Zinc absorption
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Zinc Absorption: Key Influencing Factors and Implications
Introduction to Zinc Absorption
Zinc is an essential trace element crucial for numerous biological functions, including immune response, DNA synthesis, and cell division. However, zinc deficiency is prevalent in many populations, often due to factors that inhibit its absorption rather than inadequate dietary intake alone . Understanding these factors is vital for developing strategies to improve zinc nutrition, especially in vulnerable groups.
Dietary Inhibitors of Zinc Absorption
Phytate's Role in Zinc Absorption
Phytate, found in staple foods like cereals, corn, and rice, is a significant inhibitor of zinc absorption. The inositol hexaphosphates and pentaphosphates forms of phytate are particularly effective at reducing zinc absorption, while lower phosphates have minimal impact . Studies have shown that reducing phytate content through methods such as enzyme treatment, germination, fermentation, or genetic engineering can markedly improve zinc absorption 14.
Impact of Iron and Cadmium
Iron, when taken as a supplement, can negatively affect zinc absorption, although this effect is not observed when iron is present in meals as a fortificant . Additionally, environmental cadmium exposure has been shown to inhibit zinc absorption, posing a risk in areas with high cadmium levels .
Enhancers of Zinc Absorption
Protein and Amino Acids
The amount of protein in a meal positively influences zinc absorption, although the effect varies with different protein sources. For instance, casein has a modest inhibitory effect compared to other proteins . Amino acids such as histidine and methionine, along with low-molecular-weight ions like EDTA and organic acids (e.g., citrate), also enhance zinc absorption and are often used in zinc supplements .
Food Preparation Techniques
Food preparation methods that reduce phytate content, such as fermentation and germination, can significantly improve zinc absorption. For example, the absorption of zinc from wholemeal bread is higher when calcium is added in the form of milk products . Similarly, reducing the phytic acid content in cereals through specific preparation methods has been shown to enhance zinc absorption .
Zinc Absorption in Special Populations
Post-Gastric Bypass Patients
Patients undergoing Roux-en-Y gastric bypass (RYGBP) surgery experience a significant reduction in zinc absorption. Studies indicate that zinc absorption capacity decreases from 32.3% to 13.6% six months post-surgery, with no major changes observed up to 18 months after surgery . This reduction occurs despite increased supplemental zinc intake, highlighting the need for tailored nutritional strategies for these patients .
Children at Risk of Environmental Enteric Dysfunction
In Bangladeshi toddlers at risk of environmental enteric dysfunction (EED), zinc absorption from micronutrient powders (MNP) is notably low. This impaired absorption may increase dietary zinc requirements, as current MNP doses may be insufficient to meet physiological needs . Elevated biomarkers of intestinal inflammation in these children further suggest that enteropathy significantly impacts zinc absorption .
Pregnant and Lactating Women
During late pregnancy and early lactation, the physiological requirements for zinc increase. Research shows that zinc absorption upregulates to match these increased needs, regardless of dietary phytate content. This adaptation ensures that pregnant and lactating women meet their zinc requirements, although dietary adjustments may still be necessary .
Conclusion
Zinc absorption is influenced by various dietary and physiological factors, including the presence of phytate, iron, and cadmium, as well as the type and preparation of food consumed. Enhancing zinc absorption through dietary modifications and understanding the specific needs of vulnerable populations, such as post-gastric bypass patients and children at risk of EED, is crucial for addressing zinc deficiency. Continued research and tailored nutritional strategies are essential for improving zinc status in affected populations.
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