Obesity Related Kidney DiseaseMonday, March 28, 2011
Last week, I gave a talk on obesity assessment and management at the Nephrological Seminar in Heidelberg, Germany.
This annual conference, now in its 35th year, is hosted by Eberhard Ritz, who I have known for most of my professional career. Ritz, is certainly one of Germany’s pre-eminent nephrologists and as an emiritus professor still appears as active as ever, churning out article after article on a remarkably wide range of topics in nephrology and hypertension.
At this year’s Seminar, Ritz also presented an overview of the impact of obesity on kidney function. The summary of this talk was recently published in Current Opinions in Nephrology and Hypertension.
As Ritz points out, obesity has now been show to be a risk factor for chronic kidney disease, independent of its common association with diabetes and/or hypertension.
The earliest record of nephrotic range proteinuria (where patients excrete several grams of protein with their urine every day) in patients with severe obesity, was in 1974 by Weisinger. This report described four patients with severe proteinuria, which decreased with weight loss and reappeared with subsequent weight regain.
Weisinger also described a typical focal segmental glomerulosclerosis (FSGS) on histological exams of kidney biopsies from these patients, findings that appeared quite different from other causes of proteinuria (e.g. diabetic nephropathy).
Subsequent studies have confirmed similar findings in other patients with severe obesity and protienuria and between 1986 and 2000 a more than 10-fold increase in the prevalence of this problem was reported.
Also, more recently, similar (albeit less severe) FSGS has been reported even with moderate obesity as well as in obese children and adolescents.
Although proteinuria is generally reduced with weight loss, few patients manage to keep the weight off, resulting in recurrence of protein excretion and deterioration of renal function.
More recently, bariatric surgery, which generally results in much better long-term weight loss, has been reported to reduce proteinuria and stabilse renal function in obese patients with FSGS.
Of course, although FSGS appears to be the lesion that is most typically associated with obesity, it must be noted that all forms of kidney disease can be worsened by excess weight.
Unfortunately, large prospective trials of weight loss (surgical or non-surgical) to prevent the progressive loss of kidney function in patients with excess weight are lacking.
Such studies may be particularly relevant today, as type 2 diabetes, a condition that often goes into prolonged remission after bariatric surgery, is now emerging as the single most common driver of endstage kidney failure leaving patients with no option other than dialysis or kidney transplantation.
I am sure that many obese patients with progressive renal failure would likely prefer bariatric surgery to a life on dialysis – but whether or not this is indeed the best option will probably first have to be shown in a trial.
Nevertheless, I am sure that some of my readers will probably know of cases where renal function (protein excretion and/or loss of filtration rate) was affected by weight loss – I’d certainly be very interested in hearing about these observations.
Ritz E, Koleganova N, & Piecha G (2011). Is there an obesity-metabolic syndrome related glomerulopathy? Current opinion in nephrology and hypertension, 20 (1), 44-9 PMID: 21088574