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The intervention design compared villages in which pregnant and lactating mothers and their children up to seven years old received verified and recorded amounts of either atole or fresco. Table 3 presents the ingredients and the energy and nutrient concentration of the supplements, as given elsewhere [9, 10]. Atole contained a high-quality protein, whereas fresco had none. The energy concentration of atole for children older than four months was 2.8 times greater than that of fresco.

TABLE 3. Formulas and nutrient content of supplement beverages (quantities per 180-ml cup serving)

  Atole Fresco
Subjects <4 mo Older subjects
Incaparina (g) 0 13.5 0
Dry skim milk (g) 29.0 21.6 0
Sugar (g) 3.6 9.0 13.3
Flavouring (g) 0 0 2.1
Energy (kcal) 119 163 59
Protein (g) 10.3 11.5 0
Carbohydrates (g) 15.3 27.8 13.3
Fats (g) 0.2 0.8 0
Calcium (g) 0.4 0.4 0
Phosphorus (g) 0.3 0.3 0
Iron (mg) 0.2 1.2, 5.0 0, 5.0
Fluorine (mg) 0 0, 0.2 0, 0.2
Thiamine (mg) 0.1 0.4, 1.1 0, 1.1
Riboflavin (mg) 0.5 0.5, 1.5 0, 1.5
Niacin (mg) 0.3 1.3, 18.5 0, 18.5
Ascorbic acid (mg) 0 0, 4.0 0, 4.0
Vitamin A (mg) 0.5 0.5 0, 0.5

Where two values are shown, the higher value obtains as of 1 October 1971.

There were two formulations of atole, depending on age: one for children under four months old, made of powdered skim milk, and one for older children and mothers, containing Incaparina, skim milk, and sugar. Very little was consumed by children under four months old. The atole for older children was pale grey-green, felt smooth but slightly gritty in the mouth, and tasted sweet; it was served hot. The ingredients of the Incaparina were 7.83 g of ground, whole cooked corn, 5.13 g of cotton-seed flour, 0.4 g of torula yeast, 0.14 g of calcium carbonate, and 338 IU of vitamin A per 180-ml cup [11].

Incaparinas containing cotton-seed flour in proportions in relation to their energy content similar to that of the atole were tested first in animals and then in children [6]. These studies were considered carefully because, although cotton seed has high-quality protein and is inexpensive, it contains a toxin, gossypol, that might be noxious to children. The atole had even higher-quality protein than the Incaparinas tested by Bressani and Elias [6] because it contained skim milk. Nevertheless, the use of Incaparina instead of only milk reduced the cost of the supplement substantially. A supplement similar to the atole and mixed with typical home diets of the study villages was tested in rats. It contained 40% skim milk and made up 13.3% of the composite diet. A synergistic effect on growth was found; that is, growth was greater than that in rats fed either the supplement or the home diet alone [12] because the supplement and home diet complemented each other's essential amino acids profiles.

In October 1971 the riboflavin content of the atole for children older than four months was raised from 0.5 mg to 1.5 mg per serving after it was noted that the biochemical indices of riboflavin in two-year-olds consuming the product were not satisfactory [13]. Iron and a small amount of ascorbic acid to facilitate iron absorption were also added because anaemia was common in pregnant mothers, although it was not found in unsupplemented two-year-olds [13]. The contents of thiamine and niacin were increased because they were present in the iron-vitamin mix. On the basis of calculations from knowledge about water fluoridation [14], fluoride was also added at this time because the drinking water had a low fluoride content at the end of the dry season (0.166 - 0.384 ppm, compared with the recommended 1.0 ppm), when the concentrations should be highest, and because of the high frequency of dental caries in the communities. The number of decayed, extracted, or filled teeth (mostly decayed) per child was 5.8, and the number of tooth surfaces with evidence of caries was 11.9 among six-year-olds [15, 16].

The fresco was a low-calorie supplement (59 kcal) without protein. It was similar to Kool-Aid sold in the United States. Until to 1971 it contained only flavouring, colour, and sugar, but on 1 October 1971 other nutrients were added to make it more comparable to the atole. Many of these nutrients had been found in reviews of biochemical indicators in the blood and urine to be marginal in the children who drank the fresco regularly [13]. For ethical reasons, it was desired that the comparison beverage should confer some known nutritional benefit. In effect, the addition of these nutrients, including fluoride, rendered true the exhortation in all the villages to drink the atole or fresco because it was good for mothers and children. The changed formulation of the fresco also provided a better design for testing the roles of insufficient energy, protein, and other nutrients as causes of poor development in children, as discussed later.

The beverages were prepared by mixing boiled water with bagged, pre-weighed, dry ingredients. The pre-weighing and mixing were verified by quality-control measures. The quality of the powdered skim milk and the Incaparina were monitored by INCAP's Food Technology Division under the direction of Dr. Ricardo Bressani.

In all the villages, the supplements were distributed and consumed in a centrally located feeding hall for two to three hours during mid-morning and mid-afternoon, including weekends. These times were chosen because they were the easiest times for mothers and children to attend and did not interfere with usual meal times.


Medical care

Curative medical care was available free of charge to the villagers on weekdays throughout the period of the study at a clinic adjacent to the feeding centre. These services were not tied to participation in any aspect of the study. In other words, the rare non-participants had the same access to medical care as the other villagers. Instituting effective medical care was hampered by a belief then common in many nutrition field trials that one should not otherwise disturb the "natural" environment. In studies built on that assumption, medical care was given to meet the subjects' expectations but was not designed to be effective. The project staff believed this was unethical and instead instituted an effective primary health care programme, which, after initial resistance, was approved during an NIH visit at the end of 1969.

The belief that one should not otherwise disturb the natural environment in nutrition intervention studies was perhaps due to an inability to differentiate between studies seeking to prove causality between malnutrition and some outcome on the one hand and public health trials to test interventions for wider application on the other. For the latter, external validity requires that the test sites be as similar as possible to sites where the interventions will be applied. For the INCAP longitudinal study, the objective was to prove causality, and this required setting the conditions to maximize the probability of finding an effect. External validity for public health practice was irrelevant.

The medical care programme was also justified because it created stability. For example, immunizations would prevent an epidemic from striking one village and not another, as had happened in a previous INCAP nutrition field trial with dire consequences for data interpretation. As finally implemented in 1969, the study had so few degrees of freedom per treatment that unpredictability could not be tolerated.

Also, effective curative care was justified on the basis that morbidity and mortality were not outcomes of interest to the study, although later analyses gave useful results [17]. Severe malnutrition was also not an outcome of interest. Sample sizes were inadequate to assess the effects of improved diets on the frequency of severe, life-threatening malnutrition. Thus children identified at the clinic or in the homes as showing any signs of marasmus or kwashiorkor were seen immediately by the supervising physician to determine if they should receive special care. If so, they received red-dyed supplements under daily supervision of a staff worker to be sure that it was ingested. Supervision of intake was essential because severe malnutrition was associated with poor care and neglect in all the villages; for example, parental alcoholism, mental retardation, or instability, maternal employment leading to children being left under the care of young children, and prostitution in a mother-grandmother pair were some of the conditions found in families with severely malnourished children. These children were identified with a code so that they could be excluded from the analyses.

The supplement given to these children in the atole villages was the same Incaparina-based drink given at the feeding stations. In the fresco villages, it was the skimmed milk and sugar beverage offered to those under four months of age in the atole villages. The red dye was to signal that this curative treatment should not be confused with the preventive purpose of the supplement given at the feeding centre. Because of the underlying social pathology, these children also participated less in the study, so their exclusion from the analyses did not reduce the effective sample sizes. Their exclusion means that the results of this study pertain to mild to moderate malnutrition, not to severe malnutrition.

Effective medical care within the allocated budget was made possible by using auxiliary nurses instead of physicians and by streamlining the purchasing and use of effective medicines. Both innovations required a review of observed morbidity and of the cost-effectiveness of medicines. This work was done by Dr. Juan María Reyna-Barrios in the first half of 1969 and resulted in the identification of 64 diagnostic-therapeutic entities [9, 18] that accounted for more than 99% of the conditions seen in the clinics [19]. Disorders that could not be diagnosed by the auxiliary nurses because they were not included in the 64 entities and individuals with illnesses that did not evolve as expected were referred to the supervisory physician. Furthermore, arrangements were made with the Hospital Roosevelt, a teaching hospital in Guatemala City, to honor referrals and to keep INCAP informed of patients' progress and discharge.

The new system of curative care, implemented in the fall of 1969 [19], featured continuous supervision of the adequacy of the quality of history taking, diagnosis, and treatment. As the system was implemented, the results for each auxiliary nurse were graphed to assist the supervisor in his efforts to concentrate training on those requiring it most. By early 1971 the quality of care had stabilized, and more than 99% of patients were managed correctly [19]. Fewer than 1% had to be referred to the supervising physician and only 0.4% to the hospital, a substantial decline from previous experience.

The local traditional midwives were funded to attend midwifery courses given by Guatemalan public health authorities. Their care complemented that given on demand by the nurses.

All children were examined 15 days after birth by Dr. Carlos Beteta, a well-trained paediatrician in private practice, for diagnosis and treatment of neonatal ills. Dr. Beteta also examined the children at 3 months and at 1, 3, and 7 years to detect any remediable pathology that had escaped the clinic's attention. Pregnant mothers were immunized against tetanus and children against tuberculosis, diphtheria, whooping cough, tetanus, measles, and poliomyelitis [18]. Deworming medicines were offered twice a year, but the medical programme did not give health or nutrition education, except to encourage attendance at the supplementation feeding stations and participation in immunization campaigns. The curative and preventive health care services were the same in all the villages, and preventive campaigns such as deworming and immunization were carried out simultaneously in all the villages.

Initially, all deaths were reviewed to improve the quality of care. This revealed that few of the children who were referred to the hospital actually went, even though INCAP offered to pay the transportation or even to transport them. The ethnographer on our team, Victor Mejía-Pivaral, discovered that families could not afford to rent a vehicle to transport a dead child from the hospital for burial in the village. In their previous experience, hospitalized children had usually died. Guarantees by the project to return corpses to the village solved this problem, with a rise in appropriate and timely hospitalization and a decrease in deaths.

Compared with rates for the period previous to 1969, infant mortality had declined from 139 to 55 per 1,000 births by 1970-1972, and preschool mortality had decreased from 28 to 6 per 1,000 children at risk, at a total cost for primary health care of less than US$5 per villager per year. National death rates in Guatemala remained constant over this comparison period. Data collected in 1988-1989 confirmed these declines in mortality rates [17]. Visits averaged 4.2 per villager per year [19].

The type of service provided was viewed by many Latin American physicians and PAHO officials at the time as unacceptable because it did not provide medical care through physicians, even though the cost was less and the results were better than services that did [19]. That view changed during the course of the study as findings from this and other similar experiences elsewhere became known.


Other influences of the study team

The intensity of data collection and the supplementation and medical interventions required the continuous presence of four to eight well-educated persons in each village. Although they did not live in the villages, at least one of them visited each family twice a month. Exposure to new ways of seeing (and therefore of doing) things was unavoidable. These influences varied depending on the personalities of our personnel and therefore could have affected the outcomes of the study differently across villages. Therefore, the personnel involved in supplementation, medical care, home visiting, anthropometric and psychological testing, and contacts with the village leadership were stratified across the villages by rotating them through all the villages for equal periods of time, so that these interventions would not confound the analyses of the main effects of the intervention by village or increase the variance within a supplementation treatment.

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