(introduction...)

Objectives
Experimental details
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

Objectives

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.

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.

Summary of main results

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

Ingredients (gm)	Levels of protein intake (g/kg body wt/day)
	0.35	0.45	0.55
Whole egg	158	196	246
Cornstarch	296	270	260
Sugar	20	20	20
Soybean oil	41	36	30
Butter	30	30	30
Potassium phosphate	3	3	3
Calcium phosphate	3	3	3
Methyl-cellulose	6	6	6
Sodium chloride	10	10	10
Watermel on	200	200	200
Chinese cabbage	100	100	100
Mung bean noodles	200	200	200
Vitamin and mineral supplements2
Nutrients: Protein (gm)	21	27	33
Fat (gm)	81.2	84	78.4
Carbohydrate (gm)	444	423	420.6
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

1. The results obtained suggest that the 1973 FAD/WHO recommendation for young men of 0.57 9 egg protein/kg/day is inadequate. The recommended dietary allowance of protein estimated in 1972 for adults in Taiwan was 1.1 g/kg/day. That figure coincides with the present results using mixed Chinese diets.
2. The NPU of a similar mixed Chinese diet was found to be 62 when weanling rats were used as the experimental animal. In contrast, the present study with young Chinese men showed the NPU of the mixed Chinese dietary protein to be only 43. The NPU of egg protein was 55 to 58 in the present study as compared with a value of 70 obtained in our earlier studies with infants.
3. The mean nitrogen requirements of young Chinese men, based on regression analysis of the pooled data, are 127 mg (0.79 9) protein/kg/day with the mixed Chinese diet and 98 mg (0.61 9) protein/kg/day with the egg diet.

 

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
72.4±0.79	70.9±9.641	15.2+2.26	7.2+2.97	93.3±10.56	-20.9+10.30
87.9±1.03	77.9±10.47	16.9+2.20	8.7±7.37	103.6±11.81	-15.8+11.10
103.3±0.53	91.3±10.35	17.0+3.79	7.5+2.88	116.4±10.08	-12.5±10.14
121.0±0.87	99.0± 9.12	16.7±325	5.5±1.46	121.2± 8.16	- 0.2± 7.97
Egg diets
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.

FIG.1 Daily Nitrogen Balance with Chinese Mixed Diet

FIG. 2. Daily Nitrogen Balance with Egg Diet

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	Digestibility
(g/kg/day)			Apparent	True
Mixed diet
0.45	47±13a,A	45±13a,A	7g±3c	97±3
0.55	47±12a,A	45±11a,A	81±3d,e	96±3
0.65	42±10a,A	40±10a,A	84±4c,d	96±3
Egg diet
0.35	sg±17b	58±18b	75±4f	98±4
0.45	57±11b	56±11b	82±3	98±2
0.55	56±10b	55±10b	84±3f	98±2

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.