Will too much protein damage my kidneys? Cause cancer? Reduce my lifespan? At Precision Nutrition we’re always getting questions (from fitness pros and clients) about the risks of a high-protein diet. In this article we’ll set the record straight and share why protein isn’t the villain it’s made out to be.
Will eating a high-protein diet hurt me?
For years, people have been concerned with the safety of eating too much protein.
Will eating too much protein explode my kidneys?
How about my liver? My left femur?
The most common health concerns of eating more protein are:
Let’s explore these.
Claim: High protein causes kidney damage.
This concern about high protein and kidneys began with a misunderstanding of why doctors tell people with poorly functioning kidneys (usually from pre-existing kidney disease) to a eat a low-protein diet.
But there’s a big difference between avoiding protein because your kidneys are already damaged and protein actively damaging healthy kidneys.
It’s the difference between jogging with a broken leg and jogging with a perfectly healthy leg.
Jogging with a broken leg is a bad idea. Doctors would probably tell you not to jog if your leg is broken. But does jogging cause legs to break? No.
That’s the same thing with protein and kidneys.
Eating more protein does increase how much your kidneys have to work (glomerular filtration rate and creatinine clearance), just like jogging increases how much your legs have to work.
But protein hasn’t been shown to cause kidney damage — again, just like jogging isn’t going to suddenly snap your leg like a twig.
High-protein diets do result in increased metabolic waste being excreted in the urine, though, so it’s particularly important to drink plenty of water to avoid dehydration.
Verdict: There’s no evidence that high protein diets (2.2g/kg body weight) cause kidney damage in healthy adults.
Claim: High protein causes liver damage.
The liver, like the kidneys, is a major processing organ. Thus, it’s same deal as with kidneys: People with liver damage (such as cirrhosis) are told to eat less protein.
Yes, if you have liver damage or disease you should eat less protein. But if your liver is healthy, then a high-protein diet will not cause liver damage.
Verdict: There’s no evidence that high-protein diets (2.2g/kg body weight) causes liver damage in healthy adults.
Claim: High protein causes osteoporosis.
Eating more protein without also upping your fruit and vegetable intake will increase the amount of calcium you’ll lose in your pee.
That finding made some people think that eating more protein will cause osteoporosis because you’re losing bone calcium.
But there is no evidence that high protein causes osteoporosis.
If anything, not eating enough protein has been shown to cause bone loss. Bones aren’t just inert sticks of minerals — a significant proportion of bone is also protein, mostly collagen-type proteins.
Like muscle, bone is an active tissue that is constantly being broken down and rebuilt. And like muscle, bone needs those Lego building blocks.
Women aged 55 to 92 who eat more protein have higher bone density. So eating more protein improves bone density in people most at risk of having osteoporosis.
(Eating more protein plus adding resistance training: Double win for bone density.)
Verdict: High protein diets do not cause osteoporosis, and actually may prevent osteoporosis.
Claim: High protein causes cancer
Unfortunately, we still don’t have conclusive human studies on the cause of cancer and the role of protein.
There are studies that asked people how much protein they ate over their lifetime, and then looked at how often people got cancer. The research shows a connection between protein intake and cancer rates.
But these studies are correlational studies and don’t prove that protein is the cause of cancers. Plus, some researchers have gone so far to say that studies relying on subjects to recall what they ate are basically worthless because human memory is so inaccurate.
A big part of the proposed cancer and protein link comes down to confounding factors, like:
where you get your protein from — plant or animal
how you cook your protein (i.e. carbonized grilled meat)
what types of protein you’re eating (e.g. grass-fed steak versus a hot dog)
And so on.
In other words, we can’t say that any particular amount of protein causes cancer.
Verdict: Limited evidence that protein causes cancer; many other confounding factors.
Claim: High protein causes heart disease.
Eating animal-based protein daily is associated with an increased risk of fatal coronary heart disease (70 percent for men and 37 percent for women), whereas plant-based proteins aren’t linked to higher rates of heart disease.
This suggests that where you get your protein from may matter more than how much protein you eat.
However, just like cancer, the link between heart disease and high-protein diets is from questionnaires rather than a double-blind randomized study (the gold standard in research).
There are many confounding factors. For one, consider the type of animal — does seafood cause the same issues as red meat, for example?
We don’t yet know the whole story here.
Verdict: Limited evidence that protein causes heart disease and the source of protein is a major confounding factor.