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Hunger and health
Examining the nutritive value of basic foods as a tool for the study of diets in poor countries
Faculty of Medicine, Department of Nutrition, University of Chile, Santiago Norte, Chile
The diets of populations truly represent the way in which they satisfy their most basic need-to nourish themselves. The underlying dietary structure comprises the types of foods that are consumed either in larger quantities and/or more frequently. The choice of foods is largely determined by many interrelated factors, such as a strong cultural tradition transmitted directly from generation to generation, the socioeconomic situation, which may either facilitate or block the access of individuals to the foods available in the country, and geographic location, which determines what and how much can be grown.
In the dietary patterns of each country there are basic foods that are consumed in relatively high proportions, closely linked to nutritional habits that remain unaltered through time. Throughout Latin America the basic food is a cereal (table 1 ) (1). Corn predominates in most of these countries because it was widely cultivated in Indian cultures, although wheat is a major part of the diet in the southern countries, and rice is a main dietary component in Brazil and Colombia.
In order to study the nutritive value of a diet, it is necessary to design a method with adequate indicators and standards to estimate the potential of the different foods for satisfying human needs. This is a methodological challenge that must be met to make it possible to systematize studies and reproduce the results obtained in different countries.
TABLE 1. Main Foods* in the National Diets of Latin American Countries, 1972-1974
|Argentina||Wheat, meat, milk|
|Bolivia||Wheat, corn, potatoes|
|Brazil||Rice, wheat, beans|
|Chile||Wheat, meat, milk|
|Colombia||Corn, rice, cassava|
|Costa Rica||Corn, rice, wheat|
|Ecuador||*Corn, rice, wheat|
|El Salvador||Corn, sorghum, wheat|
|Guatemala||Corn, wheat, beans|
|Guyana||Rice, wheat, meat|
|Honduras||Corn, wheat, beans|
|Mexico||Corn, wheat, beans|
|Nicaragua||Corn, beans, rice|
|Paraguay||Corn, cassava, meat|
|Peru||Wheat, corn, rice|
|Uruguay||Wheat, meat, milk|
|Venezuela||Corn, wheat, milk|
*Excluding sugar and oil.
Source: FAO (1).
Table 2 shows the dietary indicators that will be used in the present analysis, which is mainly directed towards protein and energy. The protein-energy ratio (Pe%) expresses the protein concentration in energy terms (protein calories in 100 kilocalories). It has been recommended as an indicator for estimating the potential of diet to satisfy protein needs. Both the models proposed by Beaton and Swiss (2) and by Payne (3), who considers variability in energy and protein requirements, agree in recommending as safe values a Pe% of 11 to 12 for protein utilizations of about 60 per cent. The ratio of fat to energy (Fe%) is the concentration of fat expressed in energy terms (kcals of fat in 100 kilocalories), and indicates the potential of a diet to meet energy requirements. A value of 20 to 30 per cent has been recommended by a 1977 FAO/WHO expert committee (4).
The ratio of fat calories to protein calories (Fe/Pe) is a supplementary indicator of the protein-energy ratio used to avoid false interpretations in analysis of the Pe% values in diets low in fat. According to metabolic studies and the Pe% and Fe% recommendations of different committees, a value of 2.0 has been proposed as the absolute minimum standard (5). The NDpCal% is an index that integrates the quantity and quality of the protein and illustrates the advantages of expressing it in energy terms (protein calories usable in 100 keels of diet). A value of 8.0, the equivalent to that in breast milk, is considered optimal for humans, but it must be stressed that this figure represents the almost perfect utilization of human milk protein and must be adjusted upward for proteins of lesser quality.
TABLE 2. Dietary Indicators Used in Evaluating the Protential of Diets to Satisfy Energy and Protein Needs
|Dietary Indicators||Expressing||Reference values|
|Pe%||Concentration of protein in terms of energy||11-12|
|Fe%||Concentration of fat in terms of energy||20-30|
|Fe/Pe||Fat calories to protein-calorie ratio||2-2.5|
|Amino-acid||Protein quality score||-|
|NPU||Biological quality of the protein||-|
|NDpCal%||Utilizable protein calories||8*|
*Optimum value. similar to that in breast milk.
FIG. 1. Diets of 12 Rural Guatemalan Communities Plotted on a Curve Showing the Change in Amino-Acid Score of a Diet of Corn and Beans as the Proportion of Beans Is Increased
One of the main problems in studying local diets is how to represent adequately the diet of a group of individuals, of a whole community, or of an entire country. This is almost impossible to do. One of the approaches used has been to study the nutritive value of only the basic foods. This was attempted in a longitudinal dietary study carried out in 12 rural communities in Guatemala as part of the project "Fortification of Sugar with Vitamin A."
The low socio-economic groups living in rural areas have kept, to varying degrees, the cultural traditions of the Mayas, and especially their dietary habits. The diet of these populations is often monotonous, thus enabling one to: (i) establish methodological criteria for studying the nutritive value of the most frequently consumed basic foods; (ii) set realistic dietary goals within the proposed models of nutrition education, based on the nutritive value of these foods; (iii) learn the potential of adding supplements to daily meals.
Figure 1 shows the change in amino-acid score in a diet of corn and beans when the proportion of beans is increased, following the classic design of Bressani et al. (6). The communities have been plotted along this curve according to the proportion of their protein intake from corn and beans. It is clear that the communities consume different proportions of corn and bean proteins so that it would be an oversimplification to establish a prototype for all the rural communities of a country.
The communities fall into three groups, one of which, comprising 66 per cent of the communities, is close to optimum utilization of corn-bean proteins. The results show a nutritional fact we frequently forget, which is that the concept, imported from developed countries, of a local or indigenous diet is not applicable to the general diet of a developing country community, only to particular communities or regions, and that it is also necessary to consider cultural factors.
TABLE 3. Amino-Acid Scores* of the Corn-Bean Combination and of the Total Diet in 12 Rural Guatemalan Communities, with the Percentage of the Corn-Bean Combination in the Diet
|Community||Proportion of corn protein to bean protein||Amino-acid score of corn-bean combination||Percentage of corm bean combination in total diet||Amino-acid
score of total diet
|El Barreal||69 :31||73||69||86|
|Santa Maria Ixhuatán||63 :37||75||72||88|
|San Juan||67: 33||74||64||88|
|El Jícaro||62: 38||76||54||93|
|Buena Vista||92: 8||56||96||69|
|San Rafael Sacatepequez||90: 10||57||92||70|
|La Libertad||67 :33||74||66||95|
|San Carlos Alzatate||66: 34||75||75||87|
|Santa Fé||80: 20||64||76||85|
*Median of the average values obtained in the five periods of the study.
AMINO-ACID SCORE OF CORN AND BEANS IN THE DIETARY INTAKE OF THE COMMUNITIES STUDIED
A primary focus of the present analysis is a comparison of the protein quality of the corn-bean combination to that of the total diet (table 3). In this case, not only have the proportions of proteins in the basic foods been included, but also the energy percentages that they represent in the diet. In all communities there is an increase of 12 to 21 units in the amino-acid score of the diet, although the average increase is between 12 and 15 units. It is interesting to note that the same absolute increase can be obtained with such different proportions of corn and beans.
This fact demonstrates that in the lowest amino-acid scores, corresponding to a high proportion of corn proteins, similar increases can be obtained with a lower percentage of other foods. The results show that the protein quality of the diet can reach a value of 70 with an intake of corn above 90 per cent. As the protein quality of the combination improves, its consumption decreases, and the amino-acid score can reach 90, with increases similar to those obtained in lower quality combinations.
With respect to energy consumption, an unexpected result was that the communities where the diet had a high percentage of corn (more than 80 per cent) were the same ones that showed a higher per capita energy intake (table 4).
This justifies the hypothesis that the introduction of a greater variety of foods in poor communities would limit purchasing power, and people would be unable to buy and consume a greater quantity of the basic staple food. This nutritional change produces an improvement in the quality of the diet with respect to proteins, vitamins, and minerals, but diminishes the energy contribution. This puts nutritionists responsible for dietary improvement of populations into the position of having to explain clearly the reasons for promoting dietary changes aimed at improving the quality of life.
TABLE 4. Corn-Bean Combination and Per Capita Energy Consumption in Guatemalan Communities
|Community||Proportion of corn protein to bean protein||Per capita Energy consumption (kcal/day)|
|Buena Vista||92: 8||2,073|
|San Rafael Sacatepequez||90: 10||2,345|
|El Barreal||69: 31||1,759|
|San Juan||67: 33||1,490|
TABLE 5. Protein-Energy Ratios* (Pe%) of the Corn-Bean Combination and of the Total Diet in the 12 Rural Communities
|Community||Proportion of corn protein to bean protein||Pe% of corn-bean combination||Percentage of
in total diet
|Pe % of total diet|
|El Barreal||69 :31||12.8||69||12.4|
|Santa María Ixhuatán||63 :37||13.4||72||12.3|
|San Juan||65: 35||13.2||60||11.2|
|El Jícaro||62: 38||13.5||61||11.9|
|Buena Vista||94: 6||10.7||96||12.1|
|San Rafael Sacatepequez||83: 17||11.5||95||11.6|
|La Libertad||67: 33||13.0||73||12.6|
|San Carlos Alzatate||70: 30||12.7||82||12.6|
|Santa Fe||81: 19||11.6||81||12.6|
* Median of the average values obtained during the five periods of the study.
PROTEIN-ENERGY RATIO (Pe%)
As we have said, the protein-energy ratio indicates the potential of a diet to meet protein needs. The concentrations of the corn-bean combinations are very similar to those of the diets (table 5), reflecting the fact that the basic foods strongly condition dietary protein concentration. The values lie between 11 and 14 per cent, and it can be seen in figure 2 that they are all above the "safe" level recommended by Beaton and Swiss. This safe value was based on the assumption of an inter-individual variability of 20 per cent in intake of Pe%and a protein utilization of 60 per cent.
We have recently demonstrated (7) that the inter-individual variability of Pe% intake in a community similar to that studied was about 15 per cent, so that 20 per cent is not an unreasonable figure. A protein utilization of 60 per cent is also adequate, since the amino-acid scores must be corrected to a factor that accounts for the digestibility of nitrogen. Therefore, based on this criterion, the communities consume a diet that covers the protein needs of 97.5 per cent of their population.
Nevertheless, it is necessary to evaluate this indicator by introducing a dietary variable that reflects the energy density in the diets. This is the percentage of calories from fats. The diets of these communities are low in fat (fig. 3). This makes the Pe% values artificially high. Figure 4 shows that, if we increase the percentage of fat calories (Pe%) to a value of 30, the re-calculated values of Pe% will be below the reference values. This argument justifies the use of the Fe/Pe ratio as an indicator.
FIG. 2. Protein-Energy Ratios (Pe%) in the Diet of 12 Rural Guatemalan Communities
FIG 3. Fat-Energy Ratio (Fe% ) in the Diets of the 12 Rural Guatemalan Communities and 3 Industrialized Countries
FIG. 4. Calculated Effect on the Pe%of Rural Guatemalan Diets of Raising Their Fe% to 30%
FIG. 5. Pe%, NDpCal%, and NPUop in a Diet of Corn and Beans as the Proportion of Beans Is Increased
There is growing agreement that it is necessary to explore criteria and establish models for recommended dietary goals with respect to energy and proteins. These criteria must take both the dietary habits and the socio-economic level of the population into account. Here we are presenting an analysis based on the nutritional value of basic foods and the possibility of considering their nutritional ceiling as a real dietary goal, without a significant change in the dietary patterns of the groups toward whom these recommendations are aimed.
The model is based on the determination of the Pe%, NPU, and NDpCal% values of the corn-bean combination. When the proportion of bean protein is increased, protein concentration and utilization improve, so that an increase to 4.0 is produced in the NDpCal% (for corn, to 8.2) in the 50:50 combination of corn and beans (fig. 5). The break in the rhythm of the NDpCal% increase in the combinations occurs because the maximum utilization of the protein is in the 50:50 ratio of corn/beans, and beyond this proportion, it diminishes significantly. This considerable decrease is caused by a less adequate amino-acid pattern and, simultaneously, by an increase in protein concentration. The break is produced at a Pe% of 14.5.
As has already been pointed out, the Pe% values must be interpreted jointly with an index reflecting the potential of a diet to meet energy requirements. In this regard, we have recently proposed the application of the ratio (Fe/Pe) of fat calories to protein calories in the diet. We have recommended a ratio of 2.0 as a minimum acceptable value. It is then clear that the "efficient" Pe% and NDpCal% values, i.e., those in which a break is produced by an increase in NDpCal%, must be recalculated.
These figures define the potential of diets based on combinations of cereals and legumes studied in our analysis and can be considered as nutritional goals that should be met when recommendations are made for the rational use of local diets.
TABLE 6. Protein-Energy Ratio (Pe%) and NDpCal% Efficiency* of Combinations of Basic Foods
|Cereal and legume||Pe%||NDpCal%|
|Corn and beans||11.5||6.3|
|Wheat and beans||12.7||6.8|
|Rice and beans||9.2||6.2|
*Assuming a Fe/Pe ratio of 2.0.
Beaton and Swiss (2) have proposed a model for nutrition planning purposes that uses Pe% as an indicator adjusted by protein quality. It is necessary to point out that the values considered efficient in the combinations of corn-beans and wheat-beans, adjusted for an Fe/Pe ratio of 2.0 (table 6), are similar to those recommended by Beaton and Swiss, allowing for a 20 per cent intake variability of Pe% and a protein utilization of 60 per cent.
The present study suggests a model for analysing diets consisting chiefly of a combination of a cereal and a legume. Analysis of the nutritional components of this diet makes it possible to estimate the nutritional contribution it can make to realistic dietary goals and to elaboration of nutrition education models. The results in this paper caution against oversimplifying the problem of local diets and emphasize the importance of considering regional and cultural factors in the diet of any country before making recommendations for dietary changes.
1. Food and Agriculture Organization, Provisional Food Balance Sheets (FAO, Rome, 1972-1974;1977).
2. G.H. Beaton, and L.D. Swiss, Am. J. Clin. Nutr, 27: 485 11974).
3. P.R. Payne, Am. J. Clin. Nutr, 28: 281 11975).
4. Food and Agriculture Organization, World Health Organization, Dietary Fats and Oils in Human Nutrition (FAO, Rome, 1977).
5. H. Araya and G. Arroyave, Archiv. Latinoamer. Nutr., 29: 103 (1979).
6. R. Bressani, A. Valiente, and C. Tejada, J. Food Sci.. 27: 394 (1962).
7, H. Araya, B. Garcia, and G Arroyave, Archiv. Latinoamer. Nutr., vol. 30 (1980).
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