Tuesday, February 28, 2017

Study: Human Stomach Acid Levels Similar to Carrion Eaters

In Powered by Plants, I discussed the human stomach acid level according to data I could find at the time of writing.  I wrote:
 "Ancient human species lived in Africa and like all other species lacked any type of rapid refrigeration.  Animals biologically adapted to eating flesh of large game animals often obtain more meat from a kill than they can eat in a single day, despite having very large stomachs that we lack.  They will guard the carcass for several days while continuing to feed on the rotting flesh, in order to maximize return on the energy that they invested in the hunt.

"To succeed at this lifestyle, animals biologically adapted to eating flesh produce sufficient stomach acid to keep the stomach at a pH of approximately 1.0-2.0 during food digestion, a necessity for killing microbes and parasites present on raw and decaying meat and for denaturing the large amount of protein that meat supplies.

"Most studies have shown that killing of bacteria requires a pH of less than 2.0, which in humans is 'rarely maintained for any length of time, especially during food intake' [Zhu et al, 2006].  The inability of the human stomach to maintain a pH below 2.0 for very long during food digestion makes it possible for microbes to survive and even colonize the human stomach, as illustrated by the fact that humans frequently contract infections of H. pylori and zoonotic microbes such as E. coli, salmonella, and campylobacter." 
In a 2015 study entitled "The Evolution of Stomach Acidity and Its Relevance to the Human Microbiome" Beasley et al searched gastrointestinal biology, animal physiology and avian physiology textbooks, published and unpublished papers for measured stomach pHs of 68 species (25 birds and 43 mammals) from 7 trophic levels.
"Our hypothesis was that foregut-fermenting herbivores and animals that feed on prey more phylogenetically–distant from them would have the least acidic stomachs. Tukey-Kramer comparisons indicated that scavengers (both obligate and facultative) had significantly higher stomach acidities compared to herbivores (both foregut and hindgut) and specialist carnivores feeding on phylogenetically distant prey. Specifically, foregut-fermenting herbivores had the least acidic stomachs of all trophic groups while omnivores and generalist carnivores, with more intermediate pH levels, were not distinguishable from any other group (Fig 1)."
Most interesting was their finding that "humans, uniquely among the primates so far considered, appear to have stomach pH values more akin to those of carrion feeders than to those of most carnivores and omnivores."  They found human stomach pH to be an "extremely low" 1.5, contradicting the data I used in Powered by Plants.  The authors searched for an explanation:
"Baboons (Papio spp) have been argued to exhibit the most human–like of feeding and foraging strategies in terms of eclectic omnivory, but their stomachs–while considered generally acidic (pH = 3.7)–do not exhibit the extremely low pH seen in modern humans (pH = 1.5) [38]. One explanation for such acidity may be that carrion feeding was more important in humans (and more generally hominin) evolution than currently considered to be the case (although see [39]). Alternatively, in light of the number of fecal-oral pathogens that infect and kill humans, selection may have favored high stomach acidity, independent of diet, because of its role in pathogen prevention."
Humans have stomach pH lower than many other carnivores and more similar to carrion-feeding birds.  In light of humans' extreme aversion to oral contact with feces, it seems most likely that this stomach acidity evolved as an adaptation to eating meat, whether carrion or fresh meat.

This finding thus indicates that human ancestors could not survive and reproduce in their natural habitat without regularly eating microbe-laden animal flesh, and that their need to eat meat exerted a natural selection for survival and reproduction of individuals who had stomach acidity greater than many other omnivores and carnivores and similar to scavengers.

Thursday, February 2, 2017

Europeans have three times more Neanderthal genes for lipid catabolism than Asians or Africans

Europeans have three times more Neanderthal genes for lipid catabolism than Asians or Africans:

"Contemporary Europeans have as many as three times more Neanderthal variants in genes involved in lipid catabolism than Asians and Africans."

This research indicates that ancestors of Europeans were more dependent on dietary fats than Asians or Africans.  We know that these fats would have come from either wild game, nuts or seeds.

"Cracking nuts is a subsistence activity of contemporary hunter–gatherer societies worldwide, as substantiated by extensive data on the taxonomy, seasonality, gathering, cracking, consumption, and nutritional value of nuts and the gender of participants in nut-related activities."[1] Native Americans were known to consume many kinds of nuts, including various species of acorns.[1]  There exists arcahaeological evidence that prehistoric Europeans exploited and processed with hammer stones at least seven species of nuts including two species of pistachios and and two of acorns as far back as 790,000 years ago.[1

Some people have suggested that prehistoric humans would not have used nuts due to their high contents of tannins which are deemed anti-nutrients due to their potential to reduce mineral absorption. Ethnographic studies have shown that preagricultural people used methods of water processing to remove tannins from nuts.

More importantly, as I discussed in Powered by Plants, humans appear to have an evolved physiological adaptation to dietary tannins in the form of proline-rich proteins secreted in saliva.  Salivary proline-rich proteins (PRPs) help an animal extract nutritional value from plant foods by binding with dietary tannins, and studies of mice and rats have shown that PRPs neutralize the detrimental effects of tannins.[2]  About 70% of the proteins in human saliva consist of PRPs.[2]  Humans have a salivary PRP content consistent with an evolved physiological commitment to to a diet rich in tannins.

Some authors go so far as to suggest that humans have a “taste” for tannins since we seem to even seek out and prefer foods with a certain level of tannins, such as tea, red wine, beer, chocolate, smoked foods, herbs, and spices.[2]  Also, we have evidence that tannins (polyphenols, flavonoids) act as important chemopreventers of infectious and chronic diseases in humans; they have antioxidant, anti-inflammatory, vasoprotective, vasodilatory, antibacterial, antiallergic, hepatoprotective, antithrombotic, antiviral, neuroprotective, and anticarcinogenic effects.[3, 4]  Thus, classifying tannins as ‘anti-nutrients’ for humans ignores evidence of human adaptation to tannins, as well as of the benefits of tannins, so it greatly oversimplifies their influence on human health.

Nevertheless, wild game would most likely have been the dominant fat source for Neanderthals and preagricultural Europeans.  In addition, to survive long winters, Europeans would have had to depend on metabolism of both fatty foods and stored body fat during long winters when starch- and especially sugar-rich plant foods would have been relatively scarce (compared to inhabited regions of Africa and Asia).  Hence, cold climate and long winters would have exerted a strong natural selection favoring reproduction of Neanderthals and Europeans having increased numbers of variants of genes involved in lipid catabolism.

Possibly Europeans are best adapted to diets having cyclical carbohydrate contents, perhaps higher in carbohydrate and lower in fat during warmer months (when plant foods may have been more abundant) and lower in carbohydrate in cooler months (when plant foods were likely more scarce).  This accords with the macrobiotic principle of eating in harmony with the seasons.  Due to the low sugar content of northern fruits and berries, it is likely that people of European (Caucasian) descent are more sensitive to dietary fructose than people of Asian or African descent.


As a consequence, people of European descent, perhaps particularly those of Nordic genetic stock, may be more likely to be better adapted to diets higher in fats and protein, moderate in starchy whole plant foods and low in sugars, or perhaps seasonally lower in carbohydrate-rich whole plant foods, such as the Nordic Healthy diet consisting of cabbage family vegetables, native berries and nuts, native fish and seafoods, wild game or pasture-fed animals, locally grown legumes, and oats, barley and rye.  People of Asian and African descent may be more likely to be better adapted to diets more consistently high in starchy whole plant foods, possibly higher in sweet fruits, and lower in protein and fat.

A lot of the confusion about diet may dissolve when we recognize that people of different ancestry are likely suited to different diets, and that people of European stock are descended from ancestors who survived by adapting to significant seasonal fluctuations in the availability of plant and animal foods and therefore in the proportions of macronutrients in the diet.  Perhaps for Europeans the genetically appropriate diet plan fluctuates between a more plant-based warm season diet and a more animal- (or fat- and protein-) based cold season diet.

If this is so, then the findings of the China Project are likely specific to Chinese, studies on African populations produce findings specific to Africans, and studies of Europeans will be specific to Europeans.  The China Project findings do not have to be false to be inappropriate for application to non-Asians. The mistake may lie in thinking that the China Project findings apply to Europeans, or that studies of Nordic populations will help us understand the best way for Chinese to eat. 


1.  Goren-Inbar N, et al. Nuts, nut cracking, and pitted stones at Gesher Benot Ya‘aqov, Israel.  February 19, 2002; vol. 99
no. 4;
pp. 2455–2460.

2.  Mehanso H, Butler LG, Carlson DM. Dietary Tannins and Salivary Proline-Rich Proteins: Interactions, Induction, and Defense Mechanisms. Annual Review of Nutrition 1987 Jul 1;7(1):423-40.

3. Habauzit V, Morand C. Evidence for a protective effect of polyphenols-containing foods on cardiovascular health: an update for clinicians. Ther Adv Chronic Dis 2012 Mar;3(2):87-106. PMC3513903.

4. Soobrattee MA, Bahorun T, Aruoma OI. Chemopreventive actions of polyphenolic compounds in cancer. Biofactors 2006 Jan 1:27(1):19-35. 21.