Obesity can increase blood flow and pressure in the glomeruli, the kidney's filtering units. Excessive filtration, or hyperfiltration, is one possible mechanism of kidney damage, but it does not lead to kidney disease in everyone with obesity. Obesity-related glomerulopathy is a form of glomerular damage diagnosed by kidney biopsy. In a US study of 6818 biopsies, its share rose from 0.2% in 1986-1990 to 2.0% in 1996-2000, and patients' average BMI was 41.7. These data come from biopsy studies and do not describe how common the disease is among people living in Opole.
How was BMI associated with the risk of end-stage kidney failure in a study?
In a cohort of 320,252 adults from California followed for an average of 26 years, the risk of end-stage kidney failure, meaning the need for dialysis or a transplant, was compared with that of people with a normal weight. The relative risk was 1.87 with overweight, 3.57 with class I obesity, 6.12 with class II obesity and 7.07 with a BMI ≥40. The association remained after accounting for selected other factors, including blood pressure and diabetes. As an observational study, however, it does not prove that obesity alone causes kidney failure.
A meta-analysis of 39 cohorts, including 630,677 people with normal kidney function at the start of follow-up, found that obesity was associated with a higher risk of eGFR falling below 60 ml/min/1.73 m² (RR 1.28) and of developing albuminuria (RR 1.51). These are relative increases in risk of 28% and 51%. Results varied between studies, and the meta-analysis figures do not predict the outcome for an individual patient.
How do we interpret kidney results, and what do they mean for treatment?
| Test result | What it means and what we do | KDIGO category |
|---|
eGFR ≥60 ml/min/1.73 m² | Normal or slightly reduced filtration; the result does not rule out CKD. We also assess albuminuria and other abnormalities, and choose the dose and follow-ups for the product and the patient's health. | G1-G2 |
eGFR 30-59 ml/min/1.73 m² | Moderately reduced filtration; CKD is diagnosed when the change lasts at least three months. We assess persistence, ACR and other results, and assess a new abnormal result without waiting three months. | G3a-G3b |
eGFR <30 ml/min/1.73 m² | Severe kidney impairment. A nephrology assessment and a choice of medicine in line with its SmPC are needed; Wegovy and Saxenda are not recommended in severe kidney impairment. | G4-G5 |
ACR <30 mg/g | Normal or mildly increased albumin excretion. The result does not rule out CKD from other causes; we set the date of the next test individually. | A1 |
ACR 30-300 mg/g | Moderately increased albuminuria. We assess and confirm the result, taking blood pressure, glucose and eGFR into account. | A2 |
ACR >300 mg/g | Severely increased albuminuria. Further investigation is needed, including whether a nephrology consultation is indicated; ACR alone does not define the full stage of CKD. | A3 |
A diagnosis of chronic kidney disease requires changes lasting at least three months. A new abnormal result is still assessed without waiting for that period to pass. The doctor decides whether urgent investigation, a repeat test or a comparison with earlier results is needed.
Who needs particular attention to kidney function?
Kidney function needs careful monitoring in people with type 2 diabetes, high blood pressure, kidney stones or a family history of kidney disease, as well as in people taking NSAIDs long term and patients who have had acute kidney injury, for example after severe dehydration. Age is one risk factor, but it does not by itself mean a CKD diagnosis. A past contrast examination does not automatically mean kidney damage either. The doctor chooses the product and the pace of dose increases according to kidney function, tolerance and the SmPC; there is no single reduced starting dose for the whole at-risk group.
What do studies show about obesity treatment and kidney protection?
The FLOW trial included 3533 people with type 2 diabetes and CKD. In people taking semaglutide 1 mg once weekly, the risk of a composite endpoint was 24% lower in relative terms than with placebo, over a median follow-up of 3.4 years. The endpoint included kidney failure (dialysis, transplantation or sustained eGFR <15), a sustained eGFR decline of at least 50%, and death from kidney or cardiovascular causes. The 24% applies to the whole composite endpoint and does not mean the same reduction in the risk of each event. The trial was stopped early, after a planned interim analysis.
The kidney analysis of the SELECT trial involved people with overweight or obesity, established cardiovascular disease and no diabetes. It assessed a different composite endpoint, which also included persistent macroalbuminuria; cardiovascular death was not one of its components. An endpoint event occurred in 1.8% of people receiving semaglutide 2.4 mg and 2.2% of people receiving placebo, with a hazard ratio (HR) of 0.78. The absolute difference was 0.4 percentage points and the relative risk reduction was 22%. The benefit came mainly from changes in macroalbuminuria and sustained eGFR decline of at least 50%; the result does not mean 22% fewer people needed dialysis.
In a separate randomised trial of 101 people with CKD, a BMI ≥27 and no diabetes, semaglutide reduced the urine albumin-to-creatinine ratio (UACR) by 52.1% compared with placebo after 24 weeks. In the treated group itself, the fall from baseline was about 48.6%. The trial measured albumin excretion and did not assess whether dialysis or deaths decreased.
In a bariatric cohort, 4322 people who had surgery were compared with 30,919 people who did not, followed for an average of 6.1 years. Surgery was associated with a lower risk of a composite kidney outcome: the HR was 0.47 in people with diabetes and 0.52 in people without diabetes. This observational study cannot establish how much of the benefit came from weight loss and does not directly compare surgery with modern medication.
How does kidney function affect the choice of medicine?
Wegovy needs no dose change in mild or moderate kidney impairment, but it is not recommended at eGFR <30 ml/min/1.73 m². Saxenda is not recommended at a creatinine clearance <30 ml/min. Mounjaro needs no dose adjustment even in end-stage kidney failure, but experience in this group is limited and treatment requires caution. Mysimba is contraindicated in end-stage kidney failure, and in moderate or severe impairment its maximum dose is two tablets a day. These rules apply to the products named and their indications, so they are not automatically transferred to other semaglutide medicines.
Orlistat can increase oxalate excretion in the urine and lead to oxalate nephropathy, a build-up of crystals in the kidneys. This risk needs particular attention in CKD and dehydration. In June 2026, the US Food and Drug Administration (FDA) added a warning to the labelling of orlistat 60 mg sold without a prescription in the USA, after reviewing 12 reports from 2007-2023. The reports cannot show how often this complication occurs. The European SmPC for Xenical also describes the kidney risk.