It is World Kidney Day – 9th March, 2017.
The leading article in the Clinical Kidney Journal today is on obesity and chronic kidney disease, subtitled “hidden consequences of the epidemic” though I am not sure any effects of obesity are in fact that hidden – mine certainly aren’t.
The reason this article grabbed my attention is that the message for those of us with PKD that has already progressed down the curve to the later stages of CKD is actually by no means straightforward. Yes, on balance, an individual is better off if they are not obese, BUT in the later stages of CKD and in end stage renal disease (ESRD) obesity is associated with lower mortality rates. This would suggest that any advice to lose weight, to aim for a more acceptable BMI might need attenuating.
Is this just because BMI is a poor marker of obesity? We have discussed this before (see post December 2015).
BMI doesn’t tell you where the fat resides and fat that pads our internal organs, known as visceral fat, is known to be less healthy than fat lying under the skin or subcutaneous fat. Because of this fact clinicians devised measures of acceptable waist circumferences: no more than 102cm for a man or 88cm for a woman. (It seems so unfair that by virtue of hormones we women seem to draw the short straw). BUT, and it is another capitalised BUT, for those of us with PKD how can waist circumference have any reliable meaning?
Without exception our kidneys are larger than normal. Where a normal kidney will be the size of an avocado, ours can be aubergine/melon/cabbage/rugby ball sized. Just try hiding two rugby balls inside your jacket and keeping your waist circumference below 102cm – it won’t work; we will all have some degree of abdominal distension. For the same reasons the other suggested measure of waist circumference to hip circumference ratio (should be less than 0.9) will not work for us either.
However, it isn’t just that the measures for obesity are inaccurate. There are some short term protective effects from carrying more body weight even if it is more fat. Fat has the ability to bind some toxins, such as endotoxins, TNF-alpha and uremic toxins. Obesity confers a more stable haemodynamic status which can mitigate the stress response. Higher muscle mass means reserves of protein and energy that are protective in the face of short term illness. There are benefits from lower circulating actin and higher plasma gelsolin, factors that are inversely associated with mortality. Carrying some excess weight when you reach late stages of CKD or ESRD may be an advantage.
So while the main message of the journal article is that populations are increasingly obese and this is associated with increased incidence of kidney diseases, glomerulopathies, kidney stones and kidney cancer, the subtitle for us with PKD should perhaps be nuanced. I might rewrite their subtitle: the hidden benefits for the endomorph.
Csaba P. Kovesdy, Susan L. Furth, Carmine Zoccali, on behalf of the World Kidney Day Steering Committee; Obesity and kidney disease: hidden consequences of the epidemic. Clin Kidney J 2017; 10 (1): 1-8. doi: 10.1093/ckj/sfw139