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close this bookProtein-Energy Requirements of Developing Countries: Evaluation of New Data (UNU, 1981, 268 p.)
close this folderResearch papers: Protein requirements-adults, standard protocols
close this folderProtein requirements of young Chinese male adults for ordinary Chinese
View the document(introduction...)
View the documentObjectives
View the documentExperimental details
View the documentSummary of main results

Experimental details

1. Subjects
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

Items Mean1 S.D.1 Minimum Maximum
Age (years) 24.2 2.57 20 29
Body weight (kg): initial 59.4 6.89 46.2 70.2
final 58.8 6.92 45.0 69.7
Height (cm) 168.2 4.95 160.0 178.5
Height/weight 2.89 0.31 2.46 3.46
Urinary creatinine (g/day) 1.242 0.2022 0.89 1.70
Skin-fold (mm): triceps 9.6 3.56 4.0 16.0
subscapular 12.8 3.15 8.5 19.5
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)
  0.45 0.55 0.65 0.75
Rice 110 142 161 180
Cornstarch 240 225 210 196
Sugar 8 8 8 7
Soybean oil 46 40 34 31
Butter 16 15 16 16
Potassium phosphate 2.3 2.3 2.4 2.4
Calcium phosphate 2.3 2.3 2.4 2.4
Cellulose 4.5 4.5 4.8 4.8
Sodium chloride 10 10 10 10
Mung bean noodles 70 70 70 70
Wheat flour 20 24 29 33
Sweet potato 9 12 14 16
Soybean curd 56 68 81 92
Peanuts 3 4 5 5
Kale 11 17 23 25
Chinese cabbage 54 80 100 100
Carrots 30 40 53 56
Cabbage, dried 10 9.5 10 13
Bananas 7 8 10 11
Watermelon 40 50 50 50
Pork 19 23 24 37
Chicken 6 7 9 13
Egg 5 6 7 8
Fish 15 23 25 37
Whole milk 1 1.2 1.4 1.6
Skim milk 1 1.2 1.4 1.6
Vitamin and mineral supplements2  
Nutrients: Protein (gm) 25.6 31.3 37.1 42.4
Fat (gm) 96.1 88.7 96.9 94.5
Carbohydrate (gm) 388.2 399.1 372.6 370.4
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.

5. Diets
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.