Too much protein bad for the kidneys?

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Research has not shown that high protein intake would be bad for the kidneys of healthy people. However, there is an increased risk for people who already have kidney problems. To the extent that protein poses an extra burden on the kidneys, this burden is greater for protein from red meat than from fish, white meat, dairy, or egg.

“Isn’t protein bad for your kidneys?”

It happens regularly: People see you drinking a protein shake, or they ask about your diet and find out that you get 25 to 30 percent of your calories from protein. “Isn’t that bad for your kidneys?” is a question that then often gets asked suspiciously often.

I say: “suspiciously often” because the average person knows relatively little about nutrition, often cannot explain the difference between carbohydrates, fats, and protein, and what their functions and nutritional values are. Yet, this person then knows to mention such a specific property. Where does this “common knowledge” that too much protein is bad for the kidneys come from?

In the gym and online, I regularly get asked about “the danger of protein for the kidneys” by athletes who have been addressed on this matter. Often, you can also hear the irritation in such an athlete’s voice because the person who made the comment about the danger of protein is often not exactly athletic themselves. These athletes then often contemptuously say that the protein could never be more dangerous than the beer and pizzas that have earned the questioner the title “obese.”

And I think that’s exactly where the cause of this whole myth about the danger of protein for the kidneys comes from. It is no coincidence that it is often people with severe overweight who start talking about the dangers of protein for the kidneys. It is likely that they belong to a group for whom this risk actually exists.

Kidney function: What do those kidneys actually do?

First, a bit of explanation about the kidneys. In short, the kidneys do the following:

• They filter the blood by removing waste products (“blood purification”)
• They regulate the blood’s acidity
• Ensure reabsorption of nutrients
• Regulate the blood’s osmolality (concentration of substances in the plasma)
• Production of certain hormones
• Regulate blood pressure

The theory of the “warners” is that when you eat a lot of protein, the kidneys have to work harder to filter it. This increased strain on the kidneys could lead to problems over time.

The function of the kidneys is often checked by measuring the so-called glomerular filtration rate (GFR). This is the rate of filtration through a specific part of the kidneys called the glomerulus. By injecting a special substance, inulin (not insulin), and looking at when it disappears from the blood and appears in the urine, this rate of GFR can be calculated. An increase in GFR means that the kidneys have to work harder. There are other ways to measure kidney function, such as measuring the appearance of waste products in urine, such as creatinine (breakdown of phosphocreatine) and albumin.

High protein can lead to kidney complaints in certain risk groups

Quite a bit of research has been conducted on the impact of protein on the kidneys, especially among people who have diabetes, high blood pressure, overweight, or (a history of) kidney problems. Although many uncertainties remain from the various studies, one point seems certain: If you already have kidney problems, then high protein intake can worsen these. Diabetics, people with overweight, and people with high blood pressure (sometimes caused by the same overweight) have an increased chance of kidney problems. Because kidney problems are often not known by the person themselves, this group indeed needs to be careful with high protein intake.

This explains why so many people “know” that a lot of protein is bad for you. If you ask about creatine, amino acids, or other popular supplements, the person often looks at you with vacant, non-understanding eyes. But then you say: “Protein,” and the reaction is: “Protein shakes, that’s for losing weight, right?”

Due to the popularity of low-carbohydrate diets, there is a large group of people with overweight who use protein shakes. The same overweight can in many cases cause high blood pressure and diabetes, thereby increasing the risk of kidney problems. If such a person asks their doctor: “Is it healthy if I eat fewer carbohydrates and more protein?” then a well-informed doctor will indicate that there is a risk. For that person in question!

There are several studies that have shown this risk for this group (1,2,3). In these studies, participants already had kidney problems which were worsened by high protein intake (2), or somewhat reduced when protein intake was lowered (3). In these cases, kidney function was already poor, so additional strain from more protein only made it worse.

Negative influence of high protein intake in healthy people not proven

Maybe this will interest me personally someday, but for now, I mainly want to know what high protein intake does in people who do not suffer from overweight, diabetes, or pre-existing kidney problems. Then the picture looks fortunately better. No study has been able to demonstrate a link between high protein intake by healthy people and kidney problems.

About the unfounded warnings on this matter, a Finnish researcher (4) also said the following:

In conclusion, there is little if any scientific evidence supporting the above-mentioned statement. Certainly, such public warnings should be based on a thorough analysis of the scientific literature, not unsubstantiated fears and misrepresentations. For individuals with normal renal function, the risks are minimal and must be balanced against the real and established risk of continued obesity.

…Furthermore, real-world examples support this contention since kidney problems are nonexistent in the bodybuilding community in which high-protein intake has been the norm for over half a century.

A.H. Manninen, University of Oulu

“Unfounded fears and misinterpretations,” then. He continues with an argument I always mention: “Where are all those bodybuilders with kidney problems then?” Indeed, bodybuilders have been consuming large amounts of protein for over fifty years, and there has never been a wave of kidney problems following (5).

The American researcher Walser went even further in 1999 in response to failed attempts to reduce existing kidney problems by lowering protein intake (6):

…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. there is no reason to restrict protein intake in healthy individuals in order to protect the kidney.

M. Walser, Committee on Military Nutrition Research, Institute of Medicine

“2.8 grams of protein per kilo of body weight per day is safe for the kidneys”

Even more convincing was the study from Brussels among bodybuilders and other people experienced in strength training. Some of them received daily 2.8 g/kilo body weight of protein (in line with the 2-3 g/kg that many bodybuilders maintain) others received a lower dosage. The dosage of 2.8 g/kilo (thus 224 grams of protein per day for someone of 80kg) caused no problems or adverse effects on the kidneys:

To conclude, it appears that protein intake under 2.8 g.kg does not impair renal function in well-trained athletes as indicated by the measures of renal function used in this study

J.R. Poortmans, Free University of Brussels

Long-term effects of protein on kidney function

The aforementioned study covered a period of 7 days. The question is what happens when looking at chronic high intake of protein. There isn’t much, but some research has been done on this. However, the fact that all those bodybuilders after decades of high intake of protein are not now falling like flies, might already suggest what the studies on this have discovered.

Of course, there are bodybuilders who die of kidney problems (they are, after all, human). Think of “the myth” Sergio Oliva. One of my favorite bodybuilders (the only one ever to beat Arnold) who died at the age of 71 from kidney failure. Besides, this being an already somewhat advanced age, Sergio was part of about the first generation to use anabolic steroids. If his kidney failure was caused by his lifestyle, then steroid use would have contributed more to his kidney failure than protein intake. Again, if there was a link at all.

“Four years of high protein intake by old dogs does not result in kidney complaints and lowers mortality rate”

Greek researchers divided 31 elderly dogs (28 females, 3 males) into two groups (7). First, they were given the same diet for two months to establish the baseline values of kidney function. After the two months, 16 of the dogs were given the same diet for another 48 months. In this diet, 18% of the calories came from protein. The other 15 dogs were given a diet for 48 months where 34% of the calories came from protein.

In the group that received “little” protein, 10 of the 16 elderly dogs survived the four years (62.6%). In the group that received a lot of protein, this was 13 out of 15 (86.7%). More importantly (at least in this context) is that there was no significant difference in how actively the kidneys had to filter. They also saw no difference in effect on the kidneys between both groups.

“11-year long high protein intake by middle-aged women leads not to kidney complaints”

In “The nurses’ health study,” 1624 women were followed from 1989 to 2000. At the start, they were between 42 and 68 years old. They gave blood samples annually, but also filled out surveys with questions about lifestyle habits. Such followed groups can be the subject of many studies by looking for certain correlations. Thus, Harvard researchers looked at dietary habits to identify the women with high protein intake and looked at their kidney function based on blood values (8). The women with high protein intake did not have worsened kidney function unless there was already “mild” kidney problems. These were possibly exacerbated in those cases.

High protein intake was not associated with renal function decline in women with normal renal function. However, high total protein intake, particularly high intake of nondairy animal protein, may accelerate renal function decline in women with mild renal insufficiency.

E. L. Knight, Harvard Medical School

Difference between animal protein and plant protein on kidney function

In that last quote, specifically non-dairy animal protein is mentioned as a risk factor for people who already have kidney problems. Indeed, various studies show that animal protein and plant protein have different effects on the kidneys (9 to 22).

However, dairy is also animal-based, and the Harvard researchers above fortunately also make clear that protein from dairy does not have the same negative effect on the kidneys as other animal proteins. However, this distinction does not go far enough. There appears to be a significant difference between protein from red meat, which would be a risk for people with kidney problems, and protein from white meat, which does not pose this danger.

Protein from dairy did not increase GFR (rate of filtration through the kidneys and indication of heavier strain) according to Japanese research (they used cheese and protein) whereas, for example, protein from tuna did (20,21,22). Fish plays a special role anyway. Although it increases GFR according to Japanese research, a higher fish intake actually reduces the risk of a specific kidney disease (microalbuminuria) (23).

Greek researchers showed that protein from soy increased GFR (and albumin in urine) less than protein from meat (18). It’s just a pity that it’s not described what kind of animal protein.

That this is an important difference is evident from Brazilian research in which replacing red meat with white meat led to a decrease in GFR (14).

These findings together are, of course, music to the ears! After all, bodybuilders switched decades ago from red meat as the main source of protein to white meat (especially chicken and to a lesser extent turkey). The other major source of protein is dairy. Think of the whey and casein powders obtained from milk. Then there’s the good old egg, which also poses a low risk.

Conclusion: “Healthy people can just take a lot of protein from the known popular sources”

If you do not suffer from kidney problems, then high protein intake up to 2.8 grams per kilo of body weight should not cause problems. No data is known about higher intakes.

People who already have kidney problems or are a risk group for it due to overweight, high blood pressure, and/or diabetes should consider the negative effect of high protein intake. It should be said that protein from dairy and white meat has a less negative effect. Since kidney problems are not always known, risk groups would do well to get tested before starting a protein-rich diet.

For the average, healthy bodybuilder and/or strength athlete, however, there seems to be no risk to the kidneys from high protein intake. Especially not if it comes from the popular sources.

References

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