Acid Diet (High-Meat Protein) Effects on Calcium Metabolism and Bone Health – Research Review
Cao JJ, Nielsen FH. Acid diet (high-meat protein) effects on calcium metabolism and bone health. Curr Opin Clin Nutr Metab Care. 2010 Aug 16. [Epub ahead of print]
PURPOSE OF REVIEW: Update recent advancements regarding the effect of high-animal protein intakes on calcium utilization and bone health.
RECENT FINDINGS: Increased potential renal acid load resulting from a high protein (intake above the current Recommended Dietary Allowance of 0.8 g protein/kg body weight) intake has been closely associated with increased urinary calcium excretion. However, recent findings do not support the assumption that bone is lost to provide the extra calcium found in urine. Neither whole body calcium balance nor bone status indicators, negatively affected by the increased acid load. Contrary to the supposed detrimental effect of protein, the majority of epidemiological studies have shown that long-term high-protein intake increases bone mineral density and reduces bone fracture incidence. The beneficial effects of protein such as increasing intestinal calcium absorption and circulating IGF-I whereas lowering serum parathyroid hormone sufficiently offset any negative effects of the acid load of protein on bone health.
SUMMARY: On the basis of recent findings, 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. A high-protein diet with adequate calcium and fruits and vegetables is important for bone health and osteoporosis prevention.
Background
For decades now, it’s often been thought, felt or claimed that a high dietary protein intake had a detrimental effect on calcium metabolism and bone health; certainly many groups promoting low-protein dietary approaches tend to echo/parrot this idea.
This idea came around in the mid-20th century but was based on some, shall we say, questionable research. In it, totally purified proteins were given (that is, no other nutrients were present) and a loss of calcium in the body (in the urine) was documented. It was simply assumed that this had a negative impact on bone health.
Despite later research showing that it was much more complicated than this (i.e. that proteins containing other nutrients had different effects and that other parts of the diet played a major role in the overall effect), this idea is simply repeated as if it were still unquestionably true. I dealt with this issue to some degree in The Protein Book, in a chapter called Protein Controversies, which is reproduced here on the main site.
As well, there has long been a secondary data set (seemingly ignored by anti-protein folks) showing that higher protein diets actually IMPROVE bone healing following things such as breaks or fractures. Clearly the idea that ‘protein is bad for bone’ is a bit more complicated than just a soundbite. The review paper I want to look at today examines the topic in some detail.
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The Paper
The paper begins by pointing out that bone is over 50% protein to begin with and that there has long been concern that the modern Western diet is detrimental to bone health due to the production of acids within the body. This is something I imagine readers have at least seen mentioned in recent years (I get the occasional question about it) with some going so far as to claim that the body’s pH is THE KEY to all health (some even claim that a drop in cellular pH is the cause of cancer).
While it’s not quite that cut and dry, clearly the modern Western diet tends to promote the production of metabolic acids and at least some degree of metabolic acidosis. This is due to a number of factors including a high protein intake (proteins are acid promoting), insufficient fruit and vegetable intake (both of which are net base producing for the most part), along with other factors such as sodium and potassium balance (excessive sodium intake relative to potassium can increase the acid load of the body). You can find long lists of foods online in terms of their net acid or base producing potential.
And certainly, as discussed briefly in Protein Controversies, acidosis can cause problems in the body. It’s relevant to today’s paper in that the body appears to buffer this acid load by releasing calcium, presumably from bone. In that current research is suggesting that the RDA for protein is actually too low for some populations (notably older individuals) and with the current interest in high-protein diets for weight/fat loss and maintenance, it’s important to know whether or not these dietary approaches are having negative impacts on bone health.
The paper looks in some detail at the issue of acid/base balance and calcium metabolism. As noted above, the generation of metabolic acids causes a number of effects in the body, all of which could potentially impact negatively on calcium metabolism and bone health. As well, studies clearly show both that:
- The generation of metabolic acids causes increased calcium loss in the urine
- Counteracting acidosis with base-forming minerals (e.g. potassium bicarbonate) decreases calcium excretion
While the above is clear, the direct impact of dietary protein on bone health is a bit less clear with the results of more direct epidemiological data showing mixed results in terms of the actual impact on bone health. As well, citing a review by Fenton, the paper points out that:
…neither calcium balance nor the bone resorption marker, N-telopeptides, was affected by diet-induced changes in net renal acid excretion despite a significant linear relationship between an increase in renal net acid excretion and urinary calcium.
That is, while it’s clear that increased dietary acid load causes increased urinary calcium excretion, it’s less clear if this has any real direct impact on the body’s net calcium balance or overall bone health.
Moving on to more direct effects, the paper looks at the very old data (using primarily purified proteins) showing that for every increase in dietary protein by 1 gram, there was a 1 mg increase in urinary calcium loss (raising the question of why not simply scale calcium intake to protein intake to offset this); this led to the assumption that bone health was being compromised.
However, in direct contrast to this, the majority of epidemiological studies find that a higher protein intake is associated with increased bone mineral density with only a few finding a negative impact. As well, while weight loss per se tends to cause a decline in bone health, some research has found that high-protein weight loss diets reduce the loss of bone mineral content; that is, high-protein intakes on a diet are beneficial.
The primary acid formation from protein comes from the sulfur containing amino acids (cysteine and methionine) and these are found in higher amounts in animal vs. vegetable proteins; it’s often been assumed that a higher vegetable protein intake would therefore have less of an impact on bone health.
However, this also turns out to be incorrect; the paper points out that studies of high-meat protein intakes either show no overall effect on net calcium balance and a higher animal protein intake is actually associated with increased bone mineral density; as well studies show a negative association between vegetable protein and bone mineral density.
It’s worth noting that strength/power athletes, who have traditionally consumed a high-protein diet are typically found to have higher bone densities compared to sedentary individuals. As the paper points out:
Changes in bone mass, muscle mass and strength track together; thus maintenance or an increase in muscle mass and function maintains or enhances bone strength and mineral density.
And while the increase in urinary calcium excretion with increasing protein cannot be simply ignored, current data suggest that this isn’t actually due to a loss of bone mass. Rather, increased protein intake leads to increased calcium absorption from the gut; the loss in the urine is simply due to more calcium being absorbed. The increased loss is simply due to more being absorbed from the diet; interestingly, this effect is more pronounced when calcium intake is low to begin with.
In terms of mechanism, higher protein intakes raise levels of the hormone IGF-1, which stimulates bone formation; this probably explains the benefits of a high-protein intake on bone healing. As well, high protein intakes have been shown to decrease levels of parathyroid hormone (PTH), a hormone that is involved in the loss of bone mass. Low protein intakes are associated with increased PTH and lowered bone mineral density.
Finally, as I mentioned in the introduction, you can’t simply look at protein intake outside of the rest of the diet and there are clear interactions with other nutrients. I mentioned above that protein intake interacts with calcium intake, increased absorption. As well, a high protein intake has been shown to increase bone health in older individuals when calcium and Vitamin D are supplemented. Finally, ensuring a sufficient intake of fruits and vegetables (which neutralize the acid load of protein) should help to ensure the impact of dietary protein on bone health is positive rather than negative.
Summing up, the researchers conclude thus:
Although a high meat or protein intake increases renal acid load and urinary calcium excretion, recent findings do not support the claim that bone is the source of the extra calcium lost in the urine. In addition, evidence is lacking that shows high-protein intakes, including that from animal sources, affect whole body calcium balance or contribute to osteoporosis development and fracture risk.
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Summing Up
I don’t have a whole lot to add to the above conclusion. Clearly the negative impact of dietary protein on bone health would appear to be overstated to some degree. Under certain circumstances (low calcium/Vitamin D intake, insufficient intake of fruits and vegetables), it’s certainly possible that a high-protein intake could have negative impacts. But again this comes down to an issue of context. And in the context of sufficient net acid neutralizing foods (fruits, vegetables, sufficient potassium intake) along with sufficient calcium/Vitamin D intake, the impact of protein on bone health would appear to be positive overall.
Lyle,
While pinpointing an exact daily amount of fruit and vegetable intake would be based on far too many factors to make a stock recommendation, is there any way to at least ballpark it for most? I ask because a lot of those peddling greens supplements will tell you that even those making an attempt to include more fruits and vegetables often fall well short of the mark when it comes to overall intake. And while people will often say to eat a serving of fruits and/or vegetables with every meal, for those consuming copious amounts of animal protein, it is rather easy to have protein intake outpace fruit and vegetable intake when you consider that even when we consume vegetables, they are often in rather small amounts compared to said protein (and usually still lead to an imbalance, at least when viewed according to those PRAL ratings).
As an example, even when my fruit and vegetable intake is on the low end, it usually involves at least 2 servings of berries a day and 1-2 servings of mixed vegetables (usually broccoli, cauliflower, carrots, peppers, and a few other assorted veggies). This would probably qualify as a “lot” compared to an average American, but it is still a rather low intake relative to the ease wit which I consume animal protein.
I suppose what I am wondering is if there is any way to get a rough gauge of whether fruit and vegetable intake is adequate enough to do its part in offsetting meat consumption. I’m always working to bump up my intake, but efforts aside, I notice my usual intake typically settles around a very consistent mark.
Given the assorted other factors you mentioned that are involved in maintaining bone density, I would understand if this sort of question leaves too many variables to give any sort of concrete recommendation.
Hi, Lyle. I’ve seen some claims that part of any issue between sulfur AA’s and calcium excretion (specifically in studies using isolated cysteine, cystine, and methionine) may be a result of inadequate levels of hydrochloric acid and vitamin B6 (a coenzyme for cystathionine synthetase). This would seem to speak to additional factors that can muddy the waters on a topic like this, where a “it’s because of this or because of that” just doesn’t tell the entire tale.
Your coverage of this topic got me thinking about another one that often pops up in various training and nutrition circles, namely food prep methods, the anti-nutrient content (phytate, lectins, tannins, glycosides, polyphenols, protease inhibitors, etc.) of various plant foods, and overall mineral status and health, particularly in the course of a mixed diet (as opposed to more extreme styles of eating). I’m not sure if you’ve devoted coverage to this at some point in the past (or if it is even an area you’d have interest in discussing), but it would be great to see you possibly tackle it at some point down the road if you have the time and inclination (or to direct me toward where you may have touched upon it in the past). Of course I understand if you have zero interest in covering this, but I figured I’d throw it out there.
Offtopic question:
I would like your opinion on an issue, and while ideally I would wait until it directly related to the discussion at hand (i.e. your most recent posting), in practice that could leave me forever waiting. So, I hope you don’t mind my going off topic and asking out of context.
There are many in the nutrition field who claim green vegetables to be a “negative calorie food,” as in it burns more calories to digest than they provide. While most who dissent recommend they are a “zero calorie food,” for much the same reason–and to this end, you see many diets recommend “as many green vegetables as you want.”
Personally, I believe whole heartedly in a calories in vs. calories out approach. However, I am unsure where/how to reconcile green vegetables into this equation.
Where do you come out on this argument?
Thanks,
SMB.
Note: i will also be posting this same question to Martin Berkhan @ leangains.com. for the sake of full disclosure.
Great review Lyle, it confirmed what I already thought.
Thank you so, so much for this. I’ve been very worried about potential bone density loss, and found that taking calcium makes me have terrible cramps. (I take 5,000 iu of D, plus the rdi of magnesium…300, I think…and tested at 64 for D).
I do eat dairy — cheese, cottage cheese, and sautee a big handful of Italian parsley every morning before my eggs — and maybe I just need to try a different kind of calcium. If anyone has any thoughts on that, I’d be most grateful.
Oh, PS The cramps are foot cramps, terrible ones, that get me out of bed at night.
Lyle,
What is your general presumptions on food PH, notwithstanding the specific study above? Is your feeling that those who promote Higher basic foods (fruits/veggies) over Acid foods worth merit in regards to health in general, or do you find a lot of the promotion towards avoiding acidic foods pseudoscience?
I too, like Amy, have suffered leg and foot cramps while on a high protein diet, Rapid Fat Loss. Hopefully Lyle or someon will have a suggestion.
Thanks
Art
To those of you getting cramps: are you supplementing with magnesium and potassium from a good, bioavailable source? The RDA is barely enough to stave off nerve degeneration and hypokalemia and most of the sources (e.g. magnesium oxide) are barely used by the body at all and are instead excreted.
Try magnesium citrate (400-800mg/day) and potassium citrate instead. The Eades have suggested supplementing heavily with magnesium and (to a lesser extent) potassium when embarking on a high-protein/lower carb diet for years. Our modern diet simply isn’t as rich in these nutrients as it used to be, thanks to soil depletion and people’s unwillingness to eat organ meats.
Lyle (or anyone else with knowledge) feel free to correct me where I am wrong.
Agreed ,problem is supps dont contain more then 99 grams of potassium,it is almost impossible to get sufficient amounts from veggies or other food sources on a low carb diet unless your eating copious amounts,and even then Id seriously doubt your getting more then around 2500,if your counting potassium losses through cooking etc.
As far as I know,for any significant amount of potassium through supplementation your looking at prescription medication unfortunately..
One can use light salt (1/2 sodium HCL/1/2 potassium HCL) as a way to increase overall potassium intake tho it will increase sodium intake equally. Potassium salt by itself tends to be a bit bitter unfortunately.
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Wow.
fantastic write up.
I have to say, I’ve long heard of the studies concerning protein intake and increased urinary calcium, but to see that high protein can actually improve bone density is awesome.
On the topic of PH, it would be interesting to see some studies concerning PH and cancer occurrenc because so many people believe it to be the cure.
Thanks for the great post,
Talk to ya soon,
Ryan “The Fat Loss Informant”
Just commenting that instead of calling something greater than the RDA a “high-protein diet” maybe we should just call it an “adequate protein diet.” “High protein” sounds like 3g/lb or something to me.
Also, for those wanting more potassium b/c of cramping:
1. 8 oz of milk has ~400mg of potassium and only ~13g carbs
2. when you carb-up/refeed note that potatoes have even more potassium than bananas.
Finally, this is completely anecdotal evidence, but I raised my daily carb intake from 70g to 150g to allow for a few fruits/etc and better overall nutrition, and my weight loss continued unchanged despite the carb increase. FYI my exercise performance also improved. Again, sample size of one, but I suggest you test yourself and see if an extra 30-50g of carbs (especially potassium-rich carbs) stalls your fat loss or not.
Thanks for this, Lyle. I was just diagnosed with osteoporosis of the spine (-3.3 T-score) and osteopenia of the hips (-2.5 T-score), and all I seem to read is how I need to eat a low-protein diet to reduce metabolic acidosis.
It’s been mind-boggling, trying to figure out the right thing to do–both nutrition-wise and exercise-wise. I suspected something was up, since I’d lost more than an inch in height since my 20s.
At nearly 56, I believe in keeping muscle on my frame as long as I can. I find it interesting that I have been anabolic in terms of muscle, but catabolic in terms of bone. Geesh.
Along with my high-protein diet, I’ve eaten LOTS of vegetables over the years. But I have NOT supplemented with calcium, nor eaten dairy. Plus, I have a family history of osteoporosis. And, I took natural hydrocortisone for several months for adrenal fatigue, which may have contributed to my bone loss. My vitamin D levels were low until I raised them last year by taking ~10,000 IU per day.
My new doctor handed me an Rx for injectable parathyroid hormone and told me to stay on it for 2 years. (It carries a Black Box warning for osteosarcoma.) I refused. Then he told me to take a calcitonin nasal spray, “and if that doesn’t work, we’ll try alendronate.” Sigh.
I am trying to rebuild my bone naturally, without Rx drugs. Any suggestions you have would be most welcome. I train back on one day and legs on another and try to focus on exercises that will stress my upper spine and hips. I have limited my coffee to one cup a day. Drink lots of tea, take bone supps, added prunes (high flavonols) and cut my protein by a little.
What else can I do?