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close this bookProtein-Energy Requirements of Developing Countries: Evaluation of New Data (UNU, 1981, 268 p.)
close this folderProtein-energy requirements-children
close this folderCapacity of habitual Guatemalan diets to satisfy protein requirements of pre-school children with adequate dietary energy intakes
View the document(introduction...)
View the documentObjective
View the documentExperimental details
View the documentSummary of main results
View the documentComments
View the documentConclusions

Experimental details

1. Subjects

  1. Eleven boys of mixed Maya and Caucasian descent (Lading).
  2. Chronological age: 37 4 months (range: 29 to 46). Height-age: 20 4 months (range: 13 to 26).
  3. All had been treated for moderate or severe protein-energy malnutrition. They had recovered fully at least two months before beginning the studies, based on clinical, anthropometric, and biochemical criteria (plasma proteins, non-essential/essential amino acid ratio, haematological indices).
  4. Weight: 11.69 0.82 kg (range: 10.47 to 13.00). Height: 83.8 4.3 cm (range: 76.1 to 89.4). Weightfonheight, percentage of expected: 99 5 per cent (range: 92 to 109).
  5. The children were happy and active throughout the study, except for short disease episodes. Children (I.D. nos. 404, 405, 408, and 410) had febrile infections in weeks three, one, four, and six, respectively, that lasted from four to seven days. Only child 410 received antibiotics, to treat a periodontal infection. All others received symptomatic medication for upper respiratory infections. During week three, child 406 had an afebrile exanthema of unknown aetiology that disappeared spontaneously, and child 407 had an afebrile upper respiratory infection. Finally, all children except 405 had an afebrile upper respiratory infection characterized by catarrh and coughing during the last one or two weeks of the study.

A few children vomited occasionally and sometimes had slight increments in rectal temperature (<38.5 C) without other signs or symptoms of disease.

2. Study Environment
INCAP's Clinical Centre in Guatemala City; 1,500 metres above sea level. Temperature 18 to 24 C. Relative humidity 40 to 60 per cent. All children spent four to six hours each day outdoors on the grounds and playing area around the Clinical Centre, except on rainy days.

3. Physical Activity
The children were encouraged to be as physically active as healthy children who live in a good home environment. This was done through daily outdoor walks in the areas around the Clinial Centre and participation in games and other activities that required walking, running, jumping, or climbing. They were never forced to participate in those activities when they did not feel like doing so, nor were they ever pushed to exhaustion. Such activities alternated with periods of rest or sedentary play to avoid boredom or fatigue.

4. Duration of the Study
The children ate the experimental diets for at least 11 weeks, divided into the fol lowing periods:

  1. Two weeks: ad libitum intake of indigenous diet to measure each child's individual food intake.
  2. One week: ad libitum intake of indigenous diet with a higher density, whenever necessary, to ensure intakes of 87 to 97 kcal/kg/day.
  3. Eight weeks: experimental period. Metabolic and other measurements while eating the diet with 87 to 97 kcal/kg/day in ad libitum amounts. The results were analysed as two separate four-week periods, as described below.

TABLE 1. Average Composition and Frequency of Consumption of Diets Customary for Many Children of Pre-school Age in Guatemala


Intake per day (g)

Frequency of intake (days/week)

Weekly intake








Corn tortilla flour






Black bean flour






Bread (sweet roll), fresh






Vegetables (chayote, squash,or potatoes), raw






Milk products (as fluid milk equivalents)






Fruit (orange, apple, banana),fresh






Egg, fresh






Meat, raw (as beef equivalent)












Oil or lard






Total intake per week      



Mean intake per day      



Mean intake/kg/day (assuming weight of 12 kg)      



Bean: corn ratio = 15:85 by weight and 29:71 by protein contents
Animal protein = 18% of total
Energy from fat (including natural fat content of all foods) = 17% of total

TABLE 2. Menus Offered to the Children a

Days Breakfast (7 a.m.) Lunch (11 a.m.) Dinner (6.30 p.m.)
  corn and beans b corn and beans
sweet breads
corn and beans
sweet bread
  + + +
Mon. egg (1 unit) a apple chayote d
Tue. potatoes apple potatoes
Wed. chayote beef (40 g) a apple
Thu. squash potatoes potatoes
Fri. egg (1 unit) a squash squash
Sat. potatoes apple potatoes
Sun. chayote chayote potatoes
  Afternoon snack (3 p.m.):

sweet bread (13 g) a


Mon., Wed., Sat.: milk (100 ml) a

Tue., Thu., Sun.: lemonade (200 ml) a

Night drink (8 p.m.):

lemonade or water

a All foods offered ad libitum, except when noted otherwise.
b Corn-based beverage (atole), soft corn bread (tamal), and mashed black bean puree.
c Sweet bread dough prepared with sugar and lard,
d Chayote = Sechium edule.

5. Diet

  1. The diet was based on the proportions of foods eaten by pre-school children from poor socio-economic rural families (see table 1). For practical reasons of food preparation in the metabolic kitchen, fluid milk was used as the only dairy product and the vegetables and fruits were limited to those shown in table 2.
  2. The children ate three daily meals and a mid-afternoon snack (see table 2). All meals included the basic staple foods of the region (corn and black beans) plus one or two other foods that varied from meal to meal and from day to day. The snack consisted of a sweet roll and half a cup of milk or lemonade. The daily menus were repeated at seven-day intervals; that is, there were menus for Sundays, Mondays, Tuesdays, and so on. The children ate as much as they wanted and the nurses played the role of mother at meal times, encouraging but not forcing the children to eat all that was served. If a child asked for more of a food served in a meal, it was given to him except for the foods that are scarce and limited in the home environments represented by the study (meat: maximum of 40 9 once weekly; egg: maximum of one twice weekly; milk: maximum of 100 ml three times weekly). No child was forced to eat if he refused to do so. Lemonade or water was offered to the child before retiring at night. By eating ad libitum, each child determined his own intake of proteins and other nutrients for the day. Energy intake, however, was adjusted each week, based on the preceding week's intakes, to approximately 92 5 kcal/kg/day. The adjustments were made by adding more or less oil to the black beans and more or less sugar to the lemonade, or substituting water for the latter before retiring. Regardless of the preceding week's intakes, no more dietary adjustments were made in the last four weeks of the study.
  3. Since the purpose of the study was to evaluate protein and energy nutriture, the diet was supplemented with vitamins and minerals, as shown in table 3.

6. Indicators and Measurements
a. Metabolic-balance studies: Most of the children were not toilettrained. To avoid excessive limitations of physical activity, complete 24-hour urine and faecal collections were obtained at 4-day intervals so that every 28 days excrete corresponding to the seven different menus for each day of the week were collected. Urine collection began after the first morning micturition and ended after a micturition 22 to 26 hours later; volumes were adjusted to 24-hour periods. Faeces were collected between carmine red and charcoal faecal markers fed with breakfast on 2 consecutive days. When the two markers were excreted together or when there were other problems, such as losses of excrete, collections were repeated on the same day of the following week. Faeces were homogenized and dried. Their nitrogen and energy concentrations were measured in aliquots of powdered faeces by Kjeldahl analysis and bomb calorimetry, respectively. Urinary nitrogen was also determined by a Kjeldahl procedure. Each food was served in a separate dish or cup at every meal. The amounts eaten by a child were measured by weighing the corresponding containers before and after each meal, accounting for any additional servings or for losses by spillage. Aliquots of each food, as served to the children, were analysed at least four times during the study using the same methods as those for faeces. Tryptophan and benzoic acid were used as standards in each Kjeldahl and bomb calorimeter run, respectively. Total daily intakes of protein (nitrogen x 6.25) and gross energy (by bomb calorimetry) were calculated multiplying by the amounts of each food ingested.

Nitrogen balance ("apparent") was calculated by subtracting urinary and faecal nitrogen from intake. No corrections were made for integumental and other insensible nitrogen losses.

TABLE 3. Vitamin and Mineral Supplements Administered Daily

Vitamin A 2,500 I.U .
Vitamin B1 1 mg
Vitamin B2 0.5 mg
Niacinamide 5 mg
Vitamin B6 0.5 mg
Pantothenic acid 5 mg
Folic acid 30 mog
Vitamin Bl2 2 mcg
Biotin 50 mcg
Vitamin C 25 mg
Vitamin D 500 I.U.
Vitamin E 1.5 mg
Iron (as ferrous sulphate) 60 mg
iodine (as Kl) 100 mcg
Manganese sulphate 0.9 mg
Zinc sulphate 1 mg

Net energy intake was calculated as the gross value intake minus faecal energy (by bomb calorimetry). This value was used to calculate the contribution of dietary protein to total energy intake (P%), assuming that each 9 of protein ingested corresponded to 4 kcal of metabolized energy. The dietary energy retained was calculated by subtracting urinary nitrogen energy (estimated as 5 kcal/g urinary nitrogen) from the net intake. Energy balance was calculated by subtracting the total energy expenditure, as described below, and sweat losses (estimated as 0.1 kcal/kg/day, based on 8 kcal/g sweat nitrogen) from the dietary energy retained.

The daily metabolic-balance data were combined in 28-day periods that included intakes and excrete corresponding to each of the 7 days of the week. These periods were termed I and 11.

Apparent digestibility of nitrogen and apparent absorption of energy were calculated from the combined gross intakes and faecal excrete of a 28-day period.

It was assumed that collection days when a child ate little food or did not defecate much would be balanced by other collection days with higher intakes or greater faecal excretions. During collection days the children who were not toilet-trained remained in a metabolic bed during the hours in which it was expected that they would defecate and while they slept; at other times they moved and played around freely while wearing urine collection bags.

b. Basal oxygen consumption: This was measured with an oxygen diaferometer at 1 B-day intervals, each time on two separate occasions not more than 3 days apart; the lower of the two results was considered as basal. Basal conditions were defined as after a minimum of eight hours of sleep and ten hours of fasting. Measurements were done while the child was sleeping, sometimes after oral administration of chloral hydrate (4 mg/kg). Energy expenditure was calculated by indirect calorimetry, assuming a respiratory quotient of 0.82.

c. Total energy expenditure: Physical activity and energy expenditure were quantified by monitoring the children's heart rate (HR) throughout the day and calculating energy expenditure from individual determinations of heart rate and oxygen consumption (VO2). The HR-VO2 relationship was determined in each child at 14- to 21-day intervals. Heart rate was continuously monitored for at least 10 days within 7 days of determining the HR-VO2 relationship. Total daily energy expenditure was calculated from each child's heart rate and his corresponding heart rate-energy-expenditure relationship from 6 a.m. to 8 p.m. (14 hours), and from his basal energy expenditure from 8 p.m. to 6 a.m. of the following day (10 hours).

d. Anthropometry: The children were weighed naked before breakfast each morning. Body length ("height"), right arm circumference, and subcutaneous skin-fold thickness (tricipital, subscapular, and paraumbilical) were measured initially and at 14-day intervals.

e. Urinary creatinine excretion: This was measured in the 24-hour urine collections obtained for nitrogen balance. An alkaline picrate method (Jaffe) was used. The creatinine-height index (CHI ) was computed, and running or weekly averages were calculated, including and excluding data from the days when meat was eaten.

f. Other biochemical and haematological determinations: Venous blood was drawn initially and at 18-day intervals. Packed cell volume (microcentrifuge) and the concentrations of blood haemoglobin (cyanomethaemoglobin), plasma proteins (refractometry), and serum albumin (bromcresol purple) were determined, as well as the ratio of serum non-essential/essential amino acids (Whitehead).

g. Statistical analysis: Changes in weight, anthropometry, and CHI were calculated by regression analysis. Data calculated at 7-,14-, or 18-day intervals were also computed by analysis of variance. Differences between the 28-day periods were examined by the student's paired t test.

Unless otherwise noted, the data in the text and tables are expressed as the mean + standard deviation, and in the figures as the mean + standard error of the mean.