How High Protein Diets Affect The Kidneys

Protein comes from the Greek word proteos, which means the first or prime importance, and there is no debating the important role that protein plays in our health and body composition transformations.

We hear from many sources that we should be consuming more protein to gain muscle and even aid in weight loss, but how much do we really need? Does eating too much protein cause kidney damage? 

These are all very important questions and in this article we’ll dive into the latest research on this topic.    

Kidneys: What are they and why are they important

Our kidneys are one of the most important organs in our bodies. They are responsible for filtering toxins from our blood and transforming the filtered waste into urine, and much more. 

Our kidneys keep things well-regulated and in balance, as without this balance, nerves, muscles, and other tissues in your body may not work normally.

The kidneys, the bladder, and the ureters make up the urinary system.

Within the kidney, the functional unit is called the nephron, and each human kidney has approximately 1 million nephrons. The kidneys play a crucial role in the regulation of water homeostasis, electrolyte composition (e.g., sodium, chloride, potassium, bicarbonate), regulation of blood pressure, and acid–base homeostasis.

As mentioned at the beginning of this article, the kidneys filter the plasma of the blood and produce urine, which allows the kidneys to excrete metabolic waste products such as urea, ammonium, and foreign chemicals, such as drug metabolites from the body.

The kidneys are also responsible for the reabsorption of glucose and amino acids from the filtered plasma, in addition to regulating calcium and phosphate uptake (high in children).

The kidneys play a role in gluconeogenesis, which is a metabolic pathway that generates glucose from certain non-carbohydrate carbon substrates such as amino acids, and during fasting can synthesize and release glucose into the blood, producing almost 20% of the liver’s glucose capacity.

The kidneys are endocrine organs which make polypeptides called kinins, that cause vasodilation and smooth muscle contraction.

These kinins include:

• 1,25-dihydroxycholecalciferol (vitamin D3)
• Erythropoietin (stimulates production and maintenance of crucial red blood cells)
• Making and secreting renin (regulates blood pressure)

Specifically, in the kidneys, a fluid that resembles plasma is filtered through the glomerular capillaries into the renal tubules in a process called glomerular filtration.

As this glomerular filtrate passes down the tubules, its volume is reduced and its composition altered by the processes of tubular reabsorption (removal of water and solutes from the tubular fluid) and tubular secretion (secretion of solutes into the tubular fluid) to form the urine that enters the renal pelvis. From the renal pelvis, the urine passes to the bladder and is expelled to from the body by the process of urination [1].

How High Protein Diets Impact Kidney Health

One of the biggest concerns I hear from people about protein is the thought that eating too much of it will cause kidney damage or dysfunction. This is an interesting little myth that just won’t seem to die. It is one that medical professionals and lay people alike seem to buy into without hesitation.

The misconception/belief is that you take a healthy person and put them on a high protein diet, the protein will somehow negatively influence kidney function, damage this organ and promote disease.

However, there is no clear evidence that suggests a high protein intake promotes any type of renal (kidney) dysfunction in healthy people. There aren’t even studies that suggest this may happen. In fact, there is evidence that directly refutes this notion [2].

Scientists that have devoted their careers to this area of research now urge health care professionals to change their restrictive (unfounded) views on protein intake. 

These experts provide 3 crucial reasons why:

1. We know very little about the important functions of various amino acids at both the mechanistic and quantitative level. Our knowledge on protein requirements to improve health is quite limited [3].
2. Based on poor analysis techniques, previous recommendations are most likely well short of the mark [4].
3. As no evidence suggests that increasing protein intake will cause harm, when healthcare professionals caution healthy, active people about the perils of a high protein diet, it’s ignorance of the worst kind.  This is misinformation that may contribute to poor health [2-4].

A high protein intake (2-3 times the recommended daily allowance) of low-fat protein does not promote any adverse effect in healthy people. 

In fact, scientists leading the way in this field of research suggest the opposite; increasing the proportion of protein in the diet is a solid strategy that will help promote health and better results from exercise training [2-4].

How Much Protein is Too Much?

The definition of “too much” is quite subjective and dependent on the person or group defining it. What is too much protein? Is it anything that exceeds the recommended daily allowance (RDA)? 

Many people believe that the RDA is the gold standard and that you shouldn’t consume more than this, but it's actually not that clear-cut.

A little history on the 'RDA', and why it's important to understand

The RDA was developed in the United States in 1941 during World War II. The concept behind developing these RDAs for macronutrients (Protein, Carbohydrate, Fat), was to establish a minimum level of daily nutrient intake in order to help people avoid disease. Of course, avoiding disease was crucial during a time of war. 

While the RDA may have been useful 75 years ago in wartime conditions where food rations were scarce, the RDA doesn’t represent the amount of any nutrient required for optimal health or performance, only disease prevention.

So, what exactly is a high protein intake?

This is where it gets confusing and inaccurate. 

When we take a look at the scientific literature; protein intake ranges from 15-16% of total energy to as high as 35% of total calories or intakes that merely exceed the RDA of 0.8g/kg/day. 

What if I consume more than the RDA?

The International Society of Sports Nutrition conducted an extensive review of the research and recommended that protein intakes of 1.4 – 2.0g/kg/day for physically active individuals is not only safe, but may improve the training adaptations to exercise. That amount is up to two and a half times the 'RDA'.

Recent work in this area have confirmed previous investigations and found that up to 3.3g/kg/day for one year provided no harmful effects on liver and kidney function [5].  This is over 5.5 times the RDA!  This level also provided no increase in body fat. 

Again, the definition of “too much” is quite subjective and dependent on the person or group defining it, but it appears that consuming more than the RDA will improve athletic performance and promote healthy aging, while increasing protein intake doesn’t appear to increase weight or body fat.  In addition, there is no research that is able to establish a link of any kind that may suggest a particular protein amount will damage a healthy organ or body. 

So how much do you really need to reach your goals?

This depends on what you’re doing. One of the most crucial findings from contemporary research on this topic is that, a higher protein intake won’t improve your body composition unless you are engaged in a structured resistance exercise program.  

If you aspire to enhance your health and body composition with more lean muscle and less fat, the real protein experts suggest 2-3 times the RDA is not only acceptable, but highly recommended. 

So, up to 35% of your total daily energy intake is recognized as safe and effective. Once you start going much higher than this, you risk sacrificing other important sources of nutrition (e.g., fiber and fuel from other food sources). 

The estimated recommendations for protein need in many populations are constantly improving due to improved research methods to help assess protein requirements. An example of this is that the average protein requirement recommended for women aged above 65 years has increased up to 1.3 grams per kilogram of body weight per day. 

Another important recommendation from the experts is that a 25-30 gram dose of protein per meal is considered a safe effective strategy that promotes better health, satiety and loss of unwanted weight in overweight adults [6].

Protein, weight loss & body composition: Time to re-think the RDA?

Consuming higher amounts of protein can actually improve health and body composition. Over the last 10 years, there has been an ever-increasing amount of very good quality research on the benefits of increasing protein intake.

A recent study published in the FASEB Journal confirmed what physique athletes know is true.  Researchers investigated the effects of consuming different amounts of protein on body composition and muscle protein synthesis during periods of energy deficit. 

During this time participants were provided with meals yielding either .8g, 1.6g or 2.4g of protein per kg of bodyweight.  Essentially, the first group consumed the RDA, while the second group consumed 2x RDA and the third, 3x RDA.

This was a well-controlled study and researchers calculated weight maintenance calorie requirement for the individuals.  After a 10-day acclimatization period, the researchers reduced energy intake to create a 40% energy deficit.  This was maintained for 21 days. 

Body composition and muscle protein synthesis were analyzed during days 9-10 of the weight maintenance period and days 20-21 of the energy deficit period. 

Here’s what they found

Participants lost the same amount of weight regardless of the protein regimen they were on.  However, the participants receiving 2x RDA and 3x RDA of protein lost a greater amount of weight from fat mass and less from fat free mass compared to the group receiving only the RDA.

The anabolic muscle response was decreased during the period of energy deficit in those consuming only the RDA of protein. Those consuming 2x RDA or 3x RDA experienced no difference in anabolic muscle response during energy deficit. 

What does this mean to you?

It means that increasing your protein intake to 2x RDA can protect against muscle loss while in a state of energy deficit (“diet”).  It also means that any anabolic effect from ingesting that meal will not be lost due to the state of energy deficiency. 

A loss of muscle mass, especially as we age is responsible for decline in many health markers.  If increasing protein intake is a way to avoid muscle loss, then it stands to reason that this would be the way to help maintain our health as well. 

Again, current RDA recommendations are based on the amount of protein necessary to avoid disease, NOT to optimize health.  The two are not the same [7].

Who Is at Increased Risk?

It’s been shown that the glomerular filtration rate (GFR) rises after protein consumption is increased [8]. This long-term elevation in GFR may be harmful to the kidney.

However, although it is well accepted that a high-protein diet is harmful to individuals with existing kidney dysfunction, there is very little evidence that a high protein intake is dangerous to healthy individuals [8].

The National Kidney Foundation’s recommendations for nondialyzed individuals with chronic kidney disease (CKD) are below those for the overall population (0.6–0.75 g/kg/day) [9]. One study in women with mild renal insufficiency reported a significant association between protein intake and diminished renal function [10].

In another cross-sectional study including 599 adult patients diagnosed with stage 3–5 CKD, a significant correlation between high protein intake and a decrease in GFR was reported when compared with normal or low intake [11].

The idea that high protein consumption may be detrimental to those with CKD seems obvious and is well accepted. However, hyperfiltration could just be an adaptive mechanism of high protein consumption and may not necessarily be related to a decline in renal function for those individuals with normal kidney function.

With respect to kidney function, characterizing the relation between high protein intake and hydration is of great importance. As a consequence of high protein intake, an increase in solute excretion, such as urea and other nitrogenous wastes, is produced.

Thus, more water is needed to avoid dehydration. A recent study analyzed the relation between increased protein intake and hydration indexes in a 12-week randomized, crossover, controlled diet intervention analysis [12].

In the study, individuals consumed several diets containing 3.6 (high), 1.8 (moderate), and 0.8 (low) g protein/(kg/day) for 4 weeks. The amount of energy ingested was calculated for each individual according to personal requirements and activity level at baseline.

Other features, such as blood urea nitrogen, plasma osmolality, urine-specific gravity, and estimation of fluid balance, were also evaluated. No changes in fluid intake and fluid balance were reported.

Importantly, greater blood urea nitrogen was found with the high-protein diet than with the moderate- or low-protein diet, and urine-specific gravity was significantly higher with the high-protein diet than with the moderate-protein diet. Baseline plasma osmolality was higher with the high-protein diet than with the moderate- or low-protein diet.

However, no significant effect on fluid status was reported as a result of increased dietary protein [12]. In conclusion, consideration should be given before those at risk of renal disease (i.e., those with diabetes, hypertension, or cardiovascular disease) start a high-protein diet.

Further investigation is needed to clarify the impact of long-term high protein consumption on the GFR in the older population, because the GFR decreases with age. In any case, a rise in protein consumption to 1–1.5 g/kg appears to be safe and even necessary for older individuals with healthy kidney function, because it is well accepted that protein efficiency declines with age. Serum creatinine and hemoglobin A1C tests for diabetes screening and a urine test for proteinuria are useful screening tools to identify individuals for whom high protein consumption may not be advisable [13].

High-protein diets have also been linked to the risk of kidney stone formation. In one large prospective study in humans, a positive association between animal protein consumption and kidney stone formation was observed [14].

Thus, high protein consumption may be unsafe for those with inherited or underlying abnormalities associated with renal disease and development of kidney stones [15]. 

These findings suggest that higher protein consumption could be considered an independent risk factor in the development of kidney stones in predisposed individuals [16].

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References:

1. Barrett K.E., B.S.M., Brooks H.L., Yuan J., Ganong's Review of Medical Physiology 26th Edition. 2019.

2. Poortmans, J.R. and O. Dellalieux, Do regular high protein diets have potential health risks on kidney function in athletes? Int J Sport Nutr Exerc Metab, 2000. 10(1): p. 28-38.

3. Reeds, P.J. and G. Biolo, Non-protein roles of amino acids: an emerging aspect of nutrient requirements. Curr Opin Clin Nutr Metab Care, 2002. 5(1): p. 43-5.

4. Millward, D.J., et al., Protein quality assessment: impact of expanding understanding of protein and amino acid needs for optimal health. Am J Clin Nutr, 2008. 87(5): p. 1576S-1581S.

5. Antonio, J., et al., A high protein diet (3.4 g/kg/d) combined with a heavy resistance training program improves body composition in healthy trained men and women--a follow-up investigation. J Int Soc Sports Nutr, 2015. 12: p. 39.

6. Jager, R., et al., International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr, 2017. 14: p. 20.

7. Pasiakos, S.M., et al., Effects of high-protein diets on fat-free mass and muscle protein synthesis following weight loss: a randomized controlled trial. FASEB J, 2013. 27(9): p. 3837-47.

8. Friedman, A.N., High-protein diets: potential effects on the kidney in renal health and disease. Am J Kidney Dis, 2004. 44(6): p. 950-62.

9. Kopple, J.D., National kidney foundation K/DOQI clinical practice guidelines for nutrition in chronic renal failure. Am J Kidney Dis, 2001. 37(1 Suppl 2): p. S66-70.

10. Knight, E.L., et al., The impact of protein intake on renal function decline in women with normal renal function or mild renal insufficiency. Ann Intern Med, 2003. 138(6): p. 460-7.

11. Huang, M.C., et al., Inadequate energy and excess protein intakes may be associated with worsening renal function in chronic kidney disease. J Ren Nutr, 2008. 18(2): p. 187-94.

12. Martin, W.F., et al., Effects of dietary protein intake on indexes of hydration. J Am Diet Assoc, 2006. 106(4): p. 587-9.

13. FAO/WHO/UNU, Energy and protein requirements. Report of a joint FAO/WHO/UNU Expert Consultation. World Health Organ Tech Rep Ser, 1985. 724: p. 1-206.

14. Fink, H.A., et al., Diet, fluid, or supplements for secondary prevention of nephrolithiasis: a systematic review and meta-analysis of randomized trials. Eur Urol, 2009. 56(1): p. 72-80.

15. Hess, B., Nutritional aspects of stone disease. Endocrinol Metab Clin North Am, 2002. 31(4): p. 1017-30, ix-x.

16. Cuenca-Sanchez, M., D. Navas-Carrillo, and E. Orenes-Pinero, Controversies surrounding high-protein diet intake: satiating effect and kidney and bone health. Adv Nutr, 2015. 6(3): p. 260-6.