Swiss wheat – a potential source to cover micronutrients requirements in plant-based diets?
Zinc and iron deficiencies have increasingly come into the focus of health science research, as less developed but also industrialized countries are affected by these micronutrient deficiencies. Such deficiencies can be linked to inadequate intakes of iron and zinc and low dietary bioavailability of these micronutrients. As meat consumption decreases in wealthy societies due to the growing concerns of animal and environmental welfare, alternative zinc and iron sources are required. In contrast to regular meat consumption and the established alternate source through synthetic supplementation, our team focused on the research of wheat-based micronutrient sources. To what extent can the human requirement of iron and zinc be covered by plant-based diets and are they adequate for the substitution of meat as the conventional and proven iron and zinc source?
Laboratory research as a learning experience
Our project started this spring as an interdisciplinary cooperation between different institutes of ETHZ in the framework of a small research project that was funded by the World Food System Center. We were interested in conducting a practical bachelor thesis and were immediately hooked on the idea of finding an optimal mineral source for plant-based diets. Our laboratory work focused on the analysis of different Swiss wheat cultivars by determining their grain micronutrient concentrations (zinc and iron). Additionally, we were analyzing polyphenols and phytate in the grains as these compounds act as ‘antinutrients’. This means that they lower the bioavailability of zinc and iron and thereby also lower their gastric absorption.
Learning through practice
Despite the effort of the ETHZ to give students an insight into the practical everyday life of science, we were both equally challenged by the work ahead of us. However, we were motivated to implement and build on what we have learned through several laboratory internships/courses. Facing new analytical instruments, practices and theories, we spent the summer learning how to process the samples correctly and to extract the targeted substances optimally.
The iron and zinc concentrations in our samples were analyzed at the EAWAG in Dübendorf using state-of-the-art analytical instruments to perform multi-element analyses whilst the phytate and polyphenol content were tested at the Laboratory of Human Nutrition ETHZ. The samples originated from 25 Swiss wheat seeds that were planted, propagated and harvested on the field phenotyping platform at the Research Station for Plant Sciences ETH Zurich in Eschikon over several years. Compiling these wheat cultivars involved work in the seed archive of the Crop Science Group.
Promising findings
The results showed that there is a large range of zinc and iron concentrations between the different wheat cultivars. This means that there could potentially be some cultivars that could be used to produce everyday food, such as bread, that are high in zinc and/or iron. There were also significant differences between polished and unpolished grains. Polishing the wheat grains lowered their nutritional quality, as it decreased the zinc and iron concentration. Thus, consuming non-polished grains as e.g. whole grain bread would be highly beneficial in regards to the micronutrient composition. Overall the examined cultivars showed similar mineral contents as other European grains and slightly lower contents than samples from southern American countries. On the other hand, consuming non-polished samples could impair the absorption of zinc and iron, as the outer hull has the highest concentration of phytate. The concentrations were approximately three times higher in non-polished samples. This results in higher ratios of phytate to iron and zinc, which enhances the formation of zinc-phytate and iron-phytate complexes. This complex formation hinders iron and zinc from being absorbed as these cannot be ‘digested’ by humans. The same applies for polyphenols as they also form strong complexes with zinc and iron. In addition, the anatomical distribution of phenols is even more one-sided than for phytate: the polyphenol concentrations were approximately ten times higher in non-polished samples than in polished samples.
How to improve bioavailability?
There could be several ways to further improve the bioavailability of zinc and iron in wheat grains or in our wheat-based meals. As proposed by several publications, adding Vitamin C to a meal can strongly counteract phytate’s inhibitory potential. Applying enzymes to wheat food products could also minimize the inhibiting effect of phytate, as such bio-catalysts ‘digest’ the phytate for us. Hence, iron and zinc would potentially not be bound to these anti-nutrients anymore and would thus be more available for our gastric absorption. In addition, there are also agricultural measures to improve the bioavailability of zinc and iron. For instance, optimizing the phosphorus fertilization could be helpful in reducing the phytate concentration, as phytic acid is the main storage form of phosphate in wheat grains. Less use of phosphorus in agricultural production could therefore increase the bioavailability of zinc and iron in wheat for us.
Summarizing our findings, it can be said that there is definitely some potential in our locally grown wheat cultivars to provide zinc and iron for human nutrition. Given the trend of a decreasing meat consumption in Europe, wheat rich in bioavailable zinc and iron could partly compensate meat as a source for these metals. Whereas the zinc and iron concentrations in our samples were rather average compared to other countries, there is still some room for improvement that could be achieved by breeding and fertilizing optimizations. In regards to phytate and polyphenols, it can be said that consuming polished grains, which is considered to be part of the European diet, is more desirable. However, looking at the zinc and iron concentrations, non-refined grains are more suitable. Thus consuming whole grain products that are rich in iron and zinc and counteracting the inhibiting effect of phytate and polyphenol through Vitamin C intake and/or enzymatic alterations could potentially be the most adequate approach.
ABOUT THE AUTHORS
Lorenz Luder is a student, who is currently working on his master’s degree in Human Nutrition and Health at the ETH Zürich in Switzerland. He is equally fascinated by science and is highly motivated to further develop his own set of skills in regards to future practical and theoretical challenges. Following his passion for cooking and baking, it was obvious to him in which direction his bachelor's thesis and his further academic career should go. Aside from other countries’ culinary influence, he is also interested in foreign cultures and politics and their socio-demographic impact.
Lisa Konrad is a master student in Agricultural Science at ETH Zurich with the major in Plant Science. Growing up on a small farm she always wanted to do something more practical. As wheat is one of the most important crops in Switzerland and a staple food, she is really fascinated by improving such a crop. She was especially interested in the project because it has local relevance for Switzerland and zinc and iron content in non-animal products is a current topic.
Title picture: Field phenotyping platform in Eschikon (ETHZ). The photo illustrates the large variety of wheat cultivars that grow in Switzerland and Europe (Fotographer: Andi Hund, Crops Science Group, Eschikon)