Nutrition

Is Too Much Protein Bad for Your Kidneys?

admin June 13, 2022 0 13 min read

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Most people know that eating a high-protein diet benefits your health in many ways, including helping you build and maintain muscle, lose fat, and live a long, healthy life.

That said, the idea that high-protein dieting is bad for your kidneys has been kicking around for decades, making many people wonder if the benefits are worth the risks.

Is too much protein bad for your kidneys, though? 

Learn what science says in this article.

(Or if you’d prefer to skip all of the scientific mumbo jumbo and you just want to know how much of each macronutrient, how many calories, and which foods you should eat to lose weight, no problem! Just take the Legion Diet Quiz, and in less than a minute, you’ll know exactly what diet is right for you. Click here to check it out.)

 

What Is Protein?

A protein is a large molecule made up of chains of smaller compounds known as amino acids. 

You can think of amino acids as the “building blocks” of many tissues in the body, including muscle, hair, nails, and skin. 

Your body is able to synthesize 12 amino acids it needs but must obtain the final 9 from the food you eat. This is why you must eat protein to survive.

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Why Do People Think Protein Is Bad for Your Kidneys?

Your kidneys perform a number of functions, including filtering your blood to get rid of waste products, regulating blood pressure by changing your water and sodium balance, maintaining a healthy blood pH level, and creating certain hormones.

When your body metabolizes protein, it creates a substance called urea, which your kidneys remove from your blood and then flush out through your urine. The more protein you eat, the more urea your kidneys have to remove from your blood.

Some people say that this increased urea production from high-protein dieting puts more wear and tear on your kidneys, damaging them over time. 

Is Too Much Protein Bad for Your Kidneys?

A couple of long-term observational studies have shown that there’s an association between high-protein dieting and declining kidney function, particularly among people with kidney disease. Some animal research also shows that high-protein dieting may increase the likelihood of experiencing renal (kidney) issues.

However, observational studies can only show that two things are associated, not that one causes the other, and animal research has limited applicability to humans. In other words, while there’s some evidence that high-protein dieting might be no bueno for rodents and humans with kidney disease, there’s very little evidence it’s harmful for healthy people.

If we look at higher-quality evidence, such as randomized-controlled trials, virtually all show that high-protein dieting has no negative effect on kidney function in people who have healthy kidneys.

For example, a study conducted by the Free University of Brussels investigated bodybuilders and other well-trained athletes with above-average protein intake (up to ~1.3 grams per pound of body weight per day). After seven days of dietary analysis and blood work, researchers found no evidence of kidney distress.

These results were replicated by scientists at The University of Ulm, who investigated chronic protein intake on kidney function in 88 healthy volunteers, including vegetarians and bodybuilders, with protein intake as high as ~1.2 grams per pound of body weight per day (around three times the Recommended Daily Allowance). After four months, there were no signs of negative changes in kidney function.

Several similar studies conducted by a team of researchers at Nova Southeastern University investigating protein intakes as high as ~1.5-to-2 grams per pound of body weight per day have also consistently reported that protein has no adverse effects on health whatsoever.

Finally, the 2003 Nurses’ Health Study conducted by Harvard Medical School supports these findings, too. After analyzing the protein intake of 1,624 women over the course of several years, researchers found no association between high protein intake and a decline in kidney function in healthy females.

The reason for this is simple: while your kidneys do have to work a tad harder to remove the urea produced by metabolizing large amounts of protein, it’s still well within their capabilities. 

Think of it this way: Drinking more water also forces your kidneys to work harder, but you don’t hear anyone saying you should drink less to protect your kidneys (although hydration in general is a bit overhyped). The reason for this is that, like drinking lots of water, eating lots of protein is also entirely natural and something your kidneys are well-equipped to handle.

Thus, saying that eating a high-protein diet “stresses” your kidneys is like saying that charging your phone “stresses” the electrical grid, or that taking a shower “stresses” your home’s plumbing system. 

In the big scheme of things, it’s a drop in the bucket.

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How Much Protein Do You Need?

Protein needs vary from individual to individual.

The Institute of Medicine recommends that sedentary people aged 17-to-90 years old eat at least ~0.4 grams of protein per pound of body weight per day to avoid losing muscle and stave off decrepitude (though eating more is likely better if you want to flourish instead of just survive).

If you’re physically active (particularly if you regularly lift weights), you need to eat more than this to repair and build new tissue, though the exact amount is the subject of ongoing debate among scientists and depends on your body composition goals.

(If you’d like to know exactly how much protein you should eat for your goals, take the Legion Diet Quiz.)

How Much Protein Do You Need While Cutting?

While restricting your calorie intake to lose weight, your body doesn’t have an excess of calories to use as fuel. Since your fat and glycogen stores are also likely depleted, your body is primed to use muscle as a source of energy. Eating protein prevents this, so it makes sense to increase your intake while cutting.

A 2018 review published in the International Journal of Sport Nutrition and Exercise Metabolism recommends that people trying to lose weight and preserve muscle consume 0.8-to-1.1 grams per pound of body weight.

Another systematic review conducted by scientists at AUT University found that eating slightly more protein—0.8-to-1.2 grams per pound of body weight—might be better.

And yet another review suggested an even higher protein intake: 1-to-1.5 grams per pound of body weight per day. That said, the higher end of that range isn’t necessary unless you’re lean and muscular and working to get very lean (a bodybuilder preparing for a show, for instance). 

Thus, a sensible target while cutting (and the one I advocate in my fitness books for men and women, Bigger Leaner Stronger and Thinner Leaner Stronger), is 1-to-1.2 grams of protein per pound of body weight per day.

How Much Protein Do You Need While Maintaining and Bulking?

While maintaining your weight or bulking, you can take your foot off the gas a little regarding protein because your body is unlikely to use muscle for fuel when it has an abundance of calories. 

The results of a meta-analysis conducted by scientists at McMaster University that examined data from 49 studies, including 1,863 participants, showed that a good rule of thumb when “not energy restricted” is 0.7-to-1 gram per pound of body weight per day. The authors also noted that leaning toward the top end of this scale likely maximizes muscle growth.

Another review published in the Journal of the International Society of Sports Nutrition explained that 0.55-to-1 gram of protein per pound of body weight per day is adequate for supporting muscle gain so long as calories are at or above expenditure (maintenance or bulking).

Since eating toward the top end of these ranges likely maximizes muscle growth and minimizes fat gain, I think it’s sensible to do so, which is why I recommend 0.8-to-1 gram of protein per pound of body weight per day while maintaining or bulking. 

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FAQ #1: Is protein bad for your kidneys?

No, research shows that consuming a high-protein diet isn’t bad for your kidneys unless you already have a pre-existing kidney condition.

FAQ #2: What’s the connection between protein and kidney disease?

Some observational research shows that increased protein intake is associated with the progression of kidney disease.

However, most high-quality research shows that consuming a high-protein diet has no adverse effects on kidney function, provided you don’t have any pre-existing kidney problems. If you do have impaired kidney function, talk to your doctor about how much protein is safe for you to consume.

FAQ #3: Does whey protein cause kidney stones?

There’s an idea floating around that protein from any source, including whey, causes kidney stones, but the results of two reviews show there’s insufficient evidence to draw any conclusions. In other words, there’s currently no proof this is the case, and it’s probably not worth worrying about.

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