Metabolic Flexibility - Get Real

(Michael - When reality fails to meet expectations, the problem is not reality.) #162

Cellulose, a complex carbohydrate, or polysaccharide, consisting of 3,000 or more glucose units. The basic structural component of plant cell walls, cellulose comprises about 33 percent of all vegetable matter (90 percent of cotton and 50 percent of wood are cellulose) and is the most abundant of all naturally occurring organic compounds. Nondigestible by man, cellulose is a food for herbivorous animals ( e.g., cows, horses) because they retain it long enough for digestion by microorganisms present in the alimentary tract; protozoans in the gut of insects such as termites also digest cellulose.


I think due to our herbivorous primate ancestry, we retain the relic metabolic ability to metabolize carbohydrates of simpler molecular structure than cellulose. But as a family/species we gave up the guts necessary to metabolize cellulose to redirect the energy required by that big gut to feed our brains. We evolved over the course of several million years to eat primarily the nutrient dense fat and protein of other animals instead of nutrient dilute plants.

Yes, we retain the ability to utilize glucose to fuel cells that do not contain mitochondria. But we have evolved an elegant mechanism to produce all the glucose we require for those cells: gluconeogenesis. We do not need to eat it. In fact, I think gluconeogenesis is the mechanism we evolved to provide that small amount of required glucose during millions of years when eating it was impossible. It saved us from going extinct during the Pleistocene when plants were low in digestible carbohydrate and high in cellulose. If our ancestors had to rely on eating carbohydrates to get the glucose necessary to survive, we would not be here. That’s just the way it was.

You might argue that we were ‘not meant to be’ one thing or another. But until I see evidence that Pleistocene flora had a lot more digestible nutrients than it did (or I’ve seen so far), my bet is that our ancestors spent a lot more of their lives in ketosis than not. I think that’s how we were ‘meant to live’ to attain health and well-being.


Moles are cute.




(PJ) #165

I don’t think whether ‘man’ can digest it is the question if ‘gut bacteria’ can digest or utilize it though, right?

(Michael - When reality fails to meet expectations, the problem is not reality.) #166

From the source quote:

As I noted, we gave up the big guts necessary to retain it long enough in a lengthy digestive tract in favour of using that energy to support a big brain instead. Our gut bacteria are not digesting cellulose. I think you are referring to ‘soluble fiber’. Gut bacteria are digesting other polysaccharides that we metabolize.

Soluble Fiber

Soluble fiber includes gums, pectins, mucilages, and some hemicelluloses. According to the FDA, soluble fiber is listed on food labels as having calories because it does, in a roundabout way, contribute calories to the body. This is because most soluble fiber is used by the bacteria in the colon to produce short-chain fatty acids which, in turn, are used by the body as energy. These calories do not raise blood sugar, so when counting carbs, those in soluble fiber (like insoluble fiber) don’t count towards the total. This is also true of oligosaccharides, which may or may not also be listed as fiber.


Insoluble Fiber

Insoluble fiber includes cellulose, some hemicellulose, and lignins. It can be found in the seeds and skins of fruits and vegetables as well as whole grains like whole wheat and brown rice. It cannot be used by the body for energy.


(mole person) #167

He’s not calling anyone a mole person, he’s making a hypothetical reductio for the sake of illustrating his point.

This isn’t what he’s saying either. He’s not saying that the lion should feel badly about not being able to eat berries or that it’s lesser than the bear for that reason, he’s asking if, assuming that you have an optimal omnivore metabolism, it makes sense to limit your diet.

This is, in fact, the question that is under discussion here.

All that being said. Mole person is my new tag, I love it…lol.

(mole person) #168

I wouldn’t call it a relic. We aren’t likely to lose such an adaptation unless some trade off makes the loss of it more adaptive than keeping it.

No matter what we might think about whether having some plants in one’s diet is healthier than not while animal foods are plentiful, I think we can all agree that maintaining the ability to obtain nutrition from plant sources is a huge advantage over losing it, all else being equal.

I find this line of research really interesting but I’m not sure this description of the causal direction is correct. It would seem that our brain growth was dependant on our guts shrinking which in turn was dependant on a decreased reliance on plant foods.

There is a study showing that the energy used for organs is very constant across species. You can’t just evolve a super energetically expensive brain without giving up some of another organs energy consumption. It’s possible that there is no nutritional limitation to a plant diet feeding a big brain, but just this necessary trade off in organ energy usage.

The evolution of gluconeogenesis is ancient. It wasn’t evolved by humans. It goes all the way back to Cnidarians which evolved over 500 million years ago and is to be found all over the animal kingdom today, including every herbivorous vertebrate.

I think so too.

(PJ) #169

Ah, ok – thanks!

(Justin Jordan) #170

I am dubious that gut versus brain is causal in a biological sense. There are lots and lots and lots of things that can’t use hindgut fermentation to digest plant matter the way other apes can. None of them get our brains.

I’d suspect that the gut shrinkage may have lead to bigger brains because it put us at a disadvantage that created evolutionary pressure. The really simplified version is that if we lost our ability to digest a lot (but not all) of the plant matter that our ancestors did, we’d be obligated to get those calories somewhere else to survive. Since we don’t have the tools necessary for actual carnivory in a biological sense (no claws, no fangs) we had to get smarter.

So among our monkey ancestors who were less able to digest plant matter, the ones who were more clever could hunt better. And at some point, we got smart enough to tip over so that general intelligence become an evolutionary advantage on it’s own.

Which does answer a lot of questions - if eating meat alone is why we have big brains, why are we smarter than carnivores? If we lost the ability to hindgut ferment, why did other animals retain it?

If the smaller gut is just a detrimental mutation that lead to a…for lack of a better term…internal evolutionary pressure, there’s a hypothetical answer to those questions.

Speaking of questions, the whole ‘there wasn’t enough plant life in the Pleistocene for us to have a large part of diets as carbs’ - I’m not convinced. The thing is, everything alive that ISN’T in a trench in the ocean is ultimately living on solar power.

So if you hypothesize that early humans and human ancestors were deriving their food from eating other animals…well, what were those animals eating? Yes, yes, cellulose, for the most part.

But this presumes that there was a long term situation where there was, year to year, enough plant life growing to support herbivores to support humans and protohumans, but not enough for significant amounts of other plant life to grow.

I am dubious about this proposition.

Even if you buy that, you then need to explain why there are modern human populations who can and have eaten extraordinarily high percentages of their diet from carbohydrate sources with metabolic disease.

(Michael - When reality fails to meet expectations, the problem is not reality.) #171

You may find this of interest.

(Bob M) #172

Only problem is that most plants are deadly and/or can’t be digested. We can eat very few plants.

If you don’t believe me, go into the local woods or prairie and try to live on plants alone for a month.

(Justin Jordan) #173

I am aware.

But the climate idea is that there were plenty of those plants and not plants we could digest. Given that this is motivated reasoning to explain why we shouldn’t eat carbs, I am skeptical that this was so.

(I have other reasons to be dubious, ranging from the actual climate of the epoch, which varied a great since it was a couple million years, where humans and proto humans actually were, and of course, the aforementioned fact that lots of populations did in fact consume a lot of carbs as a percentage of their diet without developing metabolic diseases)

That said, your local prarie or woods does actually contain a fair bit of stuff you can eat. None of the Native American people who lived in the US actually ate carnivore diets, and the list of foods available naturally is fairly long.

(Michael - When reality fails to meet expectations, the problem is not reality.) #174

@Justin_Jordan I await your citations. Thanks.

(Justin Jordan) #175

I’ll get right on that.

(Michael - When reality fails to meet expectations, the problem is not reality.) #176

This (and few other Gibbons books) got me interested surviving on wild plant food:

I learned just how difficult it is to do it. Even 10K years into the agricultural revolution, literally thousands of plant escapees later, after seeding those domesticated and selectively bred edible plants into the ‘wild’ environment - I would quickly starve to death. I readily admit that our Pleistocene ancestors were a lot smarter than me about this, but they had much less variety to choose. I think it was amazingly fortuitous that our primate ancestors came down from the trees just when they did and spent a couple million years evolving to eat nutrient dense fat and meat. Exactly what they needed to survive the Pleistocene. Had that not occurred, the hominid family - assuming it survived at all - would still be chattering in the treetops of central Africa. I find it very interesting that all our herbivorous primate relatives are still confined to the tropics. Humans, on the other hand, have colonized every other part of the planet except Antarctica. Only because they couldn’t get there.

(Ken) #177

Another subjective opinion. In the case of people living fairly normal lifestyles, eating so many carbs in order to recompensate glycogen is unnecessary. In the case of people who are training heavy, following CKD and following a caloric restriction the other days of the week the recompensation becomes to maintain training efficiency. Metabolic effects can be profound in those type situations, and are sometimes difficult for those who have never experienced them to understand. The same type of negative effects can occur to those not training, but generally take much, much longer to occur.

(Bob M) #178

I think it’s possible that a CKD could help some people, mainly athletes. For me, I don’t see it being of much use. I want to maintain ketosis for certain reasons, and I try to avoid long term times out of ketosis. I also loathe trying to count calories (did that for years while on low fat), so I prefer not knowing how many calories I’m getting. :wink:

(Jenna Ericson) #179

I think that decreasing insulin is the best way to remain metabolically flexible. As someone said before, the definition of metabolically flexible is the ability of an organism to respond or adapt according to changes in metabolic or energy demand as well as the prevailing conditions or activity. Different activities create a demand for different fuel sources. For example, sprinting for 20 seconds will require glucose, whereas walking for an hour will probably demand more fat for fuel. If you can use both fuels efficiently depending on the situation, then you are metabolically flexible. If we think of insulin as a switch that flips the body from burning fat to burning glucose, chronically high insulin is like getting a piece of gum stuck in the switch so that it is very hard to flip it to burning fat. I think this creates a huge amount of stress on the body to produce and ingest as much glucose as possible to feed the demand for glucose. It also means that fat will get stored and will only be used for fuel when insulin goes low enough.

I have an n=1 that I’m doing that made me think about this. For the last 4 days I’ve been eating a high saturated fat, mostly animal product diet, with the exception of some berries and a little unsweetened baking chocolate. For me, I believe this is the lowest I have been able to get my insulin in a long time and maybe ever. Today my blood sugar was 73 (4.1) and my ketones were 3.0. I haven’t measured in a while, but in the past my blood sugar has been between 80 and 90 (fasted) and my ketones are usually around 0.5. Over the last few days I started having these moments where I felt like I had an annoying amount of energy, like to the point where I felt agitated and couldn’t sit still. If you had told me even a week ago that it was possible for me to have an annoying amount of energy I would have laughed. In the past there have been times when even on an easy hike I’ve felt so tired that all I wanted to do was lay down and rest. Over the weekend I was hiking and on the few steeper sections I blazed through with more energy than I’ve ever had. I also had so much energy last night that I went out and did some sprints outside after having just gotten back from the gym.

Even though I’ve been doing keto for a while it has always been hard for me to feel the benefits that most people describe. I think this is because there were other things besides carbs that were keeping my insulin up; namely, polyunsaturated fats and foods that caused an immune response. By eating Keto with mostly saturated fat and no questionable vegetation I’ve been able to feel a vast change in my energy level. I think this is because I have decreased my body’s previously excessive demands for glucose and insulin, allowing my body to use glucose only for the specific activities that it’s meant to be used for.

(Windmill Tilter) #180

A great way to check this is to eat low fat high carb for a week or two. If you’re blood sugar remains in that same stable range, you’re metabolically flexible for sure.

I’ve been trying this since Monday. It has not been good. My blood sugar has been out of control in both directions. My A1C is 5.1.

(Jenna Ericson) #181

I think there is a distinction to be made between one’s ability to efficiently utilize dietary carbohydrates vs. the ability to efficiently utilize endogenous glucose. I have realized through my recent dietary changes that I am relatively efficient at using endogenous glucose, but I am pretty positive that if I went and ate a piece of cake right now I would not fare so well. I think this is largely genetic. To paraphrase something I heard Richard Dawkins say in a podcast with Sam Harris: our genes are only successful in preparing us for the present in so far as the present is like the past.

The question then becomes, how long does it take for a population to adapt to a certain diet? I believe @amwassil has mentioned that ancient Egyptians showed signs of metabolic disfunction similar to what we see in type 2 diabetics due to a sudden boom in agriculture. It might be that in the intervening time between then and now Egyptians could have built up more of a tolerance to carbohydrates than other populations. Another example of a population that might be more tolerant to certain carbohydrates is people of Asian decent whose ancestors have presumably been eating rice for thousands of years. Native American or Australian Aborigines might have a harder time metabolizing certain forms of exogenous carbs because inversely their ancestors have not been exposed to them for as long.

Unfortunately, I think testing how genetically intolerant you are to dietary carbs would be difficult. I would image, however, that it’s safe to say that people who have success with keto are probably genetically predisposed to dietary carbohydrate intolerance.