Effect Of Phytate Intake On Metabolism Of Calcium, Iron And Zinc For The Adolescents With Calcium Supplements

Objective:To access the phytate intake of the adolescents,analysis the phytate degradation during cooking process and molar ratios ofphytate to calcium,iron and zinc in the diets of rural adolescents.Explore the best molar ratio of phytate to calcium for adolescents with different doses of calcium supplements.analysis the absorption and utilization of iron and zinc when the best ratio of phytate to calcium.Methods:A total of 304 students aged 11～16 years old(154 boys,150 gifts) were selected randomly from a middle school of Huairou District in Beijing.The information on dietary intakes was collected using the 24-hour dietary recall method for 3 consecutive days including 2 work days and 1 rest day by trained interviewers.Calculate the phytate intake according to the content of different food and the degradation in different food after cooking and the molar ratio of phytate to calcium,iron and zinc.40 boys and 40 gifts were selected randomly from the investigated students.They will be divided into four groups respectively according to the calcium supplements.Except for the control group which can only get Calcium from the food.there were three other intervention groups based on a six-month randomized,double-blind,controlled,intervention study for the different calcium intakes, respectively 800mg/d,1100mg/d and 1400mg/d.A 10-day metabolic balance studies was conducted after the calcium intervention to analysis metabolism of calcium,iron and zinc. Compute the molar ratio of phytate to calcium,iron and zinc,tofind out the effect of the molar ratio of phytate to calcium on the absorption rate and retention rate of calcium,iron and zinc.Results:1) the average degradation of phytate after cooking comes to 58.0%. the phytate degradation in various corn-based foods,rise-based foods,wheat-based foods, legume-based foods and freh corn came to 77.3%,72.6%,49.2%,56.4%and 34.7% respectively.The ratios of phytate/calcium,phytate/iron,phytate/zinc,phytate×calcium/zinc were 0.10,2.1,4.4 and 34.9 respectively with no significant difference between boys and gifts(P＞0.05).There were 87.5%(the highest of all the ratios) adolescents whose ratio of phytate/iron was higher than the Standard values(boys 91.6%, gifts 83.3%);12.5%adolescents whose ratio of phytate/ calcium was higher than the Standard values;the phytate/zinc and phytatexcalcium/zinc were 4.0%and 2.0% respectively.2)When the ratio of phytate/calcium reached 0.15～0.20 for boys,the cabsorption rate and retention rate of calcium went to the max;the absorption rate and retention rate of iron was relatively higher but a low level for zinc.When the ratio of phytate/calcium reached 0.10～0.15 for girls,the cabsorption rate of calcium went to the max but the minimum for retention rate;the absorption rate and retention rate of iron was relatively higher but a lower level for zinc too.Conclusions:1.The phytate content and its molar ratio with calcium,iron,zinc will reduce a lot after cooking in chinese food. 2.The dietary phytate intake of rural adolescents was higher than those in Western developed countries and lower than those in developing countries and the average of whole chinese in 2002.3.When the dietary mola ratio of phytate/calcium with between 0.1 and 0.2 might be good for the absorption of calcium and iron,while zinc is at a lower level.