Protein Intake and Kidney Disease

A common myth about dietary protein is that a high intake of protein causes kidney disease.  The reasoning behind that myth is that, since the kidneys are responsible for filtering and excreting nitrogen, the high nitrogen content of protein could be putting a strain on the kidneys.

Where did this myth come from?

Dr. Louis Newburgh published research showing that rabbits developed kidney disease as a result of eating a diet rich in meat protein (beef).  However, this research was later criticized as unreliable, because it was noted that rabbits are herbivores.  Thus, eating beef is a substantial deviation from a rabbit’s physiology, and these findings could not be translated to our understanding of human physiology.

 

What is considered high protein?

“The Recommended Dietary Allowance (RDA) for both men and women is 0.80 grams of good quality protein/kg body weight/d.” (ref)  It’s important to note, however, that the RDA is set a level that is necessary to avoid disease from inadequate intake.  Thus, consumption of protein at less than that level is not sufficient to maintain proper health.

“High protein intake” is generally considered 1.6 g/kg/d.  From a survey of food intakes, individuals consuming the highest amount of protein at 1.5 g/kg/d protein were noted to have a very low risk of adverse effects.

Though limited research has been conducted on potential risks of high protein intake, there is no evidence that amino acid intake from high protein intake poses any risk. (ref)

 

What actually causes kidney disease?

By far, the top 2 causes of kidney disease are diabetes and hypertension, accounting for more than 2/3 of chronic kidney disease. (ref)

Arguably, these are part of the same disease, Insulin Resistance, but are recognized as the 2 most proximate causes.

 

High protein in individuals with healthy kidneys

Rest assured that there is no evidence to indicate that high protein intake is harmful in individuals with healthy kidneys, reinforced by multiple studies.

In the absence of pre-existing kidney disease, high protein intake has no negative effect on kidney function. (ref)

High protein diets in conjunction with low carbohydrate intake show improvement in kidney function. (ref)

Diets consisting of higher protein improves kidney function in otherwise healthy individuals with prehypertension or hypertension. (ref)

A review of all available data as of 2005 concluded that “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.” (ref)

A study of men engaged in regular resistance training followed them for 6 months at their usual protein intake (avg 2.51 g/kg/d), followed by another 6 months at a higher protein intake (3.32 g/kg/d).  There were no adverse effects on kidney function or any other systems.  Also, of interest in this study, despite the subjects increasing calorie intake by ~400 kcal/day, there was no increase in fat mass. (ref)

Protein intake in established chronic kidney disease

When there is established kidney disease, the answer is not as clear-cut as in individuals with healthy kidneys.  Evidence is limited in this area by the fact that most studies are observational study designs and thus are not true interventional trails.

In the setting of diabetes and mild chronic kidney disease, a low carbohydrate diet with higher protein intake improves kidney function. (ref)

The American Diabetes Association even acknowledges that there is no good evidence for restricting protein intake in the setting of diabetic kidney disease:

For people with diabetes and diabetic kidney disease (either micro- or macroalbuminuria), reducing the amount of dietary protein below the usual intake is not recommended because it does not alter glycemic measures, cardiovascular risk measures, or the course of glomerular filtration rate (GFR) decline. (ref)

At some point, though, there does not appear to be any benefit to a low carbohydrate or high protein diet in advanced kidney disease.  In the setting of poor kidney function, the kidneys are struggling to keep up with normal filtration and thus are more susceptible to large loads of nitrogen, changes in electrolytes, and alterations in fluid balance.