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TABLE 2. Composition of the Experimental Diets, Weight of Foods (in Grams) at Different Levels of Protein intake

Complete 24-hour urine collections under acid were made in the last five days of each period, and aliquot portions were taken for the determination of total N. urea, and creatinine. Faeces, marked with carmine, were collected in the last five days of each diet period, pooled, and mixed in a Waring blender before sampling for analysis.

TABLE 3. Average N Balance Data (mg/kg/day) of the First Group

TABLE 4. Linear Regression of N Balance (mg/kg/day)

Mean ± SD 147.7 ± 18.6 (equivalent to 0.92 ± 0.12 9 protein/kg/day)

TABLE 5. Individual N Balance Data (mg/kg/day) of the Second Group

TABLE 6. Calculated TBV, NPU and Digestibility

TBV = True biological value. NPU = Net protein utilization.

TABLE 7. Mean Urinary Urea N Excretion at Different Levels of Protein intake in Five Experimental Periods

a. Mean ± S.D.

The energy content and the nutrients of the diet other than protein were calculated with aid of the food table.

True N balance was calculated from the last five days of urinary and faecal N losses. Miscellaneous losses of nitrogen were estimated at 5 mg/kg. Biological value (BV), net protein utilization (NPU), and both apparent and true digestibilities were calculated. The obligatory urinary and faecal losses used in the calculations were 33 and 13 mg N/kg respectively.

Summary and Main Results

Table 3 shows the N balance of the first group. All subjects were in negative balance at protein intakes of 0.42, 0.6, and 0.73 g/kg/day, and all were in positive N balance at 1.05 g/kg/day. Most of the subjects were in positive N balance at 0.9 g/kg/day. The mean of N balance, however, appeared less negative when the N intake was increased.

The linear regression analysis of N balance response of individual subjects is shown in table 4. The intercept at zero balance of individuals ranged from 129.4 to 192.5 mg N/kg/day, with the mean of the group 147.7 + 0.12 9 protein/kg/day, or 0.9 9 protein/kg/day.

As shown in table 5, five of the six subjects in the second group were in positive N balance, the other was near zero balance when on a mixed diet of 150.2 ± 2.5 mg N/kg/day, or 0.93 ± 0 02 9 protein/kg/day, for three months.

The actual energy intake of the subjects in the two series ranged from 42 to 47 kcal/kg/day. The calories from fat comprised about 31 per cent of the total energy intake. Most of the subjects spent a large part of their time in laboratory work. Therefore, the energy expenditure was in the category of light to moderate.

Table 6 shows calculated true biological value (TBV), net protein utilization (NPU), and true and apparent digestibility for an ordinary mixed Chinese diet at different N intake levels in Chinese male adults. Table 7 shows the mean urea excretion of the subjects in five the experimental periods.

10. Protein requirements of Egyptian women

Mohamed Amr Hussein

Department of Nutrition Requirements and Growth, Nutrition Institute, Cairo, Egypt

Objective

To test the capacity of the Egyptian mixed diet of the low-to-middle class to satisfy daily protein and energy needs.

Experimental Design

Subjects

Eight young adult females whose ages ranged between 18 and 27 years were the subjects of the study. The subjects were disease-free with no chronic infections or parasitic infestations, and all were from middle-class families except for one from an upper-income family. They were allowed to practice their usual daily activities, but were under continuous medical supervision during the whole period of study.

TABLE 1. Habitual Protein and Energy Intake

TABLE 2. Characteristics of Subjects and Percentage of Energy Source

TABLE 3. Subject Data before Starting the Study

The study was conducted between March and June 1981. The month of June was considered the hottest time of the study, when the temperature reached 39°C some days.

Diet

The diet consisted mainly of bread, beans, rice, potatoes, vegetables, cheese, and molasses. Jam, butter, and soft drinks were included to complete the caloric value of the diet. Components of the habitual diet of the subjects are shown in table 1.

Energy intake was determined by dietary interview and assessment of physical activity and weight pattern, and was kept constant for each individual throughout the study. Energy content of the diet was calculated using proximate composition and Atwater factors.

Four dietary protein levels were used for the study: 0.4. 0.5, 0.6, and 0.7 g/kg body wt/day (see table 2). The order of these levels varied from one subject to the other. Each dietary level was preceded by one day on a practically protein-free diet to enhance adaptation. followed by 10 days on the test protein level (except for those who lost urine specimens on one of the days, when the respective period was extended one more day).

A break of at least three days between the different protein levels was allowed, except for one subject who had a break of two days only.

Protein of animal origin varied between 11.23 to 37 5 per cent in the different dietary periods except for two subjects who had no animal protein at the 0.4 protein level (table 3).

TABLE 4. Metabolic Response to 0.4 and 0 5 g/kg of Protein Intake (mg N/kg/day)

TABLE 5 Metabolic Response to 0 6 and 0 7 g/kg of Protein Intake (mg N/kg/day)

TABLE 6. Individual Mean Nitrogen Requirement (mg/kg/day)

Measurements Taken

Anthropometric measurements included heights and weights before the start of the study. (See tables 2 and 3.) Arm circumference and skin thickness were measured at the start of each dietary phase. Body temperature and body weight were measured every morning post-voiding and before breakfast. Some subjects lost weight during the study, while others gained. Fasting blood samples were withdrawn for routine laboratory analysis, and haemoglobin was determined before starting the study. Twenty-fourhour urine was collected and analysed for creatinine and nitrogen. Stools of the last eight or nine days were pooled for nitrogen analysis.

Results

All subjects were in negative nitrogen balance at the 0.4 g/kg level except one subject who was barely in balance at +0.3 mg/kg/day (tables 4 and 5).

At the level of 0.5 9 protein/kg, five subjects were in negative balance, while the other three were in positive balance. At the two higher levels all subjects were in increasing positive balance according to the level of intake.

For each individual, a linear regression line was calculated, and the intersection of this line with zero nitrogen balance provided the estimate of the individual's mean requirement (table 6).

The set of estimates of mean individual requirements can be used to estimate the mean nitrogen requirement for these subjects. which is 77.4 mg/kg with a coefficient of variation of 6.4 per cent.

Conclusion

The mean protein requirement for the eight female subjects studied, based on the multiple dietary level individual response method, is estimated to be 0.48 g/kg/day with a coefficient of variation of 6.4 per cent.

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