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18. Short-term nitrogen balances of 49 young Turkish adults on estimated mean requirement intake levels of protein

Imran Ozalp, Meral Ozgüç, Suzan Tokol, Nevin Tasci and Ayse Baysal

Institute of Child Health Nutritional Metabolic Unit and Department of Nutrition and Dietetics Hecettepe University Medical School Ankara, Turkey

Objective

In a preliminary study, carried out on young Turkish adults consuming four graded levels of protein intake, the estimated daily protein requirement was found to be 0.61 9 protein/kg.

In this part of the study, a larger sample of adults was included to examine individual variation and to see what proportion of the population would be in positive nitrogen balance with a nitrogen intake estimated to be the mean population requirement.

Experimental Details

Forty-nine 19- to 30-year-old healthy university students (mean 22.2 yrs, SD 2.1 yrs) participated in this stage of the study. Their heights and weights are shown in table 1.

After one day of a protein-free diet, they were given 0.61 9 protein/kg/day for 10-day dietary periods. Also in this stage, mixed Turkish national foods generally consumed by the middle-class Turkish population were given, and daily caloric intakes were kept constant as much as possible. Table 2 shows the composition of the diets.

After five days of an adaptation period, 24-hour urine and stool samples were collected for the last five days. At the beginning and end of the 10-day periods, blood samples were taken and total protein, albumin, SOOT, SGPT, total lipid and cholesterol determinations were performed. No abnormalities were found.

Nitrogen value of urine, stool, and liquefied diet samples were determined by the micro-Kjeldahl method and nitrogen balances were estimated by the following equations:

ETNB (mg/kp/day): I_N - U_N - F_N - 5

TABLE 1. Summary of the Data for 49 Healthy Subjects Participating in the Study

TABLE 2. Composition of the Diet (Mean values of 49 subjects)

TABLE 3. Distribution of Nitrogen Balance

Results

For the 49 subjects:
Urinary nitrogen: mean = 66.4 mg/kg/day (standard deviation = 9.1)
Faecal nitrogen: mean = 23.0 mg/kg/day (standard deviation = 5.6)
Nitrogen balance: mean = 3.7 (standard deviation = 11.5)

The individual data are shown in table 1 and the distribution of nitrogen balance described in table 3.

Conclusion

The findings indicate large interindividual variations in nitrogen balance among subjects on the same dietary intake, in the same environmental conditions, and with no clinical disturbances. A different amount of nitrogen intake might be required to keep another population under different conditions in positive balance.

19. Short-term evaluation of the capacity of a chilean mixed diet to meet proteinenergy needs of a group of young adult males

Ricardo Uauy, Enrique Yánez, Nicholás Velasco, and Juan I. Egana

Institute of Nutrition and Food Technology. University of Chile, Santiago. Chile

Objective

1. To test the adequacy of a Chilean mixed diet fed to a large group of young adult males at the level of 1 9 of protein/kg/day in a short-term experiment.

Experimental Design

Subjects

The subjects who participated in the metabolic study were 60 army recruits in their second year of enlistment, aged 18 to 19 years (table 1). Fifty-three subjects completed the experiment.

Environment of the Study

During the experimental period the subjects continued to live in headquarters, and maintained their usual daily activities, but were exempt from exercises inducing profuse sweating. The men were under the supervision of a physician, a nurse and two dietitians. Ambient temperature ranged from 7 to 18° C.

Diet

The usual daily diet given at the military base before the study provided 1.5 to 2 9 of protein/kg/day, and the daily energy intake of the subjects was 3,200 kcal regardless of their body weight. The experimental mixed diet was programmed to give 1 9 protein/kg/day based on our previous studies. It provided 75 per cent of the protein from vegetable sources (wheat, rice, beans, potatoes) and 25 per cent from animal sources (skimmed milk).

Diets were calculated according to multiple analysis of ingredients used in the study done in our laboratories. However, the analysis of ingredients used in this study showed that the subjects actually ingested a mean of 1.13 g protein/kg/day because the wheat-flour used in this particular study contained 12.58 per cent protein (N x 5.7), which is significantly higher than the wheat flour we have ordinarily used: 9 per cent protein (N x 5,7).

This explains the discrepancy between programmed and actual protein intakes. Nevertheless, the 1.1 g/kg is in line with population protein needs according to further statistical analysis using the variability factor from our own data.

Customary energy intake for the subjects was 3,200 kcal/day. In order to choose the appropriate level of energy intake for the study, we conducted a 1 5-day observation period, controlling body weight and offering additional 100 kcal, in a stepwise fashion, to those who felt "hungry." Six of thirty subjects were given extra energy allowances.

The subjects were given three isoenergetic meals at 7.30 a.m., 12.30 p.m., and 7.30 p.m., eaten under the close supervision of a dietitian. A vitamin and mineral supplement was given each day at lunch to meet or exceed the 1974 NAS/NFC recommended dietary allowances.

Duration of the Study

Two weeks of preliminary observation followed by a ten-day metabolic balance period.

Indicators and Measurements

The subjects were weighed at onset and completion of the study before breakfast, after voiding, wearing minimal clothing and daily before lunch after removing shoes and heavy clothes. Complete 24hour urine collections were made throughout the study. Samples were collected in plastic bottles with 10 ml of 10 per cent (v/v) sulphuric acid. Aliquots were analysed immediately for total nitrogen, urea, and creatinine. Another sample was frozen for subsequent analysis if required. The urine collection of the last five days was used for computation of nitrogen balance (table 2).

Faeces were collected daily in plastic containers and kept in a freezer until analysed. Composites were made for each subject from the faecal pools of the last eight days of the experimental period and analysed for their total nitrogen content (table 2).

Blood samples were drawn from an antecubital vein after an overnight fast of 12 hours on day 1 and analysed for total serum protein, albumin, globulin, haematocrit and haemoglobin before subjects entered the study (table 3).

TABLE 1. Physical Characteristics and Energy Intake of the Subjectsa

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