## 7 Effects of the Interventions into Microbiota on the Micronutrient Status of Humans

Table 7: Studies that reported effects of pro-and/or prebiotic supplementation on micronutrient status of people with obesity or metabolic disorders. The first six studies mentioned in the table were performed on patients who underwent bariatric surgery [169; 170; 171; 172; 173; 174]. These studies are, on one hand, a good example of the influence of microbiota intervention on the micronutrient status of people because they include micronutrient supplementation in both the treatment and control groups. On the other hand, bariatric procedures alter the uptake of nutrients from the gastrointestinal tract. Hence, the effects could be different in people with intact digestive tracts. In addition, cited studies for bariatric patients all looked at the effects of probiotics and synbiotics on micronutrient status shortly after the surgery, when changes to body function were greatest due to very intensive weight loss. This, as discussed in Section 4, may have a profound impact on the micronutrient status of the body. Therefore, the results of studies with the participation of patients undergoing bariatric procedures must be discussed separately. A meta-analysis that included these six studies found that microbiota interventions improved the levels of vitamin B12 but did not have a significant effect on the status of vitamins D and B9, as well as ferritin and hemoglobin [181]. The remaining six studies included in Table 7 reported results of pro- and/or prebiotic supplementation on the micronutrient status of people with obesity [177; 178], T2D [179; 180], hypercholesterolemiaemia [175], and gestational diabetes mellitus [176]. All of these studies demonstrated the effect of microbiota intervention on micronutrient status by employing adequate controls. Other studies where the effect of joint supplementation with micronutrients and pro-/prebiotics was shown in the treatment group versus the placebo were not included. Three of the listed studies reported the effects of microbiota intervention on vitamin D status [175; 176; 177]. In two studies, vitamin D increased [175; 176], and in one, no significant change to its status compared to the control group was noted [177]. Interestingly, studies that reported significant effects both included \(L\)_reuter_ in the supplementation. Only one out of six mentioned studies looked at other vitamins apart from vitamin D (vitamin A, E, and \(\beta\)-carotene) but failed to demonstrate a statistically significant change in their status in response to microbiota intervention [175]. Among works that studied the impact of microbiota intervention on the absorption of minerals, two reported improvements in the Ca status of T2D patients who were given either symbiotic with FOS [179] or chicory inulin enriched with FOS [180], but no effect was found in hypercholesterolemia adults taking \(L\)_reuteri_ NCIMB 30242 alone [175]. Furthermore, two studies reported no effect of the intervention on serum Fe levels in T2D patients [179] and postmenopausal women with obesity [178]. Out of these two studies, only one showed that employed supplements could increase the serum concentration of Zn compared to baseline levels but not to the control [178]. On the other hand, the levels of Cu [178] and Mg [179] remained unaffected. Overall, the effects of microbiota interventions on micronutrient status reported in the studies with the participation of patients with obesity and metabolic disorders are highly heterogeneous. However, so are the employed intervention conditions and researched groups. In this situation, more research is required to establish effective interventions that could improve the micronutrient status of target populations. Nevertheless, it needs to be noted that both pre- and probiotics were shown to improve the status of some micronutrients in groups of interest, and no negative results were reported, except for the Fe status of postmenopausal women with obesity that was measured in hair [178].