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Factors influencing vitamin A intake and programmes to improve vitamin A status
T. Johns, S. L. Booth, and H. V. Kuhnlein
Factors influencing the dietary intake of vitamin A
Differential intake of provitamin A and preformed vitamin A can be explained in part by the natural variation in the nutrient content of individual foods. It is also determined by dietary beliefs and practices. In the first part of this paper, the seven general food categories presented in the preceding paper [1] are explored in terms of factors influencing their intake. The discussion of each category is divided into four sections: inclusion in the diet, exclusion from the diet, seasonal factors, and economic factors.
The sections entitled "Inclusion in the diet" provide summaries of documented use of food items rich in vitamin A activity. In some societies, certain foods are prescribed as preventive measures or as treatment for illness [2]. Traditional beliefs and practices in many societies are being modified by the influence of the media and government programmes 13, 4]. so that both historical and contemporary factors contribute to actual dietary intake. This extends to methods of food preparation which modify the vitamin A activity estimated in the raw form.
Exclusion of a food item rich in vitamin A activity from the diet can relate to dietary beliefs, although this effect is usually limited to certain sectors of the population. Certain foods are often proscribed from the diet in response to alterations in physiological status, e.g. menstruation, pregnancy and lactation, and illness. Ecological factors such as climate, soil and water, and general environmental integrity all affect the availability of a food item' particularly in regions where transport and storage facilities are not well developed. The availability of time is a determinant of food consumption, particularly time to gather and prepare food. Cross-cultural differences in parental control and dietary beliefs influence the timing of the introduction of foods rich in vitamin A activity during the weaning period' and the quantity ingested [5-8]. This has important implications for the vitamin A status of infants and children, whose liver stores of vitamin A are more rapidly depleted than those of adults and who can eat relatively small quantities of food.
The availability of foods rich in vitamin A activity is often seasonal. For example, in some regions the rainy season is marked by an abundance of wild leafy greens. When liver retinol stores are low or vitamin A status is compromised by disease, seasonal fluctuations can lead to periods of greater risk of hypovitaminosis A.
Dietary intake of foods rich in vitamin A activity is also determined by economic factors. Vitamin A intake is positively correlated with household income level [9]. This correlation is most evident when provitamin A and preformed vitamin A food sources are not readily available [7]. Market value is also linked to issues of social status associated with a given food item.
The literature about food beliefs and practices related to vitamin A intake is multidisciplinary. The sources consulted for this review include the following kinds of materials:
(In addition, some of the information from Guatemala and East Africa is based on the personal observations of the authors.)
The available literature has at least four significant limitations for our purposes:
Given the diffuse distribution of literature pertaining to food choice and intake, the references cited should of course not be interpreted as an exhaustive evaluation of all dietary beliefs and practices associated with foods rich in vitamin A activity. The discussion highlights factors that have a documented influence on vitamin A intake, and the differential nature of their influence. Most of the examples cited are very specific and cannot be extrapolated to other populations. This emphasizes the necessity of evaluating the dietary practices of a group targeted for vitamin A intervention programmes before promoting natural food sources rich in vitamin A activity.
Green vegetables, algae, and flowers
Inclusion in the diet
The literature makes ample reference to the dietary use of green leafy vegetables, particularly of gathered wild species.
Leaves of tuber-producing plants are used for sauces, and wild greens make up 80% of the total vegetable intake among certain groups in Tanzania [10-12]. The Bemba and Lamba tribes in the Zambezian woodlands identify 241 edible wild species, and boiling the leaves is the most common method of preparation [13].
Among the Twi-speaking people in Ghana,. the leaves of cocoyam are eaten regularly. The consumption of cassava leaves, however, is low; more often they are fed to poultry and other livestock [14]. Gathering is not an organized activity but is practiced by both men and women during the course of farm work.
Among the Tswana of Botswana, gathering is a female activity, and the plants within the village are rejected to avoid possible contamination by human or animal faeces [15]. The young plants are eaten fresh or are sun-dried after cooking and then shaped into cakes that can be stored up to three years. The children of this tribe also eat the flowers of certain species of wild plants.
Among the Oto and Twa of Zaire, members of both sexes participate in gathering, which includes the collection of honey, tubers, and caterpillars in addition to green leafy vegetables [16]. In some societies in Zimbabwe, both women and children gather greens that are then eaten in cooked form or are dried for storage in anticipation of drought [17]. Among the Luo of Kenya, leaves are boiled until dry, or the water is discarded, and Magadi soda is sometimes added to soften the leaves [18].
In rural Malaysia, 72 species of edible wild greens have been identified in the diet [19], which contradicts earlier literature claiming that green leafy vegetables are only used for 'taste" [20]. Consumption of the flower of the banana by children has also been documented in this region.
Among the Gujarat in India, flowers are eaten to satiety [21]. In northern India, the green leaves of root crops are eaten; in the southern part they are not [22].
In certain regions of Mexico, green leafy vegetables are considered the main source of vitamin A [23]. It has been suggested that variation in preference for different species of wild greens among populations in Oaxaca, Mexico, may reflect differences in availability according to ecological conditions and agricultural practices [24], whereas in Tlaxcala, Mexico, selective weeding encourages growth of preferred species of wild greens [25].
Several indigenous groups in western Canada use the fronds of certain species of algae to gather herring spawn, which are then eaten together [26]. Other species of algae are consumed in various forms, including fermented and dried. The young leaves of species of the celery family are preserved in seal oil by the Inupiaq Eskimos of Alaska and eaten year-round.
Dettwyler and Fishman [27] noted that the infusion of papaya leaf was used in at least one village in Mali to treat night blindness in pregnant women. In Java, it has been reported that the majority of women increase their consumption of leafy green vegetables during lactation to increase vitamin intake [28], a reflection of beliefs introduced by the media and government programmes. Among Greek immigrants in the United States, certain species of greens are believed to be health-promoting during pregnancy and post-partum [291.
The only case we have found mentioned of a society in which a green leafy vegetable has high status is that of the Wamiri of Papua New Guinea, who value taro leaves as a feast food [30].
Exclusion from the diet
As a general rule, consumption of green leafy vegetables is not limited by dietary beliefs, but they are underutilized relative to their availability and potential nutrient contribution. As pointed out by Pereira and Begum [22], those dietary restrictions that do exist may be limited to individual species of plants, so other species of greens could be substituted in promoting this category of foods rich in provitamin A.
Among the Yoruba in Nigeria, 57% of pregnant women were reported to avoid a green called "bitter leaf" because it tastes bitter [31]. Three reasons are given why pregnant women in certain regions of the Gambia do not eat enough greens: the greens dilute sauces; they dislike the taste; there is not enough time available for gathering greens [32]. A time constraint was also mentioned in reference to a generally low intake of greens among the Hopi of Arizona [33].
Several programmes under the auspices of Helen Keller International that are promoting the use of provitamin A-rich foods have been hampered by a consistent belief that infants are unable to digest green leafy vegetables [5-8]. Mothers claim that the greens cause indigestion and diarrhoea because the infants' gut is immature. In contrast, older children in these same areas are not restricted in their intake of leafy vegetables as it is assumed that their digestive system is sufficiently mature to digest greens.
Most dietary restrictions on green leafy vegetables are limited to women of child-bearing years. In Java, leaves of sweet potatoes are restricted for young, unmarried girls, as are other species for adolescents of both sexes [28]. In Telegana, India, most foods, including green leafy vegetables, are restricted 3 to 30 days post-partum [34] but are then prescribed during lactation. In Hawaii, there are dietary restrictions for individual species of algae, but they were not detailed by the author [35].
Another concept of dietary restriction is encountered within the humoral classification of foods, the most well-documented being the "hot-cold" classification. The humoral theory of disease is based on the principle that diseases are caused by imbalance, so treatment is designed to restore the balance [36]. Molony [37] reports that a systematic coding system is used in assigning a classification to individual food items. These cultural classifications exhibit intracultural variation and are subject to rapid modification through culture contact and cultural diffusion. Latin American immigrants in the I United States generally classify greens as "cold" [38], as do societies in Guatemala [39], China [40], and Malaysia [41]. The implications of a "cold" classification relate to proscription during illness and certain seasons. In Malaysia it is thought that "cold" foods delay recovery from illness and that excess consumption can cause diarrhoea and fever. These foods are avoided during the rainy season, when the individual feels cold, and postpartum. In contrast, the certain species of greens, such as mustard greens, are classified as "hot" and are avoided by pregnant women [41]. Excessive intake of these ' hot" species is thought to cause sore throat or fever.
In Zimbabwe [11] and the Philippines [42], there are inadequate plant resources because of deforestation, a shift to an agricultural economy and monocropping, and overpopulation. This leads to a decrease in intake of green leafy vegetables without substitution of other vitamin A sources. In contrast, green leafy vegetables are abundant but are underutilized by populations in Liberia [11], India [22], and Papua New Guinea [43] and among the Quechua in Peru [44] and the Haustec in Mexico [45]. Among nomadic tribes in Afghanistan, green leafy vegetables are eaten by children but are not an important dietary item for adults [46]. Nomads in Iran do not eat them [47]. Likewise, while edible algae are available, they is not eaten by the Seri of Mexico [48].
Members of the Jain religious group in south Rajasthan, India, do not eat wild greens during the rainy season despite their availability, because they believe that preparation/consumption of these greens would result in the religiously undesirable death of worms living on the plants (P. Sundaram, personal communication).
Seasonal patterns
Most accounts of green leafy vegetable intake make reference to seasonal availability and consumption. The diversity of available edible species increases in the rainy season, as, for example. was documented in the Zambezian woodland [13]. In regions of the Gambia, green leaves make an important contribution to total vitamin A intake during the non-mango season, which is between July and November [49]. Among the Sandawe in Tanzania, greens are gathered during the December-to-April rainy season and then dried and stored for later use [12]. Among the Oto and Twa in Zaire, while most species of wild greens are eaten during the rainy season, there is an increased consumption of cassava leaves during the dry season [16]. In societies in which people buy their greens from the market, such as the urban populations in Iraq, there is also an increase in intake of green leafy vegetables during summer months when they are abundant and low in price [50]. This fluctuation in the intake of greens does not occur in the United States [51], nor in the Twi-speaking regions of Ghana [52].
Economic considerations
There are few accounts of green leafy vegetables having an important economic role, although they are often used during periods of food shortages and economic constraints. Reliance on gathered plant sources would allow for greater expenditures on other foods. The Bemba and Lamba tribes are said to have an important retail trade in cassava leaves [13]. In at least one community in Ethiopia where there is no documented xerophthalmia and the average intake of greens among children is three times per week, the production and selling of leafy green vegetables is the responsibility of local prisoners [53]. With extensive urban migration from the rural areas, certain species of greens are becoming important crops in urban markets in Guatemala, Kenya, and Tanzania. Shoots of the ostrich fern, commonly referred to as "fiddle-heads," are cooked or frozen for later use by some indigenous groups in Canada [26]. However, they are gaining such popularity as a specialty food among non-indigenous groups that the wild population of this species is being depleted.
Most references to economic issues associated with leafy vegetables refer to social status. In Hyderabad, India [54], Swaziland [55], and the highlands of Mexico [56], while green leafy vegetables are part of the traditional economy, their consumption is associated with poverty. Therefore consumption of wild greens is inversely associated with economic prosperity. In Tanzania, vegetable intake, hence provitamin A intake, may be higher in the "lean" season than after the harvest, which reflects the inferior status associated with these plants [57]. In contrast, in Iran there is higher consumption of green vegetables with increased economic status [58].
Fruits
Inclusion in the diet
In Indonesia, mangoes and papayas are introduced early in the weaning process, with a positive correlation between intake and the absence of xerophthalmia [59]. Among the Malays. fruit is eaten in substantial quantities by pregnant women [19]. Wilson [60] suggests that there is a global dietary belief that promotes the intake of those foods for which there are cravings during pregnancy, fruits being one of the more common food groups. When these cravings are not met, it is generally believed that marks will appear on the newborn that resemble the fruit not consumed.
There are numerous references to the popularity of fruit among children because of its sweet taste and soft texture. As fruits are often classified as food for children, there appears to be little competition with adult members of the household for them. In the Taita Hills of Kenya, where xerophthalmia has not been documented, fruit is eaten as a snack or as a meal replacement, especially by children [61]. In season, children eat fruit on an average of seven or more times per week, while adult women have an average weekly intake of one piece of fruit. Assignment to tasks outside the house allows the children to forage for these fruits, of which 97 species are classified as edible. Not all edible species are actually eaten; different species may be preferred by members of different ethnic groups within the same ecological region. The concept of fruit as "children's food" is also found among the Mbuti in eastern Zaire [62], in Swaziland [63], and in regions of Mali where treats purchased at markets for children include provitamin A-rich fruits such as mangoes and papayas [27].
Fruit use has apparently not been affected by deforestation in the Condo area of Zimbabwe, where fruit consumption is correlated with a shortage of cultivated resources and is not in synchrony with the fruiting season [3].
Among the Tiruray in the Philippines, immature papaya is used as a vegetable, whereas mature papaya is eaten as a fruit [42]. Differential preference for ripeness in mangoes among Gambian women affects the nutrient intake since provitamin A activity varies with the stage of maturation [32].
The Seri of Mexico have numerous methods of preparing fruit for consumption, as described by Felger and Moser [48], although some species are consumed raw. In a Jivaro community in the Amazonas department of Peru, plantain is usually prepared by boiling or by roasting over coals [64]. At least 17 varieties of bananas and plantain have been documented in the diet, and these fruits are introduced into the diet by one year of age. There are numerous reports of consumption of berries in the form of jam or jelly among indigenous groups in Canada [26]. The Wood Cree eat cranberries raw, stewed, or served with fish and/or meat, or mix them with boiled fish eggs, liver, air bladders, and fat. There is frequent mention of plant foods being eaten with fat or oil, which is a suitable vehicle to increase the absorption of the provitamin A they contain.
In the Condo area of Zimbabwe, fruit is eaten for its perceived nutrient value (61"/o of those interviewed) and/or taste (52"/o) [3]. Among the Yoruba in Nigeria, plantain and papaya are perceived as being nutritious for pregnant women by 91% and 59% respectively of women interviewed [31]. In Tamil Nadu in India, green plantain is eaten by some at puberty for a strengthening effect, whereas it is avoided by others because it is believed to have a weakening effect [65].
Exclusion from the diet
In lava, fruits are restricted for young unmarried girls, infants, and adolescents, and also for women during lactation because it is thought that negative effects will be passed through the breast milk to the infant [28]. Among forest-dwelling tribes in Gujarat in India there is also some avoidance of fruits by lactating women for fear of gastrointestinal upset in the child, showing a similar concept of the transfer of the effect of the restricted food from the mother to the infant via the breast milk [21]. Forest fruit is not given to infants in Gujarat for fear of choking the infant. In contrast, older children eat fruit to satiety, although these fruits are proscribed during illness.
Among the Yoruba in Nigeria, papaya is restricted for barren women because sterility is thought to be caused by worms, and papaya and other sweet fruits are considered to be delicacies for worms [66]. Likewise, these fruits are restricted for individuals with helminthic infection. Papayas as well as mangoes are avoided during pregnancy in Tamil Nadu, India, where these fruits are classified as "hot" and thought to have the capacity to induce abortion [67]. This has also been documented among the forest-dwelling tribes in Gujarat [21] and among the Jain religious group in south Rajasthan, India (P. Sundaram, personal communication). In contrast, in Malaysia, papaya is classified as 'cold" [41], and its intake is restricted because it is believed to aggravate illnesses classified as "cold," examples being malaria and xerophthalmia [68]. Among different ethnic groups interviewed in the United States, particularly those from northern Mexico, fruits are classified as "cold" and therefore are avoided during menses [38]. Tomatoes are also avoided as they are believed to cause menstrual blood to congeal in the uterus, causing cancer. Chili is classified as a "hot" food in Malaysia and is considered a cause of stomach-ache, diarrhoea, fever, and sweating [41].
Seasonal patterns
Most descriptions of fruit intake make reference to the seasonal availability that creates periods of variable risk of hypovitaminosis A. The increase in provitamin A intake attributable to the mango season in regions of Brazil confounded the evaluation of the impact of a prophylaxis programme in the same region [69]. In the Taita Hills in Kenya, papaya is available year-round, whereas most fruits are limited to the period between March and August [61]. This is a pat tern similar to that observed in south-eastern regions of Ghana [14]. Seasonal variation is also evident in the Gambia, where the mango season coincides with the season for red palm oil [32]. In contrast, in the United States consumption of specific raw fruits is seasonal but the availability of canned and dried fruit allows for year-round consumption [51].
Economic considerations
In Java, it has been observed that fruit intake is more frequent among women in higher income groups [28]. Similarly, in Hyderabad, India, tomatoes are considered a prestige food and are eaten more frequently by the wealthier segments of the population [54]. In Iran fruits are consumed in low quantities because of economic restraints [58]. In contrast, children who gather wild fruits in the Taita Hills in Kenya are able to eat these as an alternative to the high-priced commercial snack foods available on the school compounds [61].
Plants with vitamin A stores
Inclusion in the diet
Most roots and tubers are devoid of carotenoid activity, so it is very difficult to identify dietary beliefs and practices in the literature that affect provitamin A intake. Plant storage organs have classically been singled out in nutrition and anthropological studies for their dietary protein and energy contribution to the diet, with little emphasis on their potential contribution to provitamin A intake. In view of these limitations, dietary beliefs and practices related to plant storage organs are probably underrepresented in this literature review.
Plant storage organs are of importance to numerous African societies, and many different methods of preparation are observed [13]. The most common methods of preparation among groups in the Zambezian woodland region are boiling and roasting over an open fire. In the New Guinea highlands, sweet potatoes are the staple food, but "strong" tasting species are not introduced into the diet of children until they are two years old [43]. Species of the squash family are also documented dietary items, but they are seasonal in availability and consumption. In Hyderabad, India, tubers are the least consumed of all plant foods, but of these sweet potatoes are the most popular [54].
In the United States, carrots are ranked as the second largest contributor to total vitamin A intake [70]. Likewise in Ethiopia, in communities where the prevalence of xerophthalmia is low, carrots make an important contribution to vitamin A intake in children [53]. In Egypt, carrots are consumed in pickled form or are boiled and then eaten with potatoes because women argue that the crunchy texture presents difficulties, particularly for children (Wahba, personal communication). In contrast, carrots are usually eaten raw as a treat in Mali [27]. This is problematic for infants, who are often denied this rich provitamin A source because mothers are concerned about possible damage to their teeth from the hard texture of carrots.
A questionnaire identifying dietary beliefs was used in a low-cost housing resettlement in Papua New Guinea [71]. Of the households interviewed, 13% identified sweet potatoes as healthy for children and 12% also identified pumpkins as having health-promoting properties. During lactation, sweet potatoes were perceived as a healthy food (80% of all respondents), with 47% of the respondents stating that, in general, vitamin A-rich tubers were preferable food to plain rice.
Exclusion from the diet
Wild roots and tubers are not widely consumed by the Luo in Kenya, which may be related to availability [18]. They are not eaten at all by nomads in Iraq [47].
Dietary restrictions are documented, with emphasis on the classification of these foods as 'cold," as previously discussed. In Malaysia, the majority of green and yellow vegetables are classified as "cold," and consequently their intake is restricted because they are believed to aggravate illnesses like malaria and skin infections [68]. This includes the squash family, members of which are classified as "windy" [41]. As 'windy" foods are thought to cause aching veins' weak legs and bones and rheumatism, they are generally limited in the diet. A similar classification exists among the Gujarat in India, although pumpkin is classified as "hot," and its consumption is therefore governed by the beliefs relating to "hot" foods. Likewise in Malaysia, tubers, including the sweet potato, are classified as "hot" and are only eaten during the rainy season, at night, or when the body feels cold [41]. As a general rule, "hot" foods are restricted for pregnant women.
Seasonal patterns
In the United States, sweet potatoes, carrots, and other vitamin A-rich vegetables are consumed yearround, with few if any seasonal fluctuations [51]. In contrast, roots and tubers are reported to be seasonal in their availability and intake in Iran and Papua New Guinea [30, 58].
Economic considerations
We encountered little mention in the literature of the economic role plant storage organs may have for those societies consuming them. However, according to FAO food balance sheets, sweet potatoes are classified as a main staple food crop in Burundi, Kenya, Rwanda, Tanzania, and Uganda [72]. In Iran. it has been noted that there is a lower intake of roots and tubers among the low-income groups [58]. Likewise, their consumption is erratic in Ethiopia because of constraints on cash flow [53]. It was found that the large inter-family variation in the intake of plant storage organs was explained in part by the family purchasing priority.
Plant oils
Inclusion in the diet
There is very little literature available on dietary beliefs surrounding the use of plant oils other than the documented use of red palm oil in certain regions of Africa. Given the small quantities that are used in the cooking process, they are particularly difficult to quantify in a dietary survey [73].
Among the Mbuti of eastern Zaire, red palm oil is used for cooking purposes whenever it is available [62]. The Oto and the Twa use palm oil as a base for a sauce in which spiced cassava leaves are added [16]. In those communities in Nigeria and Zambia where red palm oil is consumed regularly in the diet, xerophthalmia is not endemic [74, 75]. In the Yoruba tribe in Ghana and Nigeria, mothers are known to give one teaspoon (5 g) of palm oil as a treatment to infants with measles [76].
As discussed in the preceding paper [1], red palm and buriti palm oil are the richest known sources of provitamin A. While other plant oils have little if any vitamin A activity, their contribution to vitamin A intake is important for the absorption of this nutrient [77]. Therefore, promotion of dietary fat should not be limited to those oils known to be rich in vitamin A activity, although the latter arguably would have the greatest impact on improving dietary vitamin A intake.
Exclusion from the diet
We have found no documented cases of dietary restrictions relating to plant oils, although in several regions, including communities in Zambia [74] and Liberia [11], red palm oil was available but not consumed.
Seasonal patterns
In the Gambia, which has a well documented reliance on red palm oil for cooking purposes, it is seasonal in availability, coinciding with the mango season [32]. During this period between April and June, the average intake of vitamin A and provitamin A is at its peak for the year.
Economic considerations
Red palm oil is expensive in most regions because of the labour-intensive processing required for the final product. As a consequence its dietary use is often limited by price and availability [27, 32]. In India, when dietary fat in the form of ghee is prohibitive in cost, groundnut (peanut) oil is used as an alternative [54].
Milk, milk products, and eggs
Inclusion in the diet
Abrams [78] states that all human cultures include some form of animal protein and fat in the diet. From a survey of 383 cultures represented in the Food Habits Survey of the Human Relations Area Files, of the two classifications of animal produce most commonly consumed, Abrams tabulated 363 societies consuming chicken meat and eggs, and 196 consuming cattle meat and milk.
Reports of egg consumption are few in the literature compared to the numerous dietary restrictions on eggs. In Tamil Nadu, India, eggs are prescribed at the age of menarche, as they are thought to increase fertility [65], although current economic constraints are limiting this belief. In Nigeria, only 14.5% of Yoruba women interviewed considered eggs a healthy food during pregnancy [31]. In Indonesia, eggs are the only preformed vitamin A source consumed significantly more by children who do not show signs of xerophthalmia than by their vitamin A-deficient peers [73]. In China, preservation methods prolong the shelf life of duck or hen eggs without substantially reducing the preformed vitamin A content [79].
There is more documentation of the use of milk, particularly among nomadic groups. In Hyderabad, India, products used for the early supplementation of breast milk include cow milk, buffalo milk, and commercial milk preparations [54]. In this same region, buttermilk is one of the few foods prescribed for adults during diarrhoeal attacks. In Ethiopia, milk makes an important contribution to the intake of preformed vitamin A among children [53]. Both milk and boiled or fried eggs are consumed with more frequency by traditional hunter-gatherer groups in the Philippines than by their peasant counterparts [42].
Among nomadic groups, milk and its by-products have important dietary roles [46, 80]. Among nomads in Uganda, the milk from cows, goats, and sheep is consumed by the women and children who remain in permanent settlements [11]. Milk is made sour by the addition of urine to facilitate storage. The use of sour milk has been documented elsewhere, including Iraq [SO]. Milk, yoghurt, and ghee are the only sources of vitamin A for the nomadic tribes in Iraq, and are mixed with bread or whole wheat [47]. Casimir [46] describes in detail the methods of utilizing milk observed among nomads in Afghanistan. Milk is not allowed to boil when heated prior to souring, and this is thought to preserve vitamins. Lactose-intolerant individuals consume fermented products like yoghurt. Among the Masai in Kenya, the traditional diet is cows' milk with maize meal, and milk is consumed fresh or in tea [80]. Milk and butter are principle weaning foods, introduced between 18 and 24 months of age. Yoghurt is also consumed in large quantities among the Masai.
Exclusion from the diet
Dietary restrictions relating to eggs are numerous, particulary for women of child-bearing age. In Tamil Nadu, there is a decrease in consumption of eggs during the third trimester of pregnancy as it is thought that they promote the growth of the foetus, thus creating a difficult delivery [67]. A similar dietary restriction applies to milk in Hyderabad [54]. Among certain tribes in the Gambia, Uganda, and Tanzania, eggs are restricted for women and girls as they are thought to cause sterility, and among certain groups in Zambia and Zimbabwe? eggs are restricted for children up to seven years old for fear of inducing convulsions [11]. The Masai do not eat eggs under any circumstances, although this pattern has been changing recently among those who are becoming acculturated. Among the Tswana of Botswana, eggs from 13 species of wild birds are eaten by young males and occasionally by adult men, but are restricted for girls and women of child-bearing age [15].
In Iran, eggs are classified as "cold." so they are eaten less during warmer periods, sometimes being replaced by vegetable dishes [58]. A survey of hunter-gatherer societies [81] found restrictions on the consumption of eggs during pregnancy among the Walbiri (an Australian aboriginal society), during lactation among the Inuit, and at menarche among the Hare Indians. Among the Wamira in Papua New Guinea, eggs are restricted for those individuals who have the bird as their lineage totem [30]. Dettwyler and Fishman [27] observed dietary prescription for eggs in two villages in Mali, where eggs were considered good for the foetus and the pregnant woman; but in another village eggs were restricted during pregnancy because they were believed to cause a difficult delivery. In this latter community, it was also believed that eggs are bad for children because they interfere with physical development. In Honduras, milk and eggs are restricted during gastrointestinal illness to "avoid contamination of the intestinal wound" [82].
With respect to milk intake, Simoons [83] offers three possible explanations as to why "non-milking" areas have emerged: lactose intolerance, a perception of milk as an unpleasant secretion, and a view that it is suitable only for feeding calves. In the Luapala Valley in Zambia, milk and other animal products are not available for consumption because of the presence of the tsetse fly [74]. However, in some regions of Zimbabwe, goat milk is available but not consumed [11]. In some regions of Uganda, it is argued that milk should not be mixed with any other foods, either in a dish or in the stomach, so several hours must pass between the ingestion of milk and other foods. Among the Masai, whole milk is not given to infants because it is thought that fat in the milk forms lumps that can choke the child if it vomits [80].
Seasonal patterns
In the Gambia, milk and eggs are consumed only during the dry season [32]. Among nomadic tribes, milk products are fermented and stored to augment the diet during the dry season, when milk production decreases [46]. This has also been demonstrated among the Sandawe in Tanzania, where cattle struggle to survive during the dry season [12]. Among the Masai, milk availability has seasonal fluctuations according to rainfall and the number of cattle owned by the individual [80]. As permanent settlements are encouraged by the government, there is even more of a decrease in milk production during the dry season.
Economic considerations
The prices of milk, milk products, and eggs have been cited as limiting factors in dietary intake. Eggs and milk are sold instead of being consumed at the local level in the Gambia [32], in Hyderabad. India [54], and in Amazonas, Peru [64]. Among the Fula tribe in the Gambia, milk is often exchanged for grain and housing during the dry season [ 11].
Fish
Inclusion in the diet
Among the Miskito of Nicaragua, dietary preferences used to determine the intensity and frequency of fishing expeditions [84]. This ethnic group distinguishes high-quality animal flesh, which it terms 'meat," from lower quality 'flesh," which includes certain shellfish. "Meat" is used to fulfil kinship ties and obligations, and "flesh" is never served at important meals. The Tiruray hunter-gatherers in the Philippines eat numerous freshwater species of fish, whereas those shifting to a peasant lifestyle eat only purchased dried fish [42]. Among the Wamiri of Papua New Guinea, fish are the most stable source of preformed vitamin A [30]. Twenty species of freshwater fish, more than 50 species of saltwater fish, and numerous shellfish are included in the diet.
Methods of preparing fish vary among societies. Only boiled or roasted freshwater fish are consumed in the Luapala Valley in Zambia [74]. As fish are eviscerated prior to preparation in some societies, most, if not all, of the preformed vitamin A is removed. In south-eastern regions of Ghana. fish are prepared by similar methods [ 14].
In parts of Mali, some women believe that fish oil gives strength to the foetus [27]. Among Chinese in Hong Kong, fish liver oil is used to treat baldness and bronchitis and to prevent coughs and asthma [40].
Exclusion from the diet
Fish, being classified as an animal product, are proscribed for religous reasons among the Brahmin caste in Tamil Nadu, India, [65] and among Buddists in Hong Kong [40]. Likewise, fish are restricted at menarche in Tamil Nadu for non-vegetarian women. This has also been documented in Hyderabad, India [54].
Among the Nootka of western British Columbia, spring salmon, seal, bass, and whale are restricted during lactation and at menarche [81]. Among the Kisarwe in Tanzania, catfish are restricted for women and girls of child-bearing age, with other fish species restricted for this group among the Busoga and the Buganda of Uganda [11].
Although many restrictions relating to fish are reported from Java, including one which associates fish intake with worm infestation in infants, only 20% of mothers interviewed reported knowledge or use of dietary restrictions [28]. In contrast, Kahn [30] gives a detailed description of dietary beliefs that relate to fish species, with some consumed exclusively by the elders of the community, others only by men. These dietary restrictions determine the fishing techniques and scheduling, which is both a female and male activity.
Species-specific dietary restrictions have also been observed among the Miskito of Nicaragua, while other ethnic groups in the region consume fish species rejected by the Miskito [84]. Masai and Sambuni pastoralists in East Africa traditionally express a revulsion towards the consumption of fish.
Seasonal patterns
Among the Sandawe in Tanzania, freshwater fish are caught in April and May and then are eaten in dried form when the rivers dry up [12]. The Wamiri have an elaborate system of procuring fish in accordance with the seasons [30]. River fishing by the women of the community is only practiced in the dry season, while shellfish are collected by women and children primarily during the rainy season. Ocean fishing, which is considered a male activity, is year-round.
Economic considerations
The species of fish currently caught by the Miskito of Nicaragua no longer reflect the dietary preferences of the society [84]. With developing commercial markets for different fish, the perception of what is valuable is determined by what can be sold. Likewise, in the Luapala province of Zambia, and among the Kigezi of Uganda, fishing is a successful industry, hut not enough fish reach the local level for consumption [11]. Dettwyler and Fishman [27] also found that in parts of Mali fish are often sold for cash to buy other foods or nonfood items.
Organ meat and other meat
Inclusion in the diet
The few reports that we encountered that describe the consumption of wild game make no mention of which, if any, organs are eaten. For example, wild game is caught, albeit erratically, in the Papua New Guinea highlands [43], among the Tswana of Botswana (with some fowl species valued only by the elders) [15], in Amazonas, Peru [64], and among the Ache in Paraguay [85]. The viscera, particularly the liver, of chickens and other animals are consumed by groups in Malaysia as a treatment for night blindness [68], among the Tabora of Tanzania [11], and the Tiruray in the Philippines [42].
A review of the foods eaten by groups in the circumpolar area makes numerous references to the popularity of these vitamin A-rich foods, where raw seal liver is prescribed for adults during illness [86]. However, many of the references cited are dated and do not reflect current economic and political pressures that are modifying the intake of traditional foods. The traditional dietary sources of preformed vitamin A in the Inuit diet are very high in vitamin A activity, leading at least one author to speculate that the form of hysteria known as "pibloktoq" is a manifestation of hypervitaminosis A [87]. However, Doolan [88] argues that the current shift to marketed foods among northern native populations results in an inadequate intake of vitamin A.
In some regions of Mali, pregnant women buy and eat grilled chicken and fish in the market because affordable quantities are too small to distribute among the entire household [27]. Liver is eaten in very small quantities, and then only on market day. Children eat liver only with other foods.
Exclusion from the diet
Among the Kisarawe in Tanzania, the consumption of viscera by pregnant women is restricted [11], as is the consumption of wild game among the Yoruba in Nigeria [31]. Landy [87] did not encounter dietary proscriptions among the Inuit, although there is mention of the Copper Inuit's rejecting kidney, considering it food for dogs [86]. Among the Yoruba, chicken meat is proscribed for those diagnosed with sickle cell anaemia as it is believed that fowl bones intensify the aching associated with the disease [66].
Seasonal patterns
Among the Masai in Kenya, meat consumption is seasonal [80]. Two factors determining intake are the number of diseased or dead animals used for consumption and the timing of ceremonies. However, liver flukes, which are endemic in the region can make beef liver, at least, inedible.
Among the Baffin Inuit, consumption of ringed seal liver and other viscera is variable, both seasonally and from year to year [89].
Economic considerations
No discussion of economic value or constraints on the consumption of organ meat was found in the literature.
Summary