TNF and nutritional deficiency disease: Meanwhile, an eGFR decline could also be observed due to an increase in serum creatinine generation as a consequence of gaining muscle mass.44,45,46 Albeit speculative, it is therefore possible that the gain of muscle mass associated with improvement of IBD symptoms following anti-TNF therapy and resultant amelioration of nutritional deficiency led to an apparent decline in eGFR among patients with incident TNF inhibitor use.