Is a High Protein Intake Bad for Bones?

Tl;dr Read the very short version of this here.  For the juicy details, stay here!

Let’s start with an enticing tidbit from a paper in no less than the Journal of the American College of Nutrition, with the wonderful title, “Dietary protein: an essential nutrient for bone health.”

“In agreement with both experimental and clinical intervention studies, large prospective epidemiologic observations indicate that relatively high protein intakes, including those from animal sources are associated with increased bone mineral mass and reduced incidence of osteoporotic fractures.”

Let’s not be guilty of the same sloppy epidemiological science we accuse other nutrition camps of, though. Epidemiology can generate hypotheses, and give us ideas to think about that then need to actually be tested.  Epidemiology can’t prove cause and effect, but it can generally disprove it.  For example, in the case of dietary protein, if epidemiological findings suggest that higher protein intakes—including animal protein—are “associated with” better bone health, we can’t conclude that the protein itself is directly responsible for the stronger bones, but we can safely assume that protein isn’t harmful for bones.  And in the case of protein and bone mass, we do have pretty good clinical and experimental evidence showing that indeed, higher protein intakes do induce positive changes in bone tissue.  Not in cultured bone cells. Not in mice. In actual living, breathing humans.

It’s hard to believe that in certain circles, protein has gotten a reputation as being harmful for bone health.  After all, Paleolithic hunter-gatherer diets typically contained a large amount of meat, yet anthropologists can sometimes distinguish the remains of hunter-gatherers from those of agriculturalists solely by examining the bones: the high-protein eating hunter-gatherers typically had bones that were larger, stronger and denser, and showed fewer signs of chronic disease. 

Scientists believe the differences in physical activity between the two civilizations played a bigger role than any dietary changes, and sure, hunting and gathering no doubt required a lot of time on one’s feet, but ask any farmer: farming isn’t exactly sedentary work!  Even if a heavy physical workload was responsible for Paleolithic peoples’ stronger bones, we can still conclude that a high intake of animal protein didn’t work against building bone mass.    

So how did some people come to think that protein—animal protein, in particular—is harmful for bones?

My personal guess is, the people who absolutely, positively, cannot stomach the thought of humans eating animals, are grasping at straws.  Now that the cholesterol and saturated fat houses of cards have crumbled and the red meat fearmongers can no longer use those as the scapegoats for cardiovascular disease, they’re looking for something else—anything else, no matter how ridiculous—to make meat look bad.  (In this post, when I say “meat,” I’m referring to any animal flesh.  Other people reserve the word meat solely for red meat—especially beef—but when I say it here, I mean beef, pork, lamb, poultry, seafood, wild game, etc.)  So it’s not the saturated fat or cholesterol in meat that’s killing us.  And it’s not the TMAO.  But we know meat is bad for us, right? We know it is, so there has to be something harmful about it. 

Maybe it’s the acid load. 

Yes, Protein is Acidic, But…

“There is no evidence that diet-derived acid load is deleterious for bone health.”

Where did that truth bomb come from?  From Benefits and safety of dietary protein for bone health—an expert consensus paper endorsed by the European Society for Clinical and Economical Aspects of Osteoporosis, Osteoarthritis, and Musculoskeletal Diseases and by the International Osteoporosis Foundation.

So, not exactly some kind of shill organization fronting for ranchers, livestock farmers, fishermen, and butchers.

The assumption that a high protein intake results in reduced bone mineral density comes from the idea that protein (particularly from meat and dairy) presents an acid load upon digestion, and the body leaches calcium from the bones in order to buffer this acidity in the blood. (Calcium is good for buffering acid, which is why many over-the-counter antacids contain calcium.)  This is a great hypothesis.  It makes total sense…on paper.  The problem is, experimental evidence in humans—actual humans, with actual bones inside them—shows that it isn’t true.  Or, if it is true, and protein does cause calcium to be released from bone tissue, protein also increases calcium absorption, so the net effect on bone density is still positive—stronger bones. 

It’s true that animal proteins have an acid residue, but so do grains, yet you never hear anyone cautioning people against consuming oats and brown rice for the sake of their bone health.  (Ounce for ounce, these two grains have a higher acid potential than most meats!)  Now that low-carb diets aren’t totally verboten anymore, people might be advised to cut these carbs out to lose weight or manage their blood sugar, but to protect their bones?  Crickets. 

In case you’re confused about the acid/alkaline issue, here’s the 30-second version: the acid or alkaline residue a food presents after digestion is unrelated to whether that food tastes acidic on your tongue.  For example, tomatoes, lemons, and even apple cider vinegar are all alkaline residue foods.  Chicken breast, something that doesn’t taste acidic at all, presents an acid residue.  Hard cheeses appear to be among the most acidic foods.  The degree to which something is acidic or alkaline is called its “potential renal acid load,” and it’s a function of the minerals and amino acids it contains, rather than whether it tastes acidic or not. (Meats and dairy products are net acid-forming; vegetables and fruits are net alkaline foods, while pure fats and oils are neutral.)

Before we take a closer look at the effect of protein consumption on bones, let’s take a closer look at bones, themselves.  (If you want to read more about the acid/alkaline myth, start here.)

Bones: More Than Just Calcium

Bones aren’t just a conglomeration of minerals wrapped around nothing.  They’re not just calcium, phosphorus, magnesium and other structural elements arranged haphazardly with no scaffolding keeping them in place.  If bones were nothing but calcium, they would shatter whenever someone took a fall, like a piece of chalk dropped on the ground.  To the contrary, the author of a recent paper that uncovered new revelations about bone nanostructure said:

“Bone is an intriguing composite of essentially two materials, the flexible protein collagen and the hard mineral called apatite.” (Source)

Being that protein is a primary structural component of bone—making up as much as 50% by volume—it’s hard to fathom that consuming protein might lead to weaker bones.

This is also hard to fathom if you’ve been following the growing “zero carb” or “carnivore” faction of the low carb/keto community.  (I hope no one’s offended by my calling it a faction.  It’s not meant to be derogatory.  I like the carnivores!  Maybe “subset” is a better term.)  This is the opposite of veganism: instead of excluding anything and everything from the animal kingdom and eating exclusively things from the plant, fungi, bacteria, and algae kingdoms, these folks exclude anything and everything from the plant kingdom and consume solely animal foods.  (Some of them drink coffee, tea, and alcohol, or use culinary herbs & spices, but the majority stick to meat and water, or meat, eggs, dairy, and water.)  Some of these people have been eating this way for years.  No alkalinizing kale smoothies, no powdered green shakes with spirulina and chlorella.  If animal protein was bad for bones, these people would have crumbled into powdery heaps long ago.  If their bones were being eroded by acid, they’d be experiencing breaks and fractures constantly.  Instead, we see the opposite: people in the best health they’ve experienced in their lives.  Exercising hard.  Lifting heavy.  Is this “anecdotal?”  Yes.  But it’s also stark freaking obvious to anyone with a set of eyes that these people’s bones aren’t becoming talcum powder.

 

Perhaps my carnivore friends have read this awesome paper and know:

“A causal association between dietary acid load and osteoporotic bone disease is not supported by evidence and there is no evidence that an alkaline diet is protective of bone health.”

Okay, back to the science!

Protein is a Net Bone Builder

A systematic review and meta-analysis from no less than the National Osteoporosis Foundation, published in the American Journal of Clinical Nutrition, determined that regarding bone health, “Current evidence shows no adverse effects of higher protein intakes.”  Of course, “no adverse effects” doesn’t necessarily mean higher protein intakes are beneficial; they might be neutral and have no effect one way or the other.  However, numerous studies have shown that higher protein intake is, in fact, beneficial for bone health.    

As long as calcium intake is adequate, higher animal protein intakes are protective against hip fracture among middle-aged men and women.  In healthy post-menopausal women, animal proteins were shown to have a beneficial effect on bone strength and microstructure, with a positive association between protein intake, bone failure load, and stiffness of the peripheral skeleton.

Compared to a diet calling for a daily protein intake of 0.8 grams/kg of body weight—which is typical of “official” guidelines for protein intake—a diet calling for substantially more—1.4g/kg/day—attenuated bone loss during weight loss in overweight middle-aged adults.  This is in line with mounting evidence that older folks should consume more protein, not less.  (More on this in a bit.)  Also, keep in mind that it’s actually really important that there was less bone loss during a weight loss trial.  If you implement some kind of “weight loss” strategy, and you lose weight, was it all fat?  Or did you lose some muscle and bone, too?  This is why I emphasize fat loss rather than weight loss when I write and speak.  They are not the same!

It’s been observed over and over again that higher protein intake is beneficial for bones. According to one review, “consuming protein (including that from meat) higher than current Recommended Dietary Allowance for protein is beneficial to calcium utilization and bone health, especially in the elderly.”

Those of us in the low carb and keto communities know that government guidelines regarding carbohydrate and fat consumption are preposterous.  We might even say they’re downright harmful.  So why is everyone so afraid of disregarding guidelines about protein intake?  (If you’re worried about gluconeogenesis, don’t be.  Read this and enjoy your meat!  If you’re worried about mTOR and longevity, hold that thought until I write about it later this summer.  Or listen to this podcast and also this one.)

0.8g/kg Protein – What Gives?

Let’s take a quick look at that good ol’ Recommended Dietary Allowance. This is the oft-cited “0.8g/kg per day” for protein intake (at least in the US and Canada).  If you’re new to this stuff, this means that getting 0.8 grams of protein per kilogram of your body weight each day is enough to meet most healthy adults’ needs.  But the Food and Nutrition Board of the Institute of Medicine of the U.S. National Academies of Sciences has written that the acceptable range of protein intake as a percentage of total calories for adults is 10-35%.  Depending on someone’s total calorie intake, 35% could be a lot more than 0.8g/kg.

More importantly, the 0.8g/kg figure wasn’t meant as an ideal or optimal amount.  If anything, it might be better interpreted as a minimum protein intake to aim for.  A rock-bottom basement amount you should stay above. 

0.8g/kg was arrived at based on nitrogen balance studies.  Proteins contain nitrogen—dietary proteins as well as the structural proteins that make up your skin, nails, bones, muscles, organs, tendons, etc.  (Carbs and fat do not contain nitrogen.  Nitrogen is part of the amino group that constitutes amino acids.)  If you’re in negative nitrogen balance, it means you’re breaking down your structural proteins—that is, you’re wasting away.  (Well, not necessarily wasting away.  Breaking down tissue is a normal, necessary thing. It’s how the body gets rid of old, worn-out or damaged parts & pieces to replace them with new ones.  So you want to break things down, as long as the other part of the equation—the rebuilding—keeps up.  If it doesn’t, you become sarcopenic, dynapenic, and all sorts of bad things start to happen.)  0.8g/kg was determined to be the amount of protein that would keep most people in nitrogen balance—rebuilding as much tissue as they were breaking down.  Well, that’s great, but what if someone’s trying to build muscle, or recovering from a major trauma, and they need to rebuild skin, bones, and connective tissue?  And 0.8g/kg is intended for healthy people.  Have you taken a look around lately?  Healthy people are becoming an endangered species!

As a personal aside, based on my own current weight, if I ate 0.8g/kg, that would be around 45.5g of protein per day, and I assure you, I eat way more than that, and I’m currently in the best health and physique of my life.

According to my favorite protein researcher, Stuart Phillips, PhD:

“The RDA represents the estimated average requirement plus 2 standard deviations, determined from selected nitrogen-balance studies of which very few were performed in older individuals. This approach, which determines the minimal protein intake required to avoid net nitrogen losses, is now considered inappropriate for establishing recommendations.”

My beloved Dr. Phillips isn’t the only one sounding this alarm:

“…the reanalysis of existing nitrogen balance studies are significantly higher than current recommendations. Therefore, there is an urgent need to reassess recommendations for protein intake in adult humans.”

That’s from a paper called Evidence that protein requirements have been significantly underestimated.  Gotta love it when researchers tell it like it is. 

Bottom line: this 0.8g/kg is bollocks, and it has got to go.

Acid Trip, Part 2

Let’s revisit the acid issue, because there’s a bit more to it.

As I explained earlier, it is conventionally believed that the net acid load of protein causes calcium to leach from the bones.  The evidence for this is that higher protein diets result in increased urinary calcium excretion.  In plain English, when you eat more protein, you pee out more calcium.  So that’s a slam dunk, right?  Where’s all that calcium coming from, if not from your bones?

I’m glad you asked!

Higher protein intakes do cause increased urinary calcium excretion.  However—and this is a big however—they also cause increased calcium absorption, with the net effect being increased calcium retention: “As to the increased calciuria [calcium in the urine] that can be observed in response to an augmentation in either animal or vegetal proteins it can be explained by a stimulation of the intestinal calcium absorption.”  That’s right: stimulation of calcium absorption. Eat more protein, absorb more calcium.

Think of it this way: if person A earns $100,000 a year and spends $50,000, they’ll have more money left in the bank than person B, who earns $60,000 and spends $30,000.  Even though person A spent more money than person B, they took in more initially, so they still retained more.  With regard to protein, even if the body excretes more calcium on a higher protein diet, if it also took in more to begin with, the net effect is actually greater calcium retention.  

Moreover, the calcium excreted does not necessarily come from bone stores: “…recent findings do not support the assumption that bone is lost to provide the extra calcium found in urine.”  The excreted calcium could be some of the extra dietary calcium that the body does not require or is not able to absorb at that time.  Just because there’s calcium in your urine doesn’t mean all of it came from your bones.

Bottom line: “Neither whole body calcium balance is, nor are bone status indicators, negatively affected by the increased acid load.”

Effects of High Versus Low Protein Intake on Bones

If anything, low protein intakes are more detrimental for bone health than high protein intakes (which have never been shown to be detrimental anyway). 

According to Ted Naiman, MD, everyone’s favorite shirtless low carb doctor:

“We have a long-term, ongoing study in extremely low protein diets right now, and it’s called geriatrics.  Because adults age 70-79 in this country [the US] eat 66 grams of protein a day, and I’ll tell you what, it’s really not working out well for their sarcopenia and their osteopenia and their longevity.  It’s kind of a nightmare.  So I think I know what happens when you restrict protein, because we all know exactly what happens when you restrict protein: you get low bone density, you get low muscle mass, and the weaker you are, the faster you’re gonna die, plain and simple.” 

(The podcast that quote comes from is highly recommended. Give it a listen!)

I’ll address low protein specifically with regard to the elderly in a bit.

Sticking with bone health for now, and protein intakes above that ridiculous ol’ 0.8g/kg:

“There is agreement that diets moderate in protein (in the approximate range of 1.0-1.5 g protein/kg) are associated with normal calcium metabolism and presumably do not alter skeletal homeostasis.  Less than 30-50% of US adults consume dietary protein that could be considered moderate.”  (Source)

Are you with me here, folks?  A protein intake of 1.5g/kg—almost double the current RDA—is considered a “moderate” protein diet, not a high protein diet.  And less than nearly half the US adult population doesn’t get that much.  In other words, most adults could increase their protein intake substantially and be totally fine—if not better—with regard to bone health.  (One of my grandmothers lived on hard candy and nuts.  I’m pretty sure her frail, hunched over shape wasn’t because she ate too much meat.)

It’s even worse than the numbers above:

“…protein intake tends to decline with age.  Particularly noteworthy is that 15-38% of adult men and 27-41% of adult women have dietary protein intakes below the RDA.” (Source)

So it’s not only that lots of people aren’t consuming a “moderate” amount of protein.  Close to 40% of adult men and women aren’t even getting the measly, lousy RDA, which, you’ll remember from earlier, many experts think is too LOW.

(As an aside, if you think 38% of men and 41% of women not getting adequate protein might have something to do with rates of obesity, you’re probably right. I’ll have more on that when I eventually get around to a post on the protein leverage hypothesis.)

It gets better:

“In sharp opposition to experimental and clinical evidence, it has been alleged that proteins, particularly those from animal sources, might be deleterious for bone health by inducing chronic metabolic acidosis…”  (Source)

Didja see that?  The allegations implicating protein—especially animal protein—as being bad for bones are in sharp opposition to clinical evidence.

“…selective deficiency in dietary proteins causes marked deterioration in bone mass, micro architecture and strength, the hallmark of osteoporosis.”  (Ibid)

You might be thinking, well, who’s “deficient” in dietary protein?  If you’re reading this blog, you probably have the luxury of living in an industrialized nation, where protein is abundant and relatively inexpensive.  Is it even possible to be “deficient” in protein in this context?

Yes.  Yes, it is.  As already addressed, not only do some experts think the RDA itself could be considered a deficient protein intake, but plenty of people who don’t know any better are deliberately restricting protein on ketogenic diets for fat loss.  (Don’t do this!)  And let’s not forget the many vegans and vegetarians who are following poorly constructed diets where they’re not taking in enough protein via eggs, dairy, and/or supplemental pea, hemp, or rice proteins.  It is more than possible to have “selective deficiency in dietary proteins” even in the affluent world.  (If anything, it’s the more affluent nations where people can afford to be picky about their food, and eschew beef and cheese in favor of seitan and soy cheese.) 

Healthy adults on a low protein diet showed secondary hyperparathyroidism within just 4 days.  This means they had increased parathyroid gland activity.  When your blood calcium gets low and you’re not getting enough calcium from your diet, your parathyroid glands secrete their hormone, which increases activity of cells called osteoclasts, which break down bone tissue in order to provide calcium.  The secondary hyperparathyroidism induced by the low protein diet was attributed to a reduction in intestinal calcium absorption—precisely the opposite of what we see when people have a higher protein intake.  The researchers admitted that the long-term consequences of this are not known, but the interwebs abound with “anecdata” from long-time vegans and vegetarians who had severely compromised bone mineral density.

This was a short-term study, so we can’t automatically assume a low protein diet is bad for bone health based on this one study.  After all, sometimes wacky changes occur to various markers in the short term when people switch to a ketogenic diet, but over time, things generally become better than ever.  And we don’t like when researchers try to badmouth LCHF/keto based on short-term studies that don’t take into consideration the “transition period.”  So I wouldn’t say this one study shows definitively that low protein intake is bad for bones.  Maybe parathyroid activity would normalize after a few more weeks or months.  But, based on the weight of the totality of evidence I’ve seen, it seems safe to say skimping on protein is bad bone juju. 

Beyond Calcium Absorption & Excretion: Other Beneficial Effects of Protein on Bone

Sticking with parathyroid stuff a little longer, a study showed that, among post-menopausal women, a high protein intake (“a diet high in meat protein”) reduced parathyroid hormone levels, coupled with an increase in intestinal calcium absorption.  Again: higher protein intake, more dietary calcium absorbed.  Think of all the women out there skimping on beef, pork, and lamb, while popping calcium supplements like they’re candy.  *Sigh.* 

Another change typically seen with higher protein intakes is increased levels of the hormone IGF-1.  IGF-1 is getting a bad reputation in the keto world these days, because it sort of goes hand-in-hand with mTOR.  People seem to think the body has only two states: cancer, or autophagy.  Like there’s nothing in between.  You’re either building massive amounts of damaged and dysregulated tissue, or you’re fasting and breaking down all the bad stuff that’s built up, and you’re going to live forever.  Insulin is getting the same bad reputation.  (IGF-1 is actually short for “insulin-like growth factor-1, so I understand why people freak out.)  The thing is, IGF-1 isn’t “bad.”  Neither is insulin.  You need these hormones.  If you want to build muscle and look good nekkid, you need them.  What you don’t need is to have their levels be super high all the time so that you’re awash in them 24/7.  IGF-1 is a growth promoter.  Yes, it can get into trouble, just like insulin can, when it’s promoting aberrant growth nonstop, but IGF-1 also helps growth we want, like muscle tissue, nerve cells, skin cells, and bone tissue.     

“Dietary proteins also enhance IGF-1, a factor that exerts positive activity on skeletal development and bone formation. Consequently, dietary proteins are as essential as calcium and vitamin D for bone health and osteoporosis prevention. Furthermore, there is no consistent evidence for superiority of vegetal over animal proteins on calcium metabolism, bone loss prevention and risk reduction of fragility fractures.” (Source)

The authors of the high meat protein diet study concluded, “The increased IGF-I and decreased PTH [parathyroid] concentrations in serum, with no change in biomarkers of bone resorption or formation, indicate a high-protein diet has no adverse effects on bone health.”  (Just FYI, the “high” protein diet in the study was 20% of calories from protein: 118g/day, 68g of which came from meat, mainly beef).  It honestly makes my blood boil when I see women eating 40-50 grams of protein and wondering why they feel like garbage on keto/LCHF.

Stuart Phillips wrote:

“Current evidence indicates intakes in the range of at least 1.2 to 1.6g/(kg·day) of high-quality protein is a more ideal target for achieving optimal health outcomes in adults.” 

And

“Despite persistent beliefs to the contrary, we can find no evidence-based link between higher protein diets and renal disease or adverse bone health.”

Bottom line: eat protein. Just don’t eat it all day, every day, without stopping to breathe.  Can you eat protein for 3 meals a day?  Yes.  Should you eat it for 7 meals a day, plus 9 snacks?  No.  But I would say that about carbs and fat, too.  ;-)

A Special Word About Protein Intake for the Elderly

Researchers have recommended increasing daily protein intake for people age 65 and over to at least 1g/kg, and Dr. Phillips thinks a better minimum—minimum—would be 1.2g/kg.  Most older people aren’t getting anywhere near this much.  And remember, these recommendations are for grams per kilogram of body weight, not just lean mass.  Other researchers wrote that 1.0-1.3g/kg “is required to maintain nitrogen balance in the healthy elderly…”

Older people have what’s known as “anabolic resistance.”  The stimuli that normally lead to increased muscle mass (or at least maintenance of it) in younger people, such as weightlifting or eating protein, don’t have as powerful an effect as we age.  This means that in order to have the same effect it might have had when they were younger, an older person needs to eat even more protein.

This is no easy feat, since there are many reasons why older people tend to skimp on protein.  One, many older people are on fixed incomes, and depending on what you buy and where, “meat” can be more expensive than bread, pasta, and beans.  Two, stomach acid production naturally declines with age, so it becomes harder to properly digest protein.  If this leads to upset stomach, acid reflux, or some other GI issue, it makes sense why an older person would avoid eating a lot of animal protein.  Three, if dental/oral health is compromised and someone has pain or poorly fitted dentures, they’re not going want to chew a big steak or pork chop.  (I do think ground beef, pork, turkey, etc., would work just fine, though, as would canned fish, cold cuts, cottage cheese, and other soft proteins.)  And four, if an elderly person lives alone or has limited mobility, they’ll likely find it easier and more sensible to pour a bowl of cereal or microwave a bowl of oatmeal for a meal instead of roasting or grilling a piece of meat.  Yes, you and I can think of a zillion ways around these perceived obstacles, but for many older people who are on their own, this is the sad reality.

One thing we do know, though: “…insufficient dietary protein intakes may be a more severe problem than protein excess in the elderly.” (Source)

Okay!  That is way more than anyone ever wanted to know about this issue.  But I hope this deep-dive has dissolved your fears regarding any potential for a higher protein intake to have adverse effects on your bones.  Now, make me proud and go eat some meat!

P.S. I’m willing to write a similar post regarding protein and kidney function, if anyone out there would like me to dispel the myth that protein is bad for the kidneys. (According to Ted Naiman, “Honestly, protein restriction in chronic kidney disease is nearly mythical, and protein causing kidney damage is just a giant load of crap.” But if you want me to explain why it’s crap, I can do that. Let me know in the comments.)

P.S.  If you’d like to explore additional positive aspects of consuming red meat, you might find these papers informative: 

• Red meats: time for a paradigm shift in dietary advice
• Inclusion of red meat in healthful dietary patterns
• The role of red meat in the diet: nutrition and health benefits

The first two are from the journal Meat Science, so take that for what it’s worth.  (Although, personally, I think it’s pretty damn great that there even is a journal called Meat Science.) 

These papers celebrate red meat as a key source of micronutrients—particularly ones that are “shortfall nutrients” for many people: zinc, iron, B12, and others.  Unfortunately, they tout that “lean meats” can be part of a healthy diet, but that’s really just paying lip service to the old saturated fat myth so they could at least advance the conversation about any kind of red meat being good for you.  Baby steps, folks, baby steps.  If someone’s choosing between lean beef or no beef at all, I’d rather have them eat lean beef.  Fatty might be even better, but one step at a time, eh?

Disclaimer: Amy Berger, MS, CNS, NTP, is not a physician and Tuit Nutrition, LLC, is not a medical practice. The information contained on this site is not intended to diagnose, treat, cure, or prevent any medical condition and is not to be used as a substitute for the care and guidance of a physician. Links in this post and all others may direct you to amazon.com, where I will receive a small amount of the purchase price of any items you buy through my affiliate links.