The consequences of avoiding bread : the effect of bread avoidance on selenium status and thyroid function : Master of Science (Nutrition and Dietetics), Massey University, Albany, Auckland, New Zealand

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2021
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Massey University
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Selenium is an important nutrient for the conversion of inactive thyroxine (T4) to the active hormone triiodothyronine (T3) and therefore is vital for thyroid health. Unfortunately the New Zealand food supply is generally low in selenium due to the poor content of the soil. However, bread is often made using selenium-rich Australian wheat and therefore is a good dietary source of the nutrient. The avoidance of bread is becoming popular with the rise of lower carbohydrate diets, increasing the risk of low status and subsequent impaired thyroid function. This study aimed to investigate if avoidance of bread by mid-life women in New Zealand results in low selenium status and subsequent impaired thyroid function, as well as investigating alternate dietary sources. This study is an extension of a previous study which investigated iodine status in women who avoid bread. This study investigated selenium intake (estimated from 3-day-diet-diaries, urinary excretion and plasma concentration), status (plasma) and thyroid hormone biomarkers (T3, T4, TSH, T3:T4 ratio, Tg, TPOAb) in 37 mid-life women based in Auckland, New Zealand. Median intake estimated from 3-day diet diaries and urinary excretion was 52µg/day (36, 84) and 51 µg/day (38, 72) respectively which is below the recommended daily intake (60µg/day). It was found that 49% of participants had intakes below the estimated average requirement (50µg/day), indicating deficiency. Median plasma concentration was 118.9µg/L (107.2, 131.3) suggesting optimal status, however nearly a third of participants had low plasma concentrations below 110µg/L. Impaired thyroid function was found in 2 participants, both of whom demonstrated subclinical hyperthyroidism. Major alternate dietary sources of selenium were found to be seafood, meat, poultry and nuts. Participants who did not regularly eat these foods did not manage to meet their daily requirements for selenium intake. Overall, a high prevalence of inadequate intake was observed in women who avoid bread. Subsequently, almost a third of participants had suboptimal plasma concentrations indicating low status. Only two participants were found to have impaired thyroid function, potentially due to the lower requirements of selenium for deiodinases to function. This study highlights the importance of consuming alternate dietary sources such as seafood, meat, poultry and nuts on a regular basis if bread is removed from the diet while also emphasizing the risks that dietary trends such as bread avoidance can pose for intake of nutrients such as selenium. It could be suggested that some individuals would benefit from a greater understanding of the nutritional risks associated with bread avoidance, particularly in regard to selenium intake. Public knowledge about alternative selenium sources may not be widely held and therefore individuals may not be equipped with the information needed to make educated choices in regard to their chosen dietary patterns. An attempt to raise awareness of selenium as a nutrient as well as the best alternate dietary sources of selenium in the NZ food supply, to improve both dietary intake and status of selenium amongst at-risk groups such as those who avoid bread is highly recommended.
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