Fat Is the Preferred Fuel for Human Metabolism - Metabolic Paradigm Shift


(Michael - When reality fails to meet expectations, the problem is not reality.) #1

Struggling on keto
(Michael - When reality fails to meet expectations, the problem is not reality.) #2

There’s a lot here! Just trying to hit the highlights would result in quoting the whole thing virtually line by line. I hope others take an interest and maybe see stuff that I missed.

One of the takeaways for me, so far, is that assuming there were actually digestible carbohydrates around why would our ancestors waste time and energy gathering them?

The Obligatory Animal Fat Dietary Model

The ongoing increase in human brain size{Average human encephalization quotient (actual/expected brain mass for body weight) is slightly over 6.0, compared to values between 2.0 and 3.5 for hominids and primates [46]} had its toll: it became the most metabolically energy-expensive organ in the human body, consuming 20–25% of the adult and 70–75% of the newborn metabolic budget [47]. In order to not exceed the human limited “energy budget” (dictated by basal metabolic rate), shrinkage in gut size (another metabolically energy expensive organ) was a necessary accompaniment. It was Aiello and Wheeler [2] who suggested that gut size was a constraining factor on potential brain size, and vice versa. A shorter human gut, henceforth, had evolved to be more dependent on nutrient and energy-dense foods than other primates. The more compact, the human gut is less efficient at extracting sufficient energy and nutrition from fibrous foods and considerably more dependent on higher-density, higher bio-available foods that require less energy for their digestion per unit of energy/nutrition released. It would therefore appear that it was the human carnivorousness rather than herbivorous nature that most probably energized the process of encephalization throughout most of human history [2], [48], .

The physiological ceiling on protein intake.

It is known that diets deriving more than 50% of the calories from lean protein can lead to a negative energy balance, the so-called “rabbit starvation” due to the high metabolic costs of protein digestion [51], [52], as well as a physiological maximum capacity of the liver for urea synthesis [53], [54]. The conversion of protein to energy requires liver enzymes to dispose of nitrogen, an ingredient of amino acids which compose the protein molecule. Consumption of protein by humans is thus limited by the capacity of the liver to produce such enzymes and of the kidney to dispose of the urea – the nitrogen containing by-product from metabolism of proteins by the liver…

note: discussion here of plant nutrition which I reproduce below.

The critical role of animal fat

If dietary consumption of animal protein and raw plant food is physiologically limited, how could H. erectus provide for his caloric requirements? This question was posed by Wrangham et al. [17], [18], underlying their “Cooking Hypothesis”. However, assuming that fire was not routinely available for cooking, we propose that the answer may lie in the obligatory consumption of animal fat. Documented long-term consumption of high fat diets in traditional societies shows no negative health effects, e.g., 66% fat in the Masai diet [81], or 48% up to 70% fat in the Inuit diet ([82]:652, [4]:76). Consumption of fat by early Homo was thus suggested as a possible solution to the “protein poisoning” problem, as the result of excessive protein intake is sometime referred to ([4]:337). In addition, a strong tendency to target fat was evidenced as early as 1.9 Ma ago by bone marrow processing as seen at the Olduvai and Koobi Fora African sites ([3]:371). In addition, the facts that meat proteins digestion is costlier compared to fat [83] and that a larger percentage of protein escapes digestion while fat digestion is nearly complete [84], [85] also render animal fat a very efficient energy source.


(Michael - When reality fails to meet expectations, the problem is not reality.) #3

The Broader Context

Our direct ancestor, H. erectus , was equipped with a thick and large skull, a large brain (900 cc on average), impressive brow ridges and a strong and heavy body, heavier than that of its H. sapiens successor (e.g., [12], [13], [14]) [That would be us]. Inhabiting the old world for some 1.5 million years, H. erectus is commonly associated with the Acheulian cultural complex, which is characterized by the production of large flakes and handaxes – large tools shaped by bifacial flaking. Handaxes are interpreted as tools associated with the butchering of large game (e.g., [15], [16]). H. erectus was also suggested in recent years to have used fire [17], [18]; however the supporting evidence is inconclusive. Albeit the positive archaeological evidence from the site of Gesher Benot Ya’aqov (henceforth GBY) dated to around 780 kyr [19], [20], [21], the habitual use of fire became widely spread only after 400 kyr [22], [23], [24], [25].

Archaeological evidence seems to associate H. erectus with large and medium-sized game {Namely, Body Size Group A (BSGA Elephant, >1000 kg), BSGB (Hippopotamus, rhinoceros approx. 1000 kg), and BSGC (Giant deer, red deer, boar, bovine, 80–250 kg); (after [26])}, most conspicuously elephants, whose remains are commonly found at Acheulian sites throughout Africa, Asia, and Europe (e.g., [26], [27], [28], [29], [30]). In some instances elephant bones and tusks were also transformed into shaped tools, specifically artifacts reminiscent of the characteristic Acheulian stone handaxes [31].


(Bunny) #4

I agree with that the only difference is I make my own endogenous fat or short chained fatty acids (butyrate/ketones) in my gut rather than eating it directly which is even more awesome and convenient.

I don’t need to naw on a pound of bacon for real natural ketones and energy…lol

But I still luv bacon and eat it too!

Being a Starchivore is double the fun too…tee hee heee heee!


(Michael - When reality fails to meet expectations, the problem is not reality.) #5

The physiological ceiling on plant food intake.

The intake of plant foods can conceivably be limited due to a physiological ceiling on fiber or toxins intake, limited availability, or technological and time limitations with respect to required pre-consumption preparations, or a combination of these three factors. A significant contribution to the understanding of the physiological consequences of consuming a raw, largely plant-based diet was made by Wrangham et al. [17], [18]. A physiological limitation seems to be indicated by the poor health status of present-day dieters who base their nutrition on raw foods, manifested in sub-fecundity and amenorrhea [17], [18]. Presumably this limitation would have been markedly more acute if pre-agriculture highly fibrous plant foods were to be consumed. Limited availability is manifested by the travails of the obligated high-quality diet consumer of the savanna, the baboon. Baboons are somewhat similar to humans with respect to their ratio of colon to small intestine rendering the quality requirements of their diet comparable to an extent to that of humans. Baboons have been documented at times as devoting “almost all of their daylight hours to painstakingly seeking out small, nutritious food items….[the] adult male baboon ( Papio cynocephalus ) may pick up as many as 3000 individual food items in a single day” ([59]:103).

Nuts, or other high-quality foods of decent size appear only seasonally above ground in the savanna and such is the case in the Levant, too. But not only are they seasonal, they also require laborious collection and most of them contain phytic acid that inhibits the absorption of contained minerals. These foods also contain anti-nutrients and toxins such as trypsin, amylase and protease inhibitors as well as tannins, oxalate, and alkaloids the elimination of which can only be achieved (sometimes only partially) by pre-consumption processing like drying, soaking, sprouting, pounding, roasting, baking, boiling and fermentation. While these technologies are extensively used, mostly conjointly, in present day pre-consumption preparation of many plant foods, some were probably not practiced by H. erectus , especially those requiring accumulation and storage of produce for weeks (see, for example, [60]:173 with respect to Mongongo nuts, or [61]:31 regarding Baobab seeds). Comparing food class foraging returns among recent foragers, Stiner ([62]:160) has found the net energy yield of 3,520–6,508 kj/hour for seeds and nuts compared to 63,398 kj/hour for large game. Roots and tubers returns are not better, ranging from 1,882 kj/hour to 6,120 kj/hour. These numbers point to the substantial time investment required in gathering and preparing plant foods for consumption.

Some researchers (e.g., [63], [64]) suggested significant consumption of underground storage organs (USOs), such as tubers and roots that are not easily accessible to animals, as a possible source of high-quality plant food for early hominins in the savanna. Conklin-Brittain et al. [65] used fiber content as the principle measure defining a diet’s quality. Fibers, they claim, displace nutritious elements in limited food digestive capabilities while also trapping additional nutrients within their matrix. Consequently and in view of their relatively low fiber content (16% of dry matter compared to 34% for fruit, 46% for seeds and 44% for pith), these researchers propose significant consumption of USOs by the australopithecines. In their view, “post-canine megadondtia and low rounded thick enameled cusps are all compatible with the physical challenges imposed upon dentition by the consumption of USOs … robust gnathic architecture … [is also compatible] in keeping with the heavy chewing that would have been required to comminute USOs” ([65]:66). None of these features were preserved in H. erectus [66]. In other words, H. erectus was not well equipped to consume USOs, even as a fallback diet. Moreover, analysis of H. erectus cranial features in comparison to those of H. habilis , shows gracilization of the jaws, increased occlusal relief, and reduction in post-canine tooth size indicating a continued emphasis on the shearing of food items during mastication and a reduction in the hardness of foods consumed [67], [68]. Dental analysis thus led Ungar ([69]:617) to determine that “meat seems more likely to have been a key tough-food for early Homo than would have USOs”…

Recent support for the insignificant role of USOs in Paleolithic human diet may be derived from genetic data of present populations. Hancock et al. ([77]:8926) report that the strongest signals of recent genetic adaptations in the human genome of modern populations heavily dependent on roots and tubers, were to starch, sucrose, low folic acid contribution, and the detoxification of plant glycosides (found in tubers). The need for such an adaptation to so many specific USO attributes implies that humans were not previously adapted to consume significant quantities of USOs or any other form of dense starches for that matter. Similarly, Perry [78] reports that an increase in copies of salivary amylase gene (AMY1) begun to appear in humans probably only within the past 200 kyr. Needed to convert starch into glucose, chimpanzees have only two copies of amylase while present day humans have two to sixteen copies, indicating that adaptation to high starch consumption was probably not in place during the Middle Pleistocene (and even, as Perry discovered, is still not present in certain present day low starch consuming populations).

Another organ that should be examined when gauging the evolutionary route of humans with respect to fiber is the gut. Unlike humans, all herbivores have the ability to convert large quantities of vegetable fiber and other carbohydrates into short-chain fatty acids which they are able to absorb. Microfloral activity (i.e., fermentation) within their gastrointestinal tract ferment fibers and cellulose to produce these short-chain fatty acids. In fact, the natural diet of mammals is a high-fat diet. Therefore, any evidence of disengagement from fiber consumption would manifest itself in the colon. In weight, the human gut is about 60% of that which would be expected in a primate of similar size. This compensatory reduction, allowing for an increase in brain size while maintaining the necessary metabolic rate, stands against the notion of increased fiber consumption ([2]:204) in as much as the reduced weight is mostly attributed to a very short colon ([59]:99), which in H. sapiens comprises only 20% of their (relatively smaller) gut. In comparison, the chimpanzee’s ( Pan troglodytes ) colon comprises 52% of its gut. Aiello and Wheeler ([2]:210) infer that African H. erectus also had a relatively small gut based on the proportions of their thoracic cage and pelvis which are similar to those of H. sapiens.


(Michael - When reality fails to meet expectations, the problem is not reality.) #6

Using teeth data to gauge the physiological ceiling on plant consumption.

The need for an evolution of a coordinated digestive system, including both the teeth and the gut is described by Lucas et al. ([79]:35). Acting in concert, a coordinated effort is required to ensure flow from the molars to the gut that would not translate to an avalanche of fibrous food. These researchers’ note, in regard to the evolutionary responsiveness of the teeth’s shape and size, that the use of “any part of the body for 3000 times a day is unlikely to escape selection pressures” ([79]:39).

To estimate the physiological limitation placed on the digestion of raw fibrous foods, we thus use McHenry’s megadontia quotient, or MQ [5], [67]. MQ takes into account postcanine tooth area in relation to body mass. McHenry himself states that the MQ index was not meant to be precise, however it offers a noted sensitivity, ranging from 0.7 to 2.7 (see Table 1), and showing distinguished values of 0.9 for H. sapiens and 0.7 for the highly carnivorous H. neanderthalensis [73].

Reduction in teeth size can be attributed to either a change in diet or the use of exogenous food preparation techniques through the use of tools. It is therefore logical to start our comparison with the earliest tool-using hominin, the H. habilis . It is remarkable that the MQ (1.9) of H. habilis is closer to that of the Australopithecines and, by average, is nearly double that of the genus Homo as a whole. Given that H. habilis and H. erectus sought food in comparable savanna environments, the difference in diet, as seen from the point of view of molar size and topography, is quite extensive.

In order to get an initial estimate of a plant food ceiling we assumed a modest 10% animal diet for H. habilis (MQ = 1.9) and 80% animal diet for H. neanderthalensis (MQ = 0.7) as two extreme points. Assuming linear relation of MQ to Y – the percentage of plant food ceiling – allows the formation of a linear equation Y = 0.583MQ-0.208. The estimate for H. erectus (MQ-1.0) is thus 37.5%. We find this number to be slightly high in view of the HG record, the δ15N isotope studies, the genetics record, and a reasonable estimate of the physiological, inventory and time limitations for raw, non-cooked, plant foods such as USOs, nuts, and seeds. We have decided however to use this result in our following calculations, with the aim of maintaining strict assumptions.

For H. erectus , whose DEE is estimated at 2704 calories (see Table 2 and Table S1), we reach a maximum long-term plant protein ceiling of 1014 calories. This level of vegetal consumption means that H. erectus was indeed an omnivore whose diet was significantly varied (e.g., [80]).


(Michael - When reality fails to meet expectations, the problem is not reality.) #7

Conclusion

For more than two decades a view dominated anthropological discussions that all modern human variation derived from Africa within a relatively recent chronological framework. Recent years challenged this paradigm with new discoveries from Europe, China, and other localities, as well as by new advances in theory and methodology. These developments are now setting the stage for a new understanding of the human story in general and the emergence of modern humans in particular (e.g., [1], [39], [132], [133], [134], [135], [136], [137], [138], [139], [140], [141], [142], [143], [144], [145], [146]). In this respect, the Qesem hominins may play an important role. Analysis of their dental remains [1] suggests a much deeper time frame between at least some of the ancestral populations and modern humans than that which is assumed by the “Out of Africa” model. This, combined with previous genetic studies (e.g., [147], [148], [149], [150]), lends support to the notion of assimilation (e.g., [144]) between populations migrating “out of Africa” and populations already established in these parts of Eurasia.

It is still premature to indicate whether the Qesem hominin ancestors evolved in Africa prior to 400 kyr [136], developed blade technologies [151], [152], and then migrated to the Levant to establish the new and unique Acheulo-Yabrudian cultural complex; or whether (as may be derived from our model) we face a local, Levantine emergence of a new hominin lineage. The plethora of hominins in the Levantine Middle Paleolithic fossil record (Qafzeh, Skhul, Zuttiyeh, Tabun) and the fact that the Acheulo-Yabrudian cultural complex has no counterparts in Africa may hint in favor of local cultural and biological developments. This notion gains indirect support from the Denisova finds that raise the possibility that several different hominin groups spread out across Europe and Asia for hundreds of thousands of years, probably contributing to the emergence of modern human populations [153], [154], [155].

It should not come as a surprise that H. erectus , and its successors managed, and in fact evolved, to obtain a substantial amount of the densest form of nutritional energy available in nature – fat – to the point that it became an obligatory food source. Animal fat was an essential food source necessary in order to meet the daily energy expenditure of these Pleistocene hominins, especially taking into account their large energy-demanding brains. It should also not come as a surprise that for a predator, the disappearance of a major prey animal may be a significant reason for evolutionary change. The elephant was a uniquely large and fat-rich food-package and therefore a most attractive target during the Levantine Lower Palaeolithic Acheulian. Our calculations show that the elephant’s disappearance from the Levant just before 400 kyr was significant enough an event to have triggered the evolution of a species that was more adept, both physically and mentally, to obtain dense energy (such as fat) from a higher number of smaller, more evasive animals. The concomitant emergence of a new and innovative cultural complex – the Acheulo-Yabrudian, heralds a new set of behavioral habits including changes in hunting and sharing practices [9], [23], [45] that are relevant to our model.

Thus, the particular dietary developments and cultural innovations joined together at the end of the Lower Paleolithic period in the Levant, reflecting a link between human biological and cultural/behavioral evolution. If indeed, as we tried to show, the dependence of humans on fat was so fundamental to their existence, the application is made possible, perhaps after some refinement, of this proposed bioenergetic model to the understanding of other important developments in human evolutionary history.


(charlie3) #8

The government is resisting this idea that we should be eating more fat and less carbs. Our leaders have a food weapon for international influence when we can export agricultural commodities. Suppose everybody in the US wanted to eat the way we support? Chances are there would be a LOT LESS available for export and it would be more expensive. May be the Federal government wants us to eat animal feed instead of feeding it to the animals for reasons unrelated to our health.