Protein and Kidney Function By Jamie Hale II
Athletes, particularly in sports requiring strength and power, consume high levels of dietary protein. In fact, many athletes habitually consume protein in excess of 2.0 g/kg/day. Supplementation with amino acids will further increase dietary protein levels in these individuals. Yet there is no evidence that this population is at greater risk for kidney disease or losses in renal function. Poortsmans and Dellalieux found that protein intakes in the range of ~1.4-1.9 g/kg/day or 170-243% of the recommended dietary allowance did not impair renal function in a group of 37 athletes. We found no data in the scientific literature to link high protein intakes to increased risk for impaired kidney function in healthy, physically active men and women.
Studies that claim an increased propensity for stone formation as a result of increased protein intake should be taken at face value because propensity is a surrogate marker and does not represent actual stone formation. Further, randomized control trials have not been done to test whether an increased tendency for stone formation is enhanced with consumption of a high protein diet.
Epidemiological studies provide conflicting evidence with regard to the association between protein intake and the predisposition for kidney stone formation. In a prospective study of over 45,000 men, researchers found a direct correlation between animal protein intake and risk of stone formation. However, findings in women are difficult to interpret due to conflicting reports in the literature. While some studies have shown a direct relationship between animal protein intake and risk of stone formation in women, other work suggests an inverse relationship exists].
Conflicting findings regarding the role of dietary protein in kidney stone formation limit the development of universal guidelines with regard to a recommended protein intake for individuals at increased risk for stone formation. It is not likely that diet alone causes kidney stone formation]. Rather, metabolic abnormalities are typically the underlying cause. For example, Nguyen et al., found that high intakes of animal protein adversely affected markers of stone formation in those afflicted with a stone causing disorder, while no changes were observed in healthy individuals. It has been suggested that one must have a preexisting metabolic dysfunction before dietary protein can exert an effect relative to stone formation. This notion has been coined the “powderkeg and tinderbox” theory of renal stone disease by Jaeger. This theory asserts that dietary excesses, such as high protein intake, serve as a tinderbox which, only in tandem with a metabolic abnormality (the powderkeg), can bring about stone formation. At the present time, however, evidence showing that a high protein intake is an inherent cause of this renal abnormality or is consistently associated with increased kidney stone formation does not exist.
Conclusion – 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.
Below are a couple of abstracts looking at renal function and protein intake:
Do regular high protein diets have potential health risks on kidney function in athletes? Poortmans JR, Dellalieux O.
Department of Physiological Chemistry, Institute of Physical Education and Kinesiotherapy, Free University of Brussels, Belgium.
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 g.kg 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 g.kg does not impair renal function in well-trained athletes as indicated by the measures of renal function used in this study.
Changes in renal function during weight loss induced by high vs low-protein low-fat diets in overweight subjects. Skov AR, Toubro S, Bulow J, Krabbe K, Parving HH, Astrup A.
Research Department of Human Nutrition, The Royal Veterinary and Agricultural University, Copenhagen, Denmark.
BACKGROUND: Due to the high satiating effect of protein, a high-protein diet may be desirable in the treatment of obesity. However the long-term effect of different levels of protein intake on renal function is unclear.
OBJECTIVE: To assess the renal effects of high vs low protein contents in fat-reduced diets.
DESIGN: Randomized 6 months dietary intervention study comparing two controlled ad libitum diets with 30 energy (E%) fat content: high-protein (HP; 25 E%) or low-protein, (LP, 12 E% protein). All food was provided by self-selection in a shop at the department, and high compliance to the diet composition was confirmed by measurements of urinary nitrogen excretion.
SUBJECTS: 65 healthy, overweight and obese (25<34 kg/m2).
RESULTS: Dietary protein intake changed from 91.1 g/d to a 6 months intervention average of 70.4 g/d (P<0.05) in the LP group and from 91.4 g/d to 107.8 g/d (P<0.05) in the HP group, producing changes in glomerular filtration rate (GFR) of -7.1 ml/min in the LP group and +5. 2 ml/min in the HP group (group effect: P<0.05). Kidney volume decreased by -6.2 cm3 in the LP group and increased by +9.1 cm3 in the HP group (P<0.05), whereas albuminuria remained unchanged in all groups.
CONCLUSION: Moderate changes in dietary protein intake cause adaptive alterations in renal size and function without indications of adverse effects.
Armstrong, L, Martin, W, Rodriguez, N. Dietary Protein intake and Renal Function.
Jamie Hale has a Bachelors degree in psychology with emphasis in sports psychology from Eastern Kentucky University. Coach Hale became an official member of The World Martial Arts Hall of Fame April the 4th 2003. He is recognized for his Strength and Conditioning work with martial artists and his writings pertaining to the arts. Jamie is available for personal consultations.