The Effects of a High-Protein Diet in Real Life
Have you been accused of consuming too much protein? Lets debunk the myth.
I hear it all the time. In fact, when I teach exercise physiology, I challenge my students to find a peer-reviewed study that shows that excessive protein consumption damages the kidneys in healthy individuals. What do you think they find?
Nothing, nothing, nothing, nothing. The data is simply not there.
So why does this myth persist? Consuming more protein makes your kidneys work harder, and that’s one of the reasons. Glomerular filtration rate (GFR) and creatinine (NOT creatine) may increase, indicating that the kidneys are working harder. But does that mean there are signs of damage? Let’s investigate.
Kidneys and Proteins: The Science
To start, here’s a quote:
From SM Phillips (2014): According to the World Health Organization report on protein intake and statements from the Institute of Medicine regarding North American protein RDA, “there is no evidence to link a higher protein diet with kidney disease.”
So far, it seems that making your kidneys do more work is not inherently terrible. Your biceps work harder when you exercise your arms at the gym, and as a result, they get bigger (hypertrophy). Could your kidneys experience the same?
In 2015, researchers found that increased protein did indeed make the kidneys work harder but did not damage them (there was no increase in microalbuminuria, a sign of damage). Just like your biceps, your kidneys will grow as they work harder, but that growth is not due to damage. They were simply adapting to the pressure they were under.
So, the claim that protein is harmful is simply not supported by the available data. But what if you’re a weight lifter who trains hard and eats a lot of protein?
Show Me the Studies
If you’re an athlete or bodybuilder, you’re not doing things that are typical. Standard pencil necks used in many tests don’t make the cut, but they do.
Poortmans JR and Dellalieux O. conducted one of the earliest studies on proteins and suggested that excess protein is harmful to the kidneys. The subjects in this study were bodybuilders and other well-trained athletes who consumed a moderate or high amount of protein.
What did they find? On the other hand, bodybuilders had normal renal clearances of creatinine and urea, which are waste products, despite having higher plasma concentrations of uric acid and calcium than those on a high-protein diet. The researchers concluded that the renal function of well-trained athletes was not affected by protein intakes below 2.8 g/kg.
Brandle and his colleagues conducted another study. While not perfect, the study was the first to look at how protein affects kidney function. They found no relationship between the rate of egg white discharge (apparently, urinary egg white is a harmful variable) and gross protein intake (measured by nitrogen discharge rate).
What about Increased Body Fat and Body Mass?
Dr. Jose Antonio and his colleagues took the question to the extreme, looking at men who lifted weights and consumed a lot of protein.
In male subjects who had been trained in resistance, they used what is known as a “randomized crossover design.” The men lifted weights and consumed a lot of protein. For those who believe that the metric system was created for the sole purpose of torturing you, the reference bench press average was 126.4 kilograms, or 278 pounds.
Participants consumed a high-protein diet for eight weeks, with over 300 grams of protein per day for a 220-pound person. They added a timed heavy resistance training program. For the low-protein phase, which lasted eight weeks, they continued with their usual diet.
The results? The high-protein group consumed more calories in the form of protein, but their body composition did not change significantly; they did not gain weight despite consuming more calories. Health markers in neither group (blood lipids, glucose, renal function, etc.) changed.
Due to high protein intake, their kidneys did not launch an attack to expel them back despite eating a lot of protein. The researchers performed a sub-analysis on two of the study’s participants who consumed more protein to support their argument. They found no kidney problems (renal) in these two subjects, despite consuming 483-724% above the recommended daily allowance (RDA) of protein.
Need More Proof?
One could argue that this data is still very short-term. Most weightlifters consume a lot of protein for years or decades. And after six months of a high-protein diet? What happens to their kidneys? Dr. Jose Antonio published a year-long study. Exactly one year. That’s an eternity for scientific research.
In a randomized crossover study, they recruited fourteen healthy men who had trained in resistance for an average of almost nine years. They changed their normal diet to include a high-protein version (>3 g/kg/d), so that each subject spent an average of six months with each version.
They found that a high-protein diet (about 2.5-3.3 g/kg/d) had no negative effects on blood lipid measurements or liver and kidney function in people who followed it for a year.
Furthermore, the subjects did not gain fat despite the increased total calories during the high-protein phase. Yes, a lot of protein for a year in high-level trainers working with naturally living humans. For scientific data, there is nothing better than that.
Protein: Maybe You Need More
Worrying about eating too much protein is way down the list of things you could do to improve your health, performance, and body composition. In fact, if you’re worried about protein, it might make more sense to worry about not getting enough vitamin 212. The vast majority of people I work with improve with increased protein intake.
The vast majority of people I work with improve by increasing their protein intake. Obviously, this doesn’t give you permission to consume over 400 grams of protein per day for years in an effort to prove some lab-coated nerd wrong. At some point, it would be bad. Too much is excessive. After all, even drinking too much water can cause death.
However, there is absolutely no evidence to suggest that proteins harm the kidneys. Sit back, relax, have a top-notch protein shake, and your kidneys will be fine.