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close this bookProtein-Energy Requirements of Developing Countries: Evaluation of New Data (UNU, 1981, 268 p.)
close this folderProtein requirements-adults, other protocols
close this folderProtein needs of young adult men fed common beans (phaseolus vulgaris) in combination with starch, plantain, maize, or rice
View the document(introduction...)
View the documentObjective
View the documentExperimental details
View the documentSummary of main results
View the documentConclusions and comments

Experimental details

1. Subjects
Four sets of experiments were carried out. A total of 32 healthy young men volunteered for the study. They were laboratory technicians and maintenance employees. They were Spanish or mixed Spanish-Mayan Indian, from 23 to 35 years old, with weight ranges from 46.5 to 65.0 kg and heights from 157 to 172 cm. They did not have chronic infections or intestinal parasites.

2. Study Environment
The men lived in their homes in Guatemala City and worked at INCAP. All of their meals were eaten in the Division of Food Sciences Metabolic Unit. The daily ambient temperature ranged from 21 to 25 C in some studies and from 27 to 32 C during others. Relative humidity ranged from 72 to 85 per cent. Guatemala City is 1,510 m above sea level.

TABLE 1. Basal Diet Used in Human Metabolic Studies

Food Amount (g) kcal
Instant coffee 3 3
Sugar 25 100
Apple jelly 30 78
Toasted bread* 300 801
Margarine 80 576
Soup * * 480 144
Chayote 100 52
Apple 200 116
Artificially flavoured drink, glass 3 228
Starch cookies,*units 2 200
Carbonated beverage, bottle 1 136
Total energy - 2,434

* Made from wheat starch only
** Made from cornstarch.

3. Physical Activity
All men performed their usual chores.

4. Duration of the Study
After subjects had consumed the standard protein diet for several days, a nineday experiment was carried out. During the first three days the men ate the diet described in table 1, which provided only between 20 and 30 mg N/kg/day. After that they ate the experimental diet in which protein content was changed every two days. The three two day periods of protein intake provided 0.2, 0.4, and 0.6 9 protein/kg/day. The details of this short-term, multiple nitrogen-balance assay have been described elsewhere (Bressani et al., in H.L. Wilcke, D.T. Hopkins, and D.H. Waggle, eds., Soy Protein and Human Nutrition [Academic Press, New York, 1979] ).

5. Experimental Diets
The four experimental diets were as follows:

TABLE 2. Regression Equation between Nitrogen Intake and Nitrogen Retained of Subjects on a Diet of Wheat Starch and Black Beans (Phaseolus vulgaris)

Subject a 1 b1 Nitrogen intake for equilibrium (mg/kg/day) r
1F-HM -39.7 +0.32 124.1 0.56
2F-AF -100.9+0.86 117.3 0.93
3F-GM -50.6 + 0.47 107.6 0.71
4F-WH -85.9 + 0.80 107.4 0.83
5F-SY -35.9 + 0.30 119.7 0.99
6F-AS -63.1 +0.62 101.8 0.96
Average -62.6 + 0.55 113.8 0.75

1 NR=a+b(NI).

TABLE 3. Regression Equation between Nitrogen Intake and Nitrogen Retained of Subjects on a Diet of Tortilla and Black Beans (Phaseolus vulgaris)

Subjects a1 b1 Nitrogen intake for equilibrium (mg/kg/day) r
7T- FS -89.5 + 0.94 95.2 0 96
8T-VO -105.9 + 0.89 118.9 0.82
10T-AL -83.5 + 0.91 91.7 0 96
11T-WS -88.4 + 0.91 97.1 0 94
12T-EM -80.6 + 0.95 84.8 0 99
Average -86.9 + 0.89 97.6 0.89
  1. Common beans with wheat starch were the main energy sources (6 men participated).
  2. Corn tortillas and black beans. The maize-bean mixture was provided in proportions of 70:30 on a dry-weight basis (6 men participated).
  3. Rice and common beans fed in a 60:40 ratio, based on protein content (10 men participated). d. Common beans and cooked, mature plantain, with black beans providing between 30 and 32 per cent of total energy (12 men participated).

1 NR=a+b(NI).

The initial low-nitrogen diet provided between 2,400 and 2,500 kcal/day. Energy intake was adjusted to 45 to 50 kcal/kg/day to meet each individual's energy needs and to allow him to maintain body weight throughout the experiment. A multivitamin and mineral tablet was provided each day. Water intake was maintained at a constant level for this study.

6. Indicators and Measurements
a. The composition of the diets was calculated with AOAC methods of proximate chemical analysis. b. Urine and faeces were collected as 24 hour pools. Faecal markers were used to separate faecal collections. c. The nitrogen contents of diets, urine, and faeces were determined using the macro Kjeldahl technique. Apparent nitrogen balance was calculated by subtracting urinary and faecal nitrogen from dietary nitrogen. Apparent digestibilties were calculated, not including obligatory faecal nitrogen losses,