Experimental details

1. Absorption Studies in Soldiers
One hundred soldiers who were born and had always lived in the lowlands of Guatemala and who had been for two years at an army station (MZ) near Guatemala City were interviewed and evaluated clinically. Besides being exposed during this period to improved environmental sanitation, these men had been eating a better diet than the one commonly eaten in rural areas. From this group 13 volunteers, 18 to 22 years old, who fulfilled the following criteria were selected: (a) there was no history of acute or chronic gastrointestinal diseases; (b) the result of the physical check-up was normal; (c) there was normal urinary excretion of d-xylose five hours after an oral dose of 25 9; and (d) two direct examinations of fresh stools for ova and parasites proved negative. Table 1 gives the volunteers' pertinent characteristics.

The soldiers lived for 21 days in a metabolic unit set up at the military post infirmary in Guatemala City (altitude 1,500 metres above sea level; temperature 19 to 22 C; low humidity). The experimental protocol followed was: Days 1 and 2: adaptation to the typical rural diet. Days 3 to 18: five consecutive three-day balance periods (Balances 1 to 5). Days 19 and 20 were used to complete faecal collections. A final physical check-up was done on day 21 before discharging the subjects from the unit.

2. Absorption Studies in Men from Two Rural Communities
In 1973, two villages, Guanagazapa (GU) and Florida Aceituno (FA), located in the lowlands near the Pacific coast of Guatemala, were chosen in order to carry out a study to evaluate the effect of introducing sanitation measures on the absorptive capacity of their inhabitants. The villages were within one hour's drive from Guatemala City, with a distance of 32 km between the two villages. Their altitudes were 200 and 235 m above sea level, with an annual rainfall of 2,000 mm. Temperature was 20° C during the day and cooler at night. Their populations of 973 for GU and 923 for FA were approximately 20 per cent Maya Indian and 80 per cent Ladino (mixed Maya and Caucasian descent). Both communities had water supplies of poor quality consisting of private wells and some communal faucets.

Studies were carried out for four years in both villages, divided into three stages: (a) two years of basal studies were made (1973-1974); (b) sanitary measures were implemented in GU (test village). In December 1974 an intra-domiciliary water supply system became operative, and a sanitary education programme was started in early 1975-neither measure was implemented in FA (control village); (c) two years were spent evaluating the impact of the sanitary interventions (1975-1976).

TABLE 1. General Characteristics of the 13 Soldiers Studied

* Mean ± S.D.

In 1973, 60 male volunteers aged 14 to 45 years were randomly chosen in each community among those men who had lived there at least ten years. By 1974 some had emigrated and were replaced by others of the same ages, also chosen at random, in order to study 120 men each year. The same procedure was followed in 1975 and 1976. Therefore, at the end of the four years there was a "longitudinal" group formed of men who participated one, two, or three times in the study. Table 2 gives the number of subjects in both groups each year. All were healthy at the time of the studies. Table 3 gives their characteristics. All men had mild or moderate infestations with one or more of the following intestinal parasites: Ascaris lumbricoides, Trichuris trichiura, hookworms.

Absorption studies were carried out between May and November in four consecutive years beginning in 1973. The men were housed in groups of 8 to 10 in a rural metabolic unit built adjoining the hospital of a nearby city (Escuintla) with the same climate as that of the study villages.

TABLE 2. Number of Subjects Included in the Statistical Analyses

* One of the longitudinal subjects from FA was excluded from Balance I in 1976 due to diarrhoea.

TABLE 3. General Characteristics of the Men from Florida Aceituno (FA) and Guanagazapa (GU), 1973

* Mean ± S.D.

The groups alternated between men of each village and they lived in the metabolic unit for five days in 1973 and for eight days in each of the following years. Metabolic-balance studies began on the day after admission; in 1973 only one three-day metabolic-balance study was performed, and in each of the following years two consecutive three-day balance studies were done (hereafter referred to as Balance I and Balance II). During the last two days, faecal collections were completed and d-xylose absorption tests were carried out.

3. Rural Diet Study
The same diets were used in the absorption studies with soldiers and with men from GU and FA. The diet was prepared with the foods and recipes used by the population from which these men came, except it included certain amounts of commercial canned black beans and more animal protein, since the men did not eat meat every day at home. Table 4 gives the amounts of food offered each day, divided into three meals. These amounts provided 2,800 kcal (28 per cent of animal origin), 95 g protein (34 per cent animal protein), and 35 g fat (22 per cent animal fat). The men were encouraged, but not forced, to eat all the food served in the metabolic unit.

The maximum amount of food offered to each man from GU and FA in 1973, 1975, and 1976 provided 2,800 kcal/day, based on the mean intakes of 75 men from each village surveyed in 1972. In 1974, diets that provided 2,000, 2,400, or 2,800 kcal/day were offered during the first three days (Balance I ) to each man, depending on his personal dietary history; during the following five days (which included Balance II), food amounts equivalent to 2,800 kcal/day were offered to all men. This was done in an effort to assess the effect of the usual dietary intakes preceding admission to the metabolic unit. The proportions of nutrients offered were constant at all levels of energy intake, since the changes were achieved through proportional variations in the amounts of each food served.

4. Measurements
The amounts of each food eaten by each man were weighed at every meal, and the nutrient intake was calculated from the analyses of representative food aliquots. Complete urine and faecal collections were also obtained, using carmine red as the faecal marker. Aliquots of the foods and of the three-day stool collections from each balance period were analysed, and their contents of total energy (bomb calorimetry), nitrogen (macro-Kjeldahl), and fat (Van de Kamer) were used to calculate apparent absorptions. Urinary nitrogen was also determined (macro-Kjeldahl) to calculate apparent nitrogen balance.