|Protein-Energy Requirements of Developing Countries: Evaluation of New Data (UNU, 1981, 268 p.)|
|Research papers: Protein requirements-adults, standard protocols|
|Protein requirements of young Chinese male adults for ordinary Chinese|
Summary of main results
Mixed dietary protein and egg protein at usual levels of energy intake
P.C. Huang and C.P. Lin
Department of Biochemistry, College of Medicine, Taiwan University, Taipei, Taiwan
1. To determine the protein requirements of young Chinese male adults eating typical local diets supplying the amount of energy needed for their usual daily lives.
2. To determine the requirements of young Chinese men for egg protein when they are consuming customary amounts of energy.
Twenty-eight students 20 to 29 years old in the College of Medicine and in a junior college volunteered to participate. Twenty ate a mixed Chinese diet at one, three, or four different levels of protein intake. Thirteen of them also participated in the egg study at one, two, or three different protein levels. Eight other men participated only in the egg protein studies. All subjects remained essentially healthy throughout the experiment. Their characteristics are shown in table 1.
2. Study Environment
Subjects lived in the metabolic ward located on the College of Medicine campus throughout the experiment. Room temperature and relative humidity were 9.0 to 37.2° C and 70 to 90 per cent, respectively.
TABLE 1. Characteristics of 28 Young Chinese Men Participating in the Studies
|Body weight (kg): initial||59.4||6.89||46.2||70.2|
|Urinary creatinine (g/day)||1.242||0.2022||0.89||1.70|
|Skin-fold (mm): triceps||9.6||3.56||4.0||16.0|
|Calculated energy intake (kcal/kg/day)||42||1.94||38||46|
1 Values given are mean and standard deviation for 28 subjects.
2 Mean and standard deviation for 1,155 determinations.
TABLE 2. Ingredients and Nutrient Composition of the Chinese Mixed Diet, Planned According to the Food Balance Sheet (1976)1
|Ingredients (gm)||Levels of protein intake (g/kg body wt/day)|
|Mung bean noodles||70||70||70||70|
|Vitamin and mineral supplements2|
|Nutrients: Protein (gm)||25.6||31.3||37.1||42.4|
|Calculated calories (kcal)||2,520||2,520||2,511||2,502|
1 The amount is for a 60 kg subject.
2 Vitamins and minerals were supplemented each day to meet the National Research Council re commended allowances, using a preparation from the China Chemical and Pharmaceutical Co.
3. Physical Activity
All subjects maintained their usual school activities without unusual physical exercise.
4. Duration of the Study
On the first day of an experimental period, the subjects were given 0.1 9 of egg protein/kg followed by an experimental diet for ten days. Between the consecutive nitrogenbalance studies, the men ate their ordinary diets with more than 1.5 9 protein/kg/day for three or four days. The protein intakes with the Chinese test diets were fed in an order of 0.65, 0.45, 0.75, and 0.55 g/kg in the first and third series, and in reverse order (0.55, 0.75, 0.45, and 0.65 g/kg) in the second series. With the egg formulae, the order in which the protein levels were fed was 0.45, 0.35, and 0.55 g/kg in the first and third series; the order was reversed in the second series. Skin nitrogen losses were determined for two days during each balance period.
Food ingredients of the ordinary Chinese mixed diet were selected according to the Taiwan Food Balance Sheet of 1976. A part of the mixed diet was served as a liquid formula prepared by blending a mixture of milk, egg, sweet potato, methyl-cellulose, salt, soy bean oil, butter, and cornstarch with water in a proportion of 1:2 and steamed at about 95 C for at least 30 minutes. Details of the dietary ingredients and the nutrient composition are shown in tables 2 and 3. The test diet was provided in four meals a day, at 0730,1200, 1730, and 2200 hours.
6. Indicators and Measurements
Regression analyses of nitrogen balance on nitrogen intakes were performed to obtain the mean protein requirements. The 97.5 per cent confidence limits were calculated using the pooled data regressions. The nitrogen content of all specimens and diets was determined by a semi-micro-Kjeldahl method. Biological value (BV), net protein utilization (NPU), and apparent and true digestibilities were calculated. The obligatory urinary and faecal nitrogen losses used for the calculations were those from our previous study: 33.4 and 13.1 mg N/kg, respectively.
Table 4 and figures 1 and 2 show the nitrogen-balance data. All men were in negative nitrogen balance at an intake of 0.45 and 0.55 9 protein/kg in the mixed diets, and also at the 0.35 g level of egg protein/kg. At higher protein intakes, some subjects achieved positive nitrogen balance (figures 1 and 2).
The mean protein requirements for the mixed Chinese diet and the egg diet were 0.79 and 0.61 g/kg/day, respectively. The 97.5 per cent confidence limits for the requirements were calculated as 1.18 and 0.89 g/kg/day, respectively. The efficiency of utilization of the Chinese mixed dietary protein was 77 per cent that of the egg protein, based on relative nitrogen requirements.
TABLE 3. Composition of the Experimental Egg Diet
Levels of protein intake
|Mung bean noodles||200||200||200|
|Vitamin and mineral supplements2|
|Nutrients: Protein (gm)||21||27||33|
|Calculated calories (kcal)||2,591||2,556||2,520|
1 See footnote 1 in table 2.
2 See footnote 2 in table 2.
The actual energy intakes of the subjects in the two series of studies ranged from 38 to 46 kcal/kg. Most of the subjects spent a large part of their time in academic studies and their energy expenditure was light to moderate. When a body-weight increase of more than 0.2 kg or a decrease of more than 0.7 kg occurred, an adjustment in energy intake was made by subtraction or addition of soybean oil. Changes in body weight over the 56-day period ranged from -2.5 to +0.6 kg.
Conclusions and Comments
TABLE 4. Daily Nitrogen Balance Data1 with Chinese Mixed Diets and Egg Diets
|Nitrogen intake||Urinary nitrogen||Faecal nitrogen||Skin nitrogen||Total nitrogen loss||Nitrogen balance|
(mg/kg body weight/day)
Chinese mixed diets
|121.0±0.87||99.0± 9.12||16.7±325||5.5±1.46||121.2± 8.16||- 0.2± 7.97|
|56.3±0.74||54.8+ 8.41||13.9±2.35||8.4±3.10||77.1± 9.50||-20.8± 9.11|
|71.7±0.78||63.9± 9.76||13.1+2.39||10.5±4.28||87.4± 8.56||-15.7± 8.95|
|89.0±1.37||71.5± 7.53||14.5+2.38||6.8+2.44||92.7± 8.41||- 3.7± 7.94|
1 Mean ± S.D. of 15 subjects.
TABLE 5. Calculated Biological Value (BV), Net Protein Utilization (NPU), and True and Apparent Digestibility of the Test Dietary Proteins at Different Levels of Intake in Young Men
|Level of protein intake||BV1||NPU1||
1 Mean +S.D. (n = 15).
a,b Same letters within a column are not significantly different.
A F ratio obtained from ANOVA test is significantly lower (P<0.01) than those in egg diet series.
c-f Group means within a column followed by the same letter are significantly different: c,e, p<0,01; d,f, p<0,05.