If you're eating a high-protein diet, you've probably encountered this statement:
"That's too much protein. Aren't you worried about your kidneys?"
If you're not, this unfortunate misconception may be exactly what's preventing you from embracing it.
The problem is, the research that's commonly referenced to support this claim looks extremely legitimate at first glance:
The Nurses' Health Study followed approximately 1600 female participants for 11 years and found that eating a high-protein diet caused kidney dysfunction.
Until you dig a little deeper, and realize it's far from that. What many fail to acknowledge is that the kidney damage was only experienced in those with a pre-existing renal condition. Which is like saying:
"Someone with a busted shoulder can compromise shoulder function by lifting weights."
"A guy with a broken foot could compromise his recovery by jumping up and down."
Other than the misleading conclusions drawn from the Nurse's Study, all research on high protein diets and kidney damage shows no association when performed on healthy subjects. Even with protein intake as high as 2.8g per kg of bodyweight, the kidney's were not negatively effected.
One of the kidneys main functions is to process the waste products from the food we eat, which includes protein. Eating a high protein diet can increase the filtration work from the kidneys (hyperfiltration), but this is a:
"Perfectly normal adaptive mechanism well within the functional limits of a healthy kidney." Martin et al. 2005, Nutrition & Metabolism
Like the rest of our body, we're training the kidneys to handle more, which is not detrimental in the least bit. In the Nurse's Health Study (and similar research) those with healthy kidneys did not experience altered functionality, and many didn't even enter a state of hyperfiltration.
Moreover, there's ample evidence that high protein consumption and a corresponding state of hyperfiltration produces a more favorable adaptation from the kidneys; as over time there's less protein found in the urine (which suggests greater absorption). Since muscle maintenance and growth is dependent on optimal protein absorption and synthesis, one could argue that this adaptation following hyperfiltration is extremely beneficial.
Recent research has found no benefit to lowering protein intake for those with kidney disease. n fact, at least 1.4g/kg of bodyweight has been recommended to maintain proper nitrogen balance -- the equivalent of 127g/day for a 200lb man!
Even though this is the recommendation for someone with kidney disease, I'd guess many of you reading this (with perfectly healthy kidneys) are not coming close to that daily intake. And sadly, this may actually put you at a higher risk of kidney damage:
"It is clear that protein restriction does not prevent decline in renal function with age, and, in fact, is the major cause of that decline. A better way to prevent the decline would be to increase protein intake." Institute of Medicine
The recommendation to restrict beef, pork, fish, and lamb is not only unqualified, but if we replace these beneficial foods with sugars and starches, we more than likely increase our risk of kidney damage.
In Eat Meat And Stop Jogging, Mike identifies the common misconceptions holding you back from achieving that leaner, stronger, healthier physique.
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