Contents - Previous - Next

This is the old United Nations University website. Visit the new site at http://unu.edu

TABLE 7. BMR of Three of the Subjects of the Study

3. The BMR of three of the subjects is shown in table 7.

4. The subjects stayed in a residential metabolic unit located next to the Food and Nutrition Research Institute. The physical activities of the subjects were more or less routine. A major portion of the day was spent by two chemists in the chemical laboratory. Two to three times during the day, one chemist had to go up and down from the second floor of the FNRI building, using a stairway that has 22 steps with one landing in between. The other chemist works on the fourth floor and makes at least two trips during the day.

The two other subjects are both nutritionists. Their work activities consist mostly of desk-work and testing recipes in the kitchen. Their working area is also on the second floor of FNRI. One of the nutritionists has a family in the provinces (about 90 km from Manila) and has made about three journeys in the course of six weeks.

The three other subjects usually visit their families in the afternoon after office hours but come back before dinner time. On other days they do some shopping, attend to personal matters, got to the cinema, watch television, or read. All of them wash and iron their own clothes, including bedding. They take turns cleaning their bedroom.

In the third to fourth week of the study, three of the subjects complained of feeling very hungry just before lunchtime. The subjects tried to minimize their activities, and at weekends, during the hot months of April and May, some of them preferred to stay in their air-conditioned rooms. The working area of the subjects was not air-conditioned.

16. Long-term evaluation of the capacity of a chilean mixed diet to meet the protein-energy requirements of young adult males

Enrique Yánez and Ricardo Uauy

Institute of Nutrition and Food Technology (INTA) University of Chile. Santiago. Chile

Objective

Long-term evaluation of a Chilean mixed diet to meet the protein and energy requirements of young adult males belonging to the low-income strata, using the nitrogen-balance response to a protein level considered adequate on the basis of short-term nitrogen balance studies.

Experimental Details

Subjects

Eight men, 19 to 33 years old. Their physical characteristics and energy intakes are shown in table 1. All subjects were chosen from among volunteers belonging to the staff of the institute or among outsiders who answered a local advertisement, and who had monthly incomes that placed them within the lower tercile of the national income distribution. Their housing, sanitary conditions, and educational background were consistent with their incomes. They were healthy, based on medical history, physical examination, and laboratory analysis of haematocrit, haemoglobin, total and differential white bloodcell count, serum transaminase activities, and complete urinalysis.

Physical Activity

The men were encouraged to continue their normal daily routines, including their usual pattern of activity, but were asked to refrain from participating in competitive sports during the study. They slept in the Metabolic Unit of INTA's Clinical Research Centre.

All subjects remained under the supervision of a physician and a nurse throughout the study. Subjects G.I. and J.R. completed only 43 and 61 days, respectively, on the experimental diet and then voluntarily left.

TABLE 1. Characteristics of the Subjects

Diets

For a week the subjects were fed an egg protein diet providing 1 9 protein/kg/day and adequate calories in order to stabilize their protein nutritional status. Then the men were fed a Chilean mixed diet supplying 1 9 of protein/kg body weight/day, 75 per cent of which was of vegetable origin, for three months. The composition of the mixed diet is given in table 2. The daily dietary energy intake was determined for each subject by a dietary survey for seven consecutive days using the 24-hour recall method, If significant weight change occurred, adjustments of the calorie intake were made during the initial phase of the experiment. Vitamin and mineral supplements were provided daily to meet or exceed the 1974 NAS/NRC recommended dietary allowances. The nitrogen content of dietary ingredients and preparations was analysed by the Kjeldahl method using a macro-digestion procedure followed by a semimicro distillation of the ammonia produced into 2 per cent boric acid containing a mixed indicator. Energy intake was calculated by proximate composition and Atwater factors.

Experimental Design

The experimental period started with an initial egg-protein phase lasting seven days. A free-choice diet was eaten at INTA's cafeteria over the next three days, and on day 4 the subjects started their "Chilean mixed diet" period. Three iso-energetic-isonitrogenous meals were provided at 8 a.m., noon, and 7 p.m., and consumed under the close supervision of a dietitian. The protein sources during the mixed diet period were distributed as equally as possible in the three daily meals. Ambient temperature ranged from 10 to 20° C throughout the study.

TABLE 2. Composition of Experimental Diet

a. Multivitamin/mineral supplement

Measurements

The subjects were weighed daily at 8 a.m. with minimal clothing, before eating breakfast, and after voiding the first morning urine.

Complete 24-hour urine collections were obtained with HCl as preservative throughout the study. An aliquot was analysed for total nitrogen, urea, and creatinine. Faeces were collected daily and pooled during the eight days of each dietary period. Pools were separated by feeding autoclaved brilliant-blue and carmine-red markers. True nitrogen balance was calculated subtracting the mean daily urine and faecal nitrogen excretion from the daily N intake. Integumental and miscellaneous N losses were estimated to be 5 mg N/kg body weight/day.

Anthropometric measurements of the subjects were made at the beginning of the experimental period and afterwards at 1 5-day intervals. Fasting blood samples were drawn from an antecubital vein at 8 a.m. at the start of the stabilization period and later at regular intervals of 15 days. They were analysed for total serum protein, albumin and urea concentrations, transaminase activities, and blood cell count and haematocrit.

TABLE 3. Weight Changes of the Subjects (in kilograms)

a. Studied 43 days b. Studied 61 days

Summary of Main Results

Three subjects gained between 0.6 and 1.4 kg, while five of them lost from 0.5 to 2.7 kg (table 3). Subject R.E., who suffered from episodes of diarrhoea, lost 2.7 kg. The overall mean weight change was 0.8 kg.

The daily urinary nitrogen output ranged from 107 to 134 mg/kg/day with a mean value of 116.7 mg/kg/day. Faecal nitrogen ranged from 19.9 mg/kg/day to 36.7 mg/kg/day, with a mean value of 28.2 mg/kg/day. The apparent protein digestibility calculated from our results was 82 per cent (table 4). Means for the initial and final periods of urinary and faecal nitrogen excretion were compared using a ttest for paired data. Significant decreases were found in initial values for urinary nitrogen (P < 0.01) and faecal nitrogen (P < 0.05) (table 5).

In this study all the individuals were in positive N balance while consuming the mixed diet. The mean value for nitrogen balance was + 9.7 mg N/kg/day.

Urinary creatinine showed a slight, non-significant decrement (table 6). Urinary urea nitrogen fell from an initial value of 107.6 to 95.2 mg/kg/day (mean values for the nine initial and final days).

The anthropometric measurements did not show significant changes; al* the indices measured remained practically stable (table 7).

TABLE 4 Nitrogen Balance and Apparent Protein Digestibility (D) of Subjects Fed a Chilean Mixed Diet at 160 mg N/kg/day for Three Months

TABLE 5 Initial and Final Urinary and Faecal Nitrogen Excretion (mg N/kg/day)

TABLE 6. Initial and Final Urinary Creatinine and Urinary Urea Nitrogen (g/day)

Biochemical findings are summarized in table 8. The mean values for total protein, albumin and urea N showed small changes, but these were non-significant throughout the study. The mean value for SGOT decreased from 16.8 K.U. to 10.4 K.U., while SGPT showed only a minor decline. The mean values for haemoglobin, white blood-cells and haematocrit, also shown in table 8, remained stable during the experimental period.

Conclusions

1. All the subjects participating in this study achieved a positive nitrogen balance amounting to + 9.7 mg N/kg/day. The results suggest that the Chilean mixed diet fed at the level of 1 9 protein/kg/day adequately meets the protein requirements of young adult males.

2. The apparent protein digestibility of the mixed diet was 82 per cent.

3. The mean values for urinary and faecal N were 116.7 and 28.2 mg N/kg/day, respectively. Urinary and faecal nitrogen excretion decreased throughout the experimental period.

4. The subjects experienced a non-significant weight-loss for the entire experimental period, suggesting that the mixed diet was adequate in energy content.

5. The fact that anthropometric, biochemical, and haematological measurements underwent only minor changes reinforces the finding that the diet assayed covers both long-term protein and calorie requirements.

TABLE 7. Anthropometric Changes in the Subjects Participating in the Study (Mean ± SD)

TABLE 8. Biochemical and Hematological Changes

Contents - Previous - Next