The standard recommendation for stage 3 kidney disease is to watch fluid intake to avoid edema, keep salt intake low to avoid hypertension, and take an anti-hypertensive. Since the kidneys play a major role in maintaining normal blood pressure, and since normal blood pressure is essential to the health of the kidneys, the relationship between the two is a vicious cycle, with the worsening condition of the kidneys worsening the hypertension which damages them. The only way to break this cycle is taking anti-hypertensives.
An additional approach you might want to try is taking the Japanese drug AST-120 (Kremezin), which is a modified charcoal supplement which absorbs the toxins which accumulates in the body from defective renal function and eliminates them through the intestines. Since these toxins also damage the kidneys, absorbing them into the intestines and eliminating them slows the renal decline which proceeds on its own once diabetic renal disease begins. Here is a recent study on AST-120:
Case Rep Nephrol Dial. 2018 Jun 8;8(2):107-111
Importance of AST-120 (Kremezin®) Adherence in a Chronic Kidney Disease Patient with Diabetes.
Tomino, Y, et al.
We report herein an adult case of chronic kidney disease (CKD) associated with diabetes. The patient had been treated with insulin injection for diabetes 10 years ago. At the time of his first visit to our division for further examinations, we diagnosed him as CKD: cause © diabetes; glomerular filtration rate (GFR) (G) G5 (estimated [e] GFR, 10.2 mL/min/1.73 m2; serum creatinine of 4.90 mg/dL); and albuminuria (A) A3 (2.62 g/gCr) by the Japanese Society of Nephrology (JSN) CGA classification. Because he had complained of severe constipation and kidney function, i.e., eGFR was not improved by previous medications, we added on a minimal dosage (2 g/day) of AST-120 (Kremezin®; ordinary dose 6 g/day). After 3 months of AST-120 therapy, eGFR was increased to 17.8 mL/min/1.73 m2 (serum creatinine of 2.90-2.72 mg/dL). Although the patient used some laxative products, he could not continue to take Kremezin and completely stopped 8 months after starting this drug. Kidney function then abruptly declined and progressed to end-stage kidney disease (ESKD). In June 2017, he was introduced to hemodialysis. It appears that the adherence of Kremezin is very important for inhibiting the progression to ESKD for patients with CKD with diabetes.