Lower Non-Heme Iron Absorption in Healthy Females from Single Meals with Texturized Fava Bean Protein Compared to Beef and Cod Protein Meals: Two Single-Blinded Randomized Trials

Meat analogs based on plant protein extracts are rising in popularity as meat consumption declines. A dietary shift away from meat, which has a high iron bioavailability, may have a negative effect on the amount of iron absorbed from the diet. Iron absorption from legumes cultivated in regions not suitable for soy production, such as fava bean, has not yet been explored. The aim of this study was to evaluate non-heme iron absorption from a meal with texturized fava bean protein compared to beef and cod protein meals. The study included two single-blinded iron isotope trials in healthy Swedish women of the ages 18–45 years, each of whom served as their own control. The participants were served matched test meals containing beef and fava bean protein (Study 1) or cod and fava bean protein (Study 2) with radiolabeled non-heme iron ⁵⁵Fe and ⁵⁹Fe. The absorption of non-heme iron from test meals was measured by whole-body counting and erythrocyte incorporation. The absorption of non-heme iron, measured as erythrocyte incorporation ratio, from beef protein meal was 4.2 times higher compared to texturized fava bean meal, and absorption from cod protein meal was 2.7 times higher compared to the fava bean meal. The adjusted non-heme iron absorption, normalized to a 40% reference dose uptake, was 9.2% for cod protein meal, 21.7% for beef protein meal, and 4.2% for texturized fava bean meal. A fava bean protein meal has markedly lower iron bioavailability in healthy females compared with a meal of beef or cod protein. Therefore, a dietary shift from meat and fish protein to fava bean protein may increase the risk of iron deficiency.     

12～14岁男童体内强化去植酸豆粉中钙铁锌的吸收利用率研究

目的　为了解我国少年儿童对豆粉、去植酸豆粉和牛奶中钙、铁、锌的吸收利用率 ,通过普及饮用豆粉 ,改善我国居民蛋白质和矿物质的营养状况提供理论依据。方法　选择 57名 1 2～ 1 4岁男童 ,按年龄、身高、体重和血红蛋白含量匹配 ,分成 3组 ,分别给予强化豆粉、强化去植酸豆粉和强化牛奶 2 2 0ml,其中含钙 2 70mg、铁 4mg、锌 4mg。给予受试者用稳定性核素4 4Ca、58Fe和70 Zn标记的受试物 ,以亮蓝和镝标记粪便 ,收集粪便样品 ,测量强化去植酸豆粉、豆粉和强化牛奶中钙、铁、锌的吸收率 ;使用热离子化质谱法测定粪便中4 4Ca含量 ;应用感应耦合等离子质谱法测定粪便中58Fe和70 Zn的丰度及镝的含量 ,计算铁、锌的表观吸收率 ,并以镝的回收率进行校正。结果　豆粉组、牛奶组和去植酸豆粉组的铁吸收率分别为 (6 7± 3 8) %、(1 5 5± 9 2 ) %和 (2 0 6± 7 3) % ,钙吸收率分别为 (43 5±1 0 7) %、(64 2± 1 1 4) %和 (50 9± 6 6) % ,锌吸收率分别为 (1 1 3± 6 5) %、(31 2± 1 0 4) %和 (2 0 1±7 4) %。强化豆粉经去除植酸处理后 ,钙、铁、锌的吸收率显著高于未去植酸的豆粉 ;牛奶中钙和锌的吸收率高于去植酸强化豆粉 ;经去除植酸处理后的豆粉中铁吸收率高于牛奶 ,但差异无显著性。我国儿童由于     

Effect of protein level and protein source on zinc absorption in humans

The effect of increasing levels of various protein sources on zinc absorption from a legume-based meal was studied in humans with the use of a radionuclide technique. The meals were extrinsically labelled with 65Zn and absorption was determined from measurements of the whole-body retention of the isotope. The mean fractional zinc absorption for the 13 meals was 24.7 +/- 6.9% and was only influenced by the protein content of the meal to a limited extent (r = 0.45). However, the amount of zinc absorbed from the meals was strongly correlated with both the protein (r = 0.85) and zinc content (r = 0.86): 5.9 +/- 1.7 mumol of zinc was absorbed from the basal bean meal which had the lowest protein content; the addition of low zinc chicken doubled the protein content and increased zinc absorption to 10.3 +/- 2.0 mumol; the addition of zinc-rich beef also doubled the protein content, however, zinc absorption was increased to 15.9 +/- 4.7 mumol. It is concluded that the zinc content of the main protein source of the diet determines the amount of zinc absorbed to a large extent. However, relatively small amounts of animal protein can significantly improve the value of a legume-based meal as a source of zinc.     

Cofortification of iron-fortified flour with zinc sulfate,but not zinc oxide,decreases iron absorption in Indonesian children

BACKGROUND: Iron deficiency is a major nutritional concern in developing countries, and food fortification is a common strategy to treat it. In Indonesia wheat flour is fortified with 60 mg Fe/kg, but because of increasing concerns about marginal zinc status in at-risk populations, consideration is being given to cofortifying flour with zinc. However, little is known about the effect of zinc fortification of flour on iron bioavailability or about the optimum form of zinc supplementation. OBJECTIVE: We measured iron and zinc bioavailability from wheat-flour dumplings containing 25 g flour fortified with 60 mg Fe/kg, either alone or with 60 mg Zn/kg as zinc oxide or as zinc sulfate. DESIGN: Ninety children aged 4-8 y were recruited and assigned randomly to the 3 groups; 86 completed the study. Iron and zinc absorption were measured with established stable-isotope methods. RESULTS: Iron absorption from the flour fortified with iron only was good (15.9 +/- 6.8%), but when corrections were made for hemoglobin concentrations, it was significantly lower from the flour cofortified with zinc sulfate (11.5 +/- 4.9%; P < 0.05) but not from the flour cofortified with zinc oxide (14.0 +/- 8.9%). Zinc absorption was not significantly different between the zinc oxide and zinc sulfate cofortified flours (24.1 +/- 8.2% compared with 23.7 +/- 11.2%; P = 0.87). CONCLUSIONS: Iron and zinc appear to be highly bioavailable from foods made from fortified flour, but zinc sulfate cofortification may have a detrimental effect on iron absorption.     

Bioavailability of iron in ground beef and plant protein concentrates

Weanling male Wistar rats were fed a low iron basal diet for 4 weeks. They were then divided into 16 groups according to a randomized block design based on hemoglobin level. During the repletion period of 2 weeks, one group was fed the basal diet. The other fifteen groups received ferrous sulphate, freeze-dried ground beef, ground granular soy product, a 2:1 mixture of beef and the soy product, or rapeseed protein concentrate as iron sources at three levels. All diets were isocaloric and isonitrogenous. The efficiency of iron utilization was calculated on the basis of iron gained in hemoglobin and iron consumed, applying appropriate correction for iron obtained from the ingredients of the basal diet. The relative biological value (RBV) of iron in the test source was calculated as the ratio between the efficiency for the test and the standard source (ferrous sulphate). The RBVs were: freeze-dried ground beef, 0.53; ground soy product, 0.62; 2:1 mixture of beef and soy product, 0.71; rapeseed protein concentrate, 0.55. The low availability of iron in beef containing 60% heme iron indicated that the anemic rat is not a suitable model for normal man, since the absorption of heme iron by man is much higher than that of inorganic or non-heme iron.     

铁强化中国酱油的研究——Ⅱ、铁强化酱油的人体铁吸收试验

31名健康成年自愿者,男11名,年龄18—48岁,女20名,年龄34—52岁 (均系采取节育措施的育龄妇女),用同位素~(55)Fe和~(59)Fe外标食物,分两批作人体铁吸收试验。其结果为:上海生产出口的海鸥牌瓶装酱油,原有铁(15.8mg铁/100ml)的吸收率几何均数(下同)为6.95％,酱油强化铁量为121mg铁/100ml时的铁吸收率为4.36％,该种铁强化酱油再强化维生素C(按铁:维生素C=1:2克分子量)则铁的吸收率为8.25％,几乎增加一倍。以7.5ml(一餐用量)的铁强化酱油(75mg铁/100ml)含铁量为5.6mg进行烹调蔬菜,以大米为主食,该餐中总铁量为8.9mg,铁的吸收率为5.65％,铁的吸收量为0.5mg;该餐另加瘦猪肉100g,则铁的吸收率为9.69％,铁的吸收量为1.08mg,肉能促进铁吸收一倍;但在该蔬菜餐后饮用龙井绿茶150ml(1.5g干茶叶泡成)其铁的吸收率降至3.09％,铁的吸收量为0.27mg,降低近一半。因此,应用加铁量为75mg铁/100ml的铁强化酱油,如按每人每天平均酱油的消耗量为15—20ml铁吸收率为5.65％计算,则铁的吸收量为0.63—0.85mg,可以基本满足一般人群每天对铁的需要量要求。如该种铁强化酱油同时强化维生素C,以铁吸收率增加一倍计算,则可满足孕妇、乳母、月经过多妇女及正在生长发育的儿童青少年对铁的特殊需要。     

Caco-2 cells can be used to assess human iron bioavailability from a semipurified meal

A Caco-2 cell model with extrinsic radioiron was used to evaluate the effect of dietary factors on nonheme iron bioavailability from a semipurified meal. Study 1 was conducted to evaluate the effect of enhancers (ascorbic acid) and inhibitors (bran, phytate and tea) on iron bioavailability when added to semipurified meal containing egg albumen as a protein source. The effect of various proteins [bovine serum albumin (BSA), casein, beef and soy] on iron bioavailability was evaluated in Study 2 by substituting the above protein sources for egg albumen. Protein solubilization following in vitro digestion for individual test meals was not significantly different from the control. On the other hand, nonheme iron solubilization (0.8+/-0.0 to 5.9+/-0.3 vs. 4.9+/-0.8 mg/L) varied significantly. The total iron uptake for each meal was calculated based on the percentage of radioiron taken up and transported by Caco-2 cells and the amount of nonheme iron present in uptake solutions. Iron uptake ratios represent test/control values. With the exception of BSA and ascorbic acid, the effect of dietary factors was similar to that found in humans reported in the literature. A significant correlation (r = 0.97; P<0.0001) was found between the published human absorption data and the iron uptake by the Caco-2 cells. The results of our study indicate the usefulness of Caco-2 cells in assessing human iron absorption and the feasibility of this cell model in studying iron bioavailability from various food combinations, otherwise not easily performed in humans.     

Iron absorption is more closely related to iron status than to daily iron intake in 12- to 48-mo-old children

Few studies have evaluated iron absorption in small children after the first year of life. Our objectives were to examine the relations among iron intake, iron absorption, and iron status in a group of healthy children. We studied 28 children, ages 12 to 48 mo, after a 7-d home adaptation to a diet representative of their usual daily mineral intake. A multi-tracer stable isotope study was performed to assess iron absorption both from a meal ((58)Fe) and from a reference iron dose ((57)Fe) given with ascorbic acid without a meal. Iron intake was 6.9 +/- 2.4 mg, approximately the 35th percentile of typical U.S. intakes. Absorption of (58)Fe was related to serum ferritin (r(2) = 0.319, P = 0.0018) and more so to reference dose iron absorption (r(2) = 0.653, P < 0.0001). Iron absorption was negatively correlated with zinc intake (r(2) = 0.090, P = 0.0049) but was not correlated with iron intake (P = 0.20). However, zinc intake was not correlated with measures of iron status, including reference dose iron absorption and serum ferritin (r(2) < 0.1, P > 0.25). Total absorbed iron was similar to needs estimated by the Institute of Medicine. We conclude that iron absorption in young children is more closely related to iron status than to iron intake. Reference dose iron absorption may be superior to serum ferritin as a surrogate measure for iron status in this age group. Although zinc intake may affect iron absorption from a meal, it does not appear to have a detectable effect on overall iron status in otherwise well-nourished children.     

Iron absorption from soybean ferritin in nonanemic women

BACKGROUND: Dietary ferritin, a protein cage around an iron mineral, is an underestimated source of bioavailable iron. Plant ferritin, the most common dietary ferritin, has not been studied. Iron from animal ferritin is absorbed as well as is iron from FeSO4 in women. OBJECTIVE: The objective was to examine iron absorption from purified soybean ferritin. DESIGN: Healthy, nonanemic women (n = 16) were fed a standardized meal (bagel, cream cheese, and apple juice) containing 1 microCi 59Fe/meal as FeSO4 or (extrinsically labeled) as iron-free soybean ferritin reconstituted with the high phosphate characteristic of plant ferritin (iron:phosphorus = 4:1). Iron-free, apo-soybean ferritin was prepared (with the use of thioglycolic acid and extensive dialysis) from purified ferritin. In a randomized crossover design, the other labeled meal, which contained FeSO4 or ferritin, was given after 4 wk. The subjects received 140 microg Fe as ferritin (2.5 mg) or as FeSO4. After 28 d, whole-body 59Fe and 59Fe in red blood cells were measured before and after dosing. RESULTS: There was no significant difference in whole-body iron absorption from soybean ferritin (29.9 +/- 19.8%) and that from FeSO4 (34.3 +/- 23.6%) or in iron absorption calculated from red blood cell incorporation (33.0 +/- 20.1% for soybean ferritin and 35.3 +/- 23.4% for FeSO4), which confirmed previous results with animal ferritin that was mineralized and labeled similarly. An inverse relation was observed between serum ferritin and iron absorption from both ferritin and FeSO4, which suggested that sensors regulating iron absorption respond similarly to iron provided as ferrous salts or as ferritin mineral. CONCLUSION: Iron from soybean ferritin is well absorbed and may provide a model for novel, utilizable, plant-based forms of iron for populations with a low iron status.     

Helicobacter pylori infection, iron absorption, and gastric acid secretion in Bangladeshi children

BACKGROUND: Nonheme-iron absorption requires an acidic milieu. Reduced gastric acid output as a consequence of Helicobacter pylori infection could be an important limiting factor for iron absorption. OBJECTIVE: We measured gastric acid output and iron absorption from a non-water-soluble iron compound (ferrous fumarate) and a water-soluble iron compound (ferrous sulfate) in children with and without H. pylori infection. DESIGN: Gastric acid output was quantified before (basal acid output, or BAO) and after pentagastrin stimulation (stimulated acid output, or SAO) in 2-5-y-old children with iron deficiency anemia who were (n = 13) or were not (n = 12) infected with H. pylori. Iron absorption was measured by using a double-stable-isotope technique. H. pylori-infected children were studied before and after eradication therapy. RESULTS: BAO and SAO were significantly lower in the H. pylori-infected children (0.2 +/- 0.2 and 1.6 +/- 0.9 mmol/h, respectively) than in the uninfected children (0.9 +/- 0.7 and 3.1 +/- 0.9 mmol/h, respectively; P = 0.01 and P < 0.005). BAO and SAO improved to 0.8 +/- 1.3 and 3.3 +/- 2.4 mmol/h, respectively, after therapy. Iron absorption from ferrous sulfate was significantly greater than that from ferrous fumarate both before (geometric : 19.7% compared with 5.3%; P < 0.0001) and after (22.5% compared with 6.4%; P < 0.0001) treatment in H. pylori-infected children. Corresponding values for uninfected children were 15.6% and 5.4%, respectively (P < 0.001; n = 12). CONCLUSIONS: Iron absorption from ferrous fumarate was significantly lower than that from ferrous sulfate in both H. pylori-infected and uninfected Bangladeshi children. Treatment of H. pylori infection improved gastric acid output but did not significantly influence iron absorption. The efficacy of ferrous fumarate in iron fortification programs to prevent iron deficiency in young children should be evaluated.     

Absorption of iron from recombinant human lactoferrin in young US women

BACKGROUND: Lactoferrin is a major protein component of human milk, and it binds iron with high affinity. Because the human small intestine has receptors for lactoferrin, a role for it in iron absorption has been suggested. OBJECTIVE: The objective was to study the absorption of iron from extrinsically labeled purified recombinant human lactoferrin produced in rice and to compare it with the absorption of iron from ferrous sulfate. DESIGN: On 2 occasions 4 wk apart, healthy young women (n = 20) were fed a standardized meal supplemented in randomized order with 59Fe as lactoferrin or as ferrous sulfate. Ten subjects received lactoferrin that had been heat-treated, and 10 subjects received untreated lactoferrin. Iron absorption was measured in a whole-body counter after 14 and 28 d and also was measured by red blood cell incorporation after 28 d. RESULTS: The difference in whole-body iron absorption between heat-treated (24.6 +/- 20.8%; n = 10) and untreated (16.2 +/- 4.4%; n = 10) lactoferrin was not significant. The difference in whole-body iron absorption between the groups given lactoferrin (20.4 +/- 15.3%; n = 20) or ferrous sulfate (18.8 +/- 13.2%; n = 20) also was not significant. Serum ferritin and iron absorption were inversely correlated in subjects when they received either lactoferrin or ferrous sulfate, which suggested that iron is absorbed from the 2 sources by a similar mechanism. CONCLUSIONS: Iron is equally well absorbed from lactoferrin (whether heat-treated or untreated) and ferrous sulfate. Thus, iron provided by dietary lactoferrin is likely to be well utilized in human adults.     

Bioavailability in humans of zinc from beef: intrinsic vs extrinsic labels

Beef is a concentrated source of zinc. However, the bioavailability of Zn from beef has not been clearly established. It is also unclear whether there is a difference in absorption between intrinsic and extrinsic Zn. To address these questions, a calf was labeled with 65ZnCl2 and the meat was used as a source of intrinsically labeled beef. Twelve subjects were given a meal containing 100 g beef labeled either intrinsically or extrinsically with 65ZnCl2. Gamma-ray emissions, as determined by whole-body counting, were used to calculate Zn absorption. Absorption values were 20.9 +/- 5.5% from the extrinsic meal and 26.4 +/- 10.6% from the intrinsic meal, a difference that was not statistically significant (p greater than 0.05). Zn absorption was thus much less than the 40% assumed in establishing the 1980 Recommended Dietary Allowance for Zn. These results also indicate that extrinsic labels of Zn are valid markers of zinc absorption in beef.     

Meat protein fractions enhance nonheme iron absorption in humans

The nature of the enhancing effect of muscle tissue on nonheme iron absorption in humans is unclear but thought to be related to muscle proteins. We conducted radioiron absorption studies to compare iron absorption from proteins isolated from beef and chicken muscle with that from freeze-dried beef and chicken muscle and from egg albumin. All meals contained an equivalent amount of protein as part of a semisynthetic liquid formula. Freeze-dried beef and chicken muscle increased iron absorption 180% (P < 0.001) and 100% (P < 0.001), respectively, relative to egg albumin. When added to the meal at an equivalent protein level (15 g), the isolated beef protein and the isolated heme-free beef protein with 94 and 98% protein content, respectively, increased iron absorption to the same extent as the native beef muscle. Similarly, when added to the meal at an equivalent protein level (30 g), isolated chicken muscle protein (94% protein) increased iron absorption similarly to native chicken muscle. Iron absorption from the meal containing the isolated heme-free chicken protein, however, was 120% (P < 0.01) greater than from the meal containing freeze-dried chicken muscle, indicating that a nonprotein component of muscle tissue with iron-binding potential may have been removed or concentrated by the protein extraction and separation procedures. Our results support the hypothesis that the enhancing effect of muscle tissue on iron absorption is mainly protein related but indicate that other factors may also play a role.     

The enhancement of nonheme iron bioavailability by beef protein in the rat

Beef protein was found to enhance the bioavailability of nonheme iron in the rat. Anemic rats were fed diets containing soy protein concentrate or rice bran as the source of nonheme iron with either lactalbumin or distilled water-washed beef, which was heme free. The criteria used to determine the relative biological value (RBV) of iron was the difference between the products of final hemoglobin x final weight and initial hemoglobin x initial weight during the repletion period. Animals fed diets with only lactalbumin as a source of dietary protein and graded levels of FeSO4 (RBV of FeSO4 = 100%) served as controls. The RBV of the endogenous iron in soy protein and rice bran was found to be 91 and 46%, respectively. Substituting washed beef for lactalbumin increased the RBV of soy protein iron to 96% (results not statistically significant) and of rice bran iron to 75% (results significant, P less than or equal to 0.05). These findings demonstrate the "meat factor" effect in the rat for the first time. Two days after completion of the 11-d hemoglobin regeneration period, the apparent absorption of iron was measured during a 60-h balance period. The apparent absorption of iron by rats fed diets containing beef tended to be higher, compared to animals fed diets containing lactalbumin.     

Thiamin and cognitive impairment.

Background: Iron deficiency is a major health problem worldwide, and is associated with diets of low iron bioavailability. Non-heme iron absorption is modulated by dietary constituents, one of which is the so-called “meat factor”, present in meat, fish (oily and lean) and poultry, which is an important enhancer of iron absorption in humans. Food processing also affects iron bioavailability.

Objective: To evaluate the effect of consuming sous vide cooked salmon fish on non-heme iron bioavailability from a bean meal, rich in phytate, in iron-deficient women.

Design: Randomized crossover trial in 21 young women with low iron stores (ferritin < 30 μg/L). Two test meals were extrinsically labelled with stable isotopes of iron (Fe-57 or Fe-58). Iron bioavailability was measured as the incorporation of stable isotopes into erythrocytes 14 d after meals consumption.

Results: The addition of fish to the bean meal significantly increased (p < 0.001) iron absorption. Serum ferritin concentration and iron absorption were inversely correlated for both the bean meal (R² = 0.294, p = 0.011) and the fish and bean meal (R² = 0.401, p = 0.002).

Conclusion: Sous vide cooked salmon fish increases iron absorption from a high phytate bean meal in humans.     

Iron in ferritin or in salts (ferrous sulfate) is equally bioavailable in nonanemic women

BACKGROUND: Recent studies in humans suggest that ferritin iron in soybeans has high bioavailability. However, direct evidence for this is lacking because the soybeans were intrinsically labeled; thus, iron bound to other ligands, such as phytate, was also labeled. OBJECTIVE: The objectives of the study were to evaluate the absorption of iron from extrinsically labeled, purified ferritin (horse spleen) reconstituted with either high-phosphate iron mineral (plant-type) or low-phosphate iron mineral (animal-type) and to compare it with iron absorption from ferrous sulfate. DESIGN: Nonanemic, healthy young women were fed a standard breakfast meal supplemented with (59)Fe-labeled ferritin or ferrous sulfate, in randomized order. Fifteen subjects received ferritin with the low-phosphate iron mineral, and 15 subjects received ferritin with the high-phosphate iron mineral. Iron absorption was measured in a whole-body counter after 14 and 28 d and by red blood cell incorporation after 28 d. RESULTS: There was no significant difference in iron absorption between ferritin and ferrous sulfate: low-phosphate iron mineral ferritin (x +/- SD: 21.4 +/- 14.7%) compared with ferrous sulfate (21.9 +/- 14.6%), or high-phosphate iron mineral ferritin (22.2 +/- 19.2%) compared with ferrous sulfate (16.7 +/- 7.1%). Results obtained by using whole-body retention of iron and red blood cell incorporation differed with the type of iron, which suggests that pathways for iron uptake and utilization differed for the 2 forms. CONCLUSIONS: Iron is equally well absorbed from ferritin and ferrous sulfate independent of the phosphate content of the ferritin iron mineral. Thus, dietary ferritin iron is likely to be a good source of iron.     

Supplemental zinc lowers measures of iron status in young women with low iron reserves

Zinc and iron compete during intestinal absorption, but postabsorptive interactions between these nutrients are less clear. Understanding these interactions is important to determine when supplementation with iron or zinc is proposed. The effect of zinc supplementation (22 mg Zn/d as zinc gluconate) or of iron supplementation (100 mg Fe/d as ferrous sulfate) for 6 wk on iron and zinc metabolism and absorption was evaluated in young women with low iron reserves. Young adult women (ages 20-28 y), nonanemic but with low iron stores (plasma ferritin< 20 microg/L), participated in the 70-d study. The women were divided in two groups (zinc-supplemented, n = 11; iron-supplemented, n = 12). The supplements were taken at bedtime. Iron and zinc biochemical indices and intestinal absorption were measured on d 1 and 56. Radioiron and stable isotopes of zinc were used to measure iron and zinc absorption from a test meal. In the iron-supplemented group, blood hemoglobin, plasma ferritin and the percentage of transferrin saturation increased (P < 0.01). Zinc indices did not change. In the zinc-supplemented group, plasma ferritin and the percentage of transferrin saturation decreased (P < 0.05), whereas the plasma transferrin receptor and erythrocyte zinc protoprophyrin levels increased (P < 0.05). Plasma and urinary zinc also increased (P < 0.01). Iron absorption (%) from the test meal increased (P < 0.01), whereas zinc absorption (%) decreased (P < 0.01) compared with baseline in the Zn-supplemented women. Our results indicate that the use of iron supplements in women with marginal iron status improves iron indices with no effect on zinc status. However, use of a modest zinc supplement improves zinc indices, but also appears to induce a cellular iron deficiency and, possibly, further reduce iron status.     

Soy protein products and heme iron absorption in humans

Dual radioiron tags were used to measure both heme and nonheme iron absorption simultaneously from meat-containing meals in 76 healthy male volunteers. Partial substitution of beef with soy flour reduced the availability of nonheme iron but improved the percentage absorption of heme iron significantly (27 to 59% rise). In contradistinction three other powerful inhibitors of nonheme iron absorption, bran, tea, and desferrioxamine, had no appreciable effect on heme. Ascorbic acid (100 mg and 1000 mg in separate experiments) improved nonheme iron uptake markedly but also failed to alter the assimilation of heme. These studies demonstrate that the deleterious effects on iron nutrition of substituting soy protein for beef are partially offset by improved availability of the remaining heme iron as well as by an increase in the nonheme iron content of the meal.     

Supplementation with zinc between meals has no effect on subsequent iron absorption or on iron status of Chilean women

OBJECTIVE: Studies on the effect of zinc (Zn) supplementation on iron absorption and iron status have shown mixed results. We investigated the effect of daily supplementation with 20 mg of Zn for a period of 2 mo on iron absorption and iron status of Chilean women. METHODS: Forty-four non-anemic, clinically healthy women 35 to 45 y of age were randomly selected to receive daily 20 mg of Zn, as Zn sulfate, or a placebo between meals for a period of 2 mo. Iron and zinc biochemical indicators and iron absorption studies were assessed at baseline and at the end of the study. Iron absorption was measured using the double radioisotopic technique. RESULTS: The geometric mean (range +/- 1 standard deviation) absorption of iron before supplementation between the Zn-supplemented and placebo groups was similar (31.2, 11.2 +/- 86.3, versus 27.4, 14.4 +/- 52.2, respectively, P = 0.97). Absorption increased significantly after the 2-mo supplementation period (P = 0.049), but there were no group-wise differences at the end of the trial (34.4, 17.5 +/- 67.3, versus 39.8, 20.9 +/- 75.8, respectively, P = 0.97). The geometric mean plasma Zn concentrations did not change significantly in either group during the course of the study (P = 0.47). There was no significant effect of Zn supplementation on any of the iron indicators studied. CONCLUSION: Supplementation of 20 mg of Zn between meals for a period of 2 mo had no effect on subsequent iron absorption or iron status of Chilean women.     

A food-group based algorithm to predict non-heme iron absorption

OBJECTIVE: To develop an algorithm to predict the percentage non-heme iron absorption based on the foods contained in a meal (wholemeal cereal, tea, cheese, etc.). Existing algorithms use food constituents (phytate, polyphenols, calcium, etc.), which can be difficult to obtain. DESIGN: A meta-analysis of published studies using erythrocyte incorporation of radio-isotopic iron to measure non-heme iron absorption. METHODS: A database was compiled and foods were categorized into food groups likely to modify non-heme iron absorption. Absorption data were then adjusted to a common iron status and a weighted multiple regression was performed. RESULTS: Data from 53 research papers (3,942 individual meals) were used to produce an algorithm to predict non-heme iron absorption (R(2) =0.22, P < 0.0001). CONCLUSIONS: The percentage non-heme iron absorption can be predicted from information on the types of foods contained in a meal with similar efficacy to that of food-constituent-based algorithms (R(2) = 0.16, P= 0.0001).