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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 folderCapacity of the Chilean mixed diet to meet the protein and energy requirements of young adult males
View the document(introduction...)
View the documentExperimental details
View the documentSummary of main results
View the documentConclusions
View the documentAcknowledgements

Experimental details

1. Subjects
Eight men, 20 to 31 years old, were selected. Their initial weights, heights, and energy intakes are described in table 1. All were chosen from among volunteers who answered a local advertisement. Their monthly incomes were lower than US$150, which corresponds to the lower tercile of the national income distribution. Their housing, sanitary environment, and educational background were consistent with their incomes. They were healthy, based on medical history, physical examination, and laboratory analysis of haematocrit, haemoglobin, total and differential white blood count, serum transaminase activities, and complete urinalysis.

2. Physical Activity
The men continued their normal daily routines, including their usual patterns of activity, but refrained from participating in competitive sports during the study. They slept in the Metabolic Unit of the Institute's Clinical Research Centre. All subjects remained under the supervision of a physician and a nurse throughout the

TABLE 1. Physical Characteristics and Energy Intakes of the Subjects Participating in the Study

         

Energy intake

Subject Age (years) Weight (kg) Height (cm) W/H Index* (%) (kcal/day) (kcal/kg)
J.A. 26 55.0 161 89.5 2,800 51
H.F. 20 54.5 180 72.4 3,050 57
J.B. 25 75.0 177 104.7 3,150 42
O.G. 25 60.7 174 86.7 2,950 49
S.L. 28 59.0 166 91.1 3,000 51
M.L. 30 51.0 162 81.4 2,500 50
H.R. 25 60.5 171 88.6 2,800 47
E. R. 31 61.5 170 91.3 3,000 49
Mean 26.3 59.7 170.1 88.2 2,906 49.5
S.D. 3.4 7.2 6.8 9.2 202.6 4.2

* Based on D.B. Jelliffe, The Assessment of the Nutritional Status of the Community (World Health Organization, Geneva. 1966).

3. Diets
The subjects were fed a "Chilean mixed diet" designed according to available dietary survey information of a typical Chilean diet for the country's low-income groups. Its composition is shown in table 2. Protein was fed at 0.40, 0.55, and 0.70 g/kg of body weight per day. In addition, an egg diet that provided 0.30, 0.45, and 0.60 9 protein/kg/day was fed as a reference diet (table 2). Each subject's energy intake was calculated from his customary diet by the 24-hour dietary recall method for 15 consecutive days. All protein levels were fed with the same total dietary energy to a given individual. Vitamin and mineral supplements were provided daily to meet or exceed the 1974 NAS/NRC Food and Nutrition Board Recommended Dietary Allowances. The nitrogen content of dietary ingredients and preparations was analysed by the Kjeldahl method, using a macro digestion procedure followed by a semi-micro 45 distillation of the ammonia produced into 2 per cent boric acid containing a mixed indicator.

TABLE 2. Composition of Experimental Diets Used for Study of Protein Requirements in Young Men

Ingredient

Level of intake

  Mixed diet Egg diet
Whole dried egg powder, g - 34.3
Sucrose, g 106.4 114.0
Wheat flour, g 145.1 -
Margarine, g 54.1 67.1
Dried skim milk, g 27.9 -
Rice, g 61.4 -
Cornstarch, g - 246.9
Bean soup powder, g 46.0 -
Vegetable oil, ml 32.7 70.5
Potato flakes, g 112.0 -
Soup flavouring, g - 2.0
Apricot marmalade, g 15.0 -
Orange-flavoured beverage, g 23.6 37.5
Lemon-flavoured beverage, g - 37.5
Water, ml 1,200 1,754
Vitamin/mineral supplement1    

Food preparations:

Mixed diet: Wheat flour bread, rice/milk dessert, bean soup, potato flakes. Intake is given for a 61 kg subject.

Egg diet: Cornstarch bread, cornstarch soup, omelette, liquid egg formula, cornstarch dessert, protein free cookies. Intake is given for a 60 kg subject.

1 Multivitamin/mineral supplement, Laboratories Pfizer de Chile, Santiago, Chile. One tablet supplies: vitamin A, 5,000 I.U.; vitamin D2 1,000 I.U.; thiamin 1 mg; riboflavin 2 mg; pyridoxine 1 mg;vitamin Bl2 2 mcg; ascorbic acid 50 mg; niacinamide 12 mg; Ca pantothenate 2 mg; copper (as CuO) 70 mcg; iodine (Kl ) 50 mcg; iron 1 mg; potassium (Kl) 16 mcg; manganese (MnCO3) 28 mcg; magnesium (MgO) 108 mcg; zinc (ZnO) 71 mcg,

4. Experimental Design
Each experimental period started with a 1-day protein-free diet (NFD) followed by ten days on the experimental diet. A free-choice diet was eaten in the next three days, followed by one day on the nitrogen-free diet and ten days with another experimental level of dietary protein. The sequence of protein levels was randomly assigned to each individual. Three isoenergetic, isonitrogenous meals were provided, at 8 a.m., 1 p.m., and 7 p.m., and were consumed under the close supervision of a dietitian. The protein sources during the mixed diet period were distributed as equally as possible in the three daily meals.

5. Measurements
Complete 24-hour urine collections were obtained with HCI as a preservative throughout the study. An aliquot was analysed for total nitrogen, urea, and creatinine. Faeces were collected daily and pooled during the last eight days of each dietary period. Pools were separated by feeding autoclaved brilliant blue and carmine red markers. Nitrogen balance was calculated by subtracting the mean daily urine and faecal ( nitrogen excretion from the daily nitrogen intake. Integumental and miscellaneous nitrogen losses were estimated at 5 mg N/kg body weight/day. Body weights were measured on a 50g precision scale daily at 0800 hours, before breakfast, post-voiding, with subjects wearing minimal clothing. Fasting blood samples were drawn from an antecubital vein at 0800 hours at the beginning of the study and at the end of the lowest and highest dietary protein test periods. They were analysed for total serum protein, albumin, and urea concentrations; transaminase activities; and blood cell counts. Height; body weight; waist, gluteal, and mid-upper arm circumferences; and triceps and subscapular skin-fold thicknesses were measured at the beginning and end of each dietary level.