The addition of ketoanalogues (KAs) to a low-protein diet has been shown to mitigate the progression of pre-dialysis chronic kidney disease (CKD). The addition of inulin and calcium citrate may add further benefits, given their nephroprotective effects. In this study, we tested the changes in estimated glomerular filtration rate (eGFR), CKD symptoms, body composition, and biochemical parameters after 6 months of diet supplementation with Cetolán III, a combination of KA, inulin, and calcium citrate. We included 76 adult patients diagnosed with CKD stages 3 and 4 and not treated with renal replacement therapy in a retrospective cohort. In this cohort, participants were followed through two clinic visits at 3 and 6 months after diet supplementation. We found a slight increase in eGFR at 3 and 6 months compared with baseline, as well as a decrease in the severity of CDK-related symptoms, fat mass, and muscle mass. We observed only a slight decrease in creatinine and uric acid after 6 months of follow-up. We did not find a remarkable change in anthropometric parameters (e.g., body mass index, waist circumference, and arm muscle area). This observational study suggests that addition of KA, inulin, and calcium citrate to a low protein- diet could be associated with an improvement in eGFR and symptom severity in CKD pre-dialysis.