Current estimates of protein and energy needs for normal, healthy individuals make no distinction between population groups of different ethnic backgrounds and environments. Since the variation in protein requirement is the result of both growth potential and the modifying effect of environment on the expression of that potential, it is necessary to know what the appropriate estimates are for protein and energy requirements for different populations. Specifically, there is urgent need to obtain such data for populations living under conditions prevailing in developing countries. consuming diets differing in physical characteristics. The capacity of these diets to meet protein requirements necessary to maintain adequate protein nutritional status under prevailing environmental conditions must be determined.
Therefore, as one of the participants of the collaborative, ongoing research on "protein and energy requirements of different populations" sponsored by the United Nations University, we have carried out a study to determine the protein requirement of young Turkish adults.
1. To investigate nitrogen balance response of young adults.
2. To assess the level of protein in customary Turkish diets necessary to meet the minimal nitrogen requirement and nitrogen allowances in young adults.
Eleven male 19- to 26-year-old "healthy" university students were included in this part of the study. Their characteristics are summarized in table 1. They maintained normal activity and were free-living, but consumed their food under supervision.
After one day on a protein-free diet, they were on four dietary periods each lasting ten days. Meals were given four times a day (8 a.m., 12 noon, 4 p.m., 10.30 p.m.). Protein levels of 1.0, 0.66, 0.51, 0.36 g/kg/day were given consecutively in a descending fashion. Mixed Turkish national foods generally consumed by the middle-class Turkish population were consumed, and calorie intakes of the subjects were kept constant as much as possible. Table 2 shows the main characteristics of the diet. A vitamin supplement was also given.
After five days of adaptation period, 24-hour urine and stool collections were collected for five days. Blood samples were taken at the beginning and the end of each period, and total protein, albumin, SOOT, SGPT, total lipid, and cholesterol determinations were performed.
where FN was averaged over the entire experiment.
The study was carried out in Ankara. Its altitude is 848 metres above sea-level. In the first part of the study it was early winter and the average temperature was 6.6� C.
a. For equation Nout = a + b Nin.
Anthropometric measurements were made before and after the study and body temperature was taken daily. Daily diets were determined by Kjeldahl digestion and titration. Natural foods were used and energy content was calculated by proximate composition and Atwater factors.
Table 3 shows the nitrogen intake, urinary and faecal nitrogen losses and nitrogen balances on four different levels of protein intake. Almost all the subjects were in negative nitrogen balance in the third and fourth dietary periods which provided 0.36 and 0.51 9 protein/kg/day, respectively. The mean nitrogen balance values were negative in both periods. Decreases in body weight and serum total protein and albumin levels were also observed.
Regressions of nitrogen output on nitrogen intake are shown in table 4. The mean intake necessary for balance is found to be 0.61 9 protein/kg. The standard deviation of 0.09 gives an estimate of 0.79 g/protein/kg.
Vegetable protein constitutes the main source of protein in the Turkish national diet. This may explain why the figure obtained in our study for minimal protein requirement is higher than the values obtained in other studies in which subjects were fed protein of mostly animal origin.
The objective of this study was to examine the nitrogen balance response of adult rural workers fed different levels of protein derived from traditional diets of rice and beans.
Nine migrant male workers, aged 18 to 28, without disease, were the subjects of this study. Their habitutal diets provided 70 9 of protein and 2,800 calories per day. Their physical and biochemical characteristics are shown in tables 1 and 2. They were all admitted to our metabolic unit at the university hospital, where they stayed for three periods of eleven days each. Each period consisted of one day on a protein-free diet, five days for adaptation, and another five days for balance studies.
Their diet included rice and beans as the main source of protein, but it also had small amounts of coffee, bread, vegetables, fruits and sugar, and the meals were cooked with soya oil. The diet was calculated to provide 0.4, 0.6, and 0.8 g/kg of protein per kg of body weight for each subject in three successive periods. Energy content of foods was calculated by proximate composition and Atwater factors.
The study was carried out during the spring and summer months (average temperature 23.1� to 24.1� C). All subjects were ambulatory, and could walk about the metabolic unit, play cards, and watch television. They maintained their weight during the study and, according to urinary creatinine excretion data, their muscle mass stayed constant (table 3).
Urine was collected on a timed 24-hour basis and faeces were collected between comsumption of carmine and charcoal markers during the last five days of each period. Urinary creatinine was measured daily by a picrate method, and nitrogen in urine, faeces, and food by the Kjeldahl method. Each component of the diet was analysed separately and the intake calculated by the amount of each food consumed.
TABLE 1. Anthropometric Characteristics of the "Boias-frias"