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.