Acid Not Linked to Calcium Loss

I’ve been reviewing the scientific literature on protein and bone health. As many readers know, there has been a theory that animal protein, by way of increased sulfur amino acids, causes calcium excretion leading to osteoporosis. This theory was always on shaky ground and more recent evidence has contradicted the theory. I just read a meta-analysis on the subject and added the following to the article, Bones, Vitamin D, and Calcium, on VeganHealth.org:

“Another 2009 meta-analysis found that among five well-designed studies measuring calcium balance, net acid excretion was not associated with either decreased calcium balance or a marker of bone deterioration (48).”

The paper had an interesting list of cohort studies in the discussion:

“First, during 8 yr of follow-up, fracture risk was not reduced among a cohort of 36,217 postmenopausal women who consumed either lower protein or lower NAE [net acid excretion] diets (37). Second, wrist fracture risk was highest among 1865 peri- and postmenopausal women who consumed the lowest protein intakes over 25 yr of follow-up (38). As well, a recent 2-yr trial in 276 postmenopausal women either supplemented with potassium citrate (expected to neutralize the acid of the Western diet) or encouraged to consume increased fruit and vegetables showed that these interventions did not reduce bone turnover or decrease bone loss (36).”

The take home message, which I’ve written about before, is that not eating animal protein does not protect you from osteoporosis. Make sure you get enough calcium, vitamin D, and even (plant) protein.

References

36. Macdonald HM, Black AJ, Aucott L, Duthie G, Duthie S, Sandison R, Hardcastle AC, Lanham New SA, Fraser WD, Reid DM. Effect of potassium citrate supplementation or increased fruit and vegetable intake on bone metabolism in healthy postmenopausal women: a randomized controlled trial. Am J Clin Nutr. 2008 Aug;88(2):465-74. (Link) Free article available.

37. Dargent-Molina P, Sabia S, Touvier M, Kesse E, Bréart G, Clavel Chapelon F, Boutron-Ruault MC. Proteins, dietary acid load, and calcium and risk of postmenopausal fractures in the E3N French women prospective study. J Bone Miner Res. 2008 Dec;23(12):1915-22. (Link) Free article available.

38. Thorpe DL, Knutsen SF, Beeson WL, Rajaram S, Fraser GE. Effects of meat consumption and vegetarian diet on risk of wrist fracture over 25 years in a cohort of peri- and postmenopausal women. Public Health Nutr. 2008 Jun;11(6):564-72. Epub 2007 Aug 9. (Link) Free article available.

48. Fenton TR, Lyon AW, Eliasziw M, Tough SC, Hanley DA. Meta-analysis of the effect of the acid-ash hypothesis of osteoporosis on calcium balance. J Bone Miner Res. 2009 Nov;24(11):1835-40. (Link)

11 Responses to “Acid Not Linked to Calcium Loss”

  1. Dave Says:

    I am continually grateful that your highest priority in your nutrition work is the truth – the whole truth. Your dedication to presenting the whole picture, to dispelling propaganda on both sides, is so valuable to seekers of accurate information and especially to those following a healthy, rational, and sustainable vegan diet. Articles like this reaffirm your trustworthiness and diligence as a nutritionist to the vegan community, and really to the world at large. Thank you!

  2. Jack Norris RD Says:

    Thanks so much, Dave! That’s very nice of you to say. I’m glad you appreciate what I do. – Jack

  3. beforewisdom Says:

    I feel the same way.

    It doesn’t inspire confidence in me that so many nutritionists cherry pick information. If anything hurts my health it will be the nonflattering bits, so I want to know about those things too.

  4. Paul Rogers Says:

    Jack, the confounders are so substantial that it’s a wonder we can make any sense of the animal protein and bone debate – calcium, vitamin D, alkaline foods, physical activity, genetics, estrogen etc.

    Kerstetter, in this older review, puts the ‘sweet spot’ for protein intake at 0.9 to 1.5 gm/kg/bw/day – http://www.ajcn.org/content/78/3/584S.long
    . . . animal or vegetable protein not making much difference.

    I would conjecture though, that diets high in animal protein, Atkins et al, perhaps Paleo, poorly buffered with fruit and veg and low in Ca, might still be a risk for sub-optimal bone status. Diets high in vegetable protein might have more flexibility in calcium requirements because of acid-base issues.

    I’m not certain the observational epidemiology necessarily supports the conclusions of the experimental acid-base meta-analysis, either, your ref 48. Much of this recent work stems from the same (Fenton) team at Alberta Health Services. I’d like to see other teams report their views and studies on acid-ash before I reject this hypothesis.

    Eg, from Kerstetter:

    “In 1986, Hegsted reported in a cross-cultural study that as dietary protein intake increased, so did hip fracture rates (32). Subsequently, Abelow et al found a similar positive correlation between animal protein intake and cross-cultural age-adjusted hip fracture rates (33). Three subsequent epidemiologic studies have reached the same conclusion (34–36). In contrast, Munger et al reported higher fracture rates at low-dietary-protein intakes (37). ”

    Even in your reference 37 above, this conclusion was reached:

    “However, in the lowest quartile of calcium (<400 mg/1000 kcal), high protein intake was associated with a significant increased fracture risk (RR = 1.51 for highest versus lowest quartile; 95% CI, 1.17-1.94). An increasing fracture risk with increasing animal protein intake was also observed (trend, p < 0.0001). "

    Ultimately, your recommendations for vegans to ensure they get sufficient protein and calcium and vitamin D is good advice. Not eating animal protein does not protect against osteoporosis in itself, but eating 'excessive' animal protein might still increase the risks, all things considered.

  5. Betty Says:

    Calcium-Vitamin D-protein are necessary, but so is plenty of the right kind of exercise.

    I wonder, though, how the scientists involved in this could possibly keep track of 36,000 women over 8 years and how they eat! The devil’s in the details.

    Maybe this is about optimal protein consumption (not to mention digestion), not “high” or “low”. Maybe there’s a best amount that we need – no more and no less.

    I do recall reading an article by a herbalist who said it’s not bone density that matters (to avoid brittle bones), it’s bone flexibility. She, too, recommended plenty of protein and very well cooked leafy greens. Cooked to the point of losing their green colour. She said that when you eat marginally-cooked greens you can’t absorb the calcium well. So much for the raw food diet!

    Just passing it along!

  6. Betty Says:

    I’m back, Jack. I forgot to tell you where I read the herbalist’s article. Here it is, for what it is worth. Very, very interesting reading.

    http://www.susunweed.com/Article_Bone_Health.htm

  7. Jack Norris RD Says:

    Paul,

    Thanks for the careful analysis – I appreciate it. You might very well be right.

  8. Jack Norris RD Says:

    Betty,

    I have heard this hypothesis and I don’t have the expertise in bone mineral density issues or the time to research it in depth. What matters most is bone fractures and the data on bone fractures appears to be in alignment with the idea that protein, at “normal” (i.e., typical) intakes is not a problem for fractures:

    http://jacknorrisrd.com/?p=722

  9. razldaz Says:

    Why don’t long term vegns get studied; i mean, as if it was absolutely necessary… but since everything is all evidenced based practice, time to crack out the old paper work and do a feasibility study NOW.

  10. Jack Norris RD Says:

    Razidaz,

    There are currently two studies (EPIC and Adventist Health Study 2) underway that, between them, have 6,600 vegans. So, we should have info on long-term vegan health in the coming years.

  11. Rhys Says:

    To razldaz, there’s an older study that included vegans but isn’t long term, a rough summary can be found here https://www.ars.usda.gov/is/AR/archive/mar03/osteo0303.htm the physiologist Marta D. Van Loan is quoted as saying “…even though bone resorption was the same in both groups of volunteers, the lower amount of bone formation in the omnivore women could lead to a decrease in their bone density.”

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