STUDIES ON PROTEIN-ENERGY REQUIREMENTS OF YOUNG ADULT FEMALES IN NIGERIA

Abstract

A series of studies were carried out to determine the protein and energy requirements of young adult women in Nigeria. The requirements were estimated from nitrogen balance studies while the subjects were fed their habitual diet. All subjects maintained a constant-level of physical activity throughout the study period. The data generated from these studies were used along with FAO/WHO (1981) recommendations for other age groups to compute the per caput protein and energy requirements for a projected 1990 population of Nigeria. Nitrogen excretion was determined from the measurement of nitrogen in a total collection of urine, faeces, sweat, and menstrual fluids. The study was divided into three major phases. The first phase of the study involved the estimation of the minimum protein requirement. With a total of twelve healthy female adults of the university of Ibadan aged 21 to 32 years, short-term nitrogen balance studies were conducted using four graded levels of protein (0.3, 0.4, 0.5 and 0.6g kg⁻¹ day⁻¹) at an energy intake of 41 kCal kg⁻¹ day⁻¹. Urinary and sweat nitrogen were found to increase significantly with increase in protein intake. Faecal nitrogen however was not affected. Obligatory nitrogen losses were calculated as 22.08, 13.23 and 5.0 mg N kg⁻¹day⁻¹ for urine, faeces and sweat respectively, from regression equations relating losses to nitrogen intake. Total obligatory nitrogen loss, thus added up to 40.31 mgN kg⁻¹day⁻¹. Nitrogen balance with the four protein levels were -15.48, -5.30, +6.15 and +12.08 mg N kg⁻¹day⁻¹ in an ascending order of protein intake (0.3, 0.4, 0.5, 0.6q kg⁻¹day⁻¹) respectively. The calculated minimum nitrogen requirement was 76.0mg N kg⁻¹day⁻¹ (0.475 g protein kg⁻¹day⁻¹). Estimates of allowances for individual variation to cover 97.5% of the population (2 SD) was 95.0 mg kg⁻¹day⁻¹ (approx. 0.6g protein kg⁻¹ day⁻¹). Net protein utilization (NPU) of the diet was 54 and the biological value was 56. True digestibility of the diet protein was 96% while the apparent digestibility was 77%. The second phase of the work involved the effect of varying energy intake on the estimated minimum requirement as well as estimating the average energy requirement. Thirteen young women aged 21 - 32 years participated in the nitrogen balance study, fed on 0.47g protein kg⁻¹ day⁻¹ at two levels of dietary energy, 48.4 ± 3.70 and 33.76 ± 2.86 kCal kg⁻¹ day⁻¹ representing high and low energy intakes. Nitrogen balances were -8.26±5.61 and +10.82±6.35 mg N kg⁻¹ with the low and high energy intakes respectively. Nitrogen Balance was improved by 133 mg N/100 kCal of energy intake. The NPU of the diet was altered by the 43% increase in energy intake by 1.0-3.5 units/Kcal/kg body wt. Energy requirement was estimated on the basis of body weight maintenance, nitrogen balance and energy balance. The mean values from the three estimates were 40.05, 40.41 and 40.3 kCal kg⁻¹ respectively. Thus giving a grand mean of 40.25 kCal kg⁻¹. The third phase of the study involved a 40-day metabolic N-balance period to evaluate the long term effect of the estimated protein and energy requirements using eleven young women. The subjects received a diet providing 0.6g protein kg⁻¹day⁻¹ (safe level of protein intake) and 40 kcal kg⁻¹day⁻¹ of energy intake. All subjects except three were in positive nitrogen balance with a mean of +5.84 ± 8.59 by the end of the dietary period. The nitrogen balance data and the fairly stable blood biochemical parameter with constant body weight indicated that 0.6g protein kg⁻¹day⁻¹ at 40 kcal kg⁻¹ day⁻¹ of energy intake is sufficient to achieve N-equilibrium in a majority of young adult females. Based on this recommendation for adult females along with the recommendations for other age groups according to the FAO/WHO ad hoc Committee (1981), the per Caput protein and energy requirements for a projected 1990 population of Nigeria were estimated at 55.4 g protein day⁻¹ and 2335.4 kCal day⁻¹of energy intake.