Thursday, 22 December 2011

40 Things You Should Know – The Science (part 7)

Point 31

Dietary protein intake and renal function

Recent trends in weight loss diets have led to a substantial increase in protein intake by individuals. As a result, the safety of habitually consuming dietary protein in excess of recommended intakes has been questioned. In particular, there is concern that high protein intake may promote renal damage by chronically increasing glomerular pressure and hyperfiltration. There is, however, a serious question as to whether there is significant evidence to support this relationship in healthy individuals. In fact, some studies suggest that hyperfiltration, the purported mechanism for renal damage, is a normal adaptative mechanism that occurs in response to several physiological conditions. This paper reviews the available evidence that increased dietary protein intake is a health concern in terms of the potential to initiate or promote renal disease. While protein restriction may be appropriate for treatment of existing kidney disease, we find no significant evidence for a detrimental effect of high protein intakes on kidney function in healthy persons after centuries of a high protein Western diet.
Although excessive protein intake remains a health concern in individuals with pre-existing renal disease, the literature lacks significant research demonstrating a link between protein intake and the initiation or progression of renal disease in healthy individuals. More importantly, evidence suggests that protein-induced changes in renal function are likely a normal adaptative mechanism well within the functional limits of a healthy kidney. Without question, long-term studies are needed to clarify the scant evidence currently available regarding this relationship. At present, there is not sufficient proof to warrant public health directives aimed at restricting dietary protein intake in healthy adults for the purpose of preserving renal function.


Do regular high protein diets have potential health risks on kidney function in athletes?


Excess protein and amino acid intake have been recognized as hazardous potential implications for kidney function, leading to progressive impairment of this organ. It has been suggested in the literature, without clear evidence, that high protein intake by athletes has no harmful consequences on renal function. This study investigated body-builders (BB) and other well-trained athletes (OA) with high and medium protein intake, respectively, in order to shed light on this issue. The athletes underwent a 7-day nutrition record analysis as well as blood sample and urine collection to determine the potential renal consequences of a high protein intake. The data revealed that despite higher plasma concentration of uric acid and calcium, Group BB had renal clearances of creatinine, urea, and albumin that were within the normal range. The nitrogen balance for both groups became positive when daily protein intake exceeded 1.26 but there were no correlations between protein intake and creatinine clearance, albumin excretion rate, and calcium excretion rate. To conclude, it appears that protein intake under 2. 8 does not impair renal function in well-trained athletes as indicated by the measures of renal function used in this study

Effect of chronic dietary protein intake on the renal function in healthy subjects.



Relatively little is known about the influence of chronic oral protein intake on the kidney function. In most studies only the effect of a short-term change in protein intake [6-28 days] or the effect of an acute protein load on the glomerular filtration rate was studied. The purpose of this study was to investigate the effect of chronic oral protein intake on endogenous creatinine clearance and on the albumin excretion rate.


In a prospective study 88 healthy volunteers with normal renal function (32 vegetarians, 12 body-builders with no supplementary protein concentrates, 28 body-builders with supplementary protein concentrates and 16 subjects with no special diet) were examined. In order to investigate the effect of chronic oral protein intake, the participants were on their diet for at least 4 months.


Endogenous creatinine clearance as a measure for glomerular filtration rate varied between 32 ml/min and 197 ml/min or 34 and 186 ml/min x 1.73 m2, respectively. Nitrogen excretion rate was used as a measure for the daily protein intake, since it is known to correlate linearly with the daily protein intake. Nitrogen excretion rates ranged between 2.66 g/d and 33.93 g/d reflecting a daily protein consumption between 17 and 212 g/d or 0.29 g/kg bw/d and 2.6 g/kg bw/day, respectively. Between nitrogen excretion rate and endogenous creatinine clearance a non linear, highly significant correlation was found showing a saturation with a maximum endogenous creatinine clearance of 181.7 ml/min (dose response curve). A similar correlation was observed between urea excretion rate and endogenous creatinine clearance. Using a model for multiple regression analysis the dependence of the albumin excretion rate on nitrogen excretion rate and endogenous creatinine clearance was examined. Only a significant correlation was found between albumin excretion rate and endogenous creatinine clearance, while the correlation between albumin excretion rate and nitrogen excretion rate was not significant.


This investigation shows that chronic oral protein intake of widely varying amounts of protein is a crucial control variable for the glomerular filtration rate in subjects with healthy kidneys. It is suggested that these changes reflect in part structural changes of the glomerulus and tubules due to chronic protein intake.

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