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Food and nutrition policy

The impact of changing agricultural systems on the nutritional status of farm
Small-scale integrated agricultural production family farm
Preliminary study of income and nutritional status indicators in two ethiopian
Uses and constraints of schoolchildren's height data for planning purposes:national experiences
The demand for higher-status food and nutrition in rural India:the experience of Matar Taluka
Differential infant and child mortality rates in Bangladesh
Oral rehydration therapy-the need for a proper perspective

The impact of changing agricultural systems on the nutritional status of farm

Meredith F. Smith
Department of Foods and Nutrition, Kansas State University, Manhattan, Kan., USA

INTRODUCTION

The alleviation of world hunger has been of great concern to biological and social scientists since the end of the Second World War. Agricultural scientists have made great strides in improving both the yield and nutrient content of staple foods. Farmers have been encouraged to increase the quantity and quality of their food and cash crops so that more food will be available for export and for consumption in the urban areas. Increased production, it has been assumed, will provide farmers with more income with which to purchase food and goods that will improve their well being. Ten years after the United Nations World Food Conference in Rome, it is estimated that 500 million people are still without sufficient food [17]. This is in spite of multinational efforts to increase the amount of food available worldwide to alleviate hunger. In addition, micro level studies by economists, nutritionists, anthropologists, and others have demonstrated that increased food production on the family farm has not automatically led to improved nutritional status for the farm family [6, 14] . Changes in cropping systems that do not enable farmers to increase the quantity and quality of food available for family consumption will have no permanent effect on the wellbeing of the farm family, although they may have a positive effect on urban or wealthier families.

If the potential that exists to feed growing populations in developing countries is to be realized, new agricultural technologies must be adopted. Although, as Tripp [18] points out, it is naive to believe that changes in agricultural technologies will be planned around farmers' diets, the impact of changing agricultural systems on families, especially their nutritional status, must be identified. Farming systems research, which is location-specific and farmer oriented, can be modified to incorporate nutritional concerns into the research design if those concerns are identified during the initial reconnaissance surveys or recommendation domain studies. This paper will discuss some of the nutrition-related problems that occur when new technologies are introduced into traditional agricultural systems and suggest ways in which the impact of these new technologies on the nutritional status of the farm family might be measured.

THE IMPACT OF CHANGING AGRICULTURAL SYSTEMS ON THE FARM HOUSEHOLD

Increasing food consumption is an important goal of increasing agricultural production. Because food is a basic consumption good, Rubenstein [15] contends that increased food consumption is the primary goal of increasing food production. From a nutritional standpoint households of interest are those in which members are currently undernourished or at risk of undernutrition. Pinstrup Anderson [11] argues that changes in the food supply affect the nutritional status of household members only to the extent that food consumption is affected. Increased food production must increase food supply to the household if total food consumption is to increase or intrahousehold food allocation to become more proportional to individual need. This may occur as a result either of the consumption by farm members of an increase in food production or of the purchase of additional food with the proceeds of the sale of that increase. Pinstrup Anderson [ [11] cautions that using production expansion as a proxy for nutritional effect may be misleading if factors such as changes in the cropping system, livestock species, nutritional composition of foods produced, human energy requirements, production technologies, labour demands, or composition and control of income are ignored.

Traditional farmers have generally adapted food production practices to meet environmental, economic, and technological limitations [8]. They minimize risk by planting a variety of staple crops that mature at different times during the year. Monocropping may accentuate seasonal shortages while traditional intercropping decreases the risk of long periods of time without sufficient food. Crops are planted to take account of unpredictable rainfall, insect infestation, and different maturation rates. Even if the rains are late or birds attack the mature corn, some part of this diversified system will produce food for sale and for family consumption. Farmers also know that the weeks prior to the harvest of the new crop are a time of food shortages. Reliance on root crops of low nutritional value during this time will not have a permanent effect on nutritional status. If, however, the cash crop fails and these roots and tubers form a major portion of the diet for long periods of time, the nutritional status of household members will be seriously affected.

Household gardens provide foods that add variety and important vitamins and minerals to the staple foods regularly consumed. Hunting and gathering of leafy plants, roots, and fruits add other nutritionally important supplements. Undisturbed, these food patterns are usually nutritionally sufficient. Families producing food for auto-consumption are more likely to have greater diversity in their diet and to consume more food than families producing primarily for the market-place [16,6] . Not only does the variety of foods available for the family to eat decrease, but the household becomes more vulnerable to seasonal variations in food supply [8]. Dietary diversity can be important in determining dietary quality which, in turn, influences nutritional status [3] . Decreased corn and cacao production in south-eastern Mexico resulted in the substitution of soft drinks for pozol, a native drink of high nutritional value made from these products [7] . When pozol is allowed to ferment, the protein, niacin, and riboflavin content as well as protein quality are increased. This area of Mexico is very hot and humid so liquids make up a large portion of the diet. Substitution of soft drinks for the native beverage will have a detrimental effect on family diet, especially that of children.

Commercialization of the agricultural system, a change from subsistence to cash cropping, requires a change in inputs. To increase yield, farmers are encouraged to purchase hybrid or improved seed in place of seed saved from the previous harvest, to purchase fertilizer and pesticides, and to obtain credit to finance these expenditures. Cropping systems usually have to be changed to maximize the yield of the new seed varieties. New technologies may require more intensive labour which must be hired or supplied by the farm family. Time-use patterns change to meet new production schedules. Annual labour required to adopt the new technology of an agricultural development project in the Nigerian Tiv was estimated to increase approximately 14 per cent on an average farm [5]. However, the women's share of the total annual labour requirement increased disproportionately to that of the men. Changes in seasonal labour requirements were also more critical for the women. Although the annual labour requirement for men was more evenly distributed with the new technology, women acquired a second period of peak labour requirements.

If the new cropping system requires that the women spend more time than previously in crop production, they will have less time for household activities such as water- or wood-gathering, and food-processing, preservation and preparation. Ballweg [2] speculated that the nutritional status of children of Haitian charcoal-makers suffered due to the women's long absence from home, making and selling the charcoal. Rawson and Valverde [13] found that the nutritional status of children whose mothers rolled cigars was better than that of children whose mothers harvested coffee; although the cigar-rollers earned less income, they were able to do this at home in their spare time. If someone of equal skill is not available to assume the woman's former responsibilities or she does not receive sufficient income to purchase food or services to substitute for her time, the nutritional status of the family will suffer [ 12] . Other changes may also occur that have a negative impact on family food patterns. Women in Ghana took over yam production when the men began to use all of their time producing cacao for cash [4] . Because they had limited time to work in the fields, the women replaced the yams with cassava which required less labour. Since cassava has a lower nutritional value than yams, the overall quality of the family's diet decreased.

If the commercial or cash crop is inedible, such as cotton, coffee, or tea, proceeds from the sale may have to be used to purchase much of the family's food supply. Food needs then compete with non-food needs [6]. A farmer who produces mainly non-food crops or decreases crop diversity is more vulnerable to a crop failure, or to a yield that is only large enough to repay the credit extended, than the traditional farmer is.

Disposal of productive outputs may affect the balance of monetary control between various family members. Any change within the family farm system can upset existing structure and balance. Babcock and Zalla [1] suggest that the flow, content, and ownership of farm income may be more important to nutritional status than the amount of income. A steady, although low, source of income throughout the year may have a greater effect on nutritional status than larger, intermittent income from sale of production. Farm income in Africa has traditionally been divided according to sex. Males often receive proceeds from the sale of large animals or cash crops while women sell small animals, milk, eggs, produce from household gardens, or prepared foods. In the Tiv project, during May, June, and October approximately one-third of the women's labour was devoted to crops for which men controlled all or part of the income [5]. When women participate in the production of the cash crop but not in the decision-making or the distribution of proceeds from the sale of the crop, food supply to the household is adversely affected. Increased farm income from greater productivity may be spent on additional food only if the income is earned by the family members responsible for food acquisition or preparation [1] . The problem is exacerbated when women do not have time to maintain a garden, raise small animals or continue other income-generating activities.

If crops formerly grown for home consumption have to be purchased, the cash required to buy them would be greater than their monetary value when sold [7]. This is due to the differential between wholesale and retail prices. Nutritionally superior foods, such as fruits, vegetables, eggs, milk, chicken, fish, and meat that formerly were produced in Tabasco, Mexico, were being purchased at the time of Dewey's study. These foods were more expensive than the more prestigious but less nutritious foods such as sweet rolls, white bread, crackers, and cookies which most families had begun to substitute for the foods they formerly produced. The same effect was found in Sierra Leone, where greater dependency on the market had an adverse effect on food consumption [16] .

Household gardens that provide fruits and vegetables to supplement the family diet also provide a source of income to the woman. When a new farming system requires that the female head of the household work in the field to produce the cash crop, she may not have sufficient time to maintain the garden. This will adversely affect the nutritional status of the family by decreasing the intake of fruits and vegetables and reducing the quantity of the additional foods usually purchased with income from the sale of garden surplus.

The cost of energy required to increase productivity may be greater than the value of the output. In north-eastern Brazil income increased for the men who cut the sisal [9] . However, almost all of the additional cash earned was required to purchase more food to meet the increased energy requirements of the men themselves, and while the men were able to meet their increased needs, it was at the expense of other family members who did not receive additional food. In some cases, children received only about 50 per cent of their daily caloric requirements. Thus there was no net improvement and sometimes even a decrease in family welfare.

Families who change from subsistence to commercial farming will be able to improve their food intake and nutritional status when their incomes are high enough to allow them to purchase both required inputs and consumer goods. However, this will happen only if they spend part of the increased income on sufficient food of good nutritional quality. It is during the transitional period, when income is not yet sufficient or secure enough to meet all their needs for cash, that families are most vulnerable to inadequate food intake and malnutrition. An evaluation of the Chontalpa Plan by the National Institute of Nutrition in Mexico [10] identified the disproportionate effect that commercialization of agriculture and increased agricultural productivity had in the state of Tabasco. From a nutritional standpoint, only the middle and higher socio-economic levels benefited from the increase in productivity. This sector of the population began to consume more meat, milk, and other foods while the diet of the agricultural workers did not change. Although the number of normally nourished children increased from 13 per cent of the pre-school population to 30.6 per cent, this was due primarily to a decrease in the number of mildly malnourished children. There was no change in the proportion of moderately or severely malnourished children. The evaluation concluded that agriculture development alone did not alter food patterns of limited resource farmers, nor did it prevent malnutrition. A later study by Dewey [7] in the same region found that children from families whose per capita income was in the top 25 per cent were significantly taller than children from families with less income. This was not unexpected since height is an indicator of long-term nutritional effect.

NUTRITION RESEARCH AS A COMPONENT OF FARMING SYSTEMS RESEARCH

Farming systems research attempts to obtain a holistic understanding of the farm enterprise and to promote technology, cropping systems, and animals that are consistent with the farmer's resources and goals. Appropriate technology, crops, and animals are identified during the reconnaissance survey and/or definitive phases of project design. Nutrition concerns should be introduced at this point. The question is what indicators are most appropriate for measuring the impact of change in the farming system upon nutritional status. Nutritionists are most familiar with anthropometric or biochemical indices, ethnographic studies, food consumption surveys, and mortality and morbidity data. These are criticized as too time-consuming, costly, difficult, and specific. Economists and agronomists, on the other hand, prefer production indicators which nutritionists believe are too general and do not address differences in culture, intra-household distribution, or actual food consumption. Nutrition concerns will only be included in farming systems research when agricultural, economic, and nutritional scientists agree on appropriate methodology, The remainder of this paper will suggest data that might be collected in a field survey and how it might be used in measuring change. The intent is to open a dialogue between economists, agronomists, and nutritionists.

Indicators of nutritional change used in farming systems research must be simple to use and easy to interpret. They should not require cumbersome equipment, expensive supplies, refrigeration, or electricity. For this reason most anthropometric and biochemical indicators are difficult to incorporate into an agricultural project. The use of growth of pre-school children as an indicator will bias the research sample since it will eliminate families without young children. If time and funds permit, however, a formal nutrition survey, including anthropometric, biochemical, and clinical studies, could be conducted in collaboration with the Ministry of Health or the local health clinic.

Frequently, the results of recent nutrition studies are available either at the national ministry or at the regional public health centres. Regional or local mortality and morbidity statistics are often available at the public health clinics in the research area. These data will help identify the extent and causes of nutrition-related illnesses and deaths in the community.

Nutrition concerns of farming systems research should focus on family food supply and intra-household food distribution. Whelan [19] has proposed a subsistence potential ratio based on the household's ability to feed itself versus its need to feed itself—that is, the amount of food produced by the household during one year compared to the protein and energy requirements of the household during the same year. Although this is a good beginning, it is not specific enough. Problems with this ratio are: (a) it assumes that all foods produced for household consumption are actually consumed; (b) it assumes that foods are consumed proportional to need; and (c) it makes no allowances for seasonal variations. It is possible that the subsistence potential ratio would be the same for a family which has barely enough food to eat throughout the year and one which has sufficient except during the weeks preceding the new harvest

Since crop diversity is related to diet diversity and, ultimately, nutritional status, some indication of crop diversity must be included in estimates of household food production and acquisition. Data to be collected should include:

1. Food and non-food production from the fields—including livestock.
2. Costs of production—including seed, fertilizer, and credit.
3. Amount of crops consumed, sold, or exchanged for inputs such as labour.
4. Income from sale of food and non-food production.
5. Household food production—including food grown in the garden or yard, small animals, and food obtained through forage or gifts.
6. Income from sale of household foods.
7. Storage or processing losses.

With this data changes in foods available for family consumption as a result of a new farming system could be identified, including changes in:

1. Ratio of production to consumption: What proportion of the total farm production is sold or consumed by the family and how much additional food has to be purchased
2. Food diversity: How many animals and food crops are produced primarily for on-farm consumption?
3. Food cost: Cost of producing for on-farm consumption plus cost of food purchased; cost of food produced but not actually consumed or sold should also be calculated.

Intra-household food patterns should also be identified. The 24-hour dietary recall surveys which nutritionists generally use are difficult to administer in field surveys.

Unless highly skilled interviewers are available the dietary data collected will not be reliable, Food frequency data is easier to obtain and specific enough for most farming systems research. Preliminary discussions with informed respondents such as community or extension leaders can identify the food generally produced and consumed in the area, including the most important sources of energy and key nutrients such as protein, vitamin A, iron, and calcium.

The list of foods likely to be consumed would include: staple foods; animal products such as eggs, meat, milk, or fish; vegetables; fruits; oil, sugar, salt, or coffee; fermented beverages; and infusions or teas made from local plants. Foods usually gathered or foraged should also be on the list For each food on the list the following information should be obtained:

1. Frequency of consumption: Is it consumed year round or seasonally? How often is it eaten—daily, weekly, monthly? With what other foods is it usually combined? By whom is it usually consumed? What are the age, sex, and/or physiological differences among the consumers?
2. How is the food procured? Is it produced, purchased, received as a gift?
3. What is the average portion size? How does portion size differ for each family member?

These data can be used to identify changes in food patterns within the household, including changes in:

1. Diet diversity: changes in foods produced in the field or garden and foods purchased, including seasonal changes.
2. Ratio of consumption to need: similar to the subsistence potential ratio but also considering food available for consumption but not consumed within the household.
3. Intra-household food distribution: including an estimate of distribution proportional to need.
4. Food processing, preservation, or preparation procedures: effect of these factors on the nutritional quality of the food consumed within the household.

The most limiting factor relating to nutritional status in each household might be identified and changes in that factor measured. An example is the woman who has many duties prior to the implementation of a new farming system. The effect of the new system on her time-use should be measured. Does she have to make adaptations that have a negative effect on family food patterns? Food availability might be another limiting resource. What are the pre- and post-harvest differences in foods available for household consumption?

Continued agricultural development is imperative if growing populations in Third World countries are to survive and prosper. Programmes that address food deficits only by increasing output or improving varieties may increase production while exacerbating other problems. If nutrition concerns are included in farming systems research, the effect of changes in farming systems or technology on the well-being of the farm family can be monitored. If the new technologies have unforeseen negative consequences they will be readily identified and the new system can be modified. This is not to imply that agricultural development must be planned around the nutritional needs of the farm family. It does, however, suggest that a nutritionist should play a role in the initial project design and in the monitoring and analysis stages as well.

ACKNOWLEDGEMENTS

This paper has benefited from comments by Cornelia Butler Flora and Leslie R. Liberman, as well as by the participants in the workshop on Nutrition as a Component of Farming Systems Research and Extension (FSR/E), held at the University of Florida in Gainsville, 20-21 February 1985.

REFERENCES

1. C. Babcock and T. Zalla, Nutrition Guidelines for agriculture and Rural Development (USAID. Africa Bureau, Office of Technical Resources, Agricultural and Rural Development Division, 1984).

2. J. A. Ballweg, "Family Characteristics and Nutrition Problems of Pre-school Children in Fond Parisian, Haiti," Journal of Tropical Pediatrics, Monograph no. 23 (1972).

3. M. N. Beaudry-Darisme, L. C. Hayes-Blend, and A. G. Van Veen, "The Application of Sociological Research Methods to Food and Nutrition Problems on a Caribbean island," Ecology of Food and Nutrition, 1: 103-119 (1972).

4. J. Bukh, The Village Women in Ghana (Copenhagen Centre for Development Research, Copenhagen, 1979).

5. M. E. Burfisher and N. R. Horenstein, "Sex Roles in the Nigerian Tiv Farm Household and the Differential Impacts of Development Projects," Case Studies of the Impact of Large scale Development Projects on Women, Population Council Study, no. 2 (Kumarian Press, West Hartford, Conn., 1985).

6. K. G. Dewey, "Agricultural Development, Diet and Nutrition," Ecology of Food and Nutrition, 8: 265-273 (1979).

7. K. G. Dewey, "Nutritional Consequences of the Transformation from Subsistence to Commercial Agriculture in Tabasco, Mexico," Human Ecology, 9: 151-187 (1981).

8. P. Fleuret and A. Fleuret, "Nutrition, Consumption, and Agricultural Change," Human Organization, 39: 250-260 (1980).

9. D. R. Gross and B. A. Underwood, "Technological Change and Caloric Costs: Sisal Agriculture in North-eastern Brazil," American Anthropologist, 73: 725-740 (1971).

10. M. Hernandez, C. P. Hidalgo, J. R. Hernandez, H. Madrigal, and A. Chavez, "Effect of Economic Growth on Nutrition in a Tropical Community," Ecology of Food and Nutrition, 3: 283-291 (1974).

11. P. Pinstrup Anderson, "Incorporating Nutritional Goals into the Design of International Agricultural Research—An Overview," International Agricultural Research and Human Nutrition (International Food Policy Research Institute, Washington, D.C., 1984).

12. B. M. Popkin and F. S. Solon, "Income, Time, the Working Mother and Child Nutriture," Journal of Tropical Pediatrics and Environmental Child Health, 22: 157-166 (1976).

13. I. G. Rawson and V. Valverde, "The Etiology of Malnutrition among Preschool Children in Rural Costa Rica," Journal of Tropical Pediatrics and Environmental Child Health, 22: 12-17 (1976).

14. N. Rizvi, "Effects of Food Policy on Intra-household Food Distribution in Bangladesh," Food and Nutrition Bulletin, 5(4): 3034 (1983).

15. E. M. de Rubenstein, "Incorporating Nutritional Concerns into the Establishment of Commodity Priorities in International Research," International Agricultural Research and Human Nutrition (International Food Policy Research Institute, Washington, D.C., 1984).

16. V, E. Smith, K. Kolasa, J. Strauss, W. Whelan, and L. Bingen, "Development and Food Consumption Patterns in Rural Sierra Leone," Food and Nutrition, 7: 24-32 (1981).

17. M. S. Swaminathan, "Nutrition and Agricultural Development: New Frontiers," Food and Nutrition, 10(1): 33-41 (1984).

18. R. Tripp, "On-farm Research and Applied Nutrition: Some Suggestions for Collaboration between National Institutes of Nutrition and Agricultural Research," Food and Nutrition Bulletin, 6(3): 49-57 (1984).

19. W. P. Whelan, "Incorporating Nutritional Considerations into Farming Systems Research," Proceedings of Kansas State University's 1982 Farming Systems Research Symposium— Farming Systems in the Field (Kansas State University, Manhattan, Kan., 1982).

Small-scale integrated agricultural production family farm

R. Bressani, E. Ibáñez, and J. M. Gonzalez
Institute of Nutrition of Central America and Panama (INCAP), Guatemala City, Guatemala

This article will present data to show that under the environmental conditions existing at a site in the highlands of Guatemala, it was possible to produce enough food from one hectare of land to supply a high-quality diet at relatively low cost for a family of five with a surplus left over to feed other people. The model of production was based on research findings on ways to improve the quality of staples and incorporated the results of such research into diets of adequate nutritional value and reasonable cost. These concepts will become evident in later sections of the article. The model used and its implementation has many drawbacks and weak points, and its transfer to practical situations may be almost impossible to achieve. However, it deserves analysis and criticism, and this is the reason for its publication.

THE DIET

The diet chosen for this study was nutritionally adequate and relatively inexpensive [1]. Its ingredients, which are described in table 1, were chosen on the basis of individual nutritional needs, taking into account age and physiological state; however, for the purpose of developing a model of agricultural production, the amount of each food needed by a family of two adults and three children aged three, five, and eight was calculated from the estimated needs of each individual. These are the values shown in the second column.

TABLE 1. Food ingredients in diet of adequate nutritional and acceptable quality (g/person/day)

Source: Flores et al. [1].

As seen in the first column, the diet contained 17 different food items, of which 14 can be produced on the farm. Edible oil, sugar, and coffee were items which had to be purchased. Of the 14 other items, not all can be produced under the same environmental conditions. This diet, designed with complete knowledge of the quality and quantity of foods consumed by rural people in Guatemala, has some aspects which must be emphasized. First of all, the diet respects the food habits of the people, including corn and beans, the two basic staples of the Guatemalan diet, as important food items [2] . The diet also includes milk, eggs, and meat, which the country hopes to have as a result of agricultural research, since animal products are not unknown entities in the rural home. The diet was designed to meet the nutritional needs of the population and to incorporate into it minimum amounts of food of animal origin. The components in the diet include a group of items termed "green leaves," which designate a number of indigenous vegetables often consumed by people in rural areas. People who have migrated to cities still eat these vegetables and represent a potential market for them. These green leaves include mainly bledo (Amaranths spp.), macuy or hierbamora (Solanum spp.) chipilín (Crotalaria spp.), and others. However, the diet also includes yellow vegetables, included on the basis of their relatively high carotene content, to increase provitamin A intake [3] and thus diminish deficiencies of this nutrient in the Central American diet. Not excluded are other horticultural crops. Classical sources of energy are also included, such as potatoes and cassava, which can be replaced by yams, bananas, or plantain. In most rural areas in Central America, it is not difficult to find animals living close to the household. Although hens and chickens are most common, swine and cows are also found. These may serve as sources of income as well as provide food for the family.

One of the limitations of the diet is that not ail of its items can be grown at the specific ecological site, and obviously those not produced there must be purchased elsewhere. It is important, therefore, that food items be interchangeable.

The diet can be criticized from other points of view, such as the difficulty or high cost of producing animal food items; but this criticism should be evaluated after looking into the possibility of producing them at the farm level.

THE COMPONENTS

The High Protein Food

The idea of incorporating a high-protein food as a component of a diet as described in table 1 is related to the possibility that animal food products may not be readily available throughout the year, as well as to the cost of the diet. There are, of course, a relatively large number of possible formulations for high-protein foods; the one that was introduced in the integrated agricultural production system (to be described later on) is based on a blend of corn and soybeans [4,5] . A high-quality food results from mixture of whole soybeans and corn mixed in a 30:70 ratio as presented in figure 1. As shown, the protein quality of such a blend is higher than the protein quality of its individual components. This blend can be produced at home using the traditional technology to cook corn for tortilla preparation; it contains around 18 per cent protein and 8 per cent fat with 410 kcal/100 9 [4]. A further advantage of the formula and the process used is that it can be blended with corn mesa [4] in a 1:1 ratio by weight, producing a food with 15 per cent cooked whole soybeans and 85 per cent corn, making a high-quality tortilla with good eating characteristics [6] . There are other possibilities such as blends based on corn and beans [7], but these are not likely to be used because they constitute the main staple of the diet.

FIG. 1. Protein efficiency ratio of combination of normal or Opaque-2 maize and soybean flour

TABLE 2. Nitrogen balance in dogs fed corn alone or supplemented with milk or fish protein concentrate

Source: Bressani and De Villareal [8].

TABLE 3. Effect on rats of frequency of supplementation of corn/bean diets with small amounts of skim milk (3g/animal/day)

Sources: Braham et al. [10]. De Souse et al [9].

Animal Food Products

Animal food products are known to be foods of high nutritional quality, and therefore they need not be discussed in this article. The only point to be made is that because of their exceptionally high quality, they need not be consumed in large amounts. Different products also have a similar essential amino-acid content, and can thus be easily interchanged without altering the nutritional value of the diet. The results show an expected improvement in the quality of the diet, as demonstrated by the higher nitrogen retention values [8]. A similar effect is observed in table 3 upon addition of 3 g of milk daily to a corn/bean diet [9, 10] . When this amount is provided only every two days the performance of the animals decreases, showing that frequency of supplementation is important. Upon conversion of the optimum levels of animal protein into minimal actual units to be consumed daily, the figures obtained from the example shown, as well as others [11] are: 50 to 60 ml of milk per 100 g of dry food per day; 30 g of chicken meat per 100 g of food per day; and 14 g of fish per 100 g of food per day. The only condition is that they be consumed daily.

Food Legumes

One of the main ingredients of the diet is the common black bean, the preferred food legume of the Guatemalan population. Two types are produced, those of determinate growth and those of determinate growth. From the diet's point of view either type plays the same role; however, for the model to be presented, the undeterminate type was grown, since it can be intercropped with corn. Thus beans can be interchanged, not only between cultivars of the same species, but also between different species, since their chemical composition and protein quality are similar [12]. However, it should be pointed out that immature beans are nutritionally superior to mature seeds of the same species. This is shown in table 4, where immature pigeon peas, both raw and cooked, have a higher protein quality than mature seeds. This of course opens up options for production and consumption [13,141, as part of family gardens. The supplementary value of common beans and other food legumes to cereal grains is also alike, as represented in figure 2 [12,15].

TABLE 4. Protein quality in rat assay of immature and mature pigeon pea grain, raw and cooked

a. Average weight gain: 44 g.

TABLE 5. Partial chemical composition and essential amino-acid content of selected Guatemalan indigenous vegetables

a. Nitrogen x 6.25.
Source: Bressani [16].

FIG. 2. Protein quality of cereal grain/food legume mixtures

Indigenous Green Leaves

The indigenous green leaves—bledo, hierbamora, and chipilin—merit some discussion. Table 5 shows the partial chemical composition of these materials, as well as the essential amino-acid pattern. Protein content on a dry weight basis is around 30 per cent and the food contains close to 10 per cent crude fibre [16]. The essential amino-acid content is relatively good compared with the FAO/ WHO pattern [17] . All the green leaves are good sources of Iysine, although deficient in sulphur amino-acid content. Furthermore, they also contain high amounts of carotene and other water-soluble vitamins as well as essential minerals [18] . The sulphur amino-acid deficiency is readily apparent in the results of table 6, in which a significant improvement in protein quality takes place upon methionine supplementation [16]. Finally, it is of interest to show that the use of these leaves, as exemplified by the use of amaranth leaves as a supplement to a 90 per cent corn and 10 per cent bean diet (shown in table 7), improves the nutritional quality of the diet [16] . The supplementary effect takes place, whether or not supplemental vitamins and minerals are added to the basal diet, and this effect was interpreted to mean that the green leaves can serve as a source of various nutrients.

Potatoes and Other Root Crops

There are a number of root crops which can be produced; however, the potato would be the root crop of choice. Although its protein content is low, its quality is high. Table 8 shows some results of an evaluation in which potatoes, cassava, and plantain were fed with black beans and evaluated in adult human subjects and rats [19,20]. The results show excellent values for the bean/potato combination and low values for cassava and plantain; nevertheless, these last two foods are traditionally eaten by the people and should therefore be included in the diet. Table 8 indicates that people who eat them also eat more supplementary proteins, such as beans.

Cereal Grains

With respect to cereal grains, it is difficult to find one environment which will produce all of them; however, because of the similarity of their nutrient content, they can be interchanged without major change in the nutritive value of the diet, the more so when they are part of a mixed diet. Figure 3 shows the protein quality values of mixtures of the three cereal grains selected. Rice, having a better quality, improves the quality of corn and wheat, but this can be observed only when the grains are tested by themselves and not as components of the diet [21]. The diet is probably high in wheat products, owing to the well-established tendency for higher consumption of these foods Programmes have been developed to reduce as much as possible the consumption of wheat when it has been made into extended flours.

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