Can keto cause shortness of breath?

(Marlow) #43

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.

(Michael - When reality fails to meet expectations, the problem is not reality.) #44

@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.

(Bacon by any other name would taste just as great.) #45

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.

(Michael - When reality fails to meet expectations, the problem is not reality.) #46

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 = 1.0

When 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.

(Bacon by any other name would taste just as great.) #47

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.

(Michael - When reality fails to meet expectations, the problem is not reality.) #48

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 = 1.0

Oxidation 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!

(Marlow) #49

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.

(Michael - When reality fails to meet expectations, the problem is not reality.) #50

Curious what cost? Oxygen is free.

(Doug) #51

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.

(April Hayes) #52

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.