Are there any benefits to metabolic flexibility?


Some people tell me that metabolic flexibility is important for health (not sure about the specifics as they didn’t mention the science behind the reasons) and since I consume zero carbs, I am not metabolically flexible hence it’s not necessarily good for long-term health. Are there actually any proven benefits to switching between fat and carbs?

(Old Baconian) #2

Glucose-burning, glycolysis, is something every cell of the body can do. The cells never lose their ability to metabolise glucose. The people who are metabolically inflexible are those who have eaten a high-carbohydrate for some time, because the body disables certain metabolic processes at the cellular level, and too much glucose causes damage to mitochondria. This is why there is an adaptation period when we go keto, since only the mitochondria can metabolise fatty acids and ketones. The mitochondria need to be repaired, and the pathways reactivated. So you will maintain your metabolic flexibility by eating keto, not by eating carbohydrate.

(Todd Allen) #3

I think “metabolic flexibility” with respect to carbs is similar to a teetotaler improving their tolerance for alcohol by taking up drinking. That is not to say there are zero benefits to moderate consumption of carbs or alcohol but rather whatever benefits there might be are likely independent of the body’s ramping up processes to dispose of those substances.


I’ll answer your question with a question… Our bodies are able to burn multiple fuel sources right? Does it sound right to you that when you decide to burn some fuel from a different source you bloat, feel like crap, consider the next morning whether you are sick or not just because you ate something different? Seems to me a system designed to burn multiple fuels should actually be able to do it without severe blowback!

You use the word benefit, I’d just call it your body being optimal instead of being hypersensitive to a fuel source it’s supposed to be able to burn through.

Before I went to TKD/CKD I did standard keto for years, before I got myself flexible If I ate a carby meal meaning a real one) I’d wake up the next day with a dry mouth, my joints would hurt, i usually had a low grade headache, completely felt like crap and usually wasn’t right for at least that day, sometimes two, I’d also bloat for days.

Post Flexibility but before CKD/TKD If I ate keto all week I was fine, If I decided to eat a “normal” meal out with friend… NOTHING happened, I just burned that fuel and went back to ketosis. Just like that, no noticeable difference at ALL! Thats the way our metabolisms should work.

People make excuses/argument about “health”, like people that are mainly eating keto are thinking about “health” if they go to a party and know they want to put away a couple beers and a burger, it’s about being able to decide to be “normal” without life sucking for 3 days for doing something everybody else can do without issue.

I can’t think of a positive reason for intentionally creating a hypersensitive digestive system. If I give it fuel, it’s job is to burn it and move on, not complain about it and make me feel like crap in the process.

(Old Baconian) #5

A lot of the reasons people come up with for why eating carbohydrate is a good thing, bear an eery resemblance to the reasoning of newly-sober alcoholics as to why drinking alcohol is essential to health.

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

So-called ‘metabolic flexibility’ in popular understanding is what @lfod14 seems to think as posted above. True metabolic flexibility occurs at the cellular level, not at your plate. As noted above by @PaulL we do not lose our ability to oxidize glucose simply because it’s an essential fuel for those cells without mitochondria. Even when we are fully in ketosis, we still oxidize glucose every hour every day. It’s when we are not in ketosis and/or have damaged mitochondria that our cells do not oxidize fatty acids and ketones or only inefficiently. That’s metabolic inflexibility.

If you experience the symptoms listed by @lfod14 above when you ‘put away a couple of beers and burger’ it just means you have a messed up metabolism. When your metabolism is normal - in ketosis and metabolically flexible in the real meaning - a couple of beers and a burger don’t cause you any problems. @lfod14 says he can do it now without the bloat and crappy feeling - hooray for him, he’s done a great job of healing his metabolism. Just not by eating carbs as he thinks.

In other words, claiming that people ought to eat “in moderation” from all potential food sources, is failing to recognise that some foods are simply more nutritious than others. There is no virtue in eating something simply because you can, even if it is a source of nutrients. It must always come back to a comparison with the best alternative.



What is CKD/TKD?

Edit: never mind, I’ve found it on the net.

(Bob M) #8

I don’t eat CKD/TKD. Had ice cream “cake” yesterday due to a party for my daughter. Got familiar, head-spinning carb hit. Ate keto before, keto after. Rode my racing bike this morning. Feel fine.

Personally, I got fat by drinking good beer, eating pizza, then eating ice cream. I try to avoid these (haven’t had a beer in so long I can’t remember; do eat pizza and ice cream on special occasions).

Regardless, I think wheat is bad for humans. It’s not a good thing to eat for the vast majority of us. And I believe beer is the most obesogenic “food” on the planet. At least for me it is.

If you want to become “metabolically flexible”, I suggest eating some carbs that might not be as bad. Heck, even potatoes or white rice might not be as bad.

Also, when I wore my CGM for a year, the worst glucose readings I got – by far – were from pizza. Very high for very long. So, I try to limit pizza to special occasions.

And wheat causes me allergies and chest congestion. So, I try to minimize its use.

(Jack Bennett) #9

If you’re curious about operating at a “low-carb but not keto-low” level, some resources that might be useful are Perfect Health Diet (Paul and Shou-Ching Jaminet) and The P:E Diet (Ted Naiman and William Shewfelt).

In particular, the PHD book talks about some reasons and anecdotes for operating around 100g/d with what they call “safe starches” (low-toxicity, non-allergenic starch sources like white rice or potato). Whether this is valuable or beneficial for you might come down to your own metabolism and genetics.


We should consider that in the human digestive tract we start absorbing nutrients from the time we start eating and chewing. The small intestine allows the uptake of food nutrients broken down by chewing and mixing with stomach acid and bile. Then the food moves through the ileo-caecal junction into the bacterial rich large intestine where components of the food eaten are feeding the main population of the gut biome, bile and water are reabsorbed and things that were more difficult to digest are helped along by microbial digestion. So, we end up with a “healthy” poop of indigestible fibre and mainly bacterial biomass, ready resource to use as humanure to feed our external gardens and food forests.

The importance of foods variation, seasonally and daily has some supposition as to maintaining a healthy gut biome. The variety of gut microbe species varies with each meal. The key thing is to have small seed colonies available to quickly reproduce depending on the nutrients presented to the large bowel. Antibiotics can decimate these critters of our internal universe. Some concern is expressed at rigid adherence to a very restricted diet (as in low variety of foods) may cause some microbes to become extinct. That may affect flexibility in gaining, digesting or detoxifying what we eat.

Some thoughts to ferment.


from this post: In pre-industrial times, before we had restaurants and grocery stores, humans were metabolically flexible by necessity. Some days there was plenty of food, and other days there wasn’t enough to go around. Metabolic flexibility allowed people to go days without eating and feel fine. The same is true, to some degree, in our modern society, such as when we’re doing high-intensity exercise or have high levels of energy expenditure throughout the day—our bodies need to adapt and use the right amount of fuel, depending on the situation.

For my info it is ALL ABOUT survival point blank. Your body and thru the universe we can function on 2 fuels…ketones or glucose, if we have none of those we die point blank.

So this ‘metabolically flexible’ is what zillions of us do sometimes…one day all donuts and ice cream and pancakes and hash browns and finish the day with bags of chips and WE ATE…our body TOOK ALL it could from that…then a day we had a naked burger and a ton of chicken wings eating out and while ‘our ketones’ didn’t kick in for that ‘big ketone only’ burn…we survive…or a few days we get sick of eating the above and don’t eat for a day or 2…yes our body makes sure we survive.

It is 1000% about you and carb intake and your body and your medical issues coming into play.

One size metabolic flexibility fits all but can never fit all :wink:

It is a overall normal function of the body to switch fuel burn but how you come into your health issues and more are SO much more about it, your journey healing on healthy eating, your issues coming into this change and more that means NONE of us can say a blanket statement that metabolic flexibility is great…cause for many it never will be.

So again…all about you personally truly on this big statement of ‘is it great for all’ or ‘works against alot of us’ kinda thing.

(Joey) #12

Just found it on the 'net too. Sounds a bit complicated.

Are these keto-yet-with-occasional-carb-bursts primarily motivated by the goal of adding muscle and body-building?

(Michael - When reality fails to meet expectations, the problem is not reality.) #13

Both CKD (cyclical ketogenic diet) and TKD (targeted ketogenic diet) are based on the misconception that carbs are necessary and the ketogenic diet is less than adequate because it minimizes carbs. Advocates ignore the scientific facts that there is no minimum required consumption of carbs and no carb deficiency resulting from their lack. CKD and TKD are, in fact, self-fulfilling. Going in and out of ketosis regularly by eating carbs interferes with both ketosis and fat adaptation, and disrupts metabolic flexibility, which I noted above occurs at the cellular level not on your plate.

(Butter Withaspoon) #14

Evolutionarily speaking there is an advantage in being able to get energy from a wider range of sources. If you didn’t catch a kangaroo you can prepare and roast yam daisies on the fire. The advantage of burning carbohydrates and fats exists when it’s hard work to get enough food.
In richer countries in 2021 calories are over abundant- it’s the opposite problem.

For the rarer person who can switch between higher carbs and no carbs and go in and out of ketosis without it being very noticeable, the benefit is that they can be grateful to still have a healthy metabolism. Once you’ve sustained a lot of metabolic damage, it’s not certain how much flexibility you could get back, probably not worth it for most people

(Joey) #15

Yeah, it was my initial impression too, i.e., that there’s no training benefit to going in & out of ketosis. Volek/Phinney experiments proved otherwise, no?

Makes sense. Then again, evolutionarily speaking, there’s a benefit to being able to coagulate blood after suffering major flesh wounds. Doesn’t mean that cutting oneself to promote scabbing is a smart training method. :wink:


I think they might be.

I’m not for any WOE that involves too much counting. I can’t imagine our ancestors measuring the amount of fat/carb/protein in a meal.

If one keeps to basic ingredients that could potentially grow/live near you as opposed to food prepared by others and or coming through the post, and avoid the sweet/starchy things, I think most people would be ok.

(Joey) #17

While not doing much counting, our ancestors weren’t eating 90% of what one finds throughout the inside aisles of a typical grocery market. Stick to the perimeter walls and counting may not add much marginal benefit.

I’m inclined to agree with the basic ingredient hypothesis, although being nearby and being healthy are not always related (life on a corn farm?).

Another thought that arises from ancestral eating patterns is to eat foods “in season.” E.g., eating fruit throughout the year - when it’s only available (nearby) for a few of weeks out of fifty-two - might not be so ancestral after all?

(Michael - When reality fails to meet expectations, the problem is not reality.) #18

Except. For 3 1/2 million years there were no yams to roast. What folks forget is that all the digestible carb loaded ‘food’ available now was not available until post agricultural revolution and most of it not until a couple hundred years ago or less. Our Pleistocene ancestors did not have a ‘carb option’. Even those who were still in tropical Africa.

Metabolic flexibility is the cellular ability to switch between gluconeogenetic synthesized glucose and diet derived fats and proteins. For our ancestors that meant from meat. Our Pleistocene ancestors were not stupid. They did not waste time and energy gathering plants/roots that were 90+% indigestible cellulose and lignin.

(Michael - When reality fails to meet expectations, the problem is not reality.) #19

Like Joey says, of course, our ancestors didn’t do any counting simply because they ate protein and fat. Period. There were no carb options. They adapted to the meat and fat they ate over several million years. So we are adapted. Carbs have only been an option for maybe 8k years and they’ve been a nutritional disaster - see Michael Eades, et al. Industrial seed oils have been around for 100+ years and are proving to be an even bigger nutritional disaster. If you don’t want to count, eat ruminant meat. Otherwise, you’ll have to count at least a little.

(Butter Withaspoon) #20

The people in my country have well developed traditions around the plant foods they ate, so much rich story and knowledge of country. Local to here there are yams and some other roots and bulbs. The culture goes back many 10s of thousands of years. So this is what I model, the big kangaroo or goanna or snake on the fire is the main and vital part, plants gathered and processed in very particular ways are a sideline