Protein is an essential nutrient that plays a vital role in building and repairing tissues, maintaining muscle mass, and supporting the body’s metabolic functions. Yet, there continues to be debate not only about the optimal amount of protein you need for optimal health, but also about the potential impact a high-protein diet may have on kidney function. Let’s dig into the latest research to understand more.
First… how the kidneys work.
The kidneys are two bean-shaped organs located on either side of the spine that filter the blood, removing waste products and excess fluids, and maintaining the body's fluid balance. The kidneys excrete waste products in the form of urine, which then travels through the ureters to the bladder, where it is stored until it is eliminated from the body.
Second… how protein impacts kidney function.
The kidneys play a crucial role in eliminating wastes from protein metabolism. When protein is broken down, it produces urea and creatinine, two byproducts that the kidneys must remove from the body. High-protein diets can increase the workload on the kidneys and may hurt renal function.
Now… here’s where things get a little complicated.
There's conflicting evidence about the impact of protein intake on renal function. Some studies suggest that a high-protein diet can increase the risk of kidney damage and decline in renal function, particularly in people with kidney damage or kidney disease. Other studies, though, have found no significant impact of high protein intake on the kidneys in people without kidney disease or reduced kidney function.
So… what’s the deal?
It seems like the type of protein source might play a role. Animal protein sources, such as meat, dairy, and eggs, contain high levels of sulfur-containing amino acids, which produce more byproducts that need to be eliminated by the kidneys. On the other hand, plant-based proteins—think lentils, black beans, peanuts, almonds, tofu, tempeh—contain lower levels of sulfur-containing amino acids, which may reduce the workload on the kidneys.
A 2003 study published in the Annals of Internal Medicine found that high intake of nondairy animal protein may accelerate a decline in kidney function in women with mild renal dysfunction (although for women with normal kidney function, the study showed no impact). Another study, published earlier this year in the journal Nutrients, found that a plant-dominated, low-protein diet may help delay the progression of chronic kidney disease (CKD), as well as manage complications of CKD.
What about current protein recommendations?
The recommended daily allowance (RDA) for protein intake is 0.8 grams per kilogram (kg) of bodyweight (roughly 0.35 grams per bodyweight pound) for the average sedentary adult. But some experts believe that this recommendation is too low, especially for athletes, active adults, and older adults who may need more protein to maintain muscle mass and prevent muscle loss.
In fact, for most people who exercise, the International Society of Sports Nutrition recommends a daily protein intake of 1.4 to 2.0 grams/kg (roughly 0.6 to 0.9 gram per bodyweight pound) to build and maintain muscle. And for people who train regularly, the American College of Sports Medicine recommends a similar range: 1.2-1.7 grams of protein per kilogram of bodyweight (or 0.5 to 0.8 grams per bodyweight pound). This is far below what the average competitive bodybuilder eats, which is about 2.4 grams of protein per kilogram (or roughly 1.1 grams per pound).
Nonetheless, other experts are concerned that some people are consuming too much protein, which could potentially impact their kidneys. The American Heart Association, for example, recommends that adults should aim for 5-6 ounces of protein per day, which is equivalent to about 35-42 grams of protein—lower than the current RDA guidelines, which are established by the U.S. Food and Nutrition Board.
Why the guidelines need to be updated—for everyone.
Research shows that a higher protein intake is beneficial for a variety of health reasons: building muscle and strength, maintaining bone health, managing weight, and improving metabolic health. Plus, consider this: the current guidelines are for sedentary adults. They do not consider a person’s level of physical activity, nor individual differences in protein metabolism and requirements. This means these guidelines may not be appropriate for certain populations, yet they are still weighed by doctors when making personal recommendations.
But what does this mean for people with kidney health concerns?
That’s where things get tricky. As I explain in my post on creatinine, kidney health does not look the same for everyone. A sedentary person with kidney disease will have different protein needs than a bodybuilder with one kidney and slightly reduced function. Yet, kidney function continues to be measured the same way for everybody. And this, unfortunately, means that some people may be misdiagnosed with kidney disease and are told to follow a diet that is not truly appropriate for their body.
Of course, this does not mean that people with reduced function or kidney disease should eat 200 grams of protein a day. Multiple studies have shown that high-protein diets do, in fact, impact renal function when kidney damage or kidney disease is already present. But whether every person with kidney issues should eat only 60 grams of protein a day should be questioned. The current guidelines should be updated not only to reflect the needs of athletes without kidney disease or kidney damage, but also the diverse needs of athletes with reduced kidney function.
In the end…
The impact of protein intake on renal function is a complex issue, and the type of protein source may play a role. Based on recent studies, plant-based protein sources may be a better option for people concerned kidney health. As for current protein recommendations, consult with a healthcare professional to determine your individual protein requirements, making sure you're meeting your nutritional needs while maintaining optimal kidney function.
It's all about finding the right balance and making informed choices based on the latest research, expert guidance, and your individual needs. So, go ahead and enjoy that chicken breast or plant-based protein bowl, but remember to always listen to your body and consult with a professional if you have any concerns.