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close this bookProtein-Energy Requirements of Developing Countries: Evaluation of New Data (UNU, 1981, 268 p.)
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View the documentStatistical considerations in the estimation of protein requirements
View the documentA summary analysis of the nitrogen-balance data

A summary analysis of the nitrogen-balance data

Following the standard UNU protocol, six investigators conducted a total of 11 studies on adults. This presentation summarizes these studies.

Skin Losses

One investigator, P.C. Huang, measured skin losses of nitrogen in subjects consuming two separate diets. Analysis of his data (see table 1 ) shows that the two diets differed significantly in terms of the amount of nitrogen lost through the skin. Additionally, although skin losses did differ with different levels of intake, these differences were

TABLE 1. Skin Losses (mg N/kg/body weight)

Level

Diet

mg N/kg Mixed (n=10) Egg (n=7)
56 - 10.50
72 5.95 13.47
88 7.10 7.07
104 5.97 -
120 5.58 -
Mean: 6.15 10.35
subject S.D. 1.77 n.s.
measurement S.D. 0.75 2.75

S.D. = standard deviation.

TABLE 2. Faecal Losses (mg N/kg body weight)

Investigator Diet Levels of intake N Average faecal losses Measurement S.D.
Inoue Fish 56-104 6 12.06 1.03
Mixed 56-104 8 13.2 0.82
Soy 56-104 5 11.5 1.38
Huang Egg 56-88 6 14.3 1.47
Mixed 72-120 10 15.7 1.92
Bourges Mixed 64-112 7 27.5 4.39
Fajardo mixed (animal) 82-136 9 20.2 4.91
mixed (vegetable) 72-152 5 - 5.90
Uauy Egg 48-96 8 18.5 2.77
  Mixed 64-112 7 35.1 3.28

 

Faecal Losses

For nine of the ten studies for which faecal nitrogen values are available, there were no significant differences between those values for different levels of nitrogen intake (see table 2). The data of L. Fajardo obtained with a vegetable protein diet did indicate differences; this study examined six levels of intake from 72 to 152 mg N/kg. These results suggest that perhaps diets can be well characterized by faecal nitrogen losses. Furthermore, it appears that absorption measurements will vary with the level of intake.

Nitrogen Balance

Table 3 gives estimated means, standard deviations, and 97.5 per cent population requirements for the 11 studies. Note that the pooled coefficient of variation is 18 per cent. Table 4 shows the results of a series of standard protocol experiments conducted at MIT. Table 5 shows all these data arranged by diet.

 

TABLE 3. Nitrogen Balance (mg N/kg body weight)

Investigator Diet N Mean S.D. C.V.1 '97.5 2,3 '97 5 4
Inoue fish 8 101.0 15.7 15.6 132.5 137.6
mixed 8 106.4 24.0 22.6 154.5 145.0
soy isolate (Supro 620) 5 129.6 14.1 10.9 157.9 176.6
Huang egg 7 93.5 15.8 19.0 129.0 127.4
mixed 15 127.5 25.9 20.3 179.3 173.7
Tontisirin egg 13 123.6 17.1 13.8 157.7 168.4
Bourges mixed 8 121.4 27.2 22.4 175.8 165.4
Fajardo vegetable 8 138.6 22.3 16.1 183.2 188.8
animal 11 131.7 27.4 20.8 186.5 179.4
Uauy egg 8 98.7 8.2 8.3 115.1 134.5
mixed 7 133.4 27.5 20.6 188.4 182.4

 

Table 4 Summary of MIT Experiments

Investigator Diet No of subjects Mean requirement (S.D.) (mg N/kg) 97.5% requirement (mg N/kg)
Fajardo beef 7 83 (11) 113
wheat 7 147 (58) 200
Puig egg 7 92 (42) 125
soy isolate1 8 111 (15) 151
Wayler milk 7 93 (33) 126
beef/soy isolate1 7 96 (35) 131
beef 7 108 (20) 147
Wayler milk 6 133 (49) 181
soy isolate1 8 135 (28) 184
soy isolate2 7 114 (36) 155
Uauy wheat 6 135 (54) 184
Puig beef 6 106 (19) 144

1Supro 620 (Ralston-Purina).
2Supro 710 (Ralston-Purina).

TABLE 5. Experiments by Protein Source

    No of Mean
Diet Investigator subjects requirement
Egg Huang 7 94 (16)
  Tontisirin 13 124 (26)
  Uauy 8 99 ( 8)
  Puig 7 92 (42)
Soy isolates Inoue1 5 130 (14)
  Puig1 8 111 (15)
  Wayler1 8 135 (28)
  Wayler2 7 114 (36)
Milk Wayler 7 93 (33)
  Wayler 6 133 (49)
Beef Fajardo 7 83 (11)
  Puig 6 106 (19)
  Wayler 7 108 (20)
Wheat Fajardo 7 147 (58)
  Uauy 6 135 (54)
'`Local" Inoue 8 106 (24)
  Huang 15 128 (26)
  Bourges 8 121 (27)
  Uauy 7 133 (28)
  Fajardo 8 139 122)
  Fajardo 11 132 (27)
Other Inoue (fish) 8 101 (16)
  Wayler (beef/soy isolate) 7 96 (35)

1 Supro 620.
2 Supro 710.

TABLE 6. Repeated Subjects

Investigator Measurement

Standard deviations

Between diets Between subjects Measurement
Inoue: fish faecal nitrogen      
  vs. (mg/kg) 1.6 1.9 0.9
  mixed slope of      
    response n.s. n.s. 0.18
    mean      
    requirement      
    (mg/kg) n.s. n.s. 16.5
Uauy: egg faecal nitrogen      
  vs. (mg/kg) 16.9 2.7 2.8
  mixed slope of      
    response n.s. n.s. 0.25
    mean      
    requirement 34.1 n.s. 20.1

Paired Experiments

Two investigators, R. Uauy and G. Inoue, conducted experiments comparing two different diets using the same individuals. For these experiments, between-subject variability can be separated from withinsubject variability. The results are shown in table 6. These results suggest (a) that efficiency measures (slopes of response curves) are too variable to be of value, and (b) that the errors in determining mean requirement levels are so large (~ 20 mg/N) as to permit discrimination only between very different dietary proteins.