The aim of this systematic review was to summarize the evidence of nutritional diseases following exposure to immunosuppressive therapy among patients following kidney transplantation (kTx). A total of 24 studies met our inclusion criteria [19–42]. The assessed outcomes encompassed diabetes, body weight, lipid abnormalities, body composition, electrolyte disorders, bone status, and serum of the vitamin D and the vitamin B12 levels. The immunosuppressive medications comprised calcineurin inhibitors (CNIs) (tacrolimus (Tac), cyclosporine (CsA), mTOR inhibitors, antiproliferative, and glucocorticosteroids. Our findings indicate that, overall, immunosuppressive therapy has an effect on nutritional diseases among kTx patients. Furthermore, certain immunosuppressants demonstrate a stronger association than the others. Half of the studies regarding diabetes included in our review described Tac as a stronger risk factor for developing this disease compared to CsA. Our findings are in line with a systematic review conducted by Heisel et al., which examined diabetes and CNIs among solid organ transplant patients. Heisel et al. concluded that patients receiving Tac exhibited a higher incidence of post-transplant diabetes compared to those receiving cyclosporine [43]. Additionally, other studies have linked diabetes to the use of immunosuppressive medications, which may be reversible after modifying the immunosuppressive treatment. This includes reducing the doses of steroid drugs and replacing Tac with CsA [45]. However, in two RCTs studies concerning diabetes and immunosuppressive medications, the results from Torres and Borda were inconsistent. This underscores the necessity for further research in this area, emphasizing the importance of conducting studies of the highest quality. The causes of increased body fat mass in patients after transplantation include factors such as improved appetite, enhanced sense of taste, lack of necessity to adhere to a restrictive diet, and the use of steroid medications [45]. In proposed systematic review, three studies analyzed the effect of immunosuppressive medications on body weight, of which two were cohort studies and one cross-sectional. It was observed that obese patients more frequently used mTOR inhibitors and less often Tac [34]. In contrast, another study. noted significant increases in body weight and body mass index across both CsA and Tac groups [35]. Our findings are consistent with a scoping review that emphasized the limited evidence on this topic in the scientific literature, as well as the lack of high-quality evidence from intervention studies [46]. One of the complications associated with chronic steroid therapy is Cushing's syndrome, characterized by abdominal obesity and sarcopenia. Interestingly, steroid therapy did not demonstrate any influence on the percentage of weight gain post-transplantation in our review [27]. Dyslipidemia represents a significant and frequently encountered burden post-transplant. In our review, two studies investigated the association between immunosuppressive medications and lipid profile. Everolimus emerged as a significant risk factor for lipid abnormalities, while CsA did not show the same association. However, the results regarding the use of steroids were inconsistent. Our findings contradict the existing literature, which suggests that components contributing to lipid abnormalities include immunosuppressive medications such as steroid drugs, calcineurin inhibitors like CsA rather than Tac, and mTOR inhibitors such as sirolimus or everolimus [44]. One study assessed the effect of fast and slow Tac metabolizers on body composition [32]. As a result, there was no difference in phase angle, visceral fat area, lean body mass index (LBMI) and the proportion of lean mass as a percentage of total body mass between the subgroups of slow and fast metabolizers. In our review, mTOR inhibitors were found to be associated with the bone status post-transplant. Gregorini et al. concluded that there is a significant correlation for both osteopenia and osteoporosis with mammalian target of rapamycin (mTOR) inhibitors treatment (imTOR) among kTx patients [29]. What is more, CNIs were found to negatively affect serum 25(OH)D level [28]. The association between the immunosuppressive medication and vitamin B12 deficiency was described in one study [33]. Pontes et al. established the B12 deficiency was linked to the use of MMF. Our findings are in line with the literature which states that immunosuppressive medications contribute to development of anemia (mycophenolate mofetil/Na, Tac, azathioprine, mTOR inhibitors), blockers of the renin-angiotensin-aldosterone (RAA) system (angiotensin-converting enzyme inhibitors and angiotensin receptor antagonists), allopurinol, trimethoprim [44]. Patients without using CNIs had a lower prevalence of hypomagnesaemia, hyperkaliemia and metabolic acidosis compared with calcineurin inhibitor treatment. There was no difference in phase angle, visceral fat area, LBMI and the proportion of lean mass as a percentage of total body mass between the subgroups of slow and fast Tac metabolizers. Only one study assessed this relationship which found that patients without any CNI therapy had a lower prevalence of hypomagnesaemia, hyperkaliemia and metabolic acidosis compared with calcineurin inhibitor treatment. Our findings are in line with the existing literature [44]. It is necessary to monitor magnesium concentrations and in case of deficiency - depending on its severity - supplementation of this element via intravenous infusions (in the early period after transplantation) or in the form of tablets [38]. None of the studies examined an important aspects which are serum potassium and calcium levels. Among patients following kTx, variations in serum potassium concentrations are evident, encompassing both hypo- and hyperkalemia [20]. Furthermore, the distribution of studies across different outcomes may not accurately represent the prevalence or clinical significance of those outcomes post-transplant. While our review highlighted 14 studies on post-transplant diabetes, it's crucial to acknowledge that certain outcomes may garner more attention due to their clinical relevance, existing literature, or research priorities. For instance, lipid abnormalities are more prevalent than diabetes among kTx patients. The relatively low number of studies examining body weight may be due to various factors such as methodological challenges, limited resources, or research priorities. While it's important to acknowledge the discrepancies in the distribution of studied outcomes, it's also crucial to interpret the findings in the context of available evidence and research limitations. Future research efforts may benefit from addressing gaps in the literature and prioritizing areas with significant clinical implications for kTx patients.
To the best of our knowledge, this is the first systematic review that summarizes the evidence of immunosuppressive therapy and nutritional diseases of patients following kidney transplantation. A strength of our review is that we report on a large number of studies, including data from various populations. The limitations include high heterogeneity, and the low quality of studies incorporated in the review. Despite the above limitations, our findings carry significant clinical implications: i) Immunosuppressive therapy affects various nutritional diseases among post-kidney transplant patients; ii) Tac emerged as a higher potent risk factor for disease development compared to CsA; iii) Diabetes garnered the most attention in this research area. Given the heterogeneity and suboptimal quality of the studies included in our review, it is imperative that future research endeavors prioritize high-quality, prospective randomized controlled studies. These rigorous study designs can provide more reliable evidence regarding the association between immunosuppressive therapy and the nutritional status of kidney transplant recepients. Furthermore, additional longitudinal studies focusing on nutritional outcomes are warranted to enhance our understanding of the long-term effects of immunosuppressive therapy among this population. By conducting well-designed RCTs and longitudinal studies, researchers can contribute to filling the existing gaps in the literature and ultimately improve clinical management strategies for kTx patients, thereby enhancing their overall health and well-being. Finally, for a conclusive attribution of the increase in the mentioned diseases to immunosuppressive medication, forthcoming researchers ought to delve into the dietary habits of kidney transplant patients. This exploration will afford a more profound comprehension of the subject matter under study.