Evaluation On The Iron And Zinc Absorptions For The Typical Diets Of Yi And Tibetan Men And The Dietary Factors

1. PrefaceIron (Fe) and zinc (Zn) are two of the necessary micro-elements for the human body, and play important roles in the process of keeping health and preventing diseases. But the present global nutritional situation of Fe and Zn are rarely week. According to the newest report from the World Health Organization (WHO), both the global incidences of Fe and Zn deficiency are over 30%. As one of the basic way to promote the Fe and Zn nutrition status, the making and improving of the Dietary Reference Intakes (DRIs) are of great importance, which are based on the evaluation on the nutrient bioavailability and analyses of dietary components.Up to date, there are few researches on the Fe and Zn nutrition status in China, no less to say the bioavailability. For the minorities with large populationliving in the area of lower economic level, there are even no studies of their nutrient bioavailability. Faced with the serious and emergent situation, it is badly needed to carry out the related studies. In the meanwhile, with introduction and popularization of advanced techniques like the stable isotopic tracer and mass spectrometry, the more accurate and safer evaluation on the human bioavailability of Fe and Zn are getting in to practice.The present study reported the dietary Fe and Zn absorptions and dietary factors in the typical diets for Yi and Tibetan men, which was part of the key project sponsored by the National Natural Science Foundation of China. .In the study, the stable isotopic tracers of Fe and Zn were administrated followed by the fecal monitoring (FM).2. Experimental studies on the analyses of IR for Fe and Zn and spectrum for Dy and Yb with ORS-ICP-MS2.1. Objects:(1) To establish the stable and reliable methods to detect the isotopic ratio (IR) of Fe and Zn using the inductively coupled plasma spectrometer equipped with the collision/reaction cell octopole reaction system (ORS-ICP-MS).(2) Evaluation on the determination quality of dysprosium (Dy) and ytterbium (Yb) with ORS-ICP-MS.2.2. Methods:Considering the concentrations of Fe and Zn in the biological sample solutions collected and prepared from the human trial, the single element standards, mixed elements standards and biological sample solutions with the 10~100μg/L Fe and Zn were used to explore the optimum working condition to analyze the IR of Fe and Zn spikes. Before the IR analysis, tuning parameters was optimized, and He gas was used to reduce the interferences of the polyatomic ions formed by H, O, Ca, Ar, etc. and of the unknown factors in the matrix. In order to avoid isobaric interference, 56Fe and to 68Zn were chosen as the reference isotopes since the isotopic tracers for Fe and Zn were spiked with 57Fe and 67Zn respectively. By choosing the appropriate correction equation, the influences of mass discrimination and dead time were automatically corrected in the ChemStation (Rev. B.02.01.2003) work station for the ICP-MS.The determination of Dy and Yb was conducted simultaneously under the H2 interference-reduction mode of ORS-ICP-MS, and the accuracy, precise and linear regression of the method was evaluated.2.3. Results:(1) Using the He mode of ORS-ICP-MS, the RSD of IR analyses of 57Fe/56Fe and 67Zn/68Zn was less than 0.5%, and the deviation of IR (5) was less than 15 %o. The linear regressions of detected and theoretic IR for Fe and Zn were respectively as follows:Detected IR (X) = 1.98×10-4+0.99944×Theoretic IR, r2 = 0.99999; Detected IR (X) = 8.28×10-7+1.00029×Theoretic IR, r2 = 1.00000.(2) Using the H2 mode of ORS-ICP-MS, the RSD of Dy and Yb determination was less than 5%, and standard recovery was more than 85%. The linear regressions of count per second (cps) ratio and concentration for the Dy and Yb were respectively as follows: Cps ratio = 9.196×10-3Conc.+1.181×10-2, r = 0.9998; Cps ratio = 8.940×10-3Conc.+8.912×10-3, r = 0.99982.4. Conclusion:The methods of IR analysis for 57Fe/ 56Fe and 67Zn/ 68Zn, and Dy, Yb determination with ORS-ICP-MS were feasible and reliable to analyze the fecal sample solutions.3. Evaluation on the Fe and Zn absorptions for the Yi and Tibetan men with stable isotopic tracers3.1. Objectives:(1) Evaluate the dietary Fe and Zn absorptions in the typical diets for Yi and Tibetan men with the Fe and Zn stable isotopic tracers;(2) Analyze the stable isotopic tracers and rare earth elements (REEs) Dy and Yb;(3) Compare the absorptions evaluated by fecal monitoring and mass balance.3.2. Methods:Typical diets for Y\ and Tibetan men were designed based on the data from3-day field dietary surveys on the Yi and Tibetan adults. 10 Yi subjects and 11 subjects recruited from two schools in the Yi and Tibetan autonomy areas respectively, and were apparently healthy having no history of gastrointestinal dysfunction. Fasted at least for 12hrs, they were orally administrated 3.0mg Fe tracer with 57Fe enriched and Dy (1.2mg for the Yi and 2.0mg for the Tibetan) in each meal for 2 days, and with the last meal of Fe tracer administration, 4.0mg Zn tracer with 67Zn enriched for both groups and 1.0mg Yb for the Tibetan were orally administrated. The samples of diet, fecal and urine in the basal status (before the tracer intakes) were collected for one day. And then, fecal monitoring and sample collections lasted for 9 days once upon the tracer intakes.Fecal samples were thoroughly digested by HNO3-H2O2 in the microwave system. IR of 57Fe/56Fe, 67Zn/68Zn and REEs were determined with ORS-ICP-MS. The total Fe and Zn concentrations were determined with the optical emission spectrometry. The Fe and Zn absorptions were calculated with the isotope dilution technique.The absorptions for Fe and Zn with mass balance were previously described by our research team. And the data of mass balance were cited to compare with fecal monitoring.3.3. Results:(1) After he 9-day fecal monitoring, the recovery of REEs were over 95%. The Fe absorptions for Yi and Tibetan men were respectively 6.5% and12.6% before the REEs recovery corrections, 6.8% and 13.0% respectively corrected by REEs recovery. The Zn absorptions for Yi and Tibetan men were respectively 18.2% and 21.0% before the REEs recovery corrections, 19.5% and 21.4% respectively corrected by REEs recovery.(2) Good linear regression was observed for the excretions of isotopic tracer and REEs.(3) Evaluated by mass balance, the Fe absorptions for Yi and Tibetan men were 15.6% and 28.3% respectively; while the Zn absorptions were 23.7% and 23.8% respectively.3.4. Conclusion:The REEs and stable isotopic tracers had the similar gastrointestinal transit process. The recovery of REEs can be used to correct the completeness of fecal sample collections. The Fe absorption for the Tibetan men was higher than that of the Yi men, while there was no significant difference for the Zn absorption between them. The results evaluated by MB and FM had significant correlation, and result of the former was higher than that of the later. The MB method was prone overestimate the Fe and Zn absorption for the systematic bias, especially for Fe.4. Analyses on the dietary factors related to Fe and Zn absorptions4.1. Objectives:Determine the intakes of dietary factors that had/might have effects on the Fe and Zn absorptions. And analyze their correlation.4.2. Methods:(1) Dietary protein was detected with the Kjeltec system (GB 5009.5-1985);(2) Dietary fat was detected with Soxhlet extraction (GB 5009.6-1985);(3) Vitamin C was detected with 2,4- dinitrophenylhydrazine (GB/T 5009.86 -2003)(4) Phytic acid was detected with ion-exchange chromatography (GB/T 5009.153-2003)(5) Dietary fiber was detected with enzymatic-gravimetric method (adapted from AOAC 985.29)(6) Calcium, iron and zinc were detected with atomic absorption spectrometry (GB/T 5009.92-2003, GB/T 5009.90-2003 and GB/T 5009.14-2003 respectively)4.3. Results:The daily intakes of some dietary components for the Yi men were 71.7g protein, 59.7g fat, 799.2mg phytic acid, 85.4mg Vitamin C, 287.5mg Ca, 23.6mg Fe, and 15.4mg Zn. These intakes for the Tibetan men were 95.2g protein, 82.3g fat, 342.0mg phytic acid, 28.3mg Vitamin C, 244.5mg Ca, 62.6mg Fe, and 23.4mg Zn. Statistic differences were presented between the two populations for each dietary factor above. The daily intake of dietary fiber for the Tibetan men was 23.4mg. The Fe absorption was reversely related with statistic significance to each one of the dietary phytic acid, Ca, Fe,and Zn. No other factors had statistic correlation to the Fe absorption or Zn absorption.4.4. Conclusion:(1) Both the Yi and Tibetan dietary patterns had their own characteristics, with imbalanced nutrient composition compared with the Chinese DRIs.(2) With comparison to those of Yi men, the higher intakes of dietary protein and heme iron of Tibetan men, in addition to the living condition of higher altitude, may improve the Fe absorption. And for Yi men, the high intake of phytic acid may contribute to the low Fe absorption.(3) Dietary fiber intake at the level of 23.8mg/d for Tibetan men had no significant effect on the Fe or Zn absorption.(4) For both the Yi and Tibetan men, Fe intakes were higher than the Adequate Intakes, Zn intakes were higher than the Recommended Nutrient Intakes, and Ca were about 1/3 of the Adequate Intakes. At the present intakes of Fe, Zn and Ca, they execute negative effect on the Fe absorption, and no effect on the Zn absorption.5. SummaryUsing the advanced techniques of isotopic tracing, isotopic dilution and mass spectrometry, the present study evaluated the dietary iron and zinc absorptions and influencing factors for the male adult of the two Chinese minorities of Yi and Tibetan. The iron absorption for Yi and Tibetan men was 6.8% and13.0% respectively, and the zinc absorption for them was 19.5% and 21.4% respectively.