4. Discussion
obesity, muscle mass, inflammation, mitochondrial dysfunction, weight loss
OBESITY, INFLAMMATION, OXIDATIVE STRESS, MITOCHONDRIAL DYSFUNCTION
In the present study, the Zn/Se co-administration enhanced RMR of the participants and increased Se serum levels and TUG performance. However, compared to the placebo group, there were no additional benefits of Zn/Se co-administration on thyroid hormones, body composition, physical fitness, and the remaining functional capacity.The most important finding in the present study was that Zn/Se co-administration enhanced RMR. Specifically, RMR in the supplementation group increased by 22.9%, while RMR in the placebo group decreased with weight loss. The placebo group results contrast other studies, where RMR had significantly decreased after weight loss attempts [The average increase in RMR of the participants in the Zn/Se co-administration group was 441 kcal/day. A positive effect of Zn and Se co-supplementation on the Basal Metabolic Rate (BMR) has also been reported by Federico et al. [In people with obesity, the increased oxidative stress, as a result of the inflammation process, can have a negative impact on mitochondrial function, with the mitochondria being unable to generate sufficient adenosine triphosphate (ATP) levels [The possible effects of Zn levels on RMR have been demonstrated in non-experimental studies. For example, Wang et al. [When discussing the effects of Zn and Se supplements on RMR, the two micronutrients’ role on oxidative stress management should also be addressed due to the effect of oxidative stress on mitochondrial dysfunction. Hasani et al. [Some interesting findings by Hasani et al. [A difference between the study conducted by Mahmoodianfard et al. [The Zn/Se combination in this work did not affect thyroid hormones since both groups’ TSH, FT3, and FT4 remained unchanged. In agreement with our study, Mahmoodianfrad et al. [Even though thyroid hormones might not be the most critical hormones associated with RMR [A lot of money is spent annually on weight loss supplements [In the present study, the body composition in the Zn/Se co-administration group improved more than the placebo group, though this difference was not statistically significant. Body mass decreased by 1.33 kg and 0.95 kg for Zn/Se co-administration and placebo group, respectively, at the end of the intervention with a mean difference of approximately 0.4 kg between groups. This number is very close to what was reported in a meta-analysis by Abdollahi et al. [In the present study, it is worth mentioning that the fat-free mass and muscle mass in the supplementation group increased by 0.61 kg and 0.58 kg, respectively. This was an unexpected finding, considering that the participants were on a hypocaloric diet and did not participate in a resistance training intervention. On the contrary, fat-free and muscle mass in the control group slightly decreased. Even though not statistically significant, the increased fat-free mass in the intervention group might have contributed to the effects of Se/Zn co-administration on body weight between groups. In line with the present study, positive results of the two micronutrients on fat-free mass and muscle mass have also been reported in previous studies. For example, in a cohort study, Zn was associated with muscle mass in an elderly population [Regarding Se’s effects on muscle mass, Cavedon et al. [In the present study, Zn/Se co-administration was found to affect functional capacity by improving the TUG performance in the intervention group by 8.8%. Furthermore, a main effect of time was detected for all functional capacity outcomes at the end of the intervention period as compared to the baseline measurement. Notably, the participants in the supplementation group improved their performance in all tests more than the control group. However, this difference was insignificant since no time x group effects were found. One study examining the relationship between Se intake and musculoskeletal function in older adults found that low Se intake was associated with a lower TUG and handgrip performance than high Se intake [A cross-sectional study examined the association between physical function (TUG performance, activities of daily leaving measurement, and handgrip and quadriceps muscle strength) and Zn levels in older people [A limitation of the present work was that we could not include separate Se and Zn groups in order to examine the effects of each micronutrient alone. This is proposed for future research. Furthermore, although the participants were instructed not to change their physical activity levels, these were not assessed during the study. A strength of the present study was that Se and Zn serum measurements were included to determine the effects of supplementation on blood levels of these micronutrients and to compare them with other studies. Furthermore, with an individualized diet plan, daily intake of Zn and Se was strictly controlled and kept below the upper limits for the two micronutrients. An advantage of the present study was that indirect calorimetry was used for the determination of RMR instead of predictive equations, which typically either overestimate or underestimate resting energy expenditure [