–70% RH

provides conditions for storage of roots for 1–2

months. Chilling injury occurs at temperatures less

than 12



C, and sprouting may occur at temperatures

above 18



Industrial Uses

0030 All yam bean roots are consumed in the fresh state.

The mature seeds have 0.12–0.43% rotenone, an

insecticide, but this has not been exploited for com-

mercial use.

See also: Amino Acids: Properties and Occurrence;

Cassava: Uses as a Raw Material; Controlled-

atmosphere Storage: Effects on Fruit and Vegetables;

Dietary Requirements of Adults; Drying: Drying Using

Natural Radiation; Fungicides; Protein: Quality

Further Reading

Coursey DG (1967) Yams. London: Longmans.

FAO (1990) Roots, Tubers, Plantains and Bananas in

Human Nutrition. FAO Food and Nutrition Ser. No.

24, Rome: Food and Agriculture Organization.

Horton D, Prain G and Gregory P (1989) High-level invest-

ment returns for global sweet potato research and devel-

opment. CIP (International Potato Center) Circular

17(3): 1–11.

Martin FW (1972) Yam Production Methods. US Depart-

ment of Agriculture Product Research Report 147.

Washington, DC: US Government Printing Office.

O’Hair SK (1990) Tropical root and tuber crops. Horticul-

tural Reviews 12: 157–196.

Onwueme IC (1978) The Tropical Tuber Crops. Chichester,

UK: John Wiley.

Ravi V and Indira P (1999) Crop physiology of sweetpotato.

Horticultural Reviews 23: 277–338.

Rubatzky VE and Yamaguchi M (1997) World Vegetables.

Principles, Production, and Nutritive Values, 2nd edn.

New York: Chapman & Hall.

Steinbauer CE and Kushman LJ (1971) Sweetpotato Cul-

ture and Diseases. US Department of Agriculture Hand-

book 388. Washington, DC: US Government Printing

Office.

Tindall HD (1983) Vegetables in the Tropics. London:

MacMillan.

Villareal RL and Griggs TD (eds) (1982) Sweet Potato.

Tainan, Taiwan: Asian Vegetable Research and Develop-

ment Center.

Edible Aroids

SKO’Hair, University of Florida, Homestead, FL, USA

D N Maynard, Universityof Florida, Bradenton, FL, USA

Background

0001There are plants from five genera within the Araceae

family that are cultured for their starch-filled storage

organs or herbaceous leaves. Most thrive in moist to

flooded conditions and are among the most shade-

tolerant of terrestrial food crops. Many are grown in

moist tropical environments where other starchy food

crops fail to flourish.

0002The edible aroids are known by many common

names, often being confused with one another by

the untrained eye. Part of the confusion arises from

the low flowering frequency of most species. Some

are cultured as foods of famine, and others are valued

as staple foods. In the Caribbean, they are often the

only food crops remaining after tropical storms.

0003All plant parts contain varying concentrations of

an acrid factor, which appears to be carried on the

surface of the needle-like calcium oxalate raphide

crystals. It is believed to be either a cysteine protein-

ase or a glucoside that causes considerable irritation

or swelling of affected tissues. Concentrations vary

considerably among genera, species, and varieties,

also being affected by plant age and cultural condi-

tions. Cooking or other processing procedures des-

troy the acrid factors in the more popular clones.

Naturalized or ‘wild’ clones need extensive process-

ing to render them palatable. Levels of acridity and

fiber content are factors that determine consumer

acceptance of varieties. Production figures are not

available for most of the crops, since they are grown

as subsistence crops in small, often mixed plantings.

Taro (Colocasia) and tannia (Xanthosoma) figures

are combined with an estimated 5 10

t being pro-

duced world-wide.

0004As with all tropical root and tuber crops, yields and

the size of individual edible portions vary consider-

ably with planting density and length of time that the

crop was allowed to remain in production. As the

density diminishes, the size of individual edible parts

increases. However, after a point, the marketable

yield or crop value for the area planted declines.

Thus, sizes of individual parts can be misleading

if planting densities are not included. Early plant

growth is characterized by the development of a

root system and foliage production. Once total plant

leaf area has reached a peak, well into the production

period, the rate of corm and cormel production

increases. This phase lasts two or more months.

5970 VEGETABLES OF TROPICAL CLIMATES/Edible Aroids

Once the corm or cormel production phase is

through, the plants of some species go dormant, and

others must be harvested to prevent excessive

amounts of sprouting and a decline in starch content

and product quality.

0005 Since all are propagated from vegetative cuttings,

the development of certified insect and disease-free

planting material is essential for optimal crop prod-

uctivity. Dasheen mosaic virus (DMV) is commonly

found throughout all genera, even in symptomless

plants. Yield reductions due to DMV infection have

been reported in both food and ornamental species.

0006 With the exception of taro and tannia, postharvest

and processing technology is very limited, since most

are considered minor crops, and mechanization is not

well developed. Like potato, the starches and carbo-

hydrates have food and industrial uses.

Elephant (Foot) Yam

0007 Plants in the genus Amorphophallus are unique

among food crops as the plant produces only one

petiole with a single umbrella-like compound leaf at

the top. A flattened edible corm is produced at the

base of the single compound leaf, enlarging from one

year to the next if left unharvested. By the end of the

first year, corms can weigh as much as 7 kg. Sections,

up to 0.5 kg, of the corm are used as planting material

for the next crop.

0008 Amorphophallus is most commonly found in

certain Pacific islands and much of Asia. In China

and Japan, a popular species is known as konjac

or konjac with production in China dating back

2000–3000 years. Its commercial value is greatest in

Japan, where it is a valued food crop. Most Amor-

phophallus varieties are separated only by species

names. Of 80–90 species, only a few are edible, with

elephant foot yam (Amorphophallus campanulatus

Bl. ex Decaisne) and konjac (konnyaku) (A. rivieri

du Rieu (syn. A. konjac K. Koch)) being the most

popular. Others are valued as novel ornamentals

or as medicinal plants. Since flowering and seed set

are commonn a few improved varieties and interspe-

cific hybrids, many with reduced levels of acridity,

exist.

0009The main carbohydrate, mannose (glucomannan),

is a soluble dietary fiber that is not absorbed by

humans. Otherwise, corms are similar in nutritional

value with the other aroids (Table 1), with the excep-

tion of vitamin A levels, which are higher. The corms

of some are considered to have medicinal value. In

Japan, consumption is believed to reduce blood chol-

esterol and triglyceride levels in humans. Refer to

individual nutrients. (See Carbohydrates: Classifica-

tion and Properties; Cholesterol: Determining Blood

Cholesterol Levels.)

0010At the end of the warm moist growing period,

plants pass through a dormant period, at which time

the corms are harvested as needed. Little information

is available on postharvest storage. In general, corms

are stored under ambient conditions.

0011The corms are processed to extract mannan, to

make a wine, and as konjac curd for food. Glucoman-

nan extracts have value as a fruit and vegetable

preservative and as a sweetening agent.

Giant Taro

0012Alocasia or giant taro (Alocasia macrorrhiza (L.)

Schott) is probably better known as an ornamental

tropical plant than as a food crop. It is easily recog-

nized by the spear-like appearance of the leaf laminae

and petioles. Other species, including A. indica

(Roxb.) Schott, A. cucullata Schott and A. fornicata

Schott have been utilized as food crops.

0013Alocasia is among the oldest of food crops in

Oceania, where, at one time, it was a staple food. Its

spread as a food crop has been limited to Oceania and

the Asian tropics. Its commercial importance is cur-

rently greater as an ornamental, than as a food crop.

tbl0001 Table 1 Average composition (per 100 g of raw product) of edible aroids

Constituent Elephant yam Giant taro Swamp taro Tannia Taro

Moisture (g) 79 84 68 64 75

Carbohydrate (g) 10 15 29 32 21

Protein (g) 1.2 0.6 0.8 2.2 2.2

Fat (g) 0.2 0.3 0.2 0.2 0.4

Fiber (g) 0.8 1.0 0.8

Ash (g) 0.8 0.3 1.2 1.0

Calcium (mg) 43 30 578 16 34

Phosphorus (mg) 22 50 28 47 62

Iron (mg) 0.6 1 1.3 0.9 1.2

Vitamin A (IU) 270

Ascorbic acid (mg) 5 8 8

Data from Leung WTW, Burtrum RRB and Chang FM (1972) Food Composition Table for Use in East Asia. Rome: Food and Agriculture Organization; Murai

MF, Pen F and Miller CD (1958) Some Tropical South Pack Island Foods. Honolulu, HI: University of Hawaii Press, with permission.

VEGETABLES OF TROPICAL CLIMATES/Edible Aroids 5971

There are only a few cultivated clones, most of which

are found in the South Pacific. Nevertheless, one

Indonesian germplasm collection reportedly contains

70 accessions. Flowering is common. However, there

is little research in breeding for improved varieties.

0014 The edible portion is the large semicompressed

stem containing many starch-filled parenchymatous

cells. During the first year of growth, the stems can

reach 12 m in height with a diameter of 6 cm and a

weight of approximately 18 kg. The plants can be left

unharvested until needed.

0015 There is little nutritional information for the stems.

However, the carbohydrate content is among the

highest of the edible aroids (Table 1). Owing to the

nature of erect stems, the structural carbohydrate

content is high. Of the edible aroids, alocasia is gen-

erally considered to be less palatable and more acrid.

0016 There is no handling or storage information on this

crop. It is harvested as needed for local consumption.

0017 There is currently no industrial use for giant taro.

Tannia

0018 Tannia (Xanthosoma sagittifolium (L.) Schott), also

known as coco(yam), malanga, tanier, or yautia,

originated in the wet valleys of northeastern South

America. It was domesticated and carried throughout

the Caribbean basin by migrating Indian tribes. There

is much confusion within this genus, with the same

plant being given more than one species name. In

addition, tannia is often confused with taro. In parts

of Africa, both are known as cocoyam, and in a few

other places, both are listed as taro.

0019 Tannia is a valued food crop in most of the Carib-

bean islands, Florida (USA), western Africa, parts of

Egypt, India, and Oceania. In most regions, it is

grown for sale in local markets. However, in Florida,

the crop is valued at $8.6 10

annually. Costa Rica

and the Dominican Republic are exporters of the

crop. There are only a few varieties of tannia, and

most have white flesh. Pink and yellow-fleshed types

are less common and occasionally classified as

X. violaceum Schott and X. atrovirens C. Koch, re-

spectively. The same clone may have more than one

common name. Common varieties in the English

speaking Caribbean are South Dade White, Bruce

and Rabess, which are white-fleshed. Vinola and

Jamaique are purple- to pink-fleshed. Flowering is

rare, and hand pollinations are required for seed pro-

duction, thus accounting for the few varieties. Formal

breeding programs in West Africa have focused on

developing root rot-resistant genotypes.

0020 The main stem of the white- and pink-fleshed types

is an inedible corm, which is occasionally boiled for

animal feed. The edible portions of these two types

are club-shaped, underground offshoots of the main

corm that develop into cormels weighing as much as

1 kg each. The main corm of the yellow-fleshed types

is the part that is consumed. Young leaves are occa-

sionally cooked as potherbs. In the western hemi-

sphere, tropics plants of X. brasiliense (Desf.) are

occasionally grown solely for their edible leaves.

0021The cormels are mostly starch, possessing the

highest starch concentrations among the edible aroids

(Table 1). The nutritional value of the leaves is con-

sidered to be comparable to spinach, complementing

the high energy level of the cormels (Table 2). (See:

Starch: Sources and Processing.)

0022Cormels of the favored clones have a natural dor-

mancy period of 1–3 months and are planted year-

round in moist production areas. They are planted

and harvested as needed. Cormels can be removed

individually or the entire plant can be uprooted. In

commercial settings, cormels are washed and pack-

aged in waxed boxes prior to shipment. The storage

period of the cormels can be extended by several

months by holding them at 7



C and 80% relative

humidity (RH). Although not common, cormels can

be dried and stored for extended periods. (See

Controlled-atmosphere Storage: Effects on Fruit and

Vegetables.)

0023Processing of tannia is limited to freezing of peeled

cormels and bagging them in consumer packs in the

form of a ready to cook frozen food. There are many

potential uses similar to those described for taro.

Taro

0024Taro (Colocasia esculenta (L.) Schott), also known as

eddoe or dasheen, originated in the Bay of Bengal

region of South-east Asia. It was carried by early

Polynesians throughout Oceania, where it became

a staple food. It is an ancient crop in Asia, being

tbl0002Table 2 Average composition (per 100 g of raw product) of

edible aroid leaves

Constituent Tannia Taro

Moisture (g) 90 90

Carbohydrate (g) 5.3 5.7

Protein (g) 2.5 2.4

Fat (g) 1.0 0.6

Fiber (g) 2.1 1.5

Ash (g) 1.3 1.3

Calcium (mg) 95 98

Phosphorus (mg) 388 49

Iron (mg) 2.0 2.0

Vitamin A (IU) 3300 180

Ascorbic acid (mg) 37 11

Data from Leung WTW, Burtrum RRB and Chang FH (1972) Food

Composition Table for Use in East Asia. Rome: Food and Agriculture

Organization, with permission.

5972 VEGETABLES OF TROPICAL CLIMATES/Edible Aroids

introduced into Japan more than 2500 years ago.

Compared with tannia, it is better adapted to exces-

sively moist areas. Many clones are grown like rice in

flooded conditions.

0025 Taro has lost some popularity in the traditional

areas of production in the South Pacific and Asia

owing to significant crop losses attributed to taro leaf

blight disease. Nevertheless, it is still widely grown in

this region, being the most important food crop. Prom-

ising levels of genetic resistance and other control

methods for this malady should help to return this

crop to traditional levels of production. Other areas

where taro is grown include most islands in the Carib-

bean, Hawaii, parts of western and northern Africa,

the Philippines, Japan, and South-east Asia. There are

more varieties of taro than all the other edible aroids

combined, with estimates exceeding 1000. Some

clones flower and set seed under natural conditions,

providing for genetic variability. Formal breeding pro-

grams in the Pacific basin and Asia have resulted in the

development of improved genotypes. Bun long and

Lehua maoli are popular varieties in Hawaii. Varieties

are most commonly separated by coloration of the

leaves and corms as well as by habit of cormel forma-

tion. One of two basic types, the dasheen, produces

one large, edible corm up to 3–5 kg in weight, with few

offshoots. The other type, the eddoe or Chinese taro,

produces a much smaller main corm with several

slightly smaller edible offshoot corms.

0026 The corms are the primary edible portion of the

plant. Young leaves and blanched leaves are also

eaten as potherbs.

0027 The nutritional composition of taro corms (Table 1)

and leaves (Table 2) are very similar to those of tannia.

0028 At harvest, approximately 2–3 cm of the petioles

should be left attached to the corm in order to

minimize problems associated with invasion by rot-

causing organisms. Losses can be reduced by allowing

time for wound periderm formation before placing

corms in bulk storage. Since there is no distinct dor-

mancy period, the shelf-life of taro is shorter than that

of tannia. Temperatures as low as 5



C can be used to

extend the storage life.

0029 In the USA, corms are sliced thinly and cooked in

hot oil, resulting in a product similar to potato chips

or crisps. Experimental procedures indicate that taro

products can include flour, cereals, bread, noodles,

cake, infant and invalid food, and beverage powder,

as well as flaked, canned, or frozen corms.

Swamp Taro

0030 Swamp taro (Cyrtosperma chamissonis (Schott)

Merr) is pre-Polynesian and considered to be among

the oldest of the South Pacific food crops.

0031Swamp taro flourishes in warm, humid climates.

Production is mostly limited to the low islands of

Micronesia, where it is primarily grown as a trad-

itional food crop. Varieties are differentiated by

their acrid factors, leaf shape, color, spininess of the

petiole, and flowering habit. The time to maturity

(measured in years) and tolerance to saltwater intru-

sion vary slightly.

0032The main corm is the edible portion of the plant,

increasing in size from one year to the next; 10-year-

old corms can weigh as much as 300 kg. Side-shoots

are used as propagules.

0033The carbohydrate content of swamp taro is similar

to that of taro and tannia (Table 1).

0034Plants are harvested as needed, except when storms

raise the salinity levels of the coastal bogs. At such

times, plants are harvested immediately and stored

until planting conditions are favorable.

0035There are no industrial uses for swamp taro.

See also: Controlled-atmosphere Storage: Effects on

Fruit and Vegetables

Further Reading

Coursey DG (1968) The edible aroids. World Crops 20:

25–30.

FAO (1990) Roots, Tubers, Plantains and Bananas in

Human Nutrition. FAO Food and Nutrition Series

No. 24. Rome: Food and Agriculture Organization.

Kay DE (1973) Root Crops. London: Tropical Products

Institute.

Leung WTW, Burtrum RRB and Chang FH (1972) Food

Composition Table for Use in East Asia. Rome: Food

and Agriculture Organization.

Murai MF, Pen F and Miller CD (1958) Some Tropical

South Pack Island Foods. Honolulu, HI: University of

Hawaii Press.

O’Hair SK and Asokan MP (1986) Edible aroids: botany

and horticulture. Horticultural Reviews 8: 43–99.

O’Hair SK, Snyder G and Morton JF (1982) Wetland taro: a

neglected crop for food, feed, and fuel. Proceedings of

the Florida State Horticultural Society 95: 367–374.

Suzuki M, Kano M, Mitani A, Mochida F and Ariki M

(1975) On the irritant substance, 3,4-diglycosilico-

benzaldehyde in taro Colocasia antiquorum. Journal of

the Japanese Society of Food and Nutrition 28: 55–59.

Terasawa F, Tsuji K, Tsuji E et al. (1979) The effects of

konjac flour on the blood lipids in the elderly subjects.

Japanese Journal of Nutrition 37: 23–28.

Thompson S (1982) Cyrtosperma chamissonis (Araceae):

ecology, distribution, and economic importance in the

South Pacific. Journal d’Agriculture Traditionelle et de

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VEGETABLES OF TROPICAL CLIMATES/Edible Aroids 5973

VEGETARIAN DIETS

J Dwyer, Jean Mayer US Department of Agriculture,

Human Nutrition Research Center on Aging at Tufts

University, Boston, MA, USA

Introduction

0001 Individuals mean different things when they refer to

themselves as vegetarians. Those who provide dietary

counseling must probe further to determine what

foods are actually avoided and also the degree of

adherence to the dietary pattern so that dietary

recommendations will be appropriate.

Prevalence and Trends in Vegetarian

Eating

0002 The prevalence of vegetarian eating patterns varies,

depending on the definition employed. Currently ap-

proximately 7% of Americans consider themselves to

be vegetarian, but fewer than 1% are lactoovo vege-

tarians who abstain from all meat, fish, and poultry

products, and even a smaller percentage – perhaps

0.1% – are vegans, who eat no animal foods at all.

Many of those who define themselves as vegetarians

are probably actually semivegetarians who limit their

consumption of some or most animal products in

favor of a plant-based diet, although they have not

adopted a dietary pattern consisting exclusively of

plants. The growing popularity of meatless meals

and meat alternatives is due in large part to increased

consumption of these products by individuals who

are not necessarily vegetarian, but who want to eat

a meatless diet.

Reasons for Adoption of Vegetarian

Patterns

0003 Individuals choose vegetarian diets for many reasons.

In western countries, the major motivation for

adopting vegetarian diets is for health reasons. Some

believe that avoidance of animal products yields

health benefits because it decreases the risks of

bacterial or other foodborne diseases (e.g., bovine

spongiform encephalopathy) that are particularly

common in unhygienically prepared animal products,

or that are associated with excessive intakes of

saturated-fat cholesterol and sodium. Others focus

on the putative health benefits of plant foods, includ-

ing not only nutrients but also phytochemicals such as

fiber, flavonoids, and other compounds that may have

as yet unrecognized health benefits. Individuals who

describe themselves as ‘ethical vegetarians’ often do

so because of personal convictions such as opposition

to the slaughter of animals for food or to what they

view as the inhumane treatment of animals raised for

food. Still others adhere to philosophies that encour-

age vegetarianism among their followers, (e.g., tran-

scendental meditators, anthroposophists), or have

religious beliefs that include vegetarian eating pat-

terns (e.g., Seventh-Day Adventists, Buddhists, some

Hindus, and other religious groups). Other people are

motivated by environmental concerns, such as the

conviction that raising food animals consumes nat-

ural resources that could otherwise be diverted to

raising plant foods. Finally, there are some individuals

who follow vegetarian diets simply out of habit. In

developing countries vegetarian eating patterns

may result from one or more of these motivations

or simply because animal foods are expensive or

unavailable to some segments of the population.

0004The degree of adherence to the chosen vegetarian

eating pattern depends on motivation, habits, and cir-

cumstances. Until recently, the degree of animal food

avoidance often predicted the extent of other food

avoidance and divergence in other lifestyles from

omnivores. Thus, vegans tended often to have belief

systems that extended not only to extensive prohib-

itions against food ingredients made from or by

animals (such as honey, casein, whey, rennet, and

gelatin) but also to nonuse of animal products such

as leather, wool, or silk and nonviolence toward

animals. Today, however, the links between diet and

belief are not so strong. Some vegans focus solely on

the eating pattern for what they view as its health

advantages but they do not necessarily subscribe to

all the other aspects of the traditional vegan belief

system and lifestyle. They are more willing to use

meat analogs, nutrient-fortified foods, and vitamin

mineral supplements, making it easier to attain nutri-

tional adequacy.

Classification of Vegetarian Eating

Patterns

0005The five major vegetarian dietary patterns are de-

scribed in Table 1. However, myriad vegetarian diet-

ary patterns exist and they are not easily described by

focusing on the single dimension of animal food

intake. Many vegetarians’ food intakes differ from

those of nonvegetarians in other ways as well. For

example, some vegetarians eschew the use of vita-

min–mineral supplements, and foods that they regard

5974 VEGETARIAN DIETS

as processed or nonorganic. Others include special

foods such as organically grown foods, soy products

such as miso, or sea vegetables that they regard as

healthful.

0006 A vegetarians eating patterns therefore encompass

a continuum of animal and other food use and varies

in the extent, intensity, and degree of alterations in

both animal and other types of food consumption,

and in its involvement with belief systems and other

lifestyles. Some vegetarians limit only animal foods.

Others may also proscribe processed foods, ‘nonor-

ganic’ foods, or foods produced through biotechnol-

ogy such as cheeses made with recombinant enzymes

and genetically modified plant foods. At the same

time, vegetarians’ dietary diversity may be consider-

able owing to the wide variety of fruits, vegetables,

nuts, legumes, meat analogs and fungi they consume.

Dietary intakes

Energy

0007 Vegans often have lower energy intakes and lower

weights than omnivores; differences are smaller and

less consistent among those who consume other vege-

tarian patterns. Vegan and, to a lesser extent, vegetar-

ian diets tend to be relatively low in caloric density,

somewhat lower in fat, and occasionally lower in

protein than those of omnivores. While lower energy

intakes pose little problem for most adults, for vegan

infants, weanlings, and small children, unless they are

fed frequently, energy intakes may be low. Nuts, nut

butters, oils, and fruit juices are concentrated sources

of calories that are usually acceptable.

Fat and Saturated Fat

0008Most vegetarian diets eaten in western countries, and

especially vegan diets, are lower in fat, saturated fat,

and cholesterol, and higher in polyunsaturated and

monounsaturated fats than are nonvegetarian pat-

terns. Their low saturated fat and cholesterol and

high dietary fibre and polyunsaturated fatty acid con-

tent decrease risk factors for coronary artery disease.

Carbohydrate

0009Intakes of carbohydrates, especially complex carbo-

hydrates and dietary fiber, tend to be higher among

vegetarians than among omnivores, and more in line

with current dietary recommendations.

Protein

0010Vegetarians usually consume less total protein and

less animal protein than omnivores but their intakes

are usually satisfactory and sustain good nutritional

status if energy intakes are adequate. Energy intake,

protein quantity, quality, and digestibility must all be

monitored on extremely restrictive vegetarian diets,

however. Sufficient energy intake is important so that

protein is available for its unique functions rather

than being utilized for energy. Protein quality is also

of potential concern, since some plant sources of

protein are limited in one or more amino acids. For

example, lysine is low in most cereal grains, sulfur-

containing amino acids (methionine and cysteine) are

lower in legumes and fruits than in other plant

sources and animal foods, threonine is lower in

cereals, and tryptophan is lower in fruits than in

most animal foods. Thus, the biological value of

vegan diets based on single cereal staples may be

poor, especially at times of rapid growth.

0011However, the protein quality of appropriate mix-

tures of plant foods is entirely satisfactory and pro-

motes good nutritional status. When dietary patterns

include several plant protein sources (e.g., legumes,

cereals, nuts and seeds, fruits, and other vegetables),

protein quality is satisfactory since the deficits in one

plant food source can be complemented by other

plant or animal products that are higher in the

tbl0001 Table 1 Common types of vegetarian dietary patterns

Pattern Comments

Meat avoiders Limit or avoid red meat and other flesh

foods; may also restrict poultry, fish,

and seafood

Lactoovo vegetarians Avoid all meat, fish, poultry, and often

fish but consume milk products and

eggs

Lactovegetarians Avoid all meat, fish, poultry, fish, and

eggs

Macrobiotics Currently popular diets are less

restrictive than those popular in the

1970s but still involve numerous

restrictions, generally including

avoidance of all meat, poultry, milk,

and eggs, but may consume fish in

small amounts. Also avoid sugar and

other refined sweeteners, members

of the nightshade family (peppers,

eggplant, tomatoes, potatoes) and

tropical fruits

Vegans Avoidance of all animal products

including meat, fish, poultry, eggs,

and dairy products

Other Raw food eaters and ‘living food’ eaters

avoid animal foods and eat raw plant

foods, including fruits, vegetables,

and cereals, with special health

foods such as wheatgrass or carrot

juice. Fruitarians consume diets

mostly of fruits, nuts, honey, and

olive oil. Rastafarians eat vegan-like

diets but avoid alcohol, salt-

preserved foods, and additives

VEGETARIAN DIETS 5975

amino acid. Soy-based infant formulas are usually

supplemented with small amounts of methionine,

and these sustain good growth in infants. If animal

foods are also included, protein quality is further

increased. Digestibility of protein sources is a concern

on some vegan diets that are fed to infants and young

children because uncooked cereals and legumes are

not well absorbed. Cooking or processing can im-

prove their absorption and inactivate amylase inhibi-

tors, lectins, tannins, and other substances in foods

that decrease bioavailability.

Iron

0012 The iron intakes of vegetarians are usually similar to

those of omnivores. However, iron bioavailability

may be decreased because nonheme iron absorption

from plant foods is influenced by the presence of

inhibitors, such as polyphenols, phytates, fiber, and

tannins. Unleavened and unrefined cereals often

contain many inhibitors. However, enhancers of

nonheme iron absorption such as citric, ascorbic,

and other organic acids that are often high in vegetar-

ian diets may increase absorption. Also small

amounts of animal foods, especially flesh foods, en-

hance absorption. Nevertheless, in infancy, preg-

nancy, the adolescent growth spurt and during other

times of high iron requirements, without supplemen-

tation iron needs may not be met. Cereals highly

fortified with iron or iron supplements may be accept-

able iron sources to supplement other iron-rich foods.

Zinc

0013 Vegetarian diets tend to be lower in zinc than

nonvegetarian diets because approximately half of

the zinc intake of western populations is from meat,

fish, and poultry. The bioavailability of zinc is lower

in cereal and other plant sources because phytate,

fiber, and other inhibitors of zinc absorption are pre-

sent, especially in unrefined foods. The presence of

inhibitors is highest on vegan diets. Vegetarian diets

should be planned to include adequate amounts of

this nutrient, but supplements are not recommended

since evidence is lacking that they are needed.

Calcium

0014 Vegetarians who consume milk products have intakes

of calcium as high as those of omnivores. Vegans have

lower calcium intakes, and their intakes of vitamin D

are also low. The major source of calcium in most

western diets is dairy products. If they are not con-

sumed or consumed in only small amounts, care must

be taken to choose plant and other foods that are high

in calcium. These include dark leafy green vegetables

(chard, broccoli, kale, dandelion, mustard greens)

and almonds that are high in calcium, fish such as

sardines with bones, calcium-fortified soy milks and

formulas, and calcium-set tofu. In recent years cal-

cium-fortified cereals, orange juice, soy milks, and

many other products have become widely available

and are acceptable options for those who eschew

milk. Supplemental calcium is another option, Cal-

cium nutriture is compromised when vitamin D nu-

tritional status is marginal since the vitamin is needed

for absorption of the mineral.

Cobalamin (Vitamin B

)

0015Vegan diets are low in vitamin B

, and other vegetar-

ian diets are also somewhat lower than nonvegetarian

diets. The reason for concern is that vitamin B

defi-

ciency causes not only a macrocytic megaloblastic

anemia but, if long continued, serious, irreversible,

neurologic and neuropsychiatric abnormalities.

These are difficult to diagnose since the characteristic

megaloblastic anemia of vitamin B

deficiency is

masked by high intakes of folic acid. Vitamin B

only found in products of animal origin, foods that

contain microorganisms capable of incorporating

the vitamin (nutritional yeast grown on vitamin B

enriched media), and vitamin B

-fortified foods

-fortified soy milk, nut milk, and cereals). Indi-

viduals such as some vegans who often do not con-

sume any of these foods are at special risk.

0016Reliable and hygienic sources of vitamin B

are

important for those who consume no animal foods.

Spirulina, kombu, tempeh, and miso contain inactive

forms of the vitamins that cannot be utilized by

human beings, and the plankton in seaweeds such as

nori are unreliable and highly variable sources of the

vitamin. Food and water are sometimes contaminated

with vitamin B

-producing bacteria but these are due

to poor hygienic practices and are not reliable sources

of the vitamin. Among individuals who are likely to

have low intakes of vitamin B

, high intakes of folic

acid may mask the development of the megaloblastic

anemia of vitamin B

deficiency – another reason

for insuring adequate intakes of vitamin B

in all

persons. For those over 50, regardless of their diets,

vitamin B

supplementation is recommended from

fortified foods or supplements because the bioavail-

abiliy of food sources of B

may be limited owing to

the presence of unrecognized atrophic gastritis.

Folic Acid

0017Folic acid intakes are often higher among vegetarians

than among omnivores because of high intakes of

fruits and vegetables. However, there is the risk of

possible inadequacy arising in persons who consume

diets consisting of vegetables which are braised or

5976 VEGETARIAN DIETS

fried at high temperatures, few fruit juices, and

cereals fortified with the nutrient. For women who

are at risk of becoming pregnant, regardless of their

dietary pattern, supplementation with 400 mg folic

acid is currently recommended to decrease risks of

neural tube defects.

Vitamin D

0018 Vitamin D is only found in animal foods such

as vitamin D-fortified dairy products and highly for-

tified cereals, and liver. Cod liver oil and menhaden

oil contain high but variable amounts of vitamin D.

More acceptable sources are water- or fat-soluble

vitamin D supplements, commercial infant formula

(both soy- and cows’ milk-based), and fortified

cereals. Sunlight exposure may be insufficient in

young infants at weaning and thereafter, and among

the elderly, especially those in northern climes with

inclement weather.

Riboflavin

0019 The major source of riboflavin in most western diets

is milk, and those who avoid milk need to select other

foods high in this nutrient.

Fiber

0020 Intakes of whole-grain cereals and nonrefined foods

and thus of dietary fiber are higher on most vegetar-

ian diets. On some vegan diets fed to small children,

fiber intakes are several times expert recommenda-

tions of 0.5 g kg

1

day

1

, and the sheer bulk of the

diet may pose a problem. In adults, vegetarians’ fiber

intakes tend to be closer to expert recommendations

than are those of nonvegetarians.

Other Nutrients

0021 Certain other nutrients such as carnitine and taurine

may be low on vegan and some restrictive vegetarian

diets, but at present the health significance of these

differences is not established. Intakes of sodium

vary on vegetarian diets; there are some reports that

sodium intakes are lower among vegans than among

omnivores. Lower sodium intakes are generally

recommended.

0022 Usually vegetarian diets are higher in thiamin, vita-

min C, b-carotene and other carotenoids, and vitamin

E than are nonvegetarian diets. Currently there is

much interest in the health effects of phytochemicals

other than nutrients that are present in plant foods,

such as the flavonoids, plant stanol esters, and other

compounds, which are likely to be higher in the diets

of vegetarians than in those of omnivores. The bene-

ficial health effects of these dietary constituents are

still under study.

Benefits

0023Vegetarians who have chosen such an eating pattern

generally enjoy their diets and are satisfied with their

lifestyles. Those who consume vegetarian diets

because of economic necessity may add animal

foods when their means permit. Differences in all-

cause mortality between vegetarians and nonvegetar-

ians are equivocal, although differences in specific

causes of mortality do seem to differ. The health

effects of vegetarian diets are more difficult to inter-

pret since vegetarians often not only have divergent

dietary patterns but lifestyles that differ in ways that

also affect their risks for disease. These include in-

creased physical activity, decreased use of tobacco

and alcohol, and moderation in food intake, all of

which can be expected also to decrease chronic dis-

ease risks regardless of what diet is consumed. Never-

theless, even after taking these factors into account,

decreased risks and later onsets for several chronic

degenerative diseases are apparent that appear to

be due to dietary pattern. In adults, vegetarian

diets are positively associated with reduced risks of

obesity, coronary artery disease, hypertension, non-

insulin-dependent diabetes mellitus, and possibly

some types of hormone-dependent cancers. Osteopor-

osis does not seem to be different from that of the

general omnivorous population among vegetarians. It

may be higher in vegans, especially if they are very

low in weight, and have low intakes of calcium and

vitamin D. However, other factors that affect risks,

such as weight-bearing exercise and nonsmoking,

may help to decrease risks. Differences in infectious

diseases between vegetarians and nonvegetarians are

not as apparent as are those with the chronic diseases

mentioned above. Foodborne illnesses that are more

frequently associated with animal foods are probably

less common among vegetarians, although there is no

evidence that other foodborne diseases are lower

among them. Although some vegetarians are more

likely to self-treat and less likely than their nonvege-

tarian counterparts to seek medical care for mild

illnesses, for severe illnesses the vast majority of vege-

tarians seek medical care. Therapeutic diet manuals

are available for those with vegetarian eating pat-

terns. However, the claims of macrobiotics, living

foods advocates, and fruitarians that their regimens

are especially or uniquely helpful for treating cancers

or other maladies are not supported.

Risks

0024Like their omnivorous counterparts, vegetarian diets

can be well or poorly planned. The risks to dietary

inadequacy increase with the number and degree of

VEGETARIAN DIETS 5977