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Miguel Layrisse, Carlos Martínez-Torres, Hernán Méndez-Castellano, Peter Taylor, Marlene Fossi, Mercedes López de Blanco, Maritza Landaeta-Jiménez, Werner Jaffe, Irene Leets, Eleonora Tropper, Maria Nieves García-Casal, and José Ramirez
Iron bioavailability was determined by the extrinsic label method in seven diets consumed by low, middle, and high socio-economic strata of the Venezuelan population. The results were compared with physiologic iron requirements and the prevalence of iron deficiency according to age and sex of others in the same strata. The iron metabolic balance obtained by comparing the iron absorption from diets with the physiologic iron requirement was negative in subjects consuming the low-bioavailability diets, being more marked in children below four years of age, and in adolescents and adult females. These groups also showed the highest prevalence of iron deficiency with and without anaemia. The metabolic iron balance in subjects consuming high iron-bioavailability diets was less negative among vulnerable groups consuming low-bioavailability diets and positive in the age and sex groups less vulnerable to iron deficiency. This information was used to identify the principal categories of dietary iron bioavailability in various regions of the world and their effect on the prevalence of iron deficiency.
The introduction in 1972 of the extrinsic tag method to measure absorption of haem and non-haem iron from food [13] marked the beginning of many contributions on iron absorption from typical meals and diets consumed in various regions of the world [4-17]. Unfortunately, these studies were not accompanied by the respective information on the prevalence of iron deficiency in the region where the diets were consumed.
The Proyecto Venezuela was a national survey on growth, nutrition, and family carried out by Fundacredesa between 1978 and 1984 in people of various socio-economic strata living in all the regions of Venezuela [18, 19]. This paper provides information on the part of the project devoted to iron bioavailability from diets consumed by these individuals and its effect on the prevalence of iron deficiency. Some of the information has been included in previous papers [16, 20-22].
Diets
Seven diets were tested: five consumed by persons of low socio-economic stratum living in Carabobo, Yaracuy, Lara, Sucre, and Zulia states and two consumed by those in the middle and high socio-economic strata living in the Caracas metropolitan region. The socioeconomic strata of the families enrolled in the Proyecto Venezuela were identified according to a slight modification of the Graffar method [18, 19, 23].
The composition of the diets from Carabobo and Yaracuy has been described previously [16] The Lara diet consists mainly of precooked maize bread consumed in all three meals; rice, black beans, and 80 g of chicken are eaten for the main meal, and pasta and scrambled eggs in the secondary meal.
The diet in Sucre consists of white wheat bread eaten at breakfast, and precooked maize bread at lunch and supper. The main meal, eaten at lunchtime, is made up of legume soups, rice, plantain, and 100 g of fish. Rice and scrambled eggs are eaten at supper.
Individuals in Zulia eat precooked maize bread at breakfast and white wheat bread at supper. For their main meal at lunchtime, they have 100 g of beef accompanied by rice and plantain. Supper consists of pasta, white cheese, and scrambled eggs.
The two basic diets of the Caracas metropolitan region are more diversified, with the main meal including generous amounts of meat, and vegetables with high amounts of ascorbic acid. One consists of white wheat bread, cheese, jam, white coffee, and margarine for breakfast; 200 g of poultry, rice, plantain, tomatoes, lettuce, and papaya for lunch; and white wheat bread, rice, and fried eggs for supper. The other diet is less diversified, except for the main meal, in which 200 g of beef, tomato and lettuce salad, and fruits are consumed. Beef (50 g) is also eaten at supper.
Study subjects
One hundred and twenty subjects voluntarily participated in this study. They were in apparent good health, and the low haemoglobin values present in some of them did not interfere with their daily work. The protocol was approved by the Committee for the Protection of Human Subjects Participating in Clinical Investigations of the Instituto Venezolano de Investigaciones Científicas. Blood haemoglobin concentration [24], packed red cell volume (microhaematocrit), serum iron concentration [25], unsaturated iron-binding capacity [26], and serum ferritin concentration measured by immunoradiometric assay (IRMA) [27] or enzyme-linked immunosorbent assay (ELISA) [28] were tested in each subject.
Preparation of radioactive material
The extrinsically labelled food for each meal was prepared by mixing radioactive iron with the vehicle according to the technique described previously [4]. The reference dose of 3 mg of iron as ferrous sulfate was prepared as published [29].
Iron absorption
All meals were given in the morning after an overnight fast. The terms breakfast, lunch, and supper were used only to identify the type of meal. No food or drink was allowed for three hours after the administration of the radioactive material. The extrinsic label 55Fe or 59Fe was mixed with the food vehicle in each meal, using approximately 0.7, micro Cl of 59Fe or 2 micro Cl of 55Fe in each test. Breakfast was given on day 1 and lunch on day 2. Blood was drawn 15 days after the administration of breakfast and lunch to determine the haematologic characteristics of the subjects and to measure the radioactivity in the blood samples. The subjects were fed supper on day 15 and given the reference dose on day 16. Blood was drawn again on day 30 to measure radioactivity.
Duplicate 10-ml blood samples together with the radioactive food and reference standard doses were prepared for radioactive counting using the technique of Dern and Hart [30, 31]. Radioactivity was measured in a liquid scintillation spectrometer. Triplicate samples of the food administered were counted simultaneously with the blood samples.
Iron absorption from the food was calculated from the 59Fe and 55Fe activity in the subjects' brood, using an estimate of blood volume based on sex, weight, and height [32]. To calculate total iron absorption from a given diet, the total non-haem iron utilization in the blood was multiplied by 0.9, since the vegetable iron content of the diets represented about 90% of the daily average consumption during a week. The total non-haem and haem iron absorption was also adjusted in healthy subjects, since about 90% of the total iron absorbed by the gastrointestinal mucosa is incorporated into the red cells, whereas in iron-deficient persons about 100% is incorporated [33].
Haem iron absorption was calculated according to the equation y = 3.34 (x)0.49, where y is the absorption of haem iron and x is the absorption of the reference dose [34]. This equation is more accurate than those previously published [15].
Chemical analysis
The total iron content of the vegetable foods and meat was determined by the digestion method [33], nonhaem iron by the method of Schricker et al. [35], phytate by the method of Haug and Lantzch [36], and tannate by the method of Price and Butler [37].
Physiologic iron requirements
The estimation of the physiologic iron requirements, according to age and sex of individuals in various socioeconomic strata, was taken from previous publications of the authors [21, 38]. The difference lies in the terms marginal, middle, upper middle, and upper socio-economic classes, which are changed here to low, middle, and high socio-economic strata, respectively.
Prevalence of iron deficiency
Blood samples were taken from 2,500 subjects living in regions where diets were tested for iron absorption, and from representatives of various socio-economic strata of the Venezuelan population. Cut-off values for the iron status indicators that predict anaemia were taken from the report on the assessment of iron nutritional status versus population based on data collected in the National Health and Nutrition Examination Survey, 1976-1980 [41] (table 1). The only exception was the group between 17 and 19 years of age, in which the cut-offs for haemoglobin and haematocrit were 13 g and 39% instead of 14 g and 42%. By using the latter cut-offs used by NHANES II, the prevalence of anaemia was much higher than the prevalence of iron deficiency.
TABLE 1. Cut-off values for the iron status indicators that predict anaemia and iron deficiency in the subjects studied
Age (years) and sex | Haemoglobin (g/dl) |
Haematocrit(%) |
Transferrin saturation(%) |
Serum ferritin mg/L |
1-2 M, | 11.0 |
33 |
< 12 |
<10 |
F 4-7 M, | 11.5 |
35 |
< 14 |
< 10 |
F 8- 10 M, | 11.5 |
35 |
< 15 |
<10 |
F 11- 13 M | 12.5 |
38 |
< 16 |
< 10 |
F | 12.0 |
36 |
< 16 |
< 10 |
14-16 M | 13.0 |
39 |
< 16 |
<12 |
F | 12.0 |
36 |
< 16 |
<12 |
17- 19 M | 13.0 |
39 |
< 16 |
<12 |
F | 12.0 |
36 |
< 16 |
< 12 |
Statistical analysis
The mean and standard error of the values for the iron absorption and ferritin concentration were calculated using their logarithms. The results were returned to the original units by taking their antilogs.
Table 2 (see TABLE 2. Nutritional content of Venezuelan diets) shows the nutrient content of the Venezuelan diets. The main meal, which represents more than 50% of the total iron intake, is usually eaten at lunchtime, with the exception of Carabobo. where it is consumed at supper. The caloric intake from the diets of people in the low socio-economic stratum varies between 1,570 and 2,220 kcal; the mean (1,872 kcal), however, is not significantly different from that observed in the two diets consumed by those in the middle and high socio-economic strata (2,()12 kcal). The difference between the two types of diets is in the contents of animal proteins and ascorbic acid, especially from the main meal, where they are more than two times higher in the diets consumed by persons in the middle and high socio-economic strata. Regarding total iron intake, the diets consumed by persons of low socio-economic status contain 21% more nonhaem iron and 254% less haem iron than those consumed by individuals of middle and high socioeconomic status.
TABLE 2. Nutritional content of Venezuelan diets
Meal |
Total food energy (kcal) |
Protein |
Fat (g) |
Carbohydrate (g) |
Ascorbic acid (mg) |
Haem iron (mg) |
Non-haem iron (mg) |
||
Animal(g) |
Vegetable(g) |
||||||||
Carabobo | B reakfast | 606 | 10.1 | 7.9 | 11.7 | 100.8 | 2.8 | 1.41 | - |
Lunch | 717 | 4.3 | 15.0 | 24.6 | 115.6 | 12.8 | - | 6.91 | |
Supper | 882 | 17.3 | 21.5 | 22.4 | 135.7 | 5.6 | 1.23 | 7.16 | |
Total | 2,205 | 31.7 | 44.4 | 58.7 | 362.1 | 21.2 | 1.23 | 15.48 | |
Yaraeuy | Breakfast | 525 | 8.4 | 7.3 | I 1.8 | I (X0.8 | 1.0 | - | 2.21 |
Luneh | 558 | 13.0 | 13.1 | 13.2 | 90.1 | 9.8 | 0.92 | 5.48 | |
Supper | 643 | 4.2 | 17.6 | 18.6 | 103.0 | 9.8 | - | 6.21 | |
Total | 1,726 | 25.6 | 30.0 | 43.6 | 293.9 | 20.6 | 0.92 | 13.90 | |
Lara | Breakfast | 557 | 7.8 | 5.9 | 13.6 | 95.1 | - | - | 1.41 |
Luneh | 763 | 16.2 | 16.9 | 25.6 | 98.7 | 28.5 | 0.66 | 5.71 | |
Supper | 722 | 11.9 | 12.3 | 12.8 | 125.3 | - | - | 3.99 | |
Total | 2,042 | 35.9 | 35.1 | 52.0 | 319.1 | 28.5 | 0.66 | 11.11 | |
Suere | Breakfast | 239 | 3.1 | 4.9 | 9.5 | 32.3 | - | - | 1.07 |
Luneh | 660 | 19.3 | 7.9 | 11.5 | 112.4 | 59.1 | 0.39 | 7.81 | |
Supper | 678 | 11.5 | 8.0 | 21.9 | 97.5 | 10 | - | 3.02 | |
Total | 1,571 | 61.8 | 20.8 | 42.9 | 242.2 | 69.1 | 0.39 | 11.90 | |
Zulia | Breakfast | 607 | 8.8 | 7.3 | 13.2 | 105.2 | - | - | 1.47 |
Luneh | 716 | 18.5 | 7.3 | 25.3 | 100.5 | 64.8 | 1.48 | 5.87 | |
Supper | 492 | 13.0 | 8.9 | 18.6 | 56.8 | - | - | 3.14 | |
Total | 1,815 | 40.3 | 23.5 | 57.1 | 262.5 | 64.8 | 1.48 | 10 56 | |
Average | Breakfast | 507 ± 69 | 7.6 ± 1.2 | 6.7 ± 0.5 | 12 ± .7 | 86.8 ± 13.7 | 1.9 ± 0.9 | - | 1.51 ± 0.19 |
Luneh | 683 ± 35 | 14.3 ± 2.7 | 12.0 ± 1.9 | 20.0 ± 3.2 | 103.5 ± 4.7 | 35. ± 11.5 | .86 ± 0.23 | 6.36 ± 0.45 | |
Supper | 683 ±63 | 11.6± 2.1 | 13.7± 2.6 | 18 9±1.7 | 103.7 ±13.7 | 8.5 ±1 4 | 1.23± 0.0 | 4.70±0.84 | |
Total | 1,872±112 | 39.1 ±6.2 | 30.8 ± 4.2 | 50.9 ± 3.3 | 295.7±21.1 | 40.8 ± 10.8 | 0.94 ± 0.19 | 12.59±0.92 | |
Caraeas | Breakfast | 590 | 11.9 | 9.5 | 22.4 | 76.0 | | 0.04 | 1.42 |
Lunch | 834 | 44.9 | 2.7 | 43.7 | 63.5 | 92.8 | 1.00 | 4.53 | |
'Supper | 631 | 13.8 | 3.7 | 32.8 | 66.4 | | | 3.58 | |
Total | 2,055 | 70.6 | 15.9 | 98.9 | 205.9 | 92.8 | 1.00 | 9.53 | |
Caracas | Breakfast | 619 | 13.7 | 7.5 | 10.0 | 105.3 | | | 1.96 |
Lunch | 701 | 45.2 | 5.4 | 27.1 | 65.0 | 108.0 | 2.96 | 5.86 | |
Supper | 657 | 22.0 | 10.4 | 16.7 | 89.5 | | 0.74 | 2.48 | |
Total | 1,977 | 80.9 | 23.3 | 53.8 | 259.8 | 108.0 | 3.72 | 10.30 | |
P values | >0.1 | <0.02 | >0.1 | >0.1 | >0.1 | <0.005 | >0.1 | >0.1 |
Inhibitors and enhancers of non-haem iron absorption
Table 3 (see TABLE 3. Mean content of inhibitors and enhancers of iron absorption from diets consumed by people of various socioeconomic strata in Venezuela) shows the amount of main inhibitors and enhancers of non-haem iron absorption in the two types of Venezuelan diets. In the main meal consumed by the low socio-economic stratum, the amount of inhibitors is about twice and of enhancers about one-half that of the other diets. Similar results were observed with the total diets, with the exception of the tannate content, which is higher in the latter diets because coffee is consumed at breakfast and supper. whereas in the low-stratum diets it is consumed only at one meal.
TABLE 3. Mean content of inhibitors and enhancers of iron absorption from diets consumed by people of various socioeconomic strata in Venezuela
Type of diet (socio-economic stratum) |
Meal |
Iron content (mg) |
Inhibitors |
Ascorbic acid, (enhancer) (mg) |
Meat (beefchicken. fish) (g) |
|
Phytate (mg) |
Tannate (mg) |
|||||
1.Low | Main meal | 7.4 | 448 | 178 | 39 | 84 |
Total diet | 13.5 | 990 | 850 | 45 | 84 | |
2.Middle and high | Main meal | 7.1 | 241 | 59 | 73 | 200 |
Total diet | 12,3 | 567 | 1.263 | 90 | 225 |
Iron absorption
Table 4 (see TABLE 4. Mean iron intake and absorption from diets that are consumed by people of various socio-economic strata in Venezuela) shows the iron absorption from the two types of diets. Moderate iron deficiency was identified in subjects with normal plasma levels of percentage of transferrin saturation and ferritin concentration who absorbed 35% iron or greater from the reference dose; overt iron deficiency was observed in those with either 16% or less of transferrin saturation or 12 mg/L or less ferritin concentration, with or without anaemia.
TABLE 4. Mean iron intake and absorption from diets that are consumed by people of various socio-economic strata in Venezuela
Type of diet (socio-economic stratum) |
Iron status of subjects tested |
Number of subjects |
Non-haem and haem iron absorption (mg) |
|||
Breakfast |
Principal meal |
Second meal |
Total |
|||
1. Low | A Normal | 44 | 0.06 | 0.47 | .22 | 0.75 |
B Moderate deficiency | 17 | 0.13 | 0.85 | 0.31 | 1.29 | |
C Overt deficiency | 22 | 0.18 | 0.96 | 0.37 | 1.51 | |
2. Middle and high | D Normal | 9 | 0.08 | 0.88 | 0.24 | 1 2 |
E Moderate deficiency | 7 | 0.16 | 1.51 | 0.42 | 2.9 | |
F Overt deficiency | 5 | 0.16 | 1.67 | .38 | 2.21 |
There was no significant difference in iron absorption at breakfast between the diets in healthy persons and those with iron deficiency. Iron absorption from the main meal represented 62% and 73% of the total iron absorbed by healthy subjects in diets of type I and type 2, respectively, and 66% and 73% in those with moderate deficiency. Iron absorption from the main meal of type-1 diets was significantly lower than that observed with type-2 diets in both groups. No significant difference was noted in the absorption between subjects with moderate and overt deficiency in the same diet. The iron absorption from the two types of diets from the second meal was not significantly different in healthy individuals and subjects with iron deficiency.
The number of subjects tested for type-2 diets was rather small for the two categories; the individual results were so similar regarding the iron absorption from the same meal, however, that they can be taken as representative of each category.
The total iron absorption from type-1 diets in healthy subjects was so low (0.75 ma) that it did not meet the physiologic iron requirement in the population who were not vulnerable to iron deficiency, such as adult men (0.91.-1.0 mg per day) [21]. This value increased to 72% more in persons with moderate iron deficiency.
Total iron absorption from type-2 diets in healthy subjects was about 50% higher than that from type- 1 diets. It increased to over 2 mg/day in moderate deficiency, covering the physiologic iron requirements of all segments of the population with the exception of women with hypermenorrhagia.
Iron metabolic balance vs prevalence of iron deficiency
Table 5 (see TABLE 5. Iron metabolic balance of persons in the low socio-economic stratum) shows the iron metabolic balance of people in the low socio-economic stratum according to age and sex. The physiologic iron requirements are taken from a previous publication [21]. The data on prevalence of iron deficiency are different from those in previous publications for the age groups 1 to 16 years due to the change of cut-off of the indicators for serum transferring saturation and ferritin [21]. Estimation of the mean iron absorption from diets in healthy subjects according to age and sex was calculated from the nutritional survey of Proyecto Venezuela. Children of ages 2 to 3 years ingested an average of 40% of the calories consumed by adults, whereas 70% of children of ages 4 to 7 years, 80% of those of ages 8 to 10 years, and those older than 11 and adolescents ingested the same amount as adults. Adolescents from the middle and high socio-economic strata consumed 10% more calories than adults.
TABLE 5. Iron metabolic balance of persons in the low socio-economic stratum
Age (years) and sex |
Physiologic iron requirements |
Iron metabolic balance (%) |
Prevalence ofi ron deficiency (%) |
||||
50th percentile |
95th percentile |
Normal iron status status |
Moderateiron deficiency |
Anaemia |
Erithropoietic+ stores deficiency |
||
2-3 | M, F | 0.52 | 0.65 | -42 | -20 | 9 | 29 |
4-7 | M | 0.63 | 0.78 | -17 | +15 | 2 | 13 |
F | 0.59 | 0.73 | - 12 | +24 | 8 | ||
8-10 | M | 0.75 | 0.94 | -20 | +10 | 3 | 15 |
F | 0.80 | 1.00 | -25 | +3 | 12 | ||
11- 13 | M | 1.10 | 1.37 | -32 | 6 | 5 | 10 |
F | 1.31 | 1.63 | -43 | -21 | 3 | 11 | |
14-16 | M | 1.52 | 1.89 | -51 | -32 | 1 | 10 |
F | 1.34 | 1.67 | -44 | - 22 | 6 | 22 | |
17-19 | M | 1.03 | 1.28 | 28 | 0 | 1 | 15 |
F | 1.23 | 1.58 | -39 | - 18 | 4 | 26 | |
Adult | M | 0.91 | 1.14 | - 18 | + 13 | 0 | 5 |
F | 1.21 | 2.43 | -38 | -47 | 5 | 23 |
The nutritionists in charge of the survey emphasized the difficulties in obtaining adequate data of the diets of adolescents due to their frequent ingestion of food between meals. The data on iron metabolic balance should be taken as approximations because of the extrapolation of the diets eaten by adults to children, according to calories consumed, especially for children below 7 years of age, in whose diet composition could be different.
The iron metabolic balance in the low socioeconomic stratum was calculated by the formula (x-y)/y, where x represents the mean iron absorption from diets in healthy subjects and y represents the 50th percentile of physiologic iron requirements. Negative iron balance was present in all groups based on age and sex, being most marked in children 2 to 3 years of age, adolescents, and adult females. These groups also showed the highest prevalence of iron deficiency with and without anaemia. The high negative iron balance in males 11 to 16 years old did not match with the relatively low prevalence of iron deficiency.
It is possible that these groups consumed more foods than those registered in the survey.
The iron metabolic balance obtained by comparing the mean iron absorption from diets in persons with moderate iron deficiency and the 95th percentile of physiologic iron requirements showed positive balance in the subjects less vulnerable to iron deficiency, that is, children between 4 and 10 years of age. and adolescent and adult males. The negative balance was less marked in the vulnerable groups. These results suggest that the increased iron absorption from these diets in persons with moderate and overt iron deficiency prevents the development of anaemia in most cases.
Table 6 (see TABLE 6. Iron metabolic balance in middle and high socio-economic strata) shows the iron metabolic balance in middle and high socio-economic strata of the Venezuelan population. Despite the increased physiologic iron requirement, the high iron bioavailability of the diets showed positive iron balance in some age groups when the mean absorption in healthy subjects and the 50th percentile of physiologic requirements were compared. Positive iron balance in all groups was found when comparing the mean absorption from diets in moderate iron deficiency and the 95th percentile of physiologic requirements. This result is confirmed by the reduction of the prevalence of iron deficiency with and without anaemia in all groups. The exception is the group of adult females, due to the higher iron requirements of those with hypermenorrhagia.
TABLE 6. Iron metabolic balance in middle and high socio-economic strata
Age (years) and sex |
Physiologic iron requirements |
Iron metabolic balance (%) |
Prevalence ofi ron deficiency (%) |
||||
50th percentile |
95th percentile |
Normal iron status status |
Moderateiron deficiency |
Anaemia |
Erithropoietic+ stores deficiency |
||
2-3 | M, F | 0.52 | 0.65 | - 8 | +28 | 8 | 18 |
4-7 | M | 0.74 | 0.92 | + 14 | +59 | 2 | 8 |
F | 0.74 | 0.92 | + 14 | +59 | 4 | ||
8-10 | M | 0.92 | 1.15 | + 14 | +45 | 3 | 8 |
F | 0.98 | 1.10 | -2 | +52 | 10 | ||
11-13 | M | 1.27 | 1.57 | -.7 | +33 | 2 | 4 |
F | 1.44 | 1.80 | - 17 | + 16 | 2 | 17 | |
14- 16 | M | 1.82 | 2.27 | -27 | + 1 | 1 | 13 |
F | 1.44 | 1.80 | -.7 | +27 | 6 | 26 | |
17-19 | M | 1.19 | 1.44 | + 10 | +59 | 0 | 10 |
F | 1.25 | 1.56 | +6 | +46 | 2 | 13 | |
Adult | M | 0.97 | 1.22 | +23 | +71 | NT | NT |
F | 1.22 | 2.43 | +2 | - 14 | NT | NT |
Iron absorption studies have detected an early stage of iron deficiency in which the non-invasive indicators are within normal limits in the subjects tested but the iron absorption from a reference dose of 3 mg iron as ferrous sulfate is increased about 35% and the nonhaem iron absorption from either a single food or a meal is approximately twice the absorption observed in healthy subjects [22, 40]. This phenomenon is not due to the physiologic daily variations in iron absorption, since it was observed in several absorption tests performed on several days in the same individuals.
These findings have been reported by several authors who showed the iron absorption from each individual participating in the study [41-45]. Hallberg called this finding "border-line iron deficiency" and used the term to define the bioavailable nutrition density, and also to extrapolate from the iron absorbed from meals to that absorbed when the absorption of the reference dose is 40% [12, 14, 46, 47]. This latter practice has been followed by other authors [48, 49].
The results presented here on iron absorption in persons with moderate iron deficiency suggest that this stage marks suppression of the regulation mechanisms of non-haem iron absorption to such an extent that the stages of increased severity of iron deficiency do not significantly change the pattern of iron absorption. It seems to be a transitory stage that changes rapidly to overt iron deficiency. This is possibly the reason why a prevalence of iron deficiency of 10% to 20% was observed in subjects who consumed a high-bioavailability diet and had moderate iron deficiency, despite the fact that positive metabolic iron balance was found in all age groups.
It has been suggested that the typical diets consumed in various regions of the world could be divided into three categories of low, intermediate, and high bioavailability, with the average absorption from a mixture of haem and non-haem iron of approximately 5%, 10%, and 15%, respectively, in individuals with no iron stores but normal iron transport [50]. The information presented here could be used to complement the definition of the bioavailability of these diets influenced by the content of inhibitors and enhancers of iron absorption, especially in the main meal, which accounts for more than 60% of the iron absorbed from the total diets.
Low-bioavailability diets are monotonous, consisting mainly of cereals, legumes, and tubers. In the main meal, the phytate content is high in relation to the iron content, and meat and ascorbic acid are usually below 50 g and 30 ma, respectively (see TABLE 7. Categories of diets according to the amount of iron-absorption inhibitors and the amount and quality of iron-absorption enhancers). In moderately iron deficient persons, the non-haem iron absorption is about 4% from the main meal, and haem and non-haem iron absorption from the total diet is less than 1 mg of iron. The low absorption from these diets explains the high prevalence of iron-deficiency anaemia in subjects of all ages, including adult men. The total iron content of the diet could be high ( > 15 mg), but part of it represents iron contamination.
TABLE 7. Categories of diets according to the amount of iron-absorption inhibitors and the amount and quality of iron-absorption enhancers
Diets according to iron bioavailability |
Main meal content |
Iron absorption in moderate iron deficiency |
||||
Phytates (mg) |
Polyphenolsa |
Meat (g) |
Ascorbic acid (mg) |
Non-haemmain meal |
Non-haem ±haem in total diet ( mg) |
|
Low | > 400 | > 500 | < 50 | < 30 | 4 | < 1 |
Intermediate | > 400 | Variable | 50-100 | 30-50 | 8 | 1.0-1.7 |
High | < 400 | Variable | > 100 | > 50 | 15 | > 1.8 |
Intermediate-bioavailability diets consist also of cereals, legumes, and tubers. In the main meal, the amount of phytate is usually high ( > 400 mg). but the intake of meat is more than 50 g and ascorbic acid usually above 30 ma. In persons with moderate iron deficiency, the non-haem iron absorption is about 8"/o in the main meal, and the haem and non-haem iron absorption from the total diet is between 1.0 and 1.7 ma. The prevalence of iron-deficiency anaemia is restricted mainly to the segments of the population vulnerable to iron deficiency, such as children below 3 years of age and menstruating women.
High-bioavailability diets are more diversified, containing a generous quantity of meat, and some vegetable foods with high ascorbic acid content and usually a small amount of phytate. The main meal usually contains more than 100 g of meat and more than 50 mg of ascorbic acid. In individuals with moderate iron deficiency, non-haem iron absorption is about 15% in the main meal, and the haem and non-haem iron absorption from the total diets is more than 1.8 mg of iron. ]Iron-deficiency anaemia is limited and less prevalent, even in children below 3 years of age and women with hypermenorrhagia.
The limited publications on iron absorption from complete diets do not provide many examples in each category of the diets described above. The typical diets consumed by low socio-economic populations of several countries in Asia and Africa could be classified in the first category, which explains the high prevalence of iron-deficiency anaemia; however, only iron absorption data from single meals have been published [8-18, 14].
Among the South American diets tested for iron absorption, that consumed by the poorest population of São Paulo, Brazil, can be placed in this category [15]. Although the main meal contained 53 g of beef, the amount of ascorbic acid was negligible. In iron deficient subjects tested, non-haem iron absorption was 4.1% from the main meal and 0.96 mg from the total diet. From the data available, the prevalence of nutritional anaemia in the municipality of São Paulo is about 40% in children between 6 and 60 months of age [51]
The five Venezuelan diets consumed by the low socio-economic population can be placed in the intermediate-bioavailability category, as can the diet consumed by the lower middle and low socioeconomic groups in the city of Santiago, Chile [15].
The diets presented in this article consumed by persons in the middle and high socio-economic strata of Caracas are among the high-bioavailability diets. According to the bioavailability of breakfast and other meals consumed by populations from industrialized countries, it is probable that most of their diets can be placed in this category [12, 13]. The descriptions of the three categories of diet suggest the importance of the amount of each of the principal inhibitors and enhancers for the iron absorption present in the meals of a given diet, especially the main meal.
The data presented here represent an effort to interpret the prevalence of iron deficiency and iron-deficiency anaemia as functions of the dietary iron absorption as well as the physiologic iron requirements in various socioeconomic strata of a given population. This was used to identify the principal categories of iron bioavailability in the diets consumed by a given population and their effect on the prevalence of iron deficiency. These preliminary results should be enhanced by future studies of iron absorption from diets consumed by other populations in relation to their prevalence of iron deficiency.