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Do Kidneys Work Harder on High Protein?

Sep 10, 2011 | By Danielle Tworek

Excess protein consumption has been at the center of speculation for decades. The work of one researcher in the early 1980s spawned the hypothesis that still plagues low-carbohydrate dieters, athletes and bodybuilders. Research in the past decade has shown that kidney function is surprisingly more adaptive than previously thought.

The Original Hypothesis

The media and even some health-care professionals have suggested that a high-protein diet puts undo strain on the kidneys. This theory would lead you to believe that a lifetime of excessive protein consumption -- that is, greater than the RDA of approximately 0.8 g of protein per kilogram of body weight per day -- will ultimately lead to kidney disease. This hypothesis arose in 1982, when the "New England Journal of Medicine" published the work of pioneer researcher B.M. Brenner and colleagues. Brenner observed increased pressure on the renal system from excess protein levels in the body. Unfortunately, Brenner’s experiments were on animals and people already suffering from renal impairments. In 1989, another study published in the same journal observed the effects of excess protein on the kidneys of healthy individuals. These researchers found that, while some portions of the renal system were mildly taxed by excess protein consumption, the kidneys ultimately maintained normal function.

Function and Consumption of Protein

Consumption of protein is essential for a multitude of functions in the human body. Proteins fuel biological pathways such as tissue repair, hormone synthesis and enzyme function, as well as provide energy. The U.S. Department of Agriculture established that most healthy individuals need between 34 and 56 g of protein per day to sustain proper biological functioning. Athletes, bodybuilders and individuals suffering from severe tissue damage often need to consume far more than the RDA in protein per day. Many well-trained athletes consume nearly 2 g per kilogram of body weight per day to sustain their activities.

Your Kidneys and Protein

Protein consumption impacts the kidneys. When you consume protein, the kidneys are responsible for filtering what your body needs and excreting the excess. A 2000 study published in “The International Journal of Sports Nutrition and Exercise Metabolism” tested athletes who consumed moderate- to high-protein diets. Although nitrogen-balance spiked temporarily when protein for a particular day exceeded 1.26 g per kilogram of bodyweight, all other levels were normal. The study concluded that protein intake below 2.8 g per kilogram of body weight per day does not impair renal function. A 2005 review published in “Nutrition and Metabolism” reviewed a series of similar studies and also concluded that high protein consumption was not dangerous to healthy individuals.

When to Limit Your Protein Intake

A 2003 study published in the “Annals of Internal Medicine” came to the same conclusions as the 2000 and 2005 studies, but with one side note. These researchers tested the renal function of women who consumed excess protein. One group already had impaired renal function, while the other had healthy kidneys. Members of the group already suffering from reduced kidney function experienced a further decline. This indicates that individuals who suffer from kidney impairment should carefully monitor their protein intake. Always consult your doctor to determine the risks to your health before making changes to your diet.

References

Article reviewed by Paula Martinac Last updated on: Sep 10, 2011

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