In the current issue of the American Journal of Clinical Nutrition, a group of “paleolithic nutrition” and “evolutionary health” researchers published an analysis of the acid-base balance of the diets of 229 hunter-gatherer societies. They concluded that, contrary to the suggestions of Loren Cordain and S. Boyd Eaton that prehistoric hunter-gatherer diets were nearly all net base-producing, about half of historically studied hunter-gatherer diets were net acid-producing.
This basically means that many hunter-gatherer groups subsisted heavily on animal protein, which is rich in sulfur-containing amino acids that increase the production and excretion of sulfuric acid during their metabolism. When the authors assumed that hunter-gatherers ate diets rich in lean meat, they estimated that over two-thirds of these groups consumed net acid-producing diets. They noted, however, that such groups tended to discard lean meat in favor of fatty portions such as marrow, brains, and tongue. When they assumed the groups were eating fattier diets, they estimated that between 40 and 60 percent of the groups consumed net acid-producing diets.
Of course these authors were not able to draw any conclusions about whether the acid-base balance of these diets had any effect on the health of the people consuming them.
Weston Price, however, was able to and did draw such conclusions. In a speech given at the New York Dental Centennial Meeting in 1934, reproduced in full in the newest expanded edition of Nutrition and Physical Degeneration, Price argued that the acid-base balance of diets had no effect on immunity to tooth decay:
It is important to note that in four of these five groups of primitive racial stocks, living on entirely different native foods and in widely divergent climates and entirely different living habits, the immunity-producing diets were found to be higher in acid factors than in base factors. In some the divergence is quite small and in others, quite large. It is also important that, in changing, from high immunity to high susceptibility diets there was no increase in potential acidity with increased susceptibility to tooth decay.
Rather than concluding that the “evolutionary diet” of humans may have been net acid-producing, Cordain, Eaton, and Melvin Konner published an editorial in the same issue of AJCN arguing that the many net acid-producing diets of historic hunter-gatherers resulted from a divergence from the ancestral alkaline diets of prehistoric hunter-gatherers.
To support their contention that hunter-gatherers eating net acid-producing diets suffered ill health because of it, they cited a single paper showing high rates of osteoporosis in skeletons of Sadlermiut Inuit from the early contact period. According to the theory that meat causes osteoporosis, excess sulfur amino acids in meat are metabolized to sulfur-based acids; as organic buffers are released from bone to neutralize the acid, the mineralized matrix of bone tissue is also dissolved.
There are two large problems with this theory: first, many accounts of the Inuit noted remarkable skeletal health; second, eating meat does not leach calcium from bone.
Did the Inuit, on the whole, really have poor skeletal health? When Price studied the Inuit he found not only nearly complete immunity to tooth decay so long as they were eating their native diet, but also a remarkable degree of muscular and skeletal perfection rarely seen among other peoples. When they began eating modern refined foods, the Inuit suffered rapid development of tooth decay and general physical degeneration, but the modern diets were no more or less acid-producing than their traditional diets.
In a 1972 article, “Mental Illness, Biology, and Culture,” published in the book Psychological Anthropology, Alfred Wallace hypothesized that hypocalcemic tetany from low levels of calcium and vitamin D underlied a phenomenon of hysteria found among Eskimos called pibloktok. Wallace noted that tetany was common among Inuit who did not have year-round access to fatty fish and fish bones, but that bone diseases were incredibly rare among the Inuit even when they faced seasonal malnutrition.
So much for the idea that acid-producing diets lead to bone disease among the Inuit.
More importantly, however, modern experimental science has thoroughly debunked the idea that eating meat leaches calcium from the bones.
Since HC Sherman first observed in 1920 that people who eat high-protein diets tend to excrete more calcium in their urine, over 25 trials have been published showing beyond a doubt that increasing dietary protein does in fact increase urinary calcium.
On the other hand there are at least four studies showing that people who eat the most protein have the slowest bone loss over time and another four showing that people who eat the most protein have the lowest fracture rate over time.
What we really care about, however, are the intervention trials, because these allow us to demonstrate cause and effect. While several of these have found modest benefits by providing protein-deficient elderly patients with small protein supplements, by far the most important intervention trial is that published by a group led by Bess Dawson-Hughes of Tufts University showing that protein intakes far beyond the minimal requirement actually improve bone health.
In this study, 16 older men and women were randomly allocated to a group made to increase their protein intake from 0.85 grams per kilogram of bodyweight, considered adequate, to 1.55 grams per kilogram of bodyweight. Another 16 people were randomly allocated to a control group and left their diet unchanged. After nine weeks, the group consuming extra protein had lower levels of bone turnover and higher bone mineral density.
The Dawson-Hughes group, contrary to many other studies, did not observe higher urinary calcium with higher protein intake. Studies conducted by Jane Kerstetter’s group at the University of Connecticut, however, showed that an even larger increase in dietary protein from 0.7 g/kg to 2.1 g/kg did, in fact increase urinary calcium, but not by leaching it from bone. Instead, they found that consuming more protein increased calcium absorption from the intestines. Markers of bone turnover tended to decrease on the high-protein diet but the decrease was not statistically significant. Kerstetter’s group is conducting ongoing investigations to determine the mechanism by which meat and protein enhance the intestinal absorption of calcium.
Does meat really leach calcium from the bones then? Not according to the scientific evidence.
Read more about the author, Chris Masterjohn, PhD, here.