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Experiments in Speed: Nutritional Ketosis

Should I be in it? Would I get laid if I do it? Would it pay my house loan? Many other questions and answers about nutritional ketosis for cycling and endurance sports in general.

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Measurement is the first step that leads to control and eventually to improvement. If you can’t measure something, you can’t understand it. If you can’t understand it, you can’t control it. If you can’t control it, you can’t improve it.
― H. James Harrington

While it is never a simple explanation, if you have to break it down, when it comes to food for health and fitness you can more or less narrow it down to:

Granted human metabolic pathways represent a plate of spaghetti and things are not as clearcut as above, the important point is that our physiology is uniquely adapted to break down fats in order to produce energy. The reasons being many, though providing 9kcal per gram compared to the measly 4kcal+water weight as available from glucose (carbohydrate). After all why would we store fat otherwise???

Since it is survival (and hence reproduction) that we are always after, putting all the eggs into one energy source basket, is rarely a good idea. As a result, we can break down all the macronutrients – proteins, carbohydrates and as I already mentioned – fats. We can synthesize most of the macronutrients and convert/re-convert them – a truly fail safe mechanism. The tricky part is that fats cannot pass the blood brain barrier and it is our brains with the vast creative ability that makes us human. Even at rest, the brain consumes significant amounts of energy and some of it must be left for the rest of the body. Therefore the next logical question is where does ALL that energy come from?

Sidenote #1: Bonking. The glucose receptors/transporters are the doors responsible for glucose getting into the cells where it can be used by the mitochondria to produce energy. The said receptors come in many varieties and not surprisingly the one with the highest affinity (GLUT3) is found in neurons. Blood glucose (90-110mg/dl) is extremely limited, coupled to the fact we store roughly 250g/2000kcal in the form of glycogen and we can burn 750+kcal/hour and only absorb ~350kcal/hour; it makes up for a train on a crash course. Therefore if/when glucose is our bodies’ primary choice of fuel when supplies get tight it is the brain that gets first dibs. When that happens the feeling that probably most of us have experienced happens – bonking/hitting the wall; in order to remain functional the brain shuts down everything that is not necessary in order to protect itself and make sure it continues to perform though at a basic level.

Energy and the Human Body


Yes lemons…kinda….As mentioned above human metabolism is a plate of spaghetti, therefore I don’t aim to put you to sleep while discussing the many similarly named intermediates that comprise the citric acid cycle.

Krebs or Citric Acid Cycle  (Source: Wikimedia Commons)

The important point is that ALL cells with mitochondria can perform the said cycle. Red blood cells are among the few that can’t. As long as a macronutrient (fat, carbohydrate, etc.) can be broken down (to any of that fancy name substances you see in the diagram at ANY step of the cycle, we can use it for energy.)

  • Carbohydrates (mainly glucose) get burned by glycolysis
  • Fats get utilized via beta oxidation as well as can be broken down to ketone bodies (ketones)
  • Proteins get broken down to their amino acids which are further chopped down to keto acids which get broken down to ketones.

Keto what says you?

The 4th fuel – Ketones

It bears repeating that insulin is the energy storage (aka fat MAKING) hormone. It is released in huge amounts mainly due to the consumption of highly refined (quickly digested) carbohydrates. It’s a direct relationship with no buts and no ifs. When carbohydrate intake is lowered and as such insulin levels decrease, the levels of another hormone glucagon go up. The body starts breaking down fatty acids and releasing stored glucose to be used as fuel. Some of the excess fatty acids get taken up by the liver and converted to ketones. If no carbs come in soon, the stored carbohydrates (glycogen) are depleted and the following things happen:

  1. The liver starts making glucose through gluconeogenesis. Proteins (muscle tissue) are the preferred raw material.
  2. The brain switches from almost 100% dependency on glucose to ~75+% ketones and some glucose for energy
  3. Fat becomes the main fuel source for all cells with the brain happily chomping down ketones and as such gluconeogenesis slows down since it is no longer the main glucose consumer. Ketone concentration in the blood increases in the range of 0.5mM to 5mM.

While it might not be so obvious to you, this is what happens when you starve yourself (or fast). As mentioned in the opening paragraphs, it is the brain that defines us (we are not headless chickens after all…) and as such it must have sufficient energy in order to run the show. If we were to continue using glucose we would have to continuously keep breaking down muscles in order to supply the raw material for gluconeogenesis. When food wasn’t a touch away we needed to be able to function optimally, otherwise we would not have survived as a species. From first glance ketosis is an emergency mechanism until food is available again. Evidence is mourning that long term ketosis is beneficial – Drs Jeff Volek and Stephen Phinney are among the pioneers in the field are and [amazon text=I highly recommend their work&asin=B005CVV2AE]. They showed that ketosis can beneficial for endurance performance. In addition a ketogenic diet has been an approved and successful treatment for childhood epilepsy.

Therefore you can jumpstart the process by fasting. HOWEVER, any food shortage is interpreted as stress.  If your body relies predominantly on fat you should be able to fast without ill effects and even do fasted workouts. Though keep in mind that stress is cumulative and in the modern fast paced society, it might be one thing too many. The other method  for entering into ketosis (gaining popularity ) is by drastically reducing carbohydrate intake so that insulin levels are kept low.

Here is a good place to make a VERY important distinction.

Ketosis and Beta oxidation (fat burning) are NOT the same thing. They can and do occur simultaneously in EVERYBODY (the degree differs; more on that below) and hence why ketones are sometimes referred as the 4th fuel. I was for a long time under the impression that fat burning was the equivalent of ketosis. I believe that a lot of people that have discovered the benefits of the so called high-fat/low carbohydrate diets, are under the same wrong/inaccurate impression. Since after couple of days after removing highly insulin producing foods (pastas, sweets, etc.), the brain switches predominantly to ketones for energy and I can personally attest that the amount and constant duration of mental awareness was (and still is!!!) something that I have never experienced. This is what is commonly referred to as “keto clarity.” Therefore it all gets labeled as ketosis and people (myself included) start wondering:

Should I be in ketosis? Would I get laid if I do so? Will it pay my house loan?

That all leads to freaking out for a lack of better word. So on to the next part…

Sidenote #2: Ketosis vs ketoacidosis. A still remember a biochemistry course in college where a reputable textbook said that ketosis is a pathological state, also refereed to as ketoacidosis. Even a good number of health professionals keep repeating that ad nauseum. If you starve long enough you enter into the said state and you can die. Yes you can starve to death, though it is not because of ketosis or ketoacidosis. In the total absence of insulin (aka Type 1 diabetes), since the cells cannot absorb nutrients, the body literally freaks out it is starving, fat metabolism, as described above goes into overdrive and since ketones are acidic as they accumulate in the blood; the buffering system gets overloaded and at concentrations of 20+mmol you can go into a coma, etc. Ketoacidosis is an extreme form of ketosis. With a functioning pancreas (that can produce insulin) and if you are not a raging alcoholic, the above simply cannot happen, it is physiologically impossible. During starvation or in low carbohydrate (<50g/day) diets, 0.2-8mmol is something we can all live happily and the long terms effects of ketosis are starting to get more positive reviews in the scientific literature.

Is Ketosis for YOU? My Experience

After years of pastas and carbohydrate rich foods as the standard endurance athlete diet, being introduced to [amazon text=Dr. Phil Maffetone’s big yellow book&asin=1616080655] lead me down a rabbit hole of high-fat diets and subsequently into ketosis. I didn’t stress too much about it since it all made sense, though since carbs were the enemy I kept them as low as possible – in simple terms that means only 1-2 pieces of fruit per day. Therefore I was curious where I was on the whole nutritonal ketosis thing. So I decided to measure it all.

While there are various gadgets in development to test the levels of ketones from the breath and or urine, what is in our blood will always be the true reflection on what is going on with our bodies, as such this is the best way. There are few commercially available meters on the market, the one available to me was [amazon text=Freestyle Optium Neo&asin=B01GCMYNKM]. Keep in mind that at the time of this writing each sample runs close to 2eur (2usd). I don’t claim that my results have any scientific value. I had a 20 pack of test strips and I tested various states (post fasted workouts, morning/afternoon, etc.). I didn’t do duplicates, statistical analysis etc. This is beyond the point I am trying to make. So what numbers did i get?

Nutritional Ketosis for Cycling_Blood Ketone Meter

The maximum level I got was 0.5mmol, with typical levels (even hours after a fasted workout), in the range of 0.2-0.3mmol. In short I was in mild ketosis, not in the true ‘nutritional ketosis territory’ (0.5-5mmol). Going even lower carb would be uncomfortable and difficult for me and my levels did NOT change after I introduced the occasional sweet potato and/or more fruits in my days – in general stopping freaking out about daily carbohydrates.

Is ketosis for YOU?  I can’t tell you that. What I can do is explain….

What Does It All Mean?

Athletes or not we need energy to survive. I am borrowing the graphs from Alan Couzens’s articles on metabolic testing. It’s a fancy term showing how our bodies use energy and how it can be drastically influenced by diet and or training methods (high intensity intervals for example). Energy (calories) coming from fat (blue) and carbohydrates (orange) are plotted vs power output (x, horizontal axis).

Glucose Burner or “Metabolically challenged athlete”

This is your currently (as of 2017) endurance athlete surviving on high carbohydrate diet (pasta, sports drinks, gels) and subscribing to the “no pain no gain” methods of training such as you have to train fast to race fast, intensity over volume (quality over quantity), etc. That was most certainly me some years back.

Nutritional Ketosis for Cycling Glucose burning athlete
‘Glucose Burner’ (Source: Alan Couzens)

Fat burning is tiny spec in the sea of orange. Why is that limiting? Remember we have 2000kcal stored, can burn 750+kcal/h and can only absorb ~350kcal/h from carbohydrates. This is before getting to the fact that glucose metabolism is highly inflammatory due to oxidative stress, among other things.

Keto Athlete

Low/restricted carbohydrate diets are gaining popularity, though if taken too far you get the following.

Nutritional Ketosis for Cycling Ketogenic Athlete Fat Burning
Keto Athlete (Source: Alan Couzens)

Fat burning is off the charts and is the predominant process even into higher intensities, though at some point, everything shuts down. You have reached a glass ceiling, like the sonic barrier that was deemed impossible to break through for airplanes. Though we managed to break it and while a metaphor, below is an example of how it should all more or less look like.

The Metabolically Optimal Athlete

Ironman and triathlons in general are metabolic limited events aka for the most part as hard as you can go is as hard as you can go and that is directly related to finishing times. Therefore how does an Elite athlete there look like?

Nutritional Ketosis for Cycling Fat and Glucose Metabolism Athlete
Metabolically Optimised Athlete (Source: Alan Couzens)

Fat metabolism is still quite significant, though as intensities ramp up, fat metabolism while still significant and even increasing at some point gives significant way to glucose. If you overlap the keto athlete and the ironman one, you see that it is both the peak and the WIDTH of fat burning that is important.

Nutritional Ketosis for Cycling -Metabolically optimal athlete
Keto Athlete vs Metabolically Optimal One (IM Kona Qualifier) (Source: Alan Couzens)

The above cases are quite illustrative (even if you are not a triathlete). You want muscles that are adept at burning both fat and glucose WHEN NEEDED. This is NOT an excuse to be pounding sugary sports drinks and eating cookies. It is an illustration on how we function and that while we can get by in extreme states, even when high performance is needed (the ‘classic athlete high carb diet/carbo loading, etc. come to mind and many Olympic medals to its name) The important part is that all systems must be functioning at their optimum. Each one has a niche (specific role) that it does best:

  • Fat – predominant energy source for all activities
  • Glucose – high bursts and/or high intensity (fight-or-flight)
  • Protein – mostly during state of starvation and/or depending on diet (ie lots of meat)
  • Ketones – brain fuel (keto clarity) as well as universal fuel for all cells; starvation fuel.

You want optimal rather than extreme. What is optimal for you and your (athletic) needs is for YOU to figure out, there is no formula and if anybody tries to convince you otherwise they are either lying or very very misinformed. If you have to eat below 50g of carbohydrates a day to enter ketosis – Fine. Remain in mild ketosis and eating 150-200g of carbohydrates a day – also fine – it is individual and you should be your own test monkey/lab rat.

Conclusion and Rant


I did it as a curiosity and the expense prevented me from REALLY obsessing about it ie testing every day, etc. I can ride for 3+h fasted without a problem (no low energy, headaches, etc), for 5h without a second thought (I get bored and sometimes annoyed of myself and my own thoughts/conversations in my head at anything longer) with only water and when I return home I am actually full with energy (ok relatively speaking); I am not ready to collapse and don’t need LOTS of coffee to even get off the couch…oh memories) and I am not dashing for the fridge in search for a quick ‘pick me up’ snack. My energy levels throughout the day are constantly high and the brain clarity doesn’t seize to amaze me. Therefore I am confident, my fat burning is at a decent level, whatever numbers on some display show. In the end this is the goal – become aware of what it takes so that you can tap into your body virtually limitless fuel supply – fat which is intertwined into so many ESSENTIAL life processes so that you ultimately achieve health and fitness. In parallel it goes into achieving awareness and being your own test monkey regarding your own life and health – whether it means amount of daily carbohydrates or other aspects.


I saved the ‘best’ for last. This is a bit of a paradox since with things as they are, no company would from the goodness of their heart go out and take the pains and money to develop such a device (blood glucose/ketone meter) if there was not an explicit need. Yet the need exists due to the avalanche, bullet train speed increase of metabolic diseases with obesity and diabetes topping the carts at 30+% of populations worldwide as of 2016. If it wasn’t for a simple entirely preventable cause – insulin resistance caused by refined carbohydrates, it wouldn’t be so bad making a profit out of it. Granted con and scam artists ‘make a living’ with much more ethically questionable ways, the exploits of the pharma industry influences me, you and everybody. The basic set for my ‘experiment’ cost me close to EUR100 (~USD100) at the time of this post. I am no diabetic so I paid it 100%. If I were, the health insurance would cover at least 70% and that takes into account that diabetics have to measure their blood glucose after every meal, and believing the advertising (and doctors!!!!?!?!?!) you are stuck with Type 2 diabetes for life (medication, consumables, etc) – you are the cash cow of the pharma industry. A healthcare system depends on healthy people being more than the sick ones, therefore eventually (and sooner than I imagine for sure) the system would collapse and when I actually need healthcare – yes I am looking at you drivers checking your phones and NOT paying attention to cyclists and other road users – I would have to pay it all out of pocket, yet a sizeable chunk of my wages (and hence MY TIME) goes into health insurance and I still pay quite a bit of premiums regardless (like Vitamin D blood tests). As we are now, there is an increasing number of people relegated to ‘life support’ with type 2 diabetes, obesity and metabolic syndrome, while the cause is simple and everybody is paying dearly in terms of money and more importantly health, more often than not not being able to refuse to do so. This is something I cannot agree with. #endrant

Burn more fat people, it’s good for everybody.

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6 replies on “Experiments in Speed: Nutritional Ketosis”

Hi Mikhail,

Thanks for the comment. I am sure I was not alone with all the questions I was having while experimenting with the so called nutritional ketosis. I am glad others find the post useful.


Love this, nutrition is so fascinating. Still so hard for so many people to give up the idea that a low fat diet is the healthy way to go. Did you end up racing any cross this year? I haven’t seen you on strava. I’m still plugging away at MAF for the winter, definitely enjoying it.

Hi Nic,
The fascinating aspect of everything (nutrition included) is getting to see and make sense of all sides of the story (aka the big picture) or as I have come to call it – be more right-brained about it. There is a pleasure in finding things out to quote Richard Feynman. Nutrition in particular is unique that it encompasses many fields such as politics, media/advertising, epidemiology and those in turn take precedence over physiology and quite often – common sense. With that being said, it is not a question of telling people that they need to eat more fat; influencing free will is difficult. It is a question of making a more educated society so that better decisions can be made by everybody and quacks and self-proclaimed ‘experts’ would simply not exist. Or as Gandhi calls it being the change you want to see in the world. While idealistic, I remember hearing a quote by Frank Zappa:
“If you wind up with a boring, miserable life because you listened to your mom, your dad, your teacher, your priest, or some guy on TV telling you how to do your shit, then YOU DESERVE IT.”

I mean no offence to anybody, though it takes stepping back and honestly evaluating your life, food, athletic performance, etc. and realizng that if you have been doing things one way (ie pounding carbs) and the results were unsatisfactory, it is madness to keep doing it and expecting different results – you have to take responsibility – own whatever it is you want to change and that includes the bad decisions and failures=). Unfortunately we let ego, fear of failure and most importantly somebody else (media, coaches, health professionals, etc.) tell us what is good for us without questioning and taking charge. This is usually the hard part – taking charge and becoming an informed consumer/athlete (took me until I was 30 years old to finally realize that…). Improvement, health, fitness and such are lifetime goals and the moment we stop asking “why?” is when we get tired/old/etc.

About racing cross you asked me the same question in a different post=); My situation is more or less the same as when I responded to you – since I am total beginner and my road license was stating otherwise, I was waiting for things to get figured out since I did not want to have my first experiences be in the PRO/1/2/3 category. As well as, I had ‘life things’ that took a lot of energy from me (I have a post on troubleshooting MAF coming next Monday) so racing was really not going to be the best decision – me making a living does not depend on it and I have nothing to prove to anybody, so no cross for me just yet=) – it is nice to have that freedom to decide – I let my body and brain be my guides. Though, I am starting to feel that I need to add some (emphasis on some) higher intensity stuff to my training (to add some glucose burning capability to my muscles to use a fancy term) and I suspect it would involve off-road riding. I am getting the road racing bug slowly as well. I will see and for sure will post my experiences positive or negative with that. I try to keep my Strava updated weekly, though sometimes I forget.

Sounds like you are having fun with MAF, this is what it is all about, keep at it, you will continue to be amazed, I am positive.


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