In their guest blog for IZiNCG, Sarah Zyba and Ryan Wessells from UC Davis describe the findings from a randomized controlled trial where the addition of exogenous phytase to small-quantity lipid-based nutrient supplements (SQ-LNS) increased absorption of zinc from a meal of millet-based porridge containing SQ-LNS in young Gambian children.
Young children in low- and middle- income countries like The Gambia are at risk for zinc deficiency because of high rates of infection and dietary zinc inadequacy common in these settings (1). Additional zinc can be provided to young children through supplementation, large-scale food fortification of staple foods, or the home fortification of complementary foods with products such as multiple micronutrient powders, fortified blended foods (e.g. Supercereal Plus) or small-quantity lipid-based nutrient supplements (SQ-LNS). SQ-LNS are typically a peanut and milk powder-based paste, fortified with vitamins and minerals and designed to be added to complementary foods (2).
However, many of the complementary foods eaten with SQ-LNS are cereal-based and high in phytate. Phytate is a phosphorus storage molecule that also binds minerals such as calcium, iron and zinc (3). Phytate is not easily digested by humans, which causes low absorption of minerals, including zinc, from foods or meals that are high in phytate. Phytase, an enzyme which breaks down phytate, can free phytate-bound zinc in the diet making it more available for absorption. Phytase is naturally found in some foods, such as wheat, in small amounts. Phytase can also be added to foods during the manufacturing process.
The primary objective of this study was to assess the effect that adding phytase to SQ-LNS had on zinc absorption. We did this by using a dual stable zinc isotope tracer method (4,5). Two SQ-LNS products were manufactured by Nutriset SAS; one was a standard formulation without phytase and one was the same formulation with 550 FTU (phytase units) of phytase added at the point of manufacture. In a collaboration between the University of California, Davis Institute for Global Nutrition, and the Medical Research Council Unit, The Gambia, we conducted a crossover double-blind randomized controlled trial in Keneba, The Gambia to test these two products.
Field staff during a training session before data collection began. Photo credit: Sarah Zyba
Thirty healthy young children 18 – 24 months of age participated in the study. For two consecutive days, children received a standard breakfast and lunch, which both consisted of a millet-based porridge and 10 g SQ-LNS. On one day, they received the SQ-LNS product with phytase, and the other day they received SQ-LNS without phytase; the order that they received the two products was randomly assigned. To measure zinc absorption from the test meals, we gave the children oral doses of two different stable zinc isotopes (Zn-67 and Zn-70) while they ate the meals; one stable zinc isotope was given with meals containing SQ-LNS with phytase, and the other stable zinc isotope was given with meals containing SQ-LNS without phytase. At the end of the second day, children received an IV infusion of a third stable zinc isotope (Zn-68). Urine samples were then collected for several days.
Field staff preparing test meals. Photo credit: Sarah Zyba
The ratio of the oral isotopes to the IV isotope (i.e. Zn-67:Zn-68 and Zn-70:Zn-68) in the urine was used to determine the fraction, or percent, of zinc absorbed from each of the test meals. By collecting weighed food records, we were also able to calculate the total amount of zinc absorbed (in mg) from millet-based porridge test meals containing SQ-LNS with or without phytase.
A study participant being fed a test meal by his mother. Photo credit: Sarah Zyba.
A study participant receiving an oral zinc stable isotope from a study fieldworker. Photo credit: Sarah Zyba
We found that the addition of phytase increased the fractional absorption of zinc from test meals containing a millet-based porridge and SQ-LNS from 8.6% to 16.0%. The total amount of zinc absorbed from the test meals more than doubled from 0.5 mg to 1.1 mg when phytase was added to the SQ-LNS.
This shows that reducing the amount of phytate in the diet by adding phytase to SQ-LNS at the point of manufacture may be an important strategy to increase zinc absorption among young children. Further studies should be conducted to determine the longer-term impact of SQ-LNS with phytase on biomarkers of zinc status and functional outcomes of zinc deficiency.
A publication with more details of the methods and results from this study can be found here.
For more information, please contact Dr. Ryan Wessells, University of California, Davis at krwessells@ucdavis.edu.
References
2. Arimond M, Zeilani M, Jungjohann S, Brown KH, Ashorn P, Allen LH, Dewey KG. Considerations in developing lipid-based nutrient supplements for prevention of undernutrition: experience from the International Lipid-Based Nutrient Supplements (iLiNS) Project. Matern Child Nutr 2015;11 Suppl 4:31–61.
3. Lonnerdal B. Phytic acid-trace element (Zn, Cu, Mn) interactions. Int J Food Sci Tech 2002;37:749–58.
4. Lopez de Romana D, Salazar M, Hambidge KM, Penny ME, Peerson JM, Krebs NF, Brown KH. Longitudinal measurements of zinc absorption in Peruvian children consuming wheat products fortified with iron only or iron and 1 of 2 amounts of zinc. Am J Clin Nutr 2005;81:637–47.
5. Islam MM, Woodhouse LR, Hossain MB, Ahmed T, Huda MN, Peerson JM, Hotz C, Brown KH. Total zinc absorption from a diet containing either conventional rice or higher-zinc rice does not differ among Bangladeshi preschool children. J Nutr 2013;143:519–25.
Further reading on strategies to increase zinc absorption:
Gibson RS, Anderson VP. A review of interventions based on dietary diversification or modification strategies with the potential to enhance intakes of total and absorbable zinc. Food Nutr Bull. 2009 Mar;30(1 Suppl):S108-43.
Gibson RS, Raboy V, King JC. Implications of phytate in plant-based foods for iron and zinc bioavailability, setting dietary requirements, and formulating programs and policies. Nutr Rev. 2018 July 13.