Do ketogenic diets have a place in human evolution?

Ketogenic diet evolution

Part 1: How to think about ketogenic diets within human evolutionary history

In the past decade ketogenic diets in humans have started to attract the attention of a few forward thinking researchers as well as a small number of online health enthusiasts. In any diet there are three main elements called macronutrients – fat, protein and carbohydrate. On a ketogenic diet most calories come from fat (65-90%), a moderate amount from protein (<10-25%) and a small amount from carbohydrate (0-15%).

A ketogenic diet is often mistaken for a high-protein diet. This is not accurate. A ketogenic diet means eating food that produces ketones, a kind of molecule in the blood that provides energy, like glucose does. Producing a high enough level of ketones is called being in ketosis and it is a metabolic state in which the body relies much less on glucose.

The who’s who of low-carbohydrate ketogenic research, headed by Accuros et al. in 2008 (1), defined ketogenic diets as containing <10% of calories from carbohydrates. There are two reasons that I prefer to give a range of 0-15%. First, scientists have not fed large populations in a controlled manner to see how much of each macronutrient is needed to shift more than half of them into nutritional ketosis (we lack empirical data on this). This is complicated by that fact that different people get into nutritional ketosis more or less easily because of various factors, like their level of insulin resistance for example. Second, scientists have not yet defined what the nutritional ketosis threshold is exactly, despite their being good approximations.

pie chart about diet

Pie chart about ketogenic diet

Before exploring the appropriateness of ketogenic diets for humans, I’d like to justify why I approach questions of human health and nutrition the way I do by introducing 2 concepts; evolution by natural selection and the consilience of evidence. It is with these in mind that I answer the question any self-respecting skeptic asks about the ketogenic diet or any other diet for that matter

Are ketogenic diets a fad or do they underpin something more substantive in human health?

Lets start with evolution by natural selection. As many of you might, I initially thought your average doctor, dietitian or nutritionist would know about the answer to the above question. Unfortunately, I realized the vast majority did not. Although the reasons for this deserve a longer discussion, the gist in my opinion is that unbeknownst to most of them, their training brushes over the most powerful idea in biology (maybe even in science!), namely natural selection.

This gets us to the heart of the matter. Proper scientific scrutiny of dietary or health practices cannot do without the lens of evolutionary biology. Richard Dawkins makes the general case for natural selection using what he calls the Explanation Ratio (2):

But what makes natural selection so special?

A powerful idea assumes little to explain much. It does lots of explanatory “heavy lifting”, while expending little in the way of assumptions or postulations. It gives you plenty of bangs for your explanatory buck. Its Explanation Ratio – what it explains, divided by what it needs to assume in order to do the explaining – is large.

If any reader knows of an idea that has a larger explanation ratio than Darwin’s, let’s hear it. Darwin’s big idea explains all of life and its consequences, and that means everything that possesses more than minimal complexity. That’s the numerator of the explanation ratio, and it is huge.

Yet the denominator in the explanatory equation is spectacularly small and simple: natural selection, the non-random survival of genes in gene pools (to put it in neo-Darwinian terms rather than Darwin’s own)

Assuming you are on board with the explanatory power of natural selection, we can now include this powerful tool in our scientific toolbox. It helps us do 2 important things. First, it helps us form hypotheses from simple principles, which is good scientific practice. Second, it allows us to filter out bad ideas, essentially throwing away those that do not fit with the theory of evolution (as best we understand it). It can ensure we fulfil the ‘first principle’ of science which famous physicist Richard Feynman summarized as

The first principle is that you must not fool yourself – and you are the easiest person to fool

Like any tool, evolution by natural selection is limited and is prone to misuse. We would do well to set ‘explanatory boundaries’ for it. Explanatory boundaries serve to outline the limits of how much an a framework or idea can tell us about something. For math heads, think of their purpose as analogous to a boundary value with additional constraints used in differential equations. In our instance of understanding diets from the evolutionary perspective, the question we can ask to help set our explanatory boundaries is:

What can natural selection tell us about ketogenic diets in humans?

The answer is that it can provide ‘ultimate’ explanations. Ultimate explanations are different from ‘proximate’ explanations. Proximate ones are given to us by clinical medical trials or biochemical experiments. Scott-Phillips et al. (3) define both terms as follows

Ultimate explanations are concerned with why a behavior exists, and proximate explanations are concerned with how it works. These two types of explanation are complementary and the distinction is critical to evolutionary explanation

Practically speaking, biochemistry and physiology tells us how ketosis (or ketogenesis) happens in humans (a proximate explanation) and evolutionary biology tells us why the state of ketosis was selected as a prominent metabolic feature of our species. Isn’t it cool, and useful, to know both the how and the why? Take the well-known problem of antibiotic resistance as an example. Molecular biologists can explain how antibiotic resistance happens by describing a chain of molecular events (the proximate cause of antibiotic resistance) but it takes a person steeped in the mechanics of natural selection to explain why bacteria developed this ability in the first place (the ultimate cause of antibiotic resistance).

Both the molecular biologist and the person steeped in evolutionary biology must derive their explanations from falsifiable and replicable experiments that test their claims. It’s a two-way street, where insights from one approach can serve to inspire or refine experiments in the other. Science is notoriously messy and a lot happens by serendipity. But we can get better at it the more we learn to ask both how and why. A note of caution is warranted at this point. Although the principles of natural selection are simple, there is a lot more to it than advantageous traits winning over disadvantageous ones. Consequently, a common fallacy arises, especially by those applying the evolutionary lens to nutrition, in the form of 2 claims:

We ate this in the past and so we should eat it nowadays

We did not eat this in the past and so we should not eat this nowadays

Both claims are incorrect. They are failed attempts at the reasonable question we should ask when thinking about nutrition:

How well or poorly adapted are we to the foods we eat nowadays?

When thinking about such a question I pull on threads from anthropology, clinical medicine, biochemistry, epidemiology and other fields. Similarly, evolutionary hypotheses often use evidence from independent and unrelated fields of study. When multiple lines of evidence converge towards a conclusion – even if individually weak – we call this consilience. Human health and nutrition are staggeringly complex, inexact sciences, lending themselves to an evolutionary framework bolstered by the consilience of evidence.

Moving on to the question of interest, let’s replace our original question of whether or not ketogenic diets are merely a fad with the more pointed question we just posed:

How well or poorly adapted are we to the foods we eat nowadays?

Keep the following thought in mind while we explore the answer. Any half-decent zookeeper asks themselves if their animals are well-adapted to the food and environment artificially provided to them. We humans are animals, and also deserve to have that same question asked of us – right?

Part 2: Are ketogenic diets evolutionarily appropriate for humans?

Lets start answering this question by first considering paleoanthropological data. There are observations made about what was eaten by hunter-gatherer groups still in existence in the last few hundred years. We can also look at clues left behind by the bones of Neanderthals and early modern Europeans. Additional clues come from

  • what tools humans had and how we used them
  • the fossils we left behind (including coprolites, literally fossilized poop!)
  • the geography and climate of where human remains are found
  • where humans fit in the tree of life relative to our hominidae kin

These are a few important examples of lines of evidence used by paleoanthropologists studying how humans became human (hominization). Many theories of hominization revolve around the influence of diet, the salience of which will be discussed in Part 3.

Advanced genetics has become a major tool for paleoanthropologists in the last few decades. The field also uses simpler methods to obtain data, such as observing how people live day to day, including what, when and how they eat. Hunter-gatherers existing in that last few hundred years as well as a handful of ones still in existence today have had their dietary habits recorded. Plainly speaking, looking at what modern-hunter gatherers ate allows us to build a picture of foods we evolved to eat. This will not reveal the whole story or even most of it, but it will give us some idea of which properties of certain foods our biology is adapted to exploit.

I will argue that observations made so far support the idea that low-carbohydrate diets were the most common kind and that ketogenic diets were less common but by no means unusual. Higher, moderate-carbohydrate diets were also quite common. On the other end of the spectrum, the late professor Staffan Lindeberg observed that there were healthy hunter-gatherers from the island of Kitava who consumed 65%-70% of their calories mainly from starchy tubers and fruit. With this broad overview in mind let’s put numbers to this so that we can refine our dietary picture.

Observational data

In 2011, Ströhle and Hahn (4) looked at the ratio of plants-to-animals in the diets of 229 hunter-gatherer and horticulturalist groups. They combined these observations with measurements of food composition from Australian Aboriginals diets. This enabled them to infer the carbohydrate content of a particular group’s diet. Tables 3 and 4 below contain their data see please dive into it. I summarize their major findings as follows:

  • A lower-carbohydrate, higher-fat diet is the most common sort of diet. Specifically, 16%-22% dietary carbohydrate is the most frequent (median and mode) macronutrient apportioning for 32.8% of groups. The 2nd most frequent is 29%-34% dietary carbohydrate for 27.9% of groups.
  • Where hunter-gatherer groups are located geographically strongly correlates with how much dietary carbohydrate they consume. Specifically, latitude intervals strongly correlate, although not linearly, with the percentage of carbohydrate in the diet. 11° to 40° North or South of the equator, dietary carbohydrate accounts for 30%-35% of calories on average whilst a sharp decrease to 20%-9% occurs from 41° to 60° above or below the equator.
  • Nearly 9 out of 10 of the diets of hunter-gatherer groups had less than a third of calories coming from carbohydrates. Specifically, “most hunter-gatherer diets (approximately 85%) were characterized by a relatively low carbohydrate intake (<35% of the total energy), which reflected the high reliance on animal-based foods of most hunter-gatherer societies
  • In the last quarter of our evolutionary timeline we started living higher up on the globe and thus had to switch to an even lower-carbohydrate diet. I am choosing the timeline of anatomically modern humans arising approximately 200,000 years ago. So specifically, “the switch to a low-carb diet (<25% of the total energy) seems to have taken place late in human evolution (ie, between 46 000 and 7 000 years ago) when our ancestors settled in higher latitude environments”.
  • The authors made the assumption that “gathered food included only plant foods” which significantly overestimates the amount of carbohydrates in the diet given that non-plant foods includes “the collection of small fauna (eg, invertebrates, insects, and eggs)”.

 

Table3

Table4

What bones contain can tells us something about what we ate

I will tell you what isotopes are in a minute. Having just considered dietary inferences derived from a combination of observations and empirical food data, now let’s consider dietary inferences derived from empirical data obtained from looking at the isotope signature of human and other animal bones. In 2009 Richards and Trinkaus compared the isotopic signatures of bones from Neanderthals, various early modern Europeans including Oase 1, modern Europeans, canids (wolves), cervids (deer) and hyenas. Before we dig into the findings, it is important to understand their reliable method for looking back into our dietary past using isotope analysis. An isotope is the variant form of an atom (or element). Take Nitrogen for example. The most common form is stable and has 7 protons + 7 neutrons, earning the name 14N. One variant of Nitrogen (or isotope) has 7 protons + 8 neutrons, earning the name 15N. The unequal number of protons and neutrons makes the atom more or less heavy compared to one with equal numbers. The atom can be ‘weighed’ by a device called a mass spectrometer. By looking at the ratio of 12Carbon (12C) to 13Carbon (13C) in a bone sample for example, I can be reasonably confident about what sort of food that land animal ate given that some animals eat C3 plants (like tubers, fruits, nuts) and others C4 plants (like maize, millet, sorghum). C3 and C4 plants refers to how these plants fix carbon during photosynthesis by joining 3 or 4 carbon atoms together, respectively.

Now that the physics underpinning isotope signatures is out of the way, lets look at what we’re particularly interested in, the diets of 2 kinds ancestral humans. The main reason is because their timelines overlap, making the comparison more relevant. The first human, a 37,000 – 42,000 year old modern male called Oase 1 found in Peştera cu Oase (Romania) in 2002. Peştera cu Oase means “The Cave with Bones”! The Neanderthal skeletons used in this study were dated to less than 50,000 years ago on average. Although not immediately relevant, I can’t help but mention that in 2015, Fu et al. (5) discovered that an ancestor of Oase 1 had sex with a Neanderthal 4 to 6 generations before his own. So what does the data indicate overall? I’ve summarized it below.

  • Neanderthals ate protein (meat, basically) mostly from land animals and probably very little to none from the sea. How much? “Each Neanderthal had δ15N values that were 3 to 5% higher than contemporary herbivores and similar to carnivores (or in some cases slightly higher)”. They are thus called “top-level” carnivores.
  • The Oase 1 human ate lots of protein from somewhere else, most likely freshwater fish.
  • Other early modern humans also ate lots of protein from the sea. How much? “[…]they consumed significant (i.e., 20–30% of dietary protein) amounts of marine foods, probably high trophic level (carnivorous) fish or marine mammals.
  • Depending on the early modern human, some ate lots of land and marine animals, maybe even including a higher proportion of those meats in their diet than the “top-level” Neanderthal carnivores did. How much? Their δ13C values “indicate that their protein came from terrestrial C3 (or freshwater) foods, yet many of them have high δ15N values, at or above the highest Neanderthal values.
  • Although the study has robust conclusions confirmed elsewhere it has limitations. First and most importantly, “the method only measures protein intake, many low-protein foods that may have been important to the diet (i.e., high caloric foods like honey, underground storage organs, and essential mineral and vitamin rich plant foods) are simply invisible to this method”. Secondly, it is hard to confirm the accuracy of certain comparisons because “comparative faunal isotopes” were sometimes lacking. Lastly, “carbon and nitrogen isotope values vary between different geographical regions, especially related to temperature and aridity”.
  • Humans ate a “wide range of diets. This does however come with 3 notes of caution. First, this does not encompass vegetarianism or veganism. I cannot emphasize this enough. Secondly, ‘variety’ here refers mainly to the origin of animal sources. All of the different human ancestors analyzed in this study were “top-level” carnivores. Third, it is correct but incomplete to state that humans are carnivores. Here, the term ‘carnivore’ refers to where humans fit hierarchically in the food chain. It is not a claim about a supposed inability to derive nutrition from plants. Humans are in fact obligate carnivores, in the sense that we did not and still cannot survive without some animal foods. Furthermore, most of the paleoanthropological evidence points to us being omnivores. My guess is that we are preferential omnivores to varying degrees according to what the climate and fauna allows. Depending on the developing (‘primitive’) group, their particular culture may have influenced their position on the spectrum of carnivory to omnivory.

Finally, lets visualize the data used for the above conclusions

Table5

In Figure 1, δ13C values below “-19” indicates a diet of primarily or only land animals. This is the case for Neanderthals (empty squares) but not for some early modern European humans (filled circles). In Figure 2, you can see that the Oase 1 human has higher δ15N values than some carnivorous wolves! High δ15N values occur in this instance because when a predator eats its prey, there is a 3%-5% δ15N enrichment. Consequently, carnivores such as wolves for example, will have higher δ15N values than their prey (such as ibex).

The takeaway here is that observations made of modern hunter-gatherers and clues from ancestral human bones support the claim that humans commonly evolved on low-carbohydrate and sometimes ketogenic diets. Seasonal changes in food availability likely swung the pendulum between higher-carbohydrate all the way down to ketogenic. In this sense, it is not correct to say that ketogenic diets are extreme diets in terms of their occurrence amongst humans.

In part 3, we will discuss how a distinguishing feature of humans – our big brains – is all the rage in hominization theories and how a high-fat diet may have been an important driver in it. However, the question is far from settled.

19 comments On Do ketogenic diets have a place in human evolution?

  • There are two problems here, best described by talks by Dr. Rosedale, which can be found on youtube: do we eat for reproductive capability, or do we eat for longevity. Evolution does not care about longevity. If you have a child, it would be best to feed him butter, eggs, liver, meat, bone broth, and starchy vegetables, to make sure he becomes as strong and healthy as possible, with good bone structure, good eyes and teeth. Basically, what Weston Price said. Later in life that child should keep the butter, bone broth, eggs and liver, decrease the meat and starchy vegs, and sharply ramp up green vegetables, sprouts and other high enzyme foods. at all times you try to intake fermented foods to counteract the vast bacterial deficit of modern lives.

    • Hi glib,

      thanks for your comments.

      Yes WAP had very good insights on diet. I would disagree about the ‘valuable’ nutritional content of grains with him, depending on the context – it’s better than white starches (like rice) or when calories are scarce maybe, but in a modern context of abundance I don’t think that holds up. However, if people are going to eat grains then sprouted and process in a less insulinogenic manner is best. So it’d be about making such products less harmful rather than healthier.

      Rosedale is right about the reasons for which we eat. However, I don’t see how this connects with the idea that we should decrease meat and starchy vegs – how you see that?

  • Unfortunately, the stable isotopes studies are probably the weakest of all the evidence.

    Schoeninger 2014 (“Stable Isotope Analyses and the Evolution of Human Diets”) explains just how misleading those isotopes can be. For instance, high carb Great Basin Foragers have higher N15 levels than those supposedly carnivorous Neanderthals. Also, hyenas and red foxes have very high N15 levels, but are known to be omnivores. Schoeninger writes:

    “Neanderthals seem less carnivorous than is often assumed when we compare their δ15 N (bone collagen) values with those of recent human populations, including recent human foragers…Richards & Schmitz (2008) concluded that high carnivory was based on the similarity between Neanderthal values (9 and 7.9) and those of a red fox (8.6), even though red foxes are noted to be omnivores (Lloyd 1981)…High relative δ15N values are common in humans, although it is far from clear how this result occurs”.

    Schoeninger suggests that since the high N15 values of hyenas and humans overlap, it may just be that humans scavenging a lot of leftover marrow bones may have skewed their N15 values.

    There’s also recent Neanderthal studies that point out that the N15 values are misleading…

    “Nitrogen isotope values in particular can be misleading. First, because of the complex nonlinear relationship between food source and consumer, it is not possible to accurately estimate the proportion of meat versus plants in the diet, since large changes in the percentage of meat are indicated only by small increases in 15N values (Ambrose et al., 2003; Hedges and Reynard, 2007). Second, unlike herbivores that acquire all of their protein from plant leaves, foraging humans usually eat plants for their carbohydrate content, and therefore focus on the starch- and sugar-rich storage organs of plants, such as USOs and seeds (Lee, 1979; Marlowe, 2010). These storage organs may have higher nitrogen values (Hedges and Reynard, 2007), and in any case provide a smaller amount of protein to the body and are therefore relatively swamped by the meat protein signal.” – pmid.us/24612646

    In other words, it may very well be that certain USOs (tubers, etc) were the main source of food. And it was certainly easier to dig up tubers than successfully hunt, with limited tools.

    • Hi Don R.,

      Thanks for your detailed comment (and references).

      As I pointed out in my article, such methods have limitations and you’ve done well to highlight a few (not all of which i agree with but for the most part, correct). However, they’re definitely not the ‘weakest form of evidence’. I cited data from such methods because they’ve been reproduced across multiple studies in different parts of the world. Most importantly though, they’re consistent with other evidence (they’re consilient). Artefacts, biochemistry, anatomy and written history points to an omnivorous species with a propensity & obligation for some degree of carnivory.

      • Yes, but all you’ve done is cherry picked whatever data makes a case for an extreme diet. Again, this is Ambiguity Fallacy—trying to fit whatever conclusions you want into whatever ambiguous cherry-picked data you can find.

        As an example, you rely on Ströhle and Hahn 2011, but fail to mention that their observations aren’t supported by more recent papers.

        For instance, all the data that people had been looking at before 2016 was for “in camp” data. In 2016 it was finally figured out that, for the tribesman used as a proxy for our Paleolithic ancestors, it had not considered all the carbs they were eating while *outside* of the camp hunting and gathering. lol

        http://www.ehbonline.org/article/S1090-5138(16)00011-8/abstract

        “Men did more than just snack while out of camp foraging, they consumed a mean of 2,405 kilocalories per foray, or approximately 90% of what is estimated to be their mean daily total energy expenditure (TEE). ”

        “…The vast majority of the kilocalories eaten while out of camp came from honey (85%).”

        [Slaps forehead]

        In other words, the papers you cited before 2016 were all wrong, because they did not consider all the large amounts of honey and carby plants they were eating outside of the camp. Furthermore, archaeological evidence of honey and starch doesn’t last as well as bones do, so the archaeological evidence tends to be biased towards whatever materials survives the longest (i.e. bones and wonky isotope data).

        Finally, despite what obsolete cherry-picked papers on limited in-camp data say, the fact that the Wild Greater Honeyguide bird exists—and co-evolved to literally “talk” with humans, over the past 2 to 5 million years—shows that honey was indeed a major staple for early hominids. The Honeyguide simply would not have evolved the way it did without millions of years of consistent human interaction. These major clues are all overlooked by all of the cherry-picked papers you cite and are highly misleading.

  • I think the strongest evidence coming from stable isotopes is the combined 13C, 15N concentrations in tropical savannas. There you can see that we have been eating C4 plants (through ruminants) and meat. C4 plants do not have USOs. You can also see a predominant ruminant-based nutrition over hundreds of thousands of year, until relatively recently. 15N may be noisy but the combined analysis is a lot less noisy.

    • “C4 plants do not have USOs”

      That’s completely incorrect. Members of the sedge family (Cyperaceae) are C4 plants. Tiger Nuts or “chufas” (Cyperus esculentus) are tubers full of starch, fiber, antioxidants and minerals and are now believed to be a staple of early hominids.

      Tiger nuts were one of the first crops to ever be domesticated in Ancient Egypt. They are easily harvested by pulling up tufts of grasses (see them on YouTube). And they have the interesting habit of rapidly multiplying, like invasive, weeds after their neighboring soil has been pulled up. Paleo Indians were known to have harvested them and their starch granules have been found on their tools.

      • I accept this point (I never thought that stuff that grows in Michigan could be C4) but I still doubt that humans evolved on sedge tubers as a staple. They are very small, and therefore inefficient foods (lots of digging for few calories). The most efficient food is ruminant meat (in terms of calories expended versus calories obtained). In regard to 15N, the best results I read compared 15N fractions of herbivores and carnivores locally. so it does not matter that the Great Basin has high 15N, the difference remains.

        • Again, false. In 2014, researchers at the University of Oxford published a paper saying:

          “The Oxford study calculates a hominin could extract sufficient nutrients from a tiger nut-based diet – i.e. around 10,000 kilojoules or 2,000 calories a day, or 80% of their required daily calorie intake – in two and half to three hours. This fits comfortably within the foraging time of five to six hours per day typical for a large-bodied primate.”

          They are extremely easy to harvest. See YouTube videos for homegrown “chufas” and you’ll see for yourself. You just grab a few blades of grass and pull. Easy peasy. 2,000 calories with 2.5-3 hours of work is nothing, and it frees up plenty of time to do other things.

          Tiger nuts are actually more nutrient-dense than red meat, and almost as nutrient-dense as liver (See Richard Nikoley’s articles on them). And their high levels of glycemic starch make them ideal raw tubers. They even taste sweet.

      • The OFT doens’t suggest tubers were a primary food for a homo sapiens – but for older species, quite possibly yes.

        • Raphael

          The fact of the matter is that we have no idea one way or the other. Whatever the real “Paleo” diet was, the data is so vague that people can find evidence to claim it was whatever they want it to be.

          This is also known as the “Ambiguity Fallacy.”

          I suspect that’s why so many keto dieters like to dig into the anthropology. They can claim an easy victory with a pile of bones at a dig site—while ignoring that there was sweet tasting tubers everywhere that took a few minutes to dig up and provided easy calories. Not to mention scientists have found evidence of the tuber starch on the tools of the (Mashantucket) Paleo Indians.

          These tubers were among the first crops ever domesticated by the Ancient Egyptians. To any reasonable person, that doesn’t seem like an accident.

        • Btw, I agree the tubers *probably* weren’t the primary food. I’m sure they ate lots of animals. And they probably also ate a lot of honey too. The very existence of the wild Greater Honey Guide—a bird that evolved to literally “talk” to humans and guide them to hives of honey—suggests that the Honey Guide and humans co-evolved over the span of at least 3 million years, according to a recent paper.

          The only way the Honey Guide could have co-evolved with humans was if we were consistently harvesting honey—the way the Masai and Hadza do.

          But, I digress. I just don’t see the evidence for ancestral keto when honey had to have been a staple for that co-evolution to take place, over millions of years.

  • so the 13C, 15N analysis was only applied to Great Basin primates? Am I completely wrong when I remember also european results? and chufa was available 12 months a year? including during the growing season?

    • Well, Cyperus esculentus (and similar sedge tubers) are invasive perennials. So, yes, available all year. They grow like crazy and you can’t get rid of them. The more you pick, the more they multiply and stick around. A single plant can produce several hundred to several thousand tubers during a single growing season. The tubers can also be dried and stored for long periods. They are quite tasty.

      I’m not quite sure what you mean by “only applied to Great Basin primates”. I didn’t say anything about Grat basin primates.

      Margaret Schoeninger’s 2014 paper says, “North American Great Basin HUMAN FORAGERS (see Figure 2) and four additional trophic systems (Schoeninger 1995b). High relative δ15N bone collagen values are common in humans, although it is far from clear how this result occurs.”

      Those populations were known “foragers.” (She literally shows a picture of them digging for food).

      • no, the tubers are not available year round. I used those in my yard for carp fishing. In the growing season they disappear. that is true everywhere.

        • Actually, It depends on the environment. Just because they don’t last all year for your area doesn’t mean they don’t last all year elsewhere.

          Take a look at the USDA page for Cyperus esculentus (USDA Symbol: CYES) and you will see that they are technically listed as a “Perennial,” which means that it can last for more than a year. If you actually take the time to read about them, you’ll find that while tubers may be viable up to 3.5 years, most only survive one winter.

        • “Tubers planted to soil depths of 80 cm produced new plants. Tubers survive soil temperatures as cold as -5oC and require a period of chilling to break dormancy and germinate. Tubers germinate when soil temperatures remain above 6oC. Under field conditions, tubers typically survive approximately 3-4 years.”

          http://threeissues.sdsu.edu/three_issues_coquillofacts02.html

          Sorry. ¯\_(ツ)_/¯

        • “When a critical daylength or temperature is reached, plants stop growing vegetatively and start to flower; however, many populations do not produce viable seed. Tubers are the only part of the plant that overwinter. Winter conditions kill basal bulbs, rhizomes, fibrous roots, and all above-ground parts. While tubers may be viable up to 3.5 years, most only survive one winter. ”

          http://threeissues.sdsu.edu/three_issues_coquillofacts02.html

  • Thank you for the article as it’s very helpful for the thesis that I’m going to present the topic of “Ketogenic Diet and Intermittent Fasting.

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