More on physical performance and ketoadaptation

The various studies on how low carbohydrate diets impact physical performance are very nuanced.  Here’s what I mean by that.

Exhibit A. Phinney 1980

Phinney 1980

In this [pioneering] study, obese patients were subjected to a variety of performance assessments in a baseline period, then after 1 and 6 weeks of weight loss via protein-sparing modified fast (1.2 g/kg ideal body weight from lean meat, fish, or fowl; probably around 80 grams of protein/d, 500-750 kcal/d). They lost a lot of weight, 23 pounds on average, two-thirds of which was body fat. There was no exercise intervention, just the performance assessments.

During the ‘exercise to exhaustion’ treadmill exercise, RQ steadily declined from baseline to week 1 to week 6, indicating progressively more reliance on fat oxidation.  This was confirmed via muscle glycogen levels pre- and post-exercise: during the baseline testing, they declined by 15%; after 6 weeks of ketoadaptation, however, they only declined by 2%, while ‘time to exhaustion’ increased by 55%.  After only 1 week of the diet, time to exhaustion plummeted, as expected, by 20%.

This was, as mentioned above, a pioneering study in the field of ketoadaptation. It also challenges one of the prevailing theories of ‘fatigue’ …while carb-adapted, the subjects fatigued after 168 minutes, with muscle glycogen levels of 1.29 (reduced by 15%); while ketoadapted, they fatigued after 249 minutes with muscle glycogen levels of 1.02 (reduced by 2%).  In other words, they had less glycogen to begin with, used less glycogen during exercise, and performed significantly better (running on fat & ketones).

Exhibit B. Vogt 2003

Highly trained endurance athletes followed a high fat (53% fat, 32% carbs) or high carb (17% fat, 68% carbs) diet for 5 weeks in a randomized crossover study. In contrast to Phinney’s study, these participants were: 1) highly trained; and 2) exercised throughout the study.

Maximal power output and VO2max during a similar ‘time to exhaustion’ test was similar after both diet periods.  Same for total work output during a 20 minute ‘all-out’ cycling time trial and half-marathon running time.  Muscle glycogen was modestly, albeit statistically non-significantly lower after ketoadaption; however, ketoadapted athletes relied on a higher proportion of fat oxidation to fuel performance as indicated by lower RQ at every level of exercise intensity:

Vogt RQ

Again, this is the essence of ketoadaptation. Physical performance as good as or better using fat and fat-derived fuels.

One reason Phinney’s glycogen-depeleted ketoadapted subjects may have done so well is their reliance on ketones (probable) and intramyocellular lipids (IMCL) (possible).  In Vogt’s study, IMCL increased from 0.69 to 1.54% after ketoadaptation…

Also, food intake and body fat declined, and training volume increased in the low fat group; whereas food intake increased, and body fat and training volume declined in the high fat group.  Reminiscent of anything?

High fat, low carb -> eat more, exercise less, STILL LOSE BODY FAT.

Vogt data

Sorcery?  No.  Diet impacts more than just mood and body composition – resting energy expenditure increased in the ketogenic dieters.  This isn’t an isolated finding.

Exhibit C. Fleming 2003 

This was another study in non-trained athletes, consuming high fat (61% fat) or control (25% fat) diets for 6 weeks.  The tests were the 30-second Wingate, to examine supramaximal performance, and a 45-minute timed ride, to examine submaximal performance.

This study differed from the previous two in several significant ways.  For starters, peak power output declined in both groups, slightly more so in the high fat group (-10% vs. -8%).  Furthermore, RQ didn’t wasn’t significantly lower during this test in the high fat group, which possibly suggests they weren’t properly ketoadapted.  In Phinney’s study, the large energy deficit ensured ketoadaptation; this study lacked that aspect, somewhat more similar to Vogt’s, although unlike Vogt’s, these participants weren’t athletes which presumably makes ketoadaptation more difficult.

There are many factors at play… I wasn’t kidding when I said these studies are very nuanced!

Exhibit D. the infamous, Paoli 2012 

These were ‘elite artistic gymnasts,’ who could likely beat you in a race running backwards.  The ketogenic phase consisted of 55% fat and much more protein than the control phase (39% fat; protein: 41% vs. 15%). The significantly higher protein content was modestly offset by slightly more calories in the control phase, which reduces the amount of protein required to maintain nitrogen balance.

In this study, performance was, for the most part, ‘maintained,’ with relative increases in a few of the tests; eg, the “legs closed barrier.”  Changes in body composition were more robust: significantly reduced body fat and increased lean body mass after 30 days of ketogenic dieting (with their normal exercise routine).

Paoli data

The major confounder in this study was the use of an herbal cocktail only in the ketogenic diet group; despite this, the results are largely in line with the other studies.  For more on this study, see here.

Exhibit E. the most dramatic one to date: Sawyer 2013 

Please see here for the details, but in brief, strength-trained athletes showed improvements in high intensity exercise performance after only 7 days of carbohydrate restriction.  The nuances of this particular study are discussed more here.

barbell

Collectively, these studies show that physical performance in both endurance and high intensity realms does not always suffer, can be maintained, and in some cases is improved by ketogenic dieting.  Important factors are duration (to ensure adequate ketoadaptation), energy balance, and regular physical activity (athletes and regular exercisers can adapt to burning fat much quicker than sedentary folks).

 

calories proper

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  • Danny J Albers

    I find after my six month zero carb, half marathon experiment I have been pretty much carb optional ever since, amount of carbs dont seem to impact my recovery or my performance one bit, even for tasks that are primarily anaerobic.

    I got no issues being keto two weeks and carby for a week, etc…

    its very good feeling. Metabolic flexibility.

    • Wenchypoo

      Are you back at your website yet? I miss you.

  • js290
    • http://nigeepoo.blogspot.com/ Nigel Kinbrum

      So more energy per carbon atom makes fatty acids a better fuel? They’re not a better fuel if your muscles are operating near lactate threshold and not actually burning any fatty acids.

      • js290

        Don’t know the difference between the Cori and TCA cycles? And, difference between serum glucose and glycogen?

        • http://nigeepoo.blogspot.com/ Nigel Kinbrum

          Yes and yes.

          Don’t know what RER ?1 means?

          • js290

            How long can one endure RER ?1?

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            Not very long. So?
            In a duel-fuel car, which is the best fuel – electricity or petrol?
            For pootling along at 30mph with minimal cost & emissions, it’s electricity.
            For high speeds, it’s petrol.
            “Best” depends on context.
            In the body, for pootling along at low to medium intensity, fatty acids are the best fuel.
            When sprinting or lifting heavy loads, glucose is the best fuel.

          • js290

            I thought you said you knew the difference between glucose and glycogen? And the difference between the Cori and TCA cycles?

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            What’s your point, exactly (other than being a PITA)?

          • js290

            The sprinting/lifting heavy loads at maximum performance are anaerobic activities. They used stored glycogen metabolized through the anaerobic pathways. Those fast twitch, fast fatiguing muscles are predominately anaerobic and cannot use fatty acids OR serum glucose as fuel. They don’t have the mitochondria for aerobic metabolism. AND, they are slow to recover. No matter how much serum glucose you have from carb loading, the fast twitch, anaerobic muscles CANNOT aerobically use glucose as fuel.

            For most people, the anaerobic pathways are triggered by a hormonal response to “adrenaline.” For well trained athletes, these muscle fibers are recruited only when needed for their particular skill. How many heats do you think Usain Bolt is fully anaerobic when he’s sprinting? I’d bet in the qualifying heats, he’s mostly aerobic (jogging, literally), where fatty acids would offer the best performance. He’s probably fully anaerobic only for the medal heat that matters.

            The question that the carbo-philes cannot answer is when in a muscle glycogen depleted state whether carb loading actually speeds up recovery or whether the extra glucose is simply shuttled through the aerobic pathway in the insulin sensitive state. That is to ask, what is the flux of dietary glucose in such a state?

            Fundamentally, Nige, I’ve seen you equivocate glycogen and glucose in various other blogs, so your continued confusion is not unexpected.

          • http://www.caloriesproper.com/ William Lagakos

            Glucose =/= glycogen. and how this relates to muscular fatigue ? Coyle et al., 1986. https://www.ncbi.nlm.nih.gov/pubmed/3525502

            Granted, it was submaximal intensity, but brilliant study, really.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            I read the study you posted a link to. Emphasis, mine.
            “We conclude that when they are fed carbohydrate, highly trained
            endurance athletes are capable of oxidizing carbohydrate at relatively
            high rates from sources other than muscle glycogen during the latter
            stages of prolonged strenuous exercise and that this postpones fatigue.”
            What, other than muscle glycogen?

          • http://www.caloriesproper.com/ William Lagakos

            In line with what js290 mentioned, blood glucose can be used to fuel exercise at submaximal intensity.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            So, where’s my confusion exactly?
            Glycogen + n(H2O) = n(Glucose)
            What’s interchanging the terms “Glycogen” & “Glucose” got to do with the Cori & TCA cycles?

          • CynicalEng

            Liver glycogen ? Muscles can only use their own glycogen, so arm muscle glycogen is no good for running or cycling.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            Liver glycogen has to be converted into blood glucose to get to muscles. As far as I’m concerned, glucose & glycogen are interchangeable.

          • js290

            http://youtu.be/ToGt_GYCUmY?t=4m9s

            “When adrenaline hits, we don’t have to get the glucose out of our liver, circulate it around to get it to our muscles so we can run. It’s there onsite, ready to go. That’s why we store glucose (glycogen) in our muscle.” Doug McGuff, MD

            Also a clarification from Dr. McGuff regarding the linked video:

            “I noticed I made a mistatement. I stated that hormone sensitive lipase (HSL) mobilized glucose. HSL actually mobilizes fatty acids from the adipocyte. It is the glycogen phosphorylase enzymes that mobilize glucose. What is correct is that both of these enzymes are triggered byadrenaline during high intensity exercise and have amplified effects through an amplification cascade.”

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            When muscle glycogen has been completely depleted (e.g. at the ~20 mile point in a standard marathon), what happens then?

            “That’s why we store glucose (glycogen) in our muscle.”
            Doug McGuff, MD seems to be conflating glucose & glycogen. You’d better chastise him, too.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            Thank you for your reply. Sorry if I occasionally get things confused. Can you be specific as to where I confused glucose with glycogen?

          • Purposelessness

            An RER above 1 implies that the buffering of lactic acid produces non respiratory CO2 (bicarbonate puffer), which also implies that you can possibly reach 1 while still burning fat. Theoretically. No idea about the practical relevance. Bill?

          • http://www.caloriesproper.com/ William Lagakos

            Yes… it will be a mix of fat+glucose, of course… but if ketoadapted, there can be substantially more fat oxidation. RER should still be lower at every level of power output… until, I think, ventilatory threshold has been exceeded.

    • http://www.caloriesproper.com/ William Lagakos

      “Not logically possible to perform worse on a better fuel”

      I don’t disagree, but studies by Veech and colleagues suggest an alternative explanation for how this happens in this case.

      Eg, https://www.ncbi.nlm.nih.gov/pubmed/7929251

      reviewed here: https://www.ncbi.nlm.nih.gov/pubmed/14769489

      • js290

        Thanks for the links! I was somewhat familiar with Veech and perfused rat heart study from Cahill’s Fuel Metabolism in Starvation paper. Not surprised that Nature would not have wasted or misused fat and figured out a way to produce and use ketone bodies.

        • http://www.caloriesproper.com/ William Lagakos

          “Cahill’s Fuel Metabolism in Starvation paper.”

          Classic!

  • John

    Bill, you should scrutinize the methodology acutely. There must be a confound because as a former D1 athlete, and having now coached D1, I’ve seen dozens if not over a hundred athletes try low carb and not one has improved or even maintained performance. And yes, many tried it long enough to become ketoadapted (> month). I’m not sure if it’s because the nature of being an athlete requires multiple workouts in a day and muscle glycogen doesn’t replenish quickly enough, the reliance on the phosphocreatine system for those of us in power-based sports, i.e. repeated bout anaerobic work causes fluctuations in PC concentrations that can’t be replenished quick enough during keto due to some latency effect, etc.? I know that the plural of anecdote isn’t evidence, but whatever the issue is, it just doesn’t work in the real world.

    That said, I can buy keto for the average person who works out 3-4 times per week and under lactate threshold for most of that time, but not for serious athletes.

    • Jane Seyless

      I also have to wonder how it works for those looking for hypertrophy.

    • Purposelessness

      The plural of anecdote is myth, not data

      • http://nigeepoo.blogspot.com/ Nigel Kinbrum

        Unless, of course, the anecdote(s) happen(s) to confirm your beliefs.

        Alternatively, they just weren’t doing it properly.

        • Purposelessness

          You need to stop treating all low carbers like the same person. I’ve been dismissing anecdotes undiscriminatingly, and resent your implication.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            Sorry for my snarky reply. That’s what tends to happen after I’ve had excessive interaction with Mr Hahn.

    • js290

      Paleo Diet & Strength Training Biochemistry | Doug McGuff M.D. | “The folklore in coaching is just abhorrent.” http://bit.ly/1wcagp4

  • http://nigeepoo.blogspot.com/ Nigel Kinbrum

    RE Exhibit B: After the high-fat diet, RER still goes up to 1.0 at very high intensity i.e. there’s still 100% of energy derived from glycogen. As there’s ~20% less glycogen in the fat-adapted athletes, they bonk ~20% sooner.

    • http://www.caloriesproper.com/ William Lagakos

      exhibit A: much less glycogen yet bonk much later

      exhibit B: same half-marathon time in both groups

      Also, look closely at the figure from Vogt (exhibit B) – at very high intensity, the ketoadapted participants are still burning more fat *statistical significance*

      • http://nigeepoo.blogspot.com/ Nigel Kinbrum

        Exhibit A: Treadmill exercise is nowhere near lactate threshold, so the adapted have an advantage over the non-adapted. However…
        Although RER is lower in the adapted than in the non-adapted, when RER ?1 in the adapted, fat-burning is still zero.

        Exhibit B: I would guess that a 0.8 x marathon would also have about the same time, as the adapted have ~0.8 x glycogen. A whole marathon, no.

        • Purposelessness

          What’s your point?

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            The point is that you can prove anything you want. If you want to run a half-marathon, you can do it keto-adapted. If you want to run a full marathon, you can’t.

          • Purposelessness

            This is an incredibly anti science sentiment. If you can prove anything you want what is the purpose of science, and further, your purpose in discussing it?

            There has been no full marathon on keto study, you can’t know that. Absence of evidence doesn’t mean it’s evidence for absence.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            Well, pardon me for getting sentimental in my old age.

            What’s with the obsession with proving that fat is “best”? Context, context, context.

          • Purposelessness

            “Collectively, these studies show that physical performance in both endurance and high intensity realms does not always suffer, can be maintained, and in some cases is improved by ketogenic dieting.”

            Yes, these are clearly the writings of someone who is “obsessed with proving fat is best”. The absolute way in which arguments are presented really gives it away.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            The “fat is best” jibe was aimed at js290.

            I’ve seen enough studies where the methodology or statistical analysis was tweaked to give a desired result, to know that anything can be “proven”.

            Are we done, now?

          • http://www.caloriesproper.com/ William Lagakos

            “If you want to run a full marathon, you can’t.”

            I’d love to see where this came from… link?

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            Can’t win, I should have written. Sorry. Do I need a link for that? Has a keto-adapted person ever won a standard marathon?

          • http://www.caloriesproper.com/ William Lagakos

            “Do I need a link for that?”
            Yes, of course. (regardless of whether it’s can’t run a marathon or can’t win one)

            “Has a keto-adapted person ever won a standard marathon?”

            I don’t know, but I don’t see the relevance…?

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            For a regular marathon runner, the ability to win is important.

            I just did a quick Google. For ultra-marathons, keto-adaptation is fine. I can’t see any sign of any keto-adapted marathon winners.

          • http://www.caloriesproper.com/ William Lagakos

            ketoadaptation is OK for half-marathons and ultra-marathons, and we have no refs showing it’s not OK for normal marathons…

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            I spotted http://primalnorth.blogspot.co.uk/p/keto-adaptation-vs-low-carb-limbo.html in the Google search results and noticed that you’d +1′d it on Google+. Emphasis, mine.
            “My thoughts and I’ll be honest again, is if you wish to engage in daily
            HIIT, you should train for fat-adaptation not keto-adaptation, and
            institute some reasonable level of carb back loading instead of some
            super-human deluding themselves into thinking they can accomplish what
            others can not.”

          • http://www.caloriesproper.com/ William Lagakos

            “because Danny said so”

            Sure, but is this why keto wouldn’t work for regular marathons? …even though it’s OK for half-marathons & ultra-marathons.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            O.K. How about you Google and find a/some keto-adapted marathon winner(s). I’m going out.

          • Jack Kruse

            Wim Hoff has now twice

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            Read what I wrote 2 days ago.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            “”Do I need a link for that?”
            Yes, of course.”
            Jack didn’t provide a link. Neither did you. Tsk!

          • Jack Kruse

            They made a movie about it……you certainly did not look to hard. It might have gone against your beliefs…….

          • http://www.caloriesproper.com/ William Lagakos

            I can’t provide any evidence proving Flying Spaghetti Monsters don’t exist, either. Admittedly, however, I also can’t provide any evidence proving they do.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            I asked you “Has a keto-adapted person ever won a standard marathon?” You quoted me 2 days ago, so I definitely didn’t just change anything and you knew.

            So, got any evidence?

            I have no idea why you’re going on about Flying Spaghetti Monsters.

          • http://www.caloriesproper.com/ William Lagakos
          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            Still no idea what you’re going on about.
            Kruse said…
            “You said run first but after you found out about Wim you bailed on your thesis. Typical.”
            You knew that what he wrote was bollix, yet you still upvoted it. I’m not wasting any more of my time on this topic.

          • Jack Kruse

            Wim Hoff has

          • http://www.caloriesproper.com/ William Lagakos

            BAREFOOT.
            at -20°C.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            http://en.wikipedia.org/wiki/Wim_Hof#Feats “In 2009 Hof completed a full marathon (42.195 kilometres (26.219 mi)), above the polar circle in Finland, in temperatures close to ?20 °C (?4 °F). Dressed in nothing but shorts, Hof finished in 5 hours and 25 minutes.” Did he win because there were no other competitors? 5h 25m is waaay slower than “normal” marathon winners.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            Link?

          • Jack Kruse

            “The real problem in speech is not precise language. The problem is clear language. The desire is to have the idea clearly communicated to the other person. It is onlynecessary to be precise when there is some doubt as to the meaning of a phrase, and then the precision should be put in the place where the doubt exists. It is really quite impossible to say anything with absolute precision, unless that thing is so abstracted from the real world as to not represent any real thing.”

            Another Feynman gem……..

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            See my above reply. SMH.

          • John

            Nigel,
            Rhetorical question I think. You may not get to choose in what form the proof arrives. Woman has been predicted to outlast man in endurance because of their higher fat reserve. The proof is getting stronger in form of winners in the last two LA marathons.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            Even skinny Kenyans have more than enough stored body-fat to fuel a marathon, yet they all carb-up. And win.

          • Jack Kruse

            I think we showed on twitter Bill it can and has been done. Now NK wants to change “can” to “win”. I’d stop feeding the monster. Some people’s beliefs are hard to overcome. Feynman always said, “The first principle is that you must not fool yourself — and you are the easiest person to fool.”

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            See my above reply. Jeez!

          • Jack Kruse

            You said run first but after you found out about Wim you bailed on your thesis. Typical.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            I corrected my error 2 days ago. Your reply was 8 hours ago. Any other excuses?

  • Jane Seyless

    Have you seen the Ben Greenfield experiments on this stuff?

    http://www.bengreenfieldfitness.com/2014/05/how-much-fat-can-you-burn/

  • libfree

    I’ll just share my own anecdotal here. I’ve gone hard core keto twice. I lost a large amount of weight the first time and didn’t notice any reduction in any measure of athletic ability but I wasn’t keeping track so I’m not 100% sure.

    I fell off the wagon and gained some of my weight back. Hence my decision last month to get strict again. This time I kept better records. I’ve also gotten much better at eating a keto diet and considering how fast my weight is coming off, I’m much more adapted this time through. compared to my last intense training period 6 months ago when I was eating more carbs, I’ve peaked about 10% time till exhaustion in burst exercises. I’m lifting a little less than 7% more.

    More significantly, I don’t have to eat something before my workouts. I’m one of those people that gets effected by carbs a lot so I’m not sure how much this applies to anyone else.

    • http://www.caloriesproper.com/ William Lagakos

      thanks for posting this. and congrats on your progress!

  • Guest

    Nigel Kinbrum

    You were asked: “How long can one endure RER ?1?”
    You answered: “Not very long. So?”

    I think that is a great question. The first point that comes to my mind is; either we do not ‘need’ long-sustained RER ?1 or we cannot sustain such a level for longer periods of time due to some physiologic/metabolic cost.

    Using our Darwinian lens & biochemistry loupe we can test the assumption “humans can rely on fat oxidation as a primary fuel for the full range of their energy requirements”. IMO this answer has been validated through a myriad of controlled trials, anthropological evidence, basic biochemistry, anecdotal evidence & so on.

    However, this doesn’t satisfy the curiosity of most commenters here. We want better resolution. This is where defining our terms & making sure we’re all discussing the same questions becomes paramount.

    Lastly, you said “When sprinting or lifting heavy loads, glucose is the best fuel.” This seems to make sense to me & has a lot of clinical data supporting it (in addition to the anecdotal stuff, which is significant).

    Are you saying that this equates to “eat more carbs for glycolytic activity?
    Or are you allowing the possibility that humans can supply these sugars through GNG pathways?

    • http://nigeepoo.blogspot.com/ Nigel Kinbrum

      I’m merely trying to address the use of the term “best”. The body uses a variable mixture of fuels, depending on what it’s doing (in the same manner as a duel-fuel car).

      I think that encouraging the body run predominantly on one fuel (whether it be carbs or fats) results in metabolic inflexibility. Thus, when the other fuel is eaten, the body doesn’t function as well as it should (e.g. Poor OGTT results after becoming fat-adapted). I don’t know if OFTT results are poor on a high-carbohydrate diet.

      That’s why I prefer a LC diet to a VLC diet.

    • http://www.caloriesproper.com/ William Lagakos

      also, it’s not entirely “fat vs. glucose.”

      I don’t think ‘fat oxidation’ in a ketoadapted athlete is the same as ‘fat oxidation’ in a high carb athlete. The former can produce more power, burning fat, than the latter.
      http://caloriesproper.com/?p=2786

  • rs711

    @nigelkinbrum:disqus
    You were asked: “How long can one endure RER ?1?”
    You answered: “Not very long. So?”

    I think that is a great question. The first point that comes to my mind is; either we do not ‘need’ long-sustained RER ?1 or we cannot sustain such a level for longer periods of time due to some physiologic/metabolic cost.

    Using our Darwinian lens & biochemistry loupe we can test the assumption “humans can rely on fat oxidation as a primary fuel for the full range of their energy requirements”. IMO this answer has been validated through a myriad of controlled trials, anthropological evidence, basic biochemistry, anecdotal evidence & so on.

    However, this doesn’t satisfy the curiosity of most commenters here. We want better resolution. This is where defining our terms & making sure we’re all discussing the same questions becomes paramount.

    Lastly, you said “When sprinting or lifting heavy loads, glucose is the best fuel.” This seems to make sense to me & has a lot of clinical data supporting it (in addition to the anecdotal stuff, which is significant).

    Are you saying that this equates to “eat more carbs for glycolytic activity?

    Or are you allowing the possibility that humans can supply these sugars through GNG pathways?

    • http://nigeepoo.blogspot.com/ Nigel Kinbrum

      I’m merely trying to address the use of the term “best”. The body uses a variable mixture of fuels, depending on what it’s doing (in the same manner as a duel-fuel car).

      I think that encouraging the body to run predominantly on one fuel (whether it be carbs or fats) results in
      metabolic inflexibility. Thus, when the other fuel is eaten, the body doesn’t function as well as it should (e.g. Poor OGTT results after becoming fat-adapted). I don’t know if OFTT results are poor on a high-carbohydrate diet.

      That’s why I prefer a LC diet to a VLC diet.

      • rs711

        Couldn’t agree more – “best” should be contextualized, always.

        I disagree that running the body predominantly on 1 fuel is necessarily a sign of “inflexibility”. Metabolic flexibility is a suitably rapid & ‘pain-free’ TRANSITION from predominantly burning 1 fuel substrate over another.

        In this modern context, it seems to me that fat adapted humans can more readily start burning sugars effectively – than the other way round. Do you agree? I’m not fully convinced either wait.

        However, I say this based on anecdotal observations in addition to the biochemical mitochondrial overhaul seen in muscle biopsies when transitioning from SAD to LC/keto for example (oversimplified, apologies).

        Common sense is great but it isn’t science. So, I freely admit the former is responsible for my inability to shake the feeling that the substantial difference in ATP units produced from a mole of glucose compared to a mole of fat strongly suggests fat **should** (?) predominate the day-to-day energy requirements (again…what is my day-to-day compared to yours? Context)

        • http://nigeepoo.blogspot.com/ Nigel Kinbrum

          It’s fairly well known that people on ketogenic diets who know that they are going to be given an OGTT (e.g. pregnant women) are advised to eat some carbohydrate prior to the OGTT to avoid failing the test & being labelled “diabetic”.

          OFTT’s are only used in studies AFAIK, so I don’t know if there’s a problem with excessive postprandial TG’s with an OFTT on a high-carb diet. I can’t see an obvious reason why there should be a problem.

        • http://www.caloriesproper.com/ William Lagakos

          “In this modern context, it seems to me that fat adapted humans can more readily start burning sugars effectively”

          This has been demonstrated, experimentally. When someone is switched to a high carb diet (FQ=1), RQ increases almost immediately. When someone is switched to a high fat diet (FQ=0.7), it takes a few days for RQ to adjust. If this person is then switched back to high carb, RQ increases almost immediately.

          • http://nigeepoo.blogspot.com/ Nigel Kinbrum

            Isn’t that due to the fact that glycogen stores are repleted relatively quickly, but depleted relatively slowly?

            What about the high postprandial BG’s in the keto-adapted after consuming high-GI carbs?

      • js290

        http://themedicalbiochemistrypage.org/fatty-acid-oxidation.php#cycle

        “The glucose-fatty acid cycle describes interrelationships of glucose and fatty acid oxidation as defined by fuel flux and fuel selection by various organs. This cycle is not a metabolic cycle such as can be defined by the
        TCA cycle as an example, but defines the dynamic interactions between these two major energy substrate pools. The glucose-fatty acid cycle was first proposed by Philip Randle and co-workers in 1963 and is, therefore, ometimes referred to as the Randle cycle or Randle hypothesis. The cycle describes how nutrients in the diet can fine-tune metabolic processes on top of the more coarse control exerted by various peptide and steroid hormones. The underlying theme of the glucose-fatty acid cycle is that the utilization of one nutrient (e.g. glucose) directly inhibits the use of the other (in this case fatty acids) without hormonal mediation.”

        • http://nigeepoo.blogspot.com/ Nigel Kinbrum

          I’m sure that this is leading somewhere. Can you please get there a little faster, as I’m going out tonight!

  • John

    Thank you Bill for a great series of posts.
    I believe there is an esoteric condition where ketoadaptation may not work so well: physical performance at very high altitude (15000 ft above sea level). RQ expressed as the ratio of CO2 (eliminated) over O2 (consumed) tells the whole story.
    I suspect my own performance suffers disproportionately (after correction for training or lack thereof) from ketoadaptation. Personally I’ve tried various interventions: ginko biloba, garlic, caffeine, green tea…May try baking soda ingestion (acidosis) and/or sodium nitrite (Nitric Oxide synthesis) next.
    Of course the other camp is not free of trouble either: a person metabolizing on carbs must be constantly refueling while facing loss of appetite and risk diversion of precious energy to food processing. Rising CO2 also discourage glycolysis. Perhaps a no-win situation for either camp.
    Is there any study that you are aware of dealing with this issue?
    JohnN

    • http://www.caloriesproper.com/ William Lagakos

      Hi John,

      Unfortunately not (to my knowledge). There aren’t very many studies at all on the topic.

  • nikcha

    Hi to all
    I am on to low carb eating for about a year. From time to time i measure my ketone levels and i have achieved 1.5 mmol/l in the morning to max 3.3 mmol/l after 1 hour easy aerobic exercise.
    What i noticed is that my max heart rate rised during this period from 195 bpm to 203 bpm (i have measured it using a polar heart rate monitor)

    Can this be possible? Am i getting younger? (my chronological age is 45)
    Any thoughts on this?

    • http://www.caloriesproper.com/ William Lagakos

      It is certainly possible, but not sure if it’s clinically relevant. How long have you been exercising? Ie, it could be a training effect…

  • http://www.caloriesproper.com/ William Lagakos

    The LCHF Runners Diet – Can you run on fat alone?
    http://talkfeed.co.za/lchf-runners-diet/