Is Eating Too Much Protein Bad For Your Kidneys?

Whenever I mention the importance of protein in our diet on social media, I get bombarded with comments like, “NO, TOO MUCH PROTEIN IS BAD FOR YOUR KIDNEYS.” I’ve received dozens of such comments, which is why I decided to write this blog post. If you or anyone you know is hung up on protein being bad for your kidneys, I hope this post will serve as a useful resource.i8

Let’s start by exploring the role of protein in the body. Then we’ll look at how the body processes protein and the kidneys’ role in this process. Next, we’ll delve into the research conducted over the past two decades on protein intake vs. kidney health. Finally, we’ll conclude with key takeaways and how you can apply this information to your own life.

What is Protein and its Role in the Body?

Protein is crucial for building and maintaining tissues in the body. When we consume protein, our digestive system breaks it down into individual amino acids. Amino acids, the “building blocks” of protein. They are responsible for repairing and building muscle tissue, transporting nutrients, forming collagen, repairing damaged cells, regulating hormones and enzymes, and so much more.

These amino acids are then transported to various parts of the body where they are used for various functions.

When protein is broken down, waste products such as urea are produced. The kidneys play a critical role in filtering out these waste products from the bloodstream and excreting them through urine. Some people believe that eating too much protein could potentially lead to kidney damage or disease because it puts too much stress on the kidneys. This assumption is misguided, as we’ll see in subsequent sections.

Let’s first take a brief detour to learn how the kidneys filter waste products. This prerequisite knowledge will be useful when we dive into the studies further in the post.

The Kidneys’ Role in Filtering Waste Products

The kidneys are bean-shaped organs just below the ribcage. Their main function is to filter waste products from the blood and excrete them through urine. This process helps maintain a balance of water, salts, and minerals in your blood.

Your kidney receives blood through the renal artery. As the blood flows through the kidneys, it passes through tiny units called nephrons. Each kidney is made up of about a million of these nephrons.

Each nephron contains a filtering unit called a glomerulus. The glomerulus allows small molecules such as water, glucose, and amino acids to pass through but prevents larger molecules like proteins and blood cells from passing. Once the nephrons filter the blood, it flows out of your kidney through the renal vein.

The filtered blood then enters a tubule where it removes additional waste products such as urea, creatinine, and uric acid.

Your body then excretes these waste products as urine.

To determine how well your kidneys are filtering waste from your blood, doctors use a mathematical formula called the glomerular filtration rate (GFR). This formula estimates your kidney function based on the level of creatinine in your blood. The higher your filtration rate, the better your kidneys are working. For instance, a GFR of 100 mL/min/1.73 m2 falls within the normal range, indicating 100% kidney function. On the other hand, a GFR of 50 mL/min/1.73 m2 means roughly 50% kidney function. A a GFR of 30 mL/min/1.73 m2 indicates 30% kidney function. And so on. These technical details should be enough for you to make sense of the studies below.

What the Research Says About High Protein Diets and Kidney Health

Now that you understand how the kidneys work, let’s look the research on high protein diets and kidney health. The research consistently shows that high dietary protein intake does NOT harm kidney function in healthy adults. High protein intake may cause harm in people with diagnosed kidney disease, but this doesn’t apply to people with healthy kidneys.

Below, you’ll find a summary of various studies that support this statement. I’ve included systemic reviews and meta-analyses at the top, with a couple of high-quality individual studies listed towards the end. While it’s impossible to include every study, I’ve included whatever meta-analysis and systemic review I could find. This provides a good representation of the research on this topic.

Note: A meta-analysis combines data from multiple studies to draw a more comprehensive conclusion about a particular question or topic. It’s like putting together pieces of a puzzle from different research to get a clearer picture. A systematic review summarizes all the available research on a specific question or topic. Researchers follow a strict method to find, evaluate, and summarize all the research studies on that topic. A systematic review typically precedes a meta-analysis. The systematic review involves a thorough and unbiased search and analysis of all relevant studies on a particular topic. This ensures that the meta-analysis is based on a comprehensive and representative set of data. This systematic approach is crucial to avoid selective bias and to ensure that the meta-analysis is reliable and valid. The meta-analysis then statistically combines the results from these studies to provide a more robust overall conclusion.

• Remer, T., et al (2023): This umbrella review of systematic reviews assessed the relationship between kidney diseases and a high protein diet. The study analyzed both randomized controlled trials and cohort studies. It investigated chronic kidney disease, kidney stones, and various kidney function parameters, such as albuminuria, glomerular filtration rate, serum urea, urinary pH, and urinary calcium excretion. The study concludes that our bodies make normal adjustments, rather than harmful ones, when we consume more protein. These changes reflect physiological regulatory responses, rather than pathometabolic responses to higher protein loads. In other words, a high-protein diet does not cause metabolic problems. Additionally, the study found no evidence that a high-protein diet triggers kidney stones or diseases.
• Devries Michaela C., et al (2018): In this systematic review and meta-analysis of randomized controlled trials, they aimed to determine whether high protein diets (≥1.5 g/kg body weight or ≥20% energy intake) have any adverse effects on kidney function, specifically glomerular filtration rate (GFR). They reviewed 2144 abstracts and selected 40 articles for full-text review. Out of these, they analyzed 28 articles and included data from 1358 participants. They found no evidence to suggest that high protein intakes have a negative impact on kidney function or GFR in healthy adults.
• Elswyk M E V., et al (2018): This study analyzed 26 studies, including randomized controlled trials and observational studies, to determine whether consuming protein above the US Recommended Daily Allowance affects kidney function, specifically glomerular filtration rate (GFR). The study concludes that higher protein intake is generally safe for healthy individuals. It has little to no impact on blood markers of kidney function or blood pressure.
• Yu Z., et al (2019): This study examined how dietary protein intake affects kidney function decline and mortality by reviewing existing epidemiological studies. The study concludes that while high protein intake does not affect kidney function in those with normal kidney function, it may be harmful to individuals with renal damage. Additionally, the study found a J-curve relationship between baseline protein intake and mortality, indicating that protein intake below 0.8 g/day per kg of ideal weight increases the long-term risk of mortality. Therefore, for people with kidney disease, a minimum protein requirement of 0.8 g/day per kg of bodyweight is recommended to avoid kidney function decline while also minimizing the mortality risks associated with low protein intake.
• Martin W., et al (2005): The paper looked at evidence from multiple studies that explore the impact of high protein consumption on individuals with normal and impaired kidney function. It concludes that while limiting protein intake may be advantageous for those with kidney disease, there is no significant evidence to suggest that high protein consumption harms kidney function or consistently leads to increased kidney stone formation in healthy people.
• Knight E., et al (2003): This study investigated the effects of high protein intake on kidney function over an 11-year period. The research involved 1,624 women from the Nurses’ Health Study, evaluating their protein intake and kidney function. The study found no significant correlation between high protein intake and kidney function decline in women with normal kidney function. However, in women with mild kidney insufficiency, higher total and nondairy animal protein intake was associated with a decline in kidney function.
• Antonio J., et al (2016): This one-year crossover study investigated the effects of a high-protein intake on healthy, resistance-trained men. The study used a randomized crossover design where participants alternated between their normal diet and a high protein diet (>3 g/kg/day). Consuming a high protein diet for one year did not have any harmful effects on blood lipids, liver, or kidney function.
• Tanaka S., et al (2023): This study used a remnant kidney model to simulate chronic kidney disease (CKD) and found that while a high-protein diet worsens glomerular injury in CKD mice, it does not cause kidney injury in healthy mice. This suggests that high-protein diets may be safe for individuals without CKD, but could be harmful for those with CKD.
• Poortmans J R., et al (2000): This study explores how high protein intake affects kidney function in bodybuilders and other well-trained athletes. It looks at indicators such as creatinine, urea, and albumin clearance. Even with higher plasma concentrations of uric acid and calcium, high protein intake (up to 2.8 g/kg) does not harm kidney function in well-trained athletes.
• Alvirdizadeh S., et al (2020): This study investigates how different types of dietary protein impact the risk of developing chronic kidney disease (CKD) using data from adults in the Tehran Lipid and Glucose Study. The research finds no significant link between total or animal protein intake and CKD incidence. However, they found a negative association between consumption of plant sources of protein and CKD risk.
• National Kidney Foundation (2004): While high-protein diets may not pose increased risk to those with normal renal function, they could be harmful for individuals with chronic kidney disease (CKD). They recommended that anyone considering a HP diet should undergo kidney function tests beforehand.
• J Am Soc Nephrol (1996): This study investigates the impact of a low-protein diet on patients with moderate renal disease. The study involved 585 patients with baseline glomerular filtration rates (GFR) of 25 to 55 mL/min/1.73 m2. The results showed that a low-protein diet initially caused a faster decline in GFR due to hemodynamic adjustments. However, over a period of three years, it led to a slower decline in GFR. This suggests that a low-protein diet may have potential benefits in slowing the progression of moderate renal disease.

So What Does This Mean For You?

Research suggests that protein may harm people with compromised kidneys, but there is no evidence to show that it is harmful for people with healthy kidneys. In fact, higher protein diets are immensely beneficial for overall health. It helps with weight loss, cardiovascular health, glycemic control, blood pressure, and so much more. On the contrary, eating a low protein diet can cause various issues like poor blood sugar regulation, reduced muscle mass, poor skin/hair/nail health, poor wound healing, weight gain, poor metabolism, weakened immune system, poor bone health, hormonal imbalances, mood swings, and reduced athletic performance. 

In light of such findings, you have to decide what is right for yourself. You can choose to live in fear of protein and neglect all the benefits it has for your metabolic health. Or you can eat a higher protein diet and experience its benefits.

It’s not black and white either. Try a higher protein diet for 3-6 months and see how you feel, physically and mentally. Run some labs to check if any of your health markers improved or worsened. If you don’t feel better on a higher protein diet, then you can always reduce your protein intake. Keep experimenting until you find the right amount of daily protein intake that works best for your body. This is the best way to discover the truth.

Conclusion

I hope this post dispelled any fears you may have had about protein intake and kidney disease. If you’re interested in increasing your protein intake, check out my articles that guide you through the process.

• How To Eat 100 Grams Of Protein Per Day (+ Example Day Of Eating)
• Indians Don’t Eat Enough Protein (Let’s Fix That)
• How To Turn Indian Meals Into High Protein Meals
• Pregnant Women Are Not Eating Enough Protein

Lastly, if you come across high-quality research conducted in the last 5 years that supports or refutes the above thesis, please share it. I’m particularly interested in meta-analyses and systemic reviews.

As always, if you have questions, please comment below!