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History of breast-feeding in Chile
Instituto de Nutrición y Tecnologia de los Alimentos (INTA), Universidad de Chile, Santiago, Chile
Although the prevalence of breast-feeding varies widely around the world, the overall recent historical trend has been one of decline. It is very difficult to isolate the historical factors that have affected the practice of breastfeeding in various populations. Nevertheless, what little information there is suggests that "modernization" is the factor responsible in most parts of the world. This process may be briefly defined as follows.
"From a historical point of view, modernization is the process of change towards social, economic, and political systems that were established in Western Europe and North America from the seventeenth century to the nineteenth century, then expanding to other European countries, and in the nineteenth and twentieth centuries to South America, Asia, and Africa."1
Some common indicators of modernization are: urbanisation, industrialization, the response to mass communication media, the frequent abandonment of farming, and literacy. Almost all nations not already modernized are in the process of becoming so.
New cultural values that have contributed to the decline of
breast-feeding have been emerging in populations undergoing
modernization. The common statement that in Europe breastfeeding
was almost universally practised until the 1930s2 has
recently been refuted by the available evidence for some areas of
Germany, Austria, and Bohemia. In the nineteenth century and
perhaps before that time, it was unusual for mothers to nurse
their children for more than a few months.3,4 In
Bavaria, where a detailed survey was made at the beginning of
this century, it was hard to find mothers who had nursed their
infants at all. In other industrialized countries, similar
declines in the practice were noted, first in urban areas and
later in rural areas, where the population followed urban
practices. This was also true in Latin America, for example in
Guatemala,5 and, as the present data indicate, in
Chile. Both countries are clear examples of this pattern,
although urbanized to different degrees. Among the multiple
factors responsible are the following:
a. greater work opportunities for women that are not readily compatible with child care;
b. spread of knowledge, often propagated by health workers, of artificial feeding methods;
c. publicity through mass media and other promotional practices for infant formulas;
d. poor nutritional status of pregnant and lactating mothers in some developing countries that reduces the duration of adequate lactation; e. increase in mothers' education and improved socio-economic status.
This paper provides historical background on the decline in the practice of breast-feeding in Chile after modernization.
DATA ON BREAST-FEEDING IN CHILE
In Chile, as well as in many underdeveloped countries that are undergoing urbanization and industrialization, the declines in breast-feeding coincide with complex cultural, social, and economic changes. In these developing countries, the process of urbanization and industrialization has led to a great urban concentration. Rural-urban migration belts have formed. In the big cities, immigrants from rural areas are in the majority. At the same time, these are the people who have been most affected by cultural changes as well as by malnutrition, infections, and the psycho-social stress of the environment.
Chile began its urbanization before industrialization was significantly advanced. In 1900, one-third of the population lived in cities, and in the 1930s, when industrialization began to acquire importance, half of the people were concentrated in these cities. Thus, urbanization in Chile was much more advanced than in the majority of Latin American countries. It was estimated that in 1976, 78 per cent of Chile's population lived in urban areas.
A summary of various studies, with published data as well as unpublished information available for analysis, is shown in Tables 1 and 2 and Fig. 1. These data and the historical background of the advance of urbanization in the country indicate that the practice of breast-feeding began to decline in Chile earlier than was formerly thought. In interpreting these data, however, some limitations should be noted.
1. All samples are affected by the deaths of infants, particularly during the first six months of life, to which most of the data are limited. Infant mortality has decreased over the years from about 200 per thousand live births in 1942 to 54 in 1976. This may affect comparability to some degree.
2. The socio-economic classifications for the families under study are not uniform. In the case of lower-class urbanites, the problem of interpretation is minor, as the majority of the samples come from the National Health Service founded in 1952, or from its predecessor, the "Caja de Seguro Obrero." For the urban middle class and rural lower class, most of the samples come from different institutions or places where various social classifications were used to determine the groups, or they were unclassified
3. In retrospective studies, record analyses are always subject to error, no matter who does the research, particularly in determining the length of the nursing period and the exact age of children being breast-fed.
4. It is easiest to compare the length of time babies are breast-fed among the different studies for the period for infants from birth to three months of age. As breast feeding is less common after three months, sample errors become relatively greater, making comparisons more difficult.
The most important observations from these studies are the following.
1. The proportion of children who were exclusively breasted for three months or longer in urban, low-class areas is similar in the various studies done between 1942 and 1977. The percentages range from 26.7 to 52 per cent, the majority of values being from 30 to 42 per cent. The variations do not show any apparent historical trend over this period. In urban lower classes, there has not been a decrease in the number of children breast-fed for three months since 1942. The variations observed appear to be due to differences among the samples, i.e., the number of cases, or characteristics of the families and eligible children. Although it cannot be disregarded that, due to sample differences, a small decrease in exclusive breastfeeding for three months is disguised, it appears that the most significant decline to the present level occurred in the 1930s, when half the country was urbanized, or perhaps even before that time.
2. In urban middle-class areas, it is noticeable that, in general, the percentage of children exclusively breast-fed for three months or longer is lower than observed in the urban lower class. This coincides with observations made in other parts of the world, where modernization has had a greater effect on the upper and middle classes, with the same tendency for breast-feeding to decline progressively, as seen during the years 1949 - 76. This trend is partly explained by an increasing access to work by middle-class mothers. By 1949, duration of breast-feeding showed statistically significant differences between working and non-working mothers (Table 1).
3. For rural lower-class areas, only six investigations could be found, covering the period from 1966 - 76 (Table 2). The percentages of children exclusively breast-fed for three months or more are similar in all groups except for a higher incidence within a small group of residents of the Arican highlands, and this deserves a separate analysis because of the high rate of infant mortality. No tendency toward decreased breast-feeding is observed during this period, and it is worth mentioning that the figures for exclusive breastfeeding in these studies are slightly higher than for the urban lower class. The foregoing implies that the major decrease in breast-feeding that occurred before 1942 in urban areas was equal to that in the rural areas under study, with the exception of the Arican altiplano and perhaps some other rural areas with similar low demographic density.
4. In terms of the proportion of infants who begin breastfeeding at birth, it is important to note the high frequency of initiation of breast-feeding in urban as well as in rural areas. The majority of available percentages are between 90 and 100 per cent.
THE DECLINE IN BREAST-FEEDING IN CHILE: THE MOST EVIDENT CAUSES AND RECOMMENDATIONS FOR DEALING WITH THEM
Given that the decline in breast-feeding is a complex, multicausal phenomenon, it is useful to focus the discussion on the factors most studied and that show the most obvious interrelations. To do this, it is necessary to outline some of the research and recommendations required to reverse the trend.
Health Teams and Breast-Feeding in Chile
Although the health services nominally support breastfeeding, their actual practices have been far from adequate. For example, mothers are not allowed to nurse for eight or more hours after giving birth, babies are given water between feedings, the father is given no information on breast-feeding, and artificial feeding is hastily resorted to for minor problems that generally could be resolved without stopping breast-feeding. A Swedish study has demonstrated that the modification of some of these practices, especially in the neonatal period, promotes breast-feeding. 6
TABLE 1. Percentage of Infants Exclusively Breast-Fed for Three Months or More in Middle- and Upper Class Urban Areas of Chile, 1949 - 1976
|Social class of mothers||Middle class||Upper||Middle||Upper|
|% Infants exclusively breast-fed for 3 most||40.7||28.0||12.8||22.0|
Based on a review of literature.
1. W. Bustamente and F. Mardones R., "Medicine Preventiva
Materno Infantil: Su Aplicación en el Servicio Nacional de
Empleados," Rev. Chilena de Pediatría, 21: 450 (1950).
2. O. Undurraga, E. Vallejos, G. Duffman, and L. Osorio, "Alimentación Materna en Poblaciones de Distinto Nivel Socio-Economico y Cultural," Cat. A de Pediat. Prof. J. Meneghello, Hosp. Roberto del Rio, Santiago, Chile.
3. A Perez and E. Toledo, "Evolución Natural de la Lactancia en Mujeres de Población Urbana," XIV Congreso Chill de Obstetrica y Ginecologia, Santiago, 7 -12 November 1971, p. 386.
4. A. Patri et al., "Investigación sobre Lactancia Materna," Centro de Nutrición, Crecimiento y Desarollo, Area Norte, Santiago, Chile, in co-operation with WHO.
TABLE 2. Percentage of Infants Exclusively Breast-Fed for Three Months or More in Lower-Class Rural Areas of Chile. 1966 - 1976
|% Infants exclusively breast-fed 3 most or more||51.0||42.0||38.0||93.0||50.0||43.0|
Based on a review of literature.
1. M. Auil, S. Valiente, A. Arteaga, M. Orellana, and D, Copaja, "Lactancia y Estado Nutritivo en 150 Nodrizas Chilenas," Nutr., Bromatol. Toxicol., 7: 82 (1968).
2. F. Mönckeberg, G. Donoso, S. Valiente, A. Maccioni, N. Merchak, F. Donoso, A. Arteago, S. Oxman, I. Barja, E, Rosales, C. Micheli, N. Castro, and I. Lacassie, "Condiciones de Vida, Medio Familiar y Examen Clínico y Bioquímico de Lactantes y Preescolares de la Provincia de Curico. "
3. O. Undurraga, E. Vallejos, G. Duffman, and L. Osorio, "Alimentación Materna en Poblaciones de Distinto Nivel Socio-Economico y Cultural," Cat. A de Pediat. Prof. J. Meneghello, Hosp. Roberto del Rio, Santiago, Chile.
4. A. Arteaga, I. Lacassie, and N. Castro, "Estudio de la Alimentacion y del Estado Nutritivo de la Población Indígena de la Pre-Cordillera de Arica," supplement to Rev. Chilena de Pediatria, Aug. 1968.
5. S.J. Plank and M.L. Milanesi, "Alimentación Infantil y Mortalidad en Chile Rural," Cuadernos MedicoSociales, Vol. 14, No. 2 (1973).
6. A. Patri et al., "Investigación sobre Lactancia Materna," Centro de Nutrición, Crecimiento y Desarollo, Area Norte, Santiago, Chile, in co-operation with WHO.
FIG. 1. Percentage of Infants Exclusively Breast-Fed for 3 Months or More in Lower-Class Urban Areas of Chile (1942-1977)
The actions of the health-care team can be explained by a number of factors.
a. Scientific knowledge regarding the physiology of lactation
has become available, on a world-wide basis, only in recent
years. Health teams need to be brought up to date on this and
other biological aspects of breast-feeding.
b. Since the 1930s, the medical profession has been faced with the following problems:
i. The duration of breast-feeding has been declining, especially among working-class mothers. 7-9
ii. Malnutrition and infant mortality rates were very high in the 1930s (abut 200 per 1000 live births).
iii. When agalactia or hypogalactia was present, mothers substituted cereal flours as food for their children, with serious effects on infant health and nutrition status.7 This led to emphasis on the need to use cow's milk rather than cereal gruels as a substitute for mother's milk. It is likely that the health teams were sometimes excessively zealous in recommending breast-milk substitutes, but it seems evident that the practice of breast-feeding declined before the large scale introduction of breast-milk substitutes in state health programmes.
Three arguments justify a general recommendation to promote breast-feeding on the part of health teams in the community.
1. Empirical evidence of the success of certain educational activities in health and nutrition carried out by the health team of the National Health Service (NHS), which covers 80 - 90 per cent of the pregnant and nursing women. The capacity of the health team to accomplish these tasks has proved effective. There have been several small-scale studies on successful ways to promote breast-feeding, some of which have been published.
2. The experiences of the NHS reveal interest on the part of communities in organizing themselves and in resolving health problems through health clubs or health volunteers. In general, a good relationship exists between health teams and community, so there should be no problem with the promotion of breast-feeding.
3. Among well-nourished mothers in developed countries educational and motivational efforts to promote the practice of breast-feeding have had positive effects. It is important to note that these efforts were undertaken by women with established community positions. Examples of this kind of activity are the successful "La Leche League" in the United States, and in Sweden mothers, with no official encouragement, themselves have reversed the decline in breast-feeding.10
Working Mothers and Breast-Feeding
Among lower-class urban populations, a small proportion of mothers work outside the home. The percentage fluctuates from 7 to 16.8 per cent according to different studies.11-33 Only in a 1977 study was the change in the practice of breastfeeding analyzed in groups of mother who work and who do not work outside of their homes. The group that had paying jobs constituted 13.3 per cent (36 mothers) of a total of 271.
For the first 45 days, practically no differences are found between the nursing practices of working and non-working mothers. From this age on, however, the decrease in numbers of infants who continue with some form of breastfeeding is greater when their mothers have some kind of remunerated employment. Fifty per cent of these mothers abandon breast-feeding at about 100 days postpartum. An equal number of infants whose mothers were not working were breast-fed for 110 days. The largest difference was observed among infants of five months of age, by which time 75 per cent of the working mothers had abandoned breastfeeding, while 75 per cent of non-working mothers continued to nurse their infants until eight months post-partum. That is to say, there was a three-month difference for those children whose mothers did not work.
Only one investigation has considered the work factor in lower-class rural areas, and here it appears to have little importance.14
No recent study has investigated associations between the work factor and breast-feeding among middle-class mothers. In 1949 a study showed a statistically significant longer duration of breast-feeding among non-working middle-class mothers than among working middle-class mothers.15 In 1967, of 88 well-to-do mothers attended by private physicians in Santiago, 74 per cent were housewives and the remainder were employed outside the home. No comparison was made of the duration of breast-feeding in these two groups.16
As has been seen, female working has been associated statistically with a shorter duration of breast-feeding in two Chilean studies of lower-class urban populations in 1971,13 and of the urban middle class in 1949.15 The need to study the work factor more carefully is evident.
In a recently published book,17 the facts of the percentage of working women over 14 years of age are analyzed. The degree of participation in the labour force by women living in the outlying slums around Santiago is clearly less (16.8 per cent) than the percentage of working women within the total population of greater Santiago in the 1970 census (26.4 per cent). Variables such as marital status, children's ages, degree of education, and working capacity influence the female work status. Other factors commonly associated with the participation of women in the labour force, such as a woman's age and number of her children, were not significant in the populations studied.
Any analysis of the relationship between a mother's working and her breast-feeding her children must consider the legal benefits available for the pregnant and nursing mother. In Chile, in 1959, the post natal leave was extended from 45 to 90 days for female factory workers (NHS), and in 1966 for white-collar workers.
The Nutritional Status of Mothers and Lactation Performance
Studies in Chile and elsewhere relating to the bearing of the nutritional status of the mother on her lactation can be summarized as follows.
1. A 1948 pilot study of supplementary feeding and nutrition education for pregnant and nursing women showed significantly higher infant birth weights and longer maternal lactation in the group of women receiving nutritional supplementation and education.8
2. Various Chilean studies since 1951 have demonstrated a statistical association between birth weight and duration of lactation.11,18-21 This association includes all categories of birth weight, and the greater the birth weight, the longer lactation lasts (Table 3; Fig. 2). This suggests that the nutritional status of the mother affects her lactation as well as fetal growth.
TABLE 3. Percentage of Infants Breast-Fed after Four Months of Age, by Birth Weight
|2,500 - 2,999||34.0|
|3,500 - 3,499||48.5|
|3,500 - 3,999||48.1|
|4,000 or more||57.1|
In turn, the importance of birth weight for infant survival is established, Puffer and Serrano22 have observed this influence not only in low birth-weight babies (2,500 g or less), but also in infants with "insufficient" birth weight (2,501 - 3,000 g), in the infant mortality rates for the Americas. The group of children weighing 3,501 - 4,000 g at birth showed the lowest rate of neonatal mortality.22 The preliminary results of a study conducted by COPAN-INUAL in 1977 (Table 4) indicate that birth weight is the factor that most explains malnutrition (weight-for-age according to the Sempé Standard) in children from 0 - 5 years of age.23
The distribution of live births by weight in Chile has been studied at the national level only for 1976, and in 62.3 per cent of live births (138,069 children). The proportion of children with low birth weight (2,501 g) was 11 per cent, with 27 per cent in the category of "insufficient" birth weight (2,501-3,000 g).24
3. There is a clear association between the nutritional status of pregnant women and infant birth weight,25 as well as between weight gain during pregnancy and birth weight.26,27 Also, there is evidence from famine studies (for example, in Holland during World War II) indicating that this association is a causal one.28
4. Also during World War II, England experienced a substantial decrease in fetal and infant mortality associated with a food-distribution priority to certain groups of pregnant and nursing mothers.29
5. There is evidence from a study carried out in Guatemala30 that a supplementary feeding programme for pregnant women can improve birth weight.
6. Various authors have indicated that certain nutritional deficits in the nursing mother affect the quantity and content of some nutrients in breast milk, and it has been observed that nutritional supplementation of the mother produced a significant increase in maternal milk volume and weight gain in the child.31-43
FIG. 2. Proportion of Infants Who Continue Breast Feeding, by Age According to Birth Weight
The historical data on nutritional intake by pregnant and nursing mothers in those socio-economic groups aided by the NHS interviewed between 1960 and 1970 show serious deficiencies of some nutrients.44 A recent study of pregnant women aided by the NHS showed, in the second half of pregnancy, that 43 per cent of the women had a similarly low protein intake. Iron and vitamin-A intakes were also deficient in one-third to one-half of this population. Anthropometry revealed 30 per cent of the women to be more than 10 per cent underweight and 15 per cent to be more than 10 per cent overweight.45
Promotion of Products for Infant Feeding
The role of publicity for artificial formulas in the historical decline in breast-feeding in Chile has not been investigated. Nonetheless, it is evident that there is now a need for regulation of such promotional efforts, given the well-recognized impact of mass communication media on the dietary habits of a population.
Contraceptive Methods and Lactation
Modern contraceptive methods cannot be considered as one of the causes of the decline in breast-feeding by mothers in the 1930s or before. It is essential that an appropriate contraceptive method be indicated for nursing mothers because, even though a significant delay in ovulation has been observed in women exclusively breast-feeding their infants, this can fluctuate from 10 weeks to 6 months, which makes lactation an unreliable contraceptive method .46
The following actions are required to promote breast feeding by mothers.
a. Nutrition education and orientation of the country's health
teams toward breast-feeding is of great priority. Instruction
programmes about breast-feeding are needed in the different
formal educational institutions.
b. The malnourished mother should be the object of nutritional supplementation, and different alternatives should be studied in order to satisfy most adequately the nutritional needs of this group.
c. The practices involved in promoting feeding formulas for infants should be analyzed in order to determine desirable regulations.
d. The nursing mother should be given contraceptive methods that will not impair lactation.
e. The data on the influence of the mother's working on duration of breast-feeding suggest that social legislation to protect pregnant and nursing mothers is required.
TABLE 4. Birth Weight vs. Nutritional Status of Children 0 - 5 Years
|Birth wt. (grams)||Nutritional status unknown||Normal||2nd and 3rd degree malnutrition||Total malnourished|
|1,000 - 1,499||-||3||60.0||-||-||2||40.0|
|1,500 - 1,999||11.1||14||51.85||6||22||10||37.0|
|2,000 - 2,499||2.14||85||60.71||14||10||52||37.14|
|2,500 - 2,999||5.03||229||57.68||24||6.04||148||37.27|
|3,000 - 3,499||2.86||485||73.15||21||3.16||159||23.98|
|3,500 - 3,999||5.34||294||78.60||11||2.94||60||16.04|
|4,000 - 4,499||6.31||79||83.15||9||2.10||10||10.52|
|4,500 - 4,999||5.0||17||85.0||-||-||2||10.0|
Data from survey in Santiago, CONPAN-INUAL, 1977.
1. S.N. Eisenstadt, Modernización, Amorrortu Editores, Buenos Aires, 1968.
2. A. Raimbault, "Lactancia Natural," L'Enfant en Milieu Tropical, No. 96 (1974).
3. J. Knodel and E. Van de Walle, "Breast Feeding, Fertility, and Infant Mortality: An Analysis of Some Early German Data," Pop. Studies 22: 109 - 131 (1967).
4. J. Knodel, "Infant Mortality and Fertility in Three Bavarian Villages: An Analysis of Family Histories from the 19th Century," Pop. Studies. Vol. 22, No. 3 (1968).
5. J. Urrutia, "Prevalencia de la Lactancia Materna en Zonas Urbanas y Rurales de Guatemala," mimeographed, Institute of Nutrition of Central America and Panama, Guatemala City, Guatemala, 1977,
6. B. Vahlquist, "Present Trends in Frequency and Duration of Breast Feeding," Bol. Asoc. Internac. Pediatria, No. 5, (Jan.1976).
7. P. Araya Ch., "Alimentación Artificial del Lactante Sano," Rev Chill Pediatría, 13: 16 (1942),
8. A. Riquelme et al., "Alimentatión en la Embarazada," Acta pediat Española, No. 113 (May 1952).
9. F . Mardones Restat, "Alimentación del Lactante Sano en Servicios de Protección Materno Infantil," Rev. Chill Pediatría, Vol. 22 (1951).
10. P. De Chateau et al., "A Study of Factors Promoting and Inhibiting Lactation," Develop. Med. Child Neurol., 19: 575-584 (1977)
11. I. Lopez et al., "Duración de la Lactancia Materna y Algunos Factores Condicionantes," Depto. de Salud Pública, Sede Norte, Universidad de Chile, Santiago, Sept. 1974.
12. K. Neva, M. Valenzuela, M. Araya, and F. Mönckeberg, "Actitudes y Conducta de Lactancia en 100 Madres de Santiago," Rev. Chil Pediatria, 44 (5) (1973).
13. U. Lopez, "Estudio de Actitudes y Hábitos de las Madres en Torno a la Lactancia Natural," study prepared for CONPAN, Depto. de Administración, Universidad de Chile, Facultad de Ciencias Económicas y Administrativas, Concepción, Chile, 1976.
14. S.J. Plank and M. L. Milanesi, "Alimentación Infantil y Mortalidad en Chile Rural," Cuadernos Médico-Sociales, Vol. 14, No. 2 (1973)
15. W. Bustamente and F Mardones R., "Medicine Preventiva Materno-Infantil: Su Aplicación en el Servicio Medico Nacional de Empleados,"Rev. Chil Pediatria, 21:450 (19501.
16. O. Undurraga et al., "Alimentación Materna en Poblaciones de Distinto Nivel Socio-Económico y Cultural"," Rev. Chill Pediatria, 1967.
17. P. Covarrubias and M. Muñoz, "Algunos Factores que Inciden en la Participación Laboral de las Mujeres de Estratos Bajos," in, Chile: Mujer y Sociedad, UNICEF, Santiago, Chile, 1978.
18. F. Mardones R., "Análisis de la Atención Materno-Infantil en la Provincia de Santiago," thesis for the degree of Specialist in Public Health, Escuela de Salubridad, Universidad de Chile, 1953.
19. CON PAN-INSED, "Informe final Estudio Retrospectivo del Plan Piloto Area Oriente (CONPAN-CARITAS) " Biblioteca CONPAN, 1978.
20. "Analisis de Datos del Consultorio Quinta Buin," study by CONPAN, 1978.
21. WHO, "La Prevencion de la Morbilidad y la Mortalidad Perinatales," Cuadernos de Salud Pública, No. 42 (1972).
22. R.R. Puffer and V.M. Serrano. "Peso al Nacer y Mortalidad InfantiI," Boll OPS, Feb., 1975.
23. CONPAN-INUAL, "Encuesta en terreno, Niños de 0 - 5 Anos, Algunas Comunas de Santiago," preliminary interim report, CONPAN, Mar. 1977.
24. Analysis performed by CONPAN (unpublished findings).
25. WHO Technical Report 302,1965.
26. J. Singer et al., "Relationship of Weight Gain during Pregnancy to Birth Weight and Infant Growth and Development in the First Year of Life," J. Obstet Gynec., Vol. 31, No. 3 (1978).
27. J.W. Simpson et al., "Responsibility of the Obstetrician to the Fetus," II, "Influence of Pre-pregnancy Weight and Pregnancy Weight Gain on Birth," J. Obstet and Gynaecology, Vol. 45, No. 5 (May 1975).
28. Z. Steins and M. Susser, "The Dutch Famine, 1944 - 1945, and the Reproductive Process," I, "Effects on Six Indices at Birth," Pediat Res., 9: 70 - 76 (1975),
29. National Academy of Sciences, Maternal Nutrition and the Course of Pregnancy. Washington, D.C., 1970.
30. A. Lechtig et al., "Maternal Nutrition and Fetal Growth in Developing Societies," Am. J. Dis. Child., Vol. 129 (April 1975),
31. D.B. Jelliffe and E.F.P. Jelliffe, "The Volume and Composition of Human Milk in Poorly Nourished Communities: A Review," Am. J. Clin Nutr., 31: 492 (1978).
32. R. Sosa, K. Marshall and J.J. Urrutia, "Feed the Nursing Mother, thereby the Infant," J. Pediat, Vol. 88, No. 4, Part I (April 1976).
33. B.S. Lindblad and R. Rahimtoola,"A Pilot Study of the Quality of Human Milk in a Lower Socio-Economic Group in Karachi, Pakistan," Acta Paediat Scand, 63: 125 (1974).
34. J.C. Edozien, M.A. Kagan and C.l. Waslien, "Protein Deficiency in Man: Results of a Nigerian Study," J. Nutr., 106:312 (1976).
35. C. Martinez and A. Chavez, "Nutrition and Development of Children of Poor Rural Areas," I, "Consumption of Mother's Milk by Infants,"Nutr. Rep. Intern., 4:139 (1971).
36. R.G. Whitehead, M.G.M. Rowland, M. Hutton, A.M. Prentice, E. Muller and A. Paul, "Factors Influencing Lactation Performance in Rural Gambian Mothers," Lancet, 2: 178 - 181 (1978).
37. A. Chavez, C. Martinez and H. Bourges, "Role of Lactation in the Nutrition of Low Socio-Economic Group," Ecology Food Nutr., 4: 688 - 690(1975).
38. M.G. Karmakari, R. Rajalakshmi and C.V. Ramakrishnary, "Studies on Human Lactation," 1, "Effect of Dietary Protein and Fat Supplementation on Protein, Fat and Essential Amino Acid Contents of Breast Milk," Acta Paediat, 52: 473 - 480 (1963).
39. C. Gopalan, "Effect of Protein in Supplementation and Some So-called 'Galactogogues'on Lactation of Poor Indian Women," Indian J. Med Res, 46: 317 - 324 (1958).
40. M,S. Read, J.P, Habicht, A. Lechtig and R.E. Klein, "Maternal Malnutrition,, Birth Weight, and Child Development," Mod Probl. Paediat, 14: 203 - 215 (1975).
41. K.V. Bailey, "Quantity and Composition of Breast Milk in Some New Guinean Populations," J. Trop. Pediat, 11: 35 (1965).
42. A.K. Deb and H.R. Lama, "Studies on Human Lactation: Dietary Nitrogen in Mother's Milk," Brit J. Nutr., 16: 65 (1962).
43. M,M Hanaty, M.R.A. Morsey, Y. Seddick, Y.A. Habib and M. El Lozy, "Maternal Nutrition and Lactation Performance," J. Trop. Pediat,18: 187 (1972).
44. M.A. Tagle and M.A. Colombara, Publicación Inv. 23/71 Depto. de Nutrición, Universidad de Chile,1971.
45. A. Arteaga et al., "Caracteristicas de la Alimentación y Estado Nutritivo de una Población de Embarazadas del Area Sur-Oriente de Santiago, 1974 - 1975," Rev. Med Chile, 105:873 (1977).
46. Nutrition Committee of the Canadian Pediatric Society/Committee on Nutrition of the American Academy of Pediatrics, Breast Feeding, 1977.
References for Fig. 1
1. Pedro Araya Ch., "Alimentación Artificial del Lactante Sano," Rev, Chil. de Pediatria, 13: 16 (1942).
2. Alfredo Riquelme et al., "Alimentación de la Embarazada," Acta Pediátrica Español, No. 113 (May 1952). (See also "La Alimentación en el Recién Nacido," edited by Howard, Hosp. Calvo Mackenna, and the mimeographed document of A. Riquelme et al., Chief, Department of Nutrición of the ex-Dirección General de Sanidad.)
3. I. Borja, D. Ballester, E. Yañez, N. Pack, M.A. Tagle, and G. Donoso, "Alimentación de la Madre, Compositión Quimica de la Leche y Duración de la Lactancia," Centro de Invest. de la Nutrición, Esc. de Salubridad, U. de Chile.
4. K. Nera, M. Valenzuela, M, Araza, and F. Mönckeberg, "Actitudes y Conducta de Lactancia en 100 Madres de Santiago," Rev. Chill Podiat, Vol. 44, No. 5 (1973).
5. F. Mönckeberg, G. Donoso, S. Valiente, et al., "Condiciones de Vida, Medio Familiar y Examen Clínico y Bioquímico de Lactantes y Preescolares de la Provincia de Curicó," Rev. Chill Pediat, 7: 491 (1967),
6. O. Undurraga, E. Vallejos, G. Duffan, and L. Osorio, "Alimentación Materna en Poblaciones de Distinto Nivel Socio-Ecónomico y Cultural," Catedra de Pediat. Prof. J. Meneghello,, Hosp. R. del Rio, Santiago, Chile.
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8. A. Patri, H. Sepúlveda, A. Avandano, M.E. Radrigán, N. González, L. Cornejo, M. Gonzalez, and G. Pozo, "Estado de Salud de la Población Infanto-Juvenil del Area Norte de Santiago en Relación a la Condición Nutricional y de su Crecimiento y Desarrollo," Colegio Medico de Chile, 12, No.3.
9. I. Lopez, E. Alvarado, S. Arcuch, C. Cabiol, and E. Rivera, "Duración de la Lactancia Materna y Alqunos Factores Condicionantes." Depto. de Salud Pública y Medicina Social, Sede Norte, and Depto. de Obstetricia, Sede Sur, Universidad de Chile, Santiago.
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11. A.M. Kaempffer, J. Alarcón, et al., "Estudio Integral de Desnutridos en un Consultorio del Area Norte," Rev. Pediatria, Vol. 44, No. 5 (1973),
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13. A. Patri et al., Preliminary report, Centro de Nutrición, Crecimiento y Desarrollo, Area Norte, Santiago, Chile.
14. "Análisis de Datos del Consultorio Quinta Buin," study by CONPAN, 1978,
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