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Adult protein requirements - large samples

17. Nitrogen balance response of young male adults fed predicted requirement levels of a Mexican rural diet
18. Short-term nitrogen balances of 49 young Turkish adults on estimated mean requirement intake levels of protein
19. Short-term evaluation of the capacity of a chilean mixed diet to meet proteinenergy needs of a group of young adult males

17. Nitrogen balance response of young male adults fed predicted requirement levels of a Mexican rural diet

Hector Bourges, Blanca Lopez-Castro, Armando Tovar, Patricia Calderón, Nimbe Torres, and Martha Villarreal

Department of Nutrition Physiology and Food Technology, National Institute of Nutrition, Mexico City, Mexico

Objective

To investigate the statistical distribution of the short-term nitrogen balance of young male subjects fed the rural Mexican diet to provide protein at a level predicted to satisfy the needs of 97.5 per cent of the population.

Experimental Details

Environment

All subjects were confined to the metabolic unit of the Instituto Nacional de la Nutrición. The ambient temperature was 22 to 26° C and the relative humidity was 40 to 70 per cent.

Subjects

The 20 subjects were young adult male (19-25 years old) mestizos from the rural areas. All but one subject had parasitic infections but all were otherwise healthy.

Diets

The model diet consisted of corn, beans and wheat pasta with protein proportions: 51.3 ± 1.2, 31.0 ± 0.7, and 6.2 ± 0.2 per cent respectively. Additionally, fruits and vegetables provided 11.5 ± 2.1 per cent of the protein. Nitrogen intake was 164.8 ± 1.3 mg N/kg body weight (predicted mean requirement plus two standard deviations). Energy intake was enough for zero balance and body weight maintenance (47.3 ± 3.6 kcal/kg). Two capsules of UNICAP were given each day.

TABLE 1. Physical Characteristics and Energy Intakes

TABLE 2. Nitrogen Balance Data (Assuming 5 mg/kg for miscellaneous losses)

TABLE 3. Distribution of Nitrogen Balance

Physical Activity

The subjects were sedentary except for 30 to 120 minutes of treadmill walking and stationary bicycle riding (50:50 per cent), depending on previous activity habits.

Duration

The whole period of study was 16 days; five days for the stabilization period, one day of depletion, five days of the pre-balance period, and five days of the balance period.

Measurements Taken

Nitrogen balance (urinary nitrogen, faecal nitrogen and dietary nitrogen), urinary urea, and creatinine. Clinical laboratory tests (VDRL, chest X-ray, faecal culture and coproparasitoscopic, blood chemistry. complete blood-count, plasma protein, serum Na, Cl, K, Ca and P. GOT, and GPT, triglycerides and plasma cholesterol, general urinalysis). Anthropometry: biceps, triceps. subscapular and supra-iliac skinfolds; arm, buttocks, and waist circumference. The changes in body fat were calculated by the Durnin method. Precision of the method was estimated by repeating the same measurement 10 times and calculating the CV. Arbitrarily, any difference within the CV was ignored.

Results and Conclusions

See tables 1, 2, and 3.

1. The level predicted to satisfy the needs of 97.5 per cent of the population was insufficient for 9 out of 20 cases (45 per cent of the population).

2. This result may be explained by the presence in this experiment of parasites and pathogenic bacteria.

3. It is possible that the assumption of a Gaussian distribution of zero intercepts is inadequate.

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