Background: Zinc (Zn) and selenium (Se) are trace elements that contribute to important biological processes in the human body. Cumulating research has demonstrated that obese people have lower Zn plasma levels compared with normal-weight people and that Se and Zn circulatory levels are inversely correlated with obesity and body fat mass. However, the evidence regarding the effects of the two micronutrients on body composition is conflicting. Furthermore, overweight and
obese individuals are commonly characterized by reduced physical performance and disrupted thyroid function. The effects of combined diet and exercise programmes on thyroid function in overweight or obese individuals have been addressed in some studies, but in most of them, aerobic exercise of moderate intensity was performed. The effects of high-intensity functional training (HIFT), a promising intervention for obesity therapy, on thyroid function have not been addressed in overweight and obese people yet. The same applies to the effects of Se and Zn cosupplementation combined with diet with or without HIFT on resting metabolic rate (RMR), thyroid function, and exercise performance in the abovementioned population. Thus, this thesis aimed to
examine the effects of Zn and Se co-supplementation on RMR, thyroid function, exercise performance, and body composition in overweight and obese people undergoing a diet with and without the addition of HIFT. Methodology: Two randomized double-blind and placebo-controlled
3 trials were conducted to examine these effects. The first interventional study, which was conducted in overweight and obese people aged 18-40 (n = 28), examined the effects of Se and Zn supplementation (Se L-selenomethionine 200 mcg/day and Zn gluconate 25 mg/day) as compared to placebo tablets containing starch combined with diet for eight weeks. The second interventional study examined the effects of the same supplements as compared to placebo tablets containing starch in overweight and obese people aged 18-40 (n = 15) undergoing diet but with the addition of two group training sessions of HIFT a week and for six weeks. RMR (indirect calorimetry), thyroid function (free triiodothyronine, free thyroxine, and thyroid stimulating hormone), body composition (bioelectrical impedance analysis technology), cardiorespiratory
fitness (VO2max test), functional capacity (two sit-to-stand tests, time up and go-TUG and handgrip strength tests) were assessed at baseline and the end of the intervention. Results: Collectively, the findings from this thesis demonstrated the positive effects of Se-Zn co-supplementation on Time up and GO performance, which was consistent between the two studies. Another consistent finding between the studies was the increase in Se serum levels in the intervention groups compared to
their placebo groups. In contrast to the unchanged Se levels of the placebo group in the first interventional study, Se levels were decreased in the placebo group in the second interventional study. Zn serum levels were not affected in either group in the first interventional study, but notably, they slightly decreased in the placebo group in the second international study, with the intervention group remaining unchanged. An increase in RMR was observed in the intervention group compared to the placebo in the first interventional study, but this increase was not consistent in the second interventional study. A time effect was detected for all body composition outcomes
in the second interventional study, except for muscle mass, but only for body fat levels in the first interventional study. Furthermore, a time x group effect was detected for body weight in thesecond interventional study, revealing the effectiveness of the co-supplementation in decreasing body weight when HIFT is added to a hypocaloric diet plan. Conclusions: Overall, this thesis contributes to a better understanding of the role of Zn and Se in obesity therapy, providing valuable information to nutrition and exercise scientists regarding appropriate nutrition and exercise plans for overweight and obese individuals. Adding HIFT to a hypocaloric diet increases the nutritional needs of Zn, and mostly Se, beyond the recommended dietary allowance (RDA), as
shown in the Second Interventional Study. Thus, emphasis must be placed on these micronutrients when designing hypocaloric diets combined with HIFT. Furthermore, increasing dietary Zn and Se beyond the RDA with the use of the supplements increased TUG performance, hence, functional capacity in overweight and obese people with or without the addition of HIFT. This is important due to the disrupted exercise tolerance often observed in overweight or obese people and to the association of decreased TUG performance with medical comorbidities. However, when using Se
and Zn supplements, the levels of these micronutrients in the blood must be closely monitored, so as not to exceed the desired levels. Lastly, combining HIFT with diet seems to be a more effective intervention regarding obesity therapy since it can improve more body composition outcomes than diet alone.