High Protein Diets, Acid Load, Calcium Loss, Osteoporosis and a 50% Increase in Diabetes Risk - Is There a Link?

Shouldn't it be obvious that the "happy medium" must be the solution, when high protein leads to brittle bones, and low protein to frail muscle? Sure! But where is this "happy medium"?
Some of you may remember my recent Facebook post "High Protein Diet in the Firing Line. Rodent Study Says: Kidneys Are at Risk". It was based on a press release you could read on all the major science-news outlets on the Internet; a press release that will give the average reader the impression that the corresponding study by Aparicio et al. would "prove" that high protein diets will ruin your kidneys and eventually jeopardize your health (read more).

Another paper (Cao. 2014), Jose Antonio, the CEO of the ISSN and the editor of the ISSN's journal posted on Facebook yesterday, didn't get as much media attention, though.

No wonder, the message of this study is after all not in line with one of the fundamental arguments you will hear, whenever you question the allegedly necessary restriction of total protein intake to 0.8g/kg, maximally 1.2g/kg protein per kilogram body weight day in the current nutritional guidelines:

"[...S]hort-term consumption of high-protein diets does not disrupt calcium homeostasis and is not detrimental to skeletal integrity."

That's not what you will learn at med-school and it is certainly not in line with the hysteria about protein intakes that are 2x or even 3x higher than the 0.8g protein per kilogram body weight we are supposed to consume. Apropos RDA, the subjects in the control group of the said study by Jay J Cao et al. consumed a diet that contained exactly those 0.8g/kg body weight that's supposed to be good for us. The 21 human guinea pigs in the treatment groups, on the other hand, consumed 2x and 3x more than the average dietitian would recommend and they did so for 31 days (Cao. 2014).
Figure 1: Protein intake (in g/day; left), mineral intake (in mg/day; middle)  and calculated renal acid load (in mEq; right) of 49 normal weight, healthy men (n=32) and women (n=7) who consumed normal (0.8g/day), high (1.6g/kg per day) and very high protein (2.4g/kg per day) energy restricted (40%) diets for 4 weeks (Cao 2014)
If you take a look at the PRAL values in Figure 1, you can see that math (not bio- or physiology!) tells us that this reckless practice could compromises the acid-base balance of the healthy, normal-weight subjects, whose energy restricted diets were modeled on the increasingly popular high protein weight loss diets.

Equations vs. experiments | PRAL vs. urinary calclium loss | theory vs. practive

The urinary analysis the scientists conducted does yet speak a very different language. There is, as the scientists emphasize in the discussion of the results no evidence that
Suppversity Suggested Read: "High protein diet = high protein loss" | more
"habitual consumption of dietary protein at levels above the RDA [would] significantly alter urinary calcium excretion, dietary calcium retention, or markers of bone turnover or BMD, despite increased urinary acidity. These results indicate that diets that are 2 or 3 times the RDA for protein are not detrimental to calcium homeostasis when calcium and vitamin D are consumed at recommended intake"
In that I would like to emphasis the importance of adequate calcium (min. 800mg/day) and vitamin D intakes (800-1000IU/day) and the fallacy of the word "habitual". The study at hand did not test the effects of "habitual" high protein consumption. It tested the effects of short-term (28 days) high protein consumption in a low calorie scenario, which is by definition less prone to produce adverse inflammatory and thus potentially pro-osteoporotic side effects (Mundy. 2007).

Not eating enough protein could increase bone loss, when you're dieting

In view of the fact that the evidence I am about to cite, stems from rodent model of postmenopausal bone metabolism, I deliberately used the word could in the headline of this paragraph. And still, the way in which the low protein diet  "negatively impacted bone mass and magnified the detrimental effects of vitD and/or estrogen deficiencies" (Marotte. 2013) in the pertinent study from the Buenos Aires University is particularly disturbing.
High dietary acid load increases diabetes risk by more than 50%: In spite of the fact that this is neither bone- nor kidney-specific, the 56% increase in diabetes risk scientists from the Gustave Roussy Institute in France report in their latest paper in Diabetology, for the 16,621 subjects with PRAL values of only 7 mEq/day is so impressive that I simply had to include it in this article. Specifically in view of the fact that a brief glimpse at the food intake of the subjects in the figure to the left will suffice to see that protein is by no means the only "acid" offender in the SAD diet.
The (postmenopausal) women the scientists try to model with their ovariectomized rats (=rats whose ovaries have been removes) are after all one of the many patient groups who are advised to carefully control their protein intake to make sure that the additional acid load will not compromise their bone health even further and that in spite of the fact that there is ample evidence that the current RDA for protein is inadequate to maintain optimal health, particularly when the total energy intake is restricted and especially in populations who are susceptible to bone loss (Kerstetter. 2005; Chernoff. 2004).
Figure 2: We know for quite some time not that low protein diets decrease the absorp- tion of protein (Kerstteter. 2005). It's not certain if this is "just" a homeastatic me- chanism to stabilize the net/acid balance.

In their 2005 study, Kerstetter et al. were in fact able to show that protein intakes that are 2.6x higher than the RDA increase the effective absorption of calcium from the diet (see Figure 2).

This increase stands in contrast to the significant decrease in calcium absorption the researchers observed in the healthy young (age: 26y) women in the low protein arm (0.7g protein per kg body weight) of the study and should remind us that a reduction in protein intake is not going to stop the insidious loss of bone that's caused by the triage of low estrogen, no exercise and a diet that may be low in protein, but high in acid producing grains (Remer. 1995) and devoid of alkaline fruit and vegetables.

I could now go more into details, but I will just leave you with the notion that the "paleo diet" is, despite its high meat content, among the most kidney-, and above all bone-friendly diets we know. In fact, its fruit and vegetables content yield a net alkaline renal load, and will lead to significant improvements in urinary calcium excretion rates (Appelet. 1997; Frassetto. 2013).   

☄ Note: If you want more about the "Paleo connection" - let me know this (best on Facebook) and what you would be most interested in and I will address that in a future SuppVersity article.
Practically speaking: The results of the Cao study tell us that you can get away with a high protein load in otherwise SAD-ly (SAD = standard American diet) normal diet in the short run. What it does not tell you is that you can keep on this kind of "just add a ton of protein to the regular junk you eat diet" with ever-increasing dietary acid loads won't hurt your kidneys, bones and pancreas (see red box) in the long run.
If you want to eat a high protein diet, that's free of kidney, bone, or general meta- bolic side effects, it will thus have to have the fruit and vegetable content of what we currently deem a "paleo diet" - a diet with a relatively high protein content, tons of vege- tables, tubers and fruit and a limited (not no!) amount of grains. This will bring your citrate, magnesium and potas- sium intake up spare calcium and help you to ward off the evermore prevalent diabesity epidemic.
Bottom line: It may be human, but still is idiotic to isolate any single macronutrient as "the reason" for osteoporosis and bone loss. Looking exclusively at what we could potentially be doing wrong is not going to help us here. Rather than that, we should look at what we can be doing right - in other words, what should we eat, if we want to maintain not just bone-, kindey-health, but also muscle- and metabolic health (note: protein alone won't help you maintain muscle mass).

If we look at the results of the previously referenced trial by Frasetto et al., in which the researchers from the University of California San Francisco, which achieved a reduction of the potential renal acid load from 28mEq (which is more than the PRAL of 7mEq that's associated with a >50% diabetes risk; see red box) to -96 mEq on a diets that differed not in macronutrient, but in food, and consequently micronutrient-, specifically mineral-content, you will be hard pressed to keep the deabte on the short-sighted  "carbohydrates are good, protein is bad and fat is the devil, anyways"-level it is currently on.

We should be talking about food, instead. Not just about "more fruit and vegetables", but also about what you will necessarily have to skip for them, if you want your diet to work: Highly processed foods, including meats(!), sodas and other sweetened drinks, white bread, candy, chips, etc. It's not that you can't ever eat any of those, but as long as any of these items is on your list of foods you eat on a daily basis, there is still room for improvement.

  • Aparicio, V. A., et al. "High-protein diets and renal status in rats." Nutrición hospitalaria: Organo oficial de la Sociedad española de nutrición parenteral y enteral 28.1 (2013): 232-237.
  • Appel, Lawrence J., et al. "A clinical trial of the effects of dietary patterns on blood pressure." New England Journal of Medicine 336.16 (1997): 1117-1124. 
  • Cao, Jay J., et al. "Calcium homeostasis and bone metabolic responses to high-protein diets during energy deficit in healthy young adults: a randomized controlled trial." The American journal of clinical nutrition 99.2 (2014): 400-407.
  • Chernoff, Ronni. "Protein and older adults." Journal of the American College of Nutrition 23.sup6 (2004): 627S-630S. 
  • Frassetto, L. A., et al. "Established dietary estimates of net acid production do not predict measured net acid excretion in patients with Type 2 diabetes on Paleolithic–Hunter–Gatherer-type diets." European journal of clinical nutrition 67.9 (2013): 899-903.
  • Kerstetter, Jane E., et al. "The impact of dietary protein on calcium absorption and kinetic measures of bone turnover in women." Journal of Clinical Endocrinology & Metabolism 90.1 (2005): 26-31.
  • Mundy, Gregory R. "Osteoporosis and inflammation." Nutrition reviews 65.s3 (2007): S147-S151.
  • Remer, Thomas, and Friedrich Manz. "Potential renal acid load of foods and its influence on urine pH." Journal of the American Dietetic Association 95.7 (1995): 791-797.
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