VO2 Max and Resting Metabolic Rate on a Cyclic Ketogenic Diet

Vo2 MaxVO2 Max and Resting Metabolic Rate on a Cyclic Ketogenic Diet

In my never ending quest to learn more about my body (with n=1 experiments, blood tests, and a Dexa Scan) I came across the idea of metabolic testing as another way to provide insight into what my physiology is doing.

Luckily I live near the Cleveland Clinic where they offer metabolic testing for very reasonable prices.  They charge $75 for the resting metabolic rate test and $125 for the VO2 Max test.

They were able to squeeze me in on November 18th, which as you can see fell 9 days after my prior carb up day, in the midst of my 10 week Carb Nite cyclic ketogenic diet experiment.

RMR and VO2max

I made sure to confirm that I was in ketosis prior to testing (0.8 mmol) and that I was fasted.  Before I go into the results, I want to do a quick review of basic exercise physiology.

Basic Exercise Physiology

  • Resting Metabolic Rate – The amount of energy in calories your body expends at rest (ie just sitting around doing absolutely nothing).  This is calculated using the VO2, VCO2, and RER.
    • There is a subtle difference between this and the Basal Metabolic Rate that I won’t go into.
  • VO2 – The amount of oxygen your body uses per minute (not just inhaled, because some oxygen is inhaled but isn’t used).
  • VCO2 – The amount of carbon dioxide exhaled per minute
  • VO2 Max – The maximum amount of oxygen your body can consume, measured at maximum effort which should also be near the maximum heart rate.  This is considered one of the best measures of cardiovascular fitness.
  • Respiratory Exchange Rate (RER) – The ratio of VCO2 : VO2
    • RER of 1.0 = Body using 100% carbs / glycogen for fuell
    • RER of 0.7 = Body using 100% fat for fuel
    • RER of 0.85 = Body using 50% fat and 50% carbs for fuel
    • Sometimes RER is referred to as the Respiratory Quotient (RQ), though there are subtle differences that I won’t go into here.

The way these values are measured is by hooking you up to a mask that is connected to a metabolic cart that contains a computer.  The whole apparatus measures the the amount of oxygen you breath in and the amount of carbon dioxide that you breath out and calculates things from there.

Resting Metabolic Rate

This test is as easy as it gets.  I showed up to the hospital and and met with the exercise physiologist who showed me around.  Then had me sit in a waiting area to make sure my body was at rest.  After 10 minutes or so she took me into the testing room, hooked me up to a facemask that was connected to the metabolic cart, turned down the lights, and had me lay down for 30 minutes.  My job was to do three things: breathe normally, relax, and NOT fall asleep.

To give you a better idea of how this test is performed here is a video that was pretty much exactly what I did.



Resting Metabolic Rate: 1390.13 kcal/day
Predicted RMR using Mifflin Equation: 1770 kcal/day
Average RER: 0.817

What do these results mean?  Well according to the Mifflin Equation, for someone with my age, height, weight, and activity level my RMR should be 1770 kcal/day.  My actual measured RMR is 1390.13 kcal/day which is well below what is predicted.  Having such a low resting caloric expenditure may explain why body recomposition has been so difficult for me, despite being ketogenic, or in this case, cyclic ketogenic.

It is well known that remaining in ketosis for prolonged periods of time can down regulate metabolism (hence the need for carb up days on Carb Nite).  Perhaps I wasn’t eating enough carbs on my Carb Nites to stave off the metabolic slow down?

I’m sure my thyroid issues played a role.  We saw that my TSH bumped up from 1.2 to 2.2 indicating that my body was heading towards hypothyroid conditions (TSH is the hormone released from the pituitary gland in your brain telling your thyroid gland to pump out more thyroid hormone).  My RT3 is also still too high indicating that the rest of my body isn’t converting T4 (the transport form of thyroid hormone) into T3 (the active form of thyroid hormone).  One of the factors that promotes this conversion is insulin… and we know that going ketogenic means very low carb which means very low circulating insulin.  My fasting insulin levels confirms this.  For a good write up on RT3 and other thyroid things, I found this site to be helpful.

Having a low Vitamin D level is also associated with a slower metabolism and slower fat loss, so my low vitamin D definitely didn’t help.

Regarding my average RER of 0.817, this equates to around 62% fat metabolism and 38% carb metabolism.  Because I was in confirmed ketosis prior to this test, I had expected this number to show that I was using a higher ratio of fat as fuel (with an RER closer to 0.7).  This number doesn’t quite add up with what I saw in the VO2 Max results which I’ll go into later, but a possible explanation was that I wasn’t fully relaxed when I took this test.

If you really want to geek out, I’ve included a link  to the raw data from this test: (2013.11.18 – RMR)

VO2 Max

For this test, I kept the same gas mask which was still connected to the metabolic cart.  They strapped on a Polar Heart Rate Sensor and directed me towards the treadmill.  Here is where the test gets tough.  They start off by taking some baseline measurements, and had me start walking at 3 mph for a few minutes as a warm up.  Then they sped me up to 4 mph.  It was here that the test truly began.  Every 60 seconds they would increase the incline of the treadmill 2 degrees, and each time they did this they recorded my heart rate and asked me to rate how tired I was.  This continued until the the treadmill was at a 14 degree incline, after which they started increasing the speed.  Once I got to 4.5 mph at 14 degrees, that was when I reached my limit and couldn’t go on anymore.

This video is closest to the protocol that I followed (protocols vary depending on location):

I actually liked this video the best because I thought it gave the best explanation as to the physiology behind the test.  I actually watched this one a couple times before going into the test just to make sure I understood everything properly.  One big difference with my test was that I didn’t get direct measurements of my blood lactate level.  The person performing my test explained that she could estimate it pretty accurately with the data that was collected.

Before going further into my results, I need to introduce a couple of other physiologic terms.  This article by Peter Attia was what got me interested in all this in the first place, so I’m just going to use the definitions that he puts forth.

Aerobic base– defined as the point at which you transition to more than 50% of your energy being derived from glycogen instead of fat.  The higher this number (i.e., the higher the level of exertion) the better, because it means you can “spare” more glycogen for when you need it, and use as much fat as possible energy.

60% peak VO2– this is roughly the highest level of energy output a well-conditioned person can sustain for several hours.  I call this “all-day speed.”  When I’m doing a very long swim or bike ride (say, north of 4 hours), this is the maximum average power output I can sustain. 

Anaerobic threshold (AT)– as we measure it, this is the point at which your body starts to accumulate lactic acid faster than it can metabolize, or clear, it.  We use this as a pretty good (but not perfect) approximation for when your body transitions from being aerobic (able to process fat or glycogen in an oxygen-rich cellular environment) to being anaerobic (only able to process glycogen in an oxygen-poor cellular environment).  Aerobic metabolism is much more efficient than anaerobic metabolism, hence you want this threshold to be as high as possible, and ideally you want this point to be determined by lactate generation, and not substrate cross-over (i.e., inability to burn fat).

Max VO2– this is where you fall off the bike or treadmill.  It’s the last bit of what we refer to as “anaerobic cap” performance.  You can only sustain it for fraction of time, but it’s a 100% glycogen-dependent state of maximum output.


VO2 Max: 43.943 ml/kg/min

According to the reference tables (samples here and here) I’m considered either in ‘good’ or ‘above average’ condition for my age group (33 years old).  I guess I wasn’t too surprised by this since I’m fairly active (BJJ, Crossfit, Weightlifting) but definitely not in elite shape, as demonstrated by my 27% body fat.  I guess it’s reassuring that I wasn’t worse than anticipated.  I would’ve really been disappointed if I landed in the below average / poor category.

Maximum Heart Rate: 180 bpm

This was the maximum heart rate I achieved before I had to stop the exam.  According to various equations my estimated max heart rate should be anywhere from 183-190 bpm.  I was definitely close enough as I could feel my heart pounding and pretty much ready to explode out of my chest.  The only times that I’ve come close to this are when I’m doing particularly rigorous Crossfit WODs… and even then I cheat a little and sneak breaks here and there.  With this test, there were no breaks!


RER: 0.699 – 0.770
Heart Rate: 94 – 131 bpm
VO2: 8.345 – 26.825 ml/kg/min
%VO2 Max: 19.0 – 61.0%

My RER here is definitely range of near 100% fat use as fuel and this is why I’m not entirely sure I trust the RER measurements obtained from the RMR test.  It doesn’t make sense ot me that during the RMR while I’m at complete rest that I’m using only around 62% fat as fuel, where as while I’m simply warming up with exercise, it goes up to 100% fat for fuel.

Hopefully someone will be able to explain this to me.

Aerobic Base:

RER: 0.805 – 0.892
Heart Rate: 138 – 145 bpm
VO2: 24.346 – 30.432 ml/kg/min
%VO2 Max: 55.4 – 69.3%

As you can see by the RER, this is the range where I’m about 50:50 carb:fat metabolism.  This is also in the range of where my 60% Peak VO2 fell.

Anaerobic Threshold:

RER: 0.974 – 0.975
Heart Rate: 161 – 166 bpm
VO2: 32.151 – 35.809 ml/kg/min
%VO2 Max: 73.2 – 81.5 %

This is the point right before my RER is 1.0, which signifies complete anaerobic and carb dependent metabolism.

Anaerobic Max:

RER: 1.001 – 1.104
Heart Rate: 166 – 180 bpm
VO2: 35.927 – 43.943 ml/kg/min
%VO2 Max: 81.8 – 100%

Here you can see my RER at 1.0 and higher indicating that I am ONLY using carbohydrates for fuel.  The exercise physiologist commented that it was good that my maximum RER got up to 1.1 because that means that I wasn’t cheating.  Apparently some people who do this test quit before they actually reach the point where they’re actually exerting maximum effort, and this shows up by having an RER that doesn’t at least reach 1.1.

Here is the link to the raw data for the geeks: (2013.11.18 – VO2 Max)

So what does all of this mean?

Well, it gives me a really good overall picture as to how my metabolism uses fuels while I’m in nutritional ketosis on a cyclic ketogenic diet.

I now know that if I work out up to a heart rate of 131 bpm I can stay in a primarily fat burning zone and that if I work out up to a heart rate of 162 bpm I can get to a point where I’m accessing 50% fat and 50% carbs as energy.

I also know that if I want to make myself more fat adapted I need to get to a point where I can raise the level in which I depart from the Aerobic Base.

In a recent podcast on the American’s Angriest Trainer Podcast with Vinnie Tortorich, Peter Attia was interviewed and they had a great discussion on the difference between fat adaptation and keto-adaptation.

Peter Attia also submitted his personal definition of fat adaptation as when the person is at 70% of their VO2 max and still has an RER below 0.760 – 0.780.

At the point where I’m at 70% of my VO2 max my RER is 0.833 – 0.869, meaning that I still have a ways to go before I’m completely fat adapted.

A few more thoughts

I definitely wish that I had a baseline RMR and VO2 max test before experimenting with ketosis to compare with.

I would be very interested to see how these values change immediately after a Carb Nite to verify Kiefer’s assertion that the massive influx of carbs can actually stimulate your metabolism.  Having a quantifiable RMR number would answer this question.

I wonder what my RMR and VO2 max would be after going for a prolonged period of time OUT of ketosis (eating 50-100 gm carbs / day).

It would also be interesting to correlate these values with any changes in my RT3 and TSH levels.

I also did this test after only 4-5 hours of sleep at the end of my last night of a week long graveyard shift, so I wonder if my chronic sleep deprivation and screwed up circadian rhythms affected my numbers.  It would be interesting to see what happens after a few weeks of normal sleep.

I learned a lot from researching and doing this test and I definitely plan on repeating it under varying conditions.

** Image above obtained from How Stuff Works

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