As a response to the question “what does ketosis have to do with breath?” I thought this might be of interest. A 2016 study found that olympic-level walkers on a low carb-high fat (LCHF) diet lost weight more than High Carb (HC) and periodized High Carb (PC) diet (you’ll need to read the study to understand. The link is provided later). No surprise there, but in terms of performance they found that the LCHF walkers were hampered by the oxygen cost of the diet. Here is a quote from the summary “because fats have a pathway to generating ATP that requires oxygen, [and the carb diets don’t require it?] it becomes apparent that a shift in fuel utilization from carbohydrate to fat for high-output energy production may not be as great of an idea as it would appear to be on the surface.”
So oxygen becomes a limiting factor in elite-level performance while in Ketosis.
Food for thought.
Here is the link.
Can keto cause shortness of breath?
@Nascenta Thanks for the link. Lots of interesting stuff.
The purpose of this new study was to determine the effects of a three-week adaptation to a low-carb, high-fat diet during an intense block of training for world-class endurance athlete race-walkers.
Maybe not purposely, but this study was designed to fail. No one, and especially world-class endurance atheletes, is going to fat adapt in 3 weeks. Compare this to Volek’s Faster study.
Conclusion: Compared to highly trained ultra-endurance athletes consuming an HC diet, long-term keto-adaptation results in extraordinarily high rates of fat oxidation, whereas muscle glycogen utilization and repletion patterns during and after a 3 hour run are similar.
This is bonkers. Glycolysis (glucose metabolism) also requires oxygen. If I recall correctly, metabolising a molecule of glucose requires about the same amount of oxygen as metabolising a fatty acid. Of course it depends on the length of the fatty acid in question, but still. Oxygen is not usually the limiting factor. Moreover, ketone bodies, being partially-metabolised fatty acids, need less oxygen to be metabolised.
Carbohydrates are oxidized through aerobic respiration using RER, resulting in an equal ratio of CO2 release and oxygen consumption; this implies that 100% of carbohydrates are consumed to produce ATP.
C6H12O2 + 6O2 → 6CO2 + 6H2O + Energy
RQ = 6CO2 /6O2 = 1.0When fat is oxidized and measured using RER, the outcome is reduced CO2 production for every oxygen molecule consumed.
C16H32O2 + 23O2 → 16CO2 + 16H2O + Energy
RQ = 16CO2 / 23O2 = 0.7
So, indeed, fat metabolism requires 30% more oxygen. However, the energy output of fat @ 9kcal per gram is 2.25 x the energy output of carbohydrate @ 4kcal per gram. Unless I’m missing something, that seems like a beneficial tradeoff. Considering, as @PaulL points out - oxygen is free.
Something looks a bit wrong there. Shouldn’t the reactions produce CO2, not O2? I was always taught that we inhale oxygen and exhale carbon dioxide.
Yes! Corrected. Thanks for pointing it out. I’ve done this a few times already, I should know it by now!
The Equations
Oxidation of a carbohydrate molecule:
6 O2 + C6H12O6 → 6CO2 + 6H2O + 38 ATP
RER = VCO2/VO2 = 6CO2/6O2 = 1.0Oxidation of a fatty acid molecule:
23O2 + C16H32O2 → 16CO2 + 16H2O + 129 ATP
RER = VCO2/VO2 = 16CO2/23O2 = 0.7
Actually, in terms of ATP fat gives you 3.4 x more energy than carbohydrate (129/38 = 3.4) at a cost of 30% more oxygen. An even better deal than I thought!
I must admit that I added the [] comment, not the authors of the study. I forgot to put a question mark. My bad. but read through the article and post what you think. For myself, I was surprised to learn about the oxygen cost of ketosis relative to glycolysis.
Curious what cost? Oxygen is free.
It’s not a huge thing, to start with. For most of us, it would not matter at all, not even when first going low-carb. I cannot see it being any concern at all as to going low-carb.
It’s an oversimplification, but we can say that we are oxidizing carbon and hydrogen atoms to make energy (or to make ATP - which is ‘energy’ for our cells; our cells use it to make things happen).
Looking at the above chemical equations that Michael posted, we’ve gotten 3.4 times as much energy from the fatty acid, but at the cost of adding 3.83 times as much oxygen. So, it’s a little less efficient than using the glucose.
The advantage to carbs there is 13%. To get the same energy from the fat, we’re having to add 13% more oxygen.
Over the long term, there is some evidence than a ketogenic diet results in our cells making more mitochondria (the ‘powerhouse’ of the cell). If so, this would be an offsetting factor, i.e. if the cells can take in more oxygen, then that would make up for having to supply more oxygen for the metabolization of fat.
It would rarely be a noticeable factor, anyway. Unless one has substantial breathing or circulatory problems, it’s no problem to supply plenty of oxygen in normal, daily life up through quite strenuous activity. So, oxygen is not going to be the limiting factor. To say, " from an oxygen cost standpoint, it’s cheaper to burn carbs" - is true, but few are ever going to notice that.
To me, this makes sense, viewing it as “the low carb group had lower insulin and thus greater access to their stored fat.”
But not much, really, and this was a study “of a three-week adaptation to a low-carb, high-fat diet during an intense block of training for world-class endurance athlete race-walkers.”
To get a better picture of the effect of “the diet,” I’d say don’t look at the first three weeks. Give the test subjects 6 weeks - or better yet - 3 months or longer on low-carb, and then do the three-week study. In the article, it’s mentioned that a different study “used athletes who had been successfully racing with a LCHF approach for at least six months.” Okay - much better.
When is the oxygen cost actually going to matter? For most people, it’s not the lack of available oxygen nor the oxygen cost of burning fat that will make the difference. It’s how fast lactic acid builds up in the muscles - this is much more related to fatigue and perceived exertion when viewing performance.
The test subjects were race-walkers, about whom much less is known than for runners. Over equivalent distances, race walkers have a substantially slower pace. At 10k, elite athletes are going about 42% faster when running, and at marathon distance it’s 39% faster.
Everybody has a limit on how much oxygen they can consume - the ‘VO2max’ thing. At longer distances, people are not using as much oxygen as they can. Training can increase one’s VO2max, and the percentage of VO2max that one can operate at for a given time, but there is still a limit on how much of the VO2max is sustainable.
Elite runners can sustain ~98% VO2max for a 5k race. For a 10k it’s about 92%, and 78% during a marathon. Race walking is less efficient and “harder” at a given speed, but the pace of race walkers is so much slower that I doubt the percentage of VO2max is higher than for runners, and I would guess that it’s less.
In the study, the test subjects did 25 kilometer race-walks where they measured oxygen use, etc. That’s halfway between a 10k distance and a marathon, so I’m thinking they were around 80-85% of VO2max. So, is oxygen really going to be the limiting factor, there?
The problems with the study that I see are the lack of time for fat-adaption to take place, and the self-selecting nature for the subjects - they picked which diet they wanted to try.
Additionally, to get a more accurate idea of what’s really going on, we need to know what the VO2max was, what percentage of it was being used, and the lactic acid situation - what the ‘vLTP’ is - their velocity at the lactic acid turnpoint.
We all have the “anaerobic threshold” which is as hard as we can exercise for a substantial amount of time without having a meaningful amount of lactic acid buildup in our blood. Below this, we don’t accumulate much fatigue. There is also a second ‘breakpoint’ which is called the vLTP. This is an increased intensity of exercise where we’re already in anaerobic territory, and the buildup of lactic acid increases a lot. This weighs very heavily on fatigue and the limits of performance.
The vLTP is going to be somewhere as a percentage of VO2max, and it varies for different people. Even among two elite athletes with similar VO2max, the vLTP can be meaningfully different. The one with the higher vLTP can go longer at a fast pace.
I know that’s a lot to read, but as a practical matter I don’t think the study can really point to the slightly higher oxygen cost of burning fat as a rational conclusion for all the study’s findings.
Im experiencing the samething now. This conversation takes a big burden off my shoulders. I didnt know to think or what was going on. Im currently under 20g carbs a day. I just dont want to mess up my weightloss process. But i do feel better when i drink water with electrolytes. I also experienced the running but was short of breath faster than usual. But while running sweat was dripping off my body like i ran a couple laps. I went to my doctor as well and everything looked fine and both doctors said it must be my keto diet. First i went to the hospital for dehydration and shortness of breath, then i went to my primary doctor for labs and he said it must be your keto diet. Neither one of the doctors told me to stop, so im still on it. Ive been on keto going on a month.
Virginia - I think you have just found the answer to why I have consistently struggled on keto for 18 months - cycling between keto and carb binges.
Last I ended up in emergency department with heart palpitations.
Today - 10 days into another attempt to lose weight on keto. I had steak, prawns and chorizo for lunch… and within 40 minutes was have heart palpitations and then ensuing ‘air hunger’.
I tried water, salt, walking etc… but couldn’t get my pulse down below high 70’s.
Taken an anti histamine and starting to feel better. Pulse back below 70 and air hunger subsiding.
Thank you!!! I will continuing trialling this, but really hope I have found my ‘why’, as every time it happened previously I thought I was in ketoacidosis!
Amazing! And here I thought I was doing good, because the high seventies is what my pulse went down to, after I started eating keto. (sigh)
Haha - we are all built differently!
Trust me, the battle I have had with my heart and health anxiety it has given me over 15 years is unreal.
IF switching to a low histamine diet is the missing link, today could be a real turning point.
NOT having palpitations would be amazing!
I’m a slow pumper. I have to work hard to get out of the 60s.
If you do more research on what a “low histamine” diet is, let us know.
I’ve been low carb/keto for 7+ years…and suddenly have had to take allergy pills again for seasonal allergies. It was great not to have to do so.
Not sure my diet is the cause, though, because my meals are mainly meat with a small amount of dairy at times. My first meal (after a 36 hour fast) was beef heart + beef chuck + blue cheese. Are there histamines in there?
All meat has histamine. The older the meat, the more histamine. Beef has more histamine than chicken, pork, or lamb, because it is aged before it is processed.
I’ve been keto for four years. I am a month and a half off of a seven month carnivore trial. During the last two months of my trial, my histamine problem got much worse. It got the the point where I couldn’t eat beef. I would get heart palpitations, stuffed nose, nausea, and severe diarrhea within an hour or two of eating it. One thing I did during the trial was cut back on my salt intake, in particular, because many of the long term carnivore advocates feel we don’t need to use salt because eating enough meat provides all the sodium we need.
I read that the enzyme we make to breakdown histamine, diamine oxidate (DAO), uses vitamin C, magnesium, and vitamin B6 (if I recall correctly). I upped my B-vitamin and Vitamin C and started taking Ancestral Supplement Kidney. Those changes did help, but the biggest help was getting back on the salt. I don’t know how low sodium could have caused histamine trouble and beef aversion, but it did. 
I’m back to getting 20g of carbs a day via fruit. It’s taken me, well, about a month and a half to fix what I messed up during my experiment. The heart palpitations are much better and I can eat beef again. Although, it still causes my pulse rate to go up and some palpitations, its not causing the other trouble that I won’t mention again. 
I’m back to supplementing about 1.25 to 1.5 teaspoons of salt a day on top of what’s in my food.
I am feeling much better now and more energetic. Is it the 20 grams of carbs, the vitamins, the salt, all of the above?
Interesting.
I know that people say that they can eat no salt if carnivore, but I’m eating very close to carnivore (depending how you define that), and still need salt. A lot of salt.
Part of that might be my propensity to sweat. For my home gym workout this morning, I sweat quite a bit. Then I went riding my bike. I came back and had some olive brine, then water, as I was thirsty.
When I was riding my racing bike, I sweat so much that it caused the steel frame to rust. (I’m using my mountain bike – on the road, though – but am about to change back to my racing bike.)
I’ve been taking some vitamin B, but only to see if it helps my homocysteine level. I don’t think it’s B6, though. I’d have to check.
As you note in your last sentence, it’s always difficult to tell. You rarely can change one thing, so that means causation is tough.
For what it’s worth, Bob, when I was growing up in Trumbull, my mother was diagnosed with severe respiratory allergies (you name it, if it was airborne, she was allergic). Her allergist tested the pollen count daily I remember that 450 was considered very high.
These days, (cough) five (cough) decades later, pollen counts routinely reach 4500 and higher. Things got so bad in the Hudson Valley, about five or six years ago, that even people who didn’t have allergies were showing symptoms.