How does exercise affect my blood ketone levels?

After 2 weeks of diligently measuring my AM fasting blood ketones and despite being in nutritional ketosis (blood ketones between 0.5 mmol – 3.0 mmol) I didn’t notice any weight loss. While I was confident that I was ketoadapted (the state in which your body preferentially metabolizes fat for fuel instead of carbs), I was a frustrated because I couldn’t quite figure out a pattern to my ketone measurements.

For example, one morning it measured 0.2 mmol, followed by 1.1 mmol the next morning, only to fall back to 0.4 mmol the morning after.

What I wanted was to attain higher levels of ketones, preferably in the 2.0 – 3.0 mmol range, but at minimum greater than 1.0 mmol.   At this point I’m not entirely sure if there actually IS a benefit to having higher measurements, but using Jimmy Moore’s n=1 experiment as an example, I saw how high his ketones were and how easily he was able to maintain them at an elevated level (sometimes he got over 4.0 mmol!) with amazing weight loss results.

I also thought intuitively (again this may or may not be correct), that if you have a higher measurement, say 3.0 mmol, and you slip up and eat more carbs, you have more room to drop while remaining in nutritional ketosis than if your measurement was 1.0 mmol.

An experiment I like to refer to is this one, in which the effects of PepsiMax on blood ketones are examined and there is a detectable drop in ketones for a few hours after drinking PepsiMax.  He started with ketone measurements in the range of around 4.4 mmol and saw them fall to as low as 2.2 mmol.  If he had begun at 0.5 mmol, then he would’ve probably dropped into the undetectable range!

Thus, I imagined a higher ketone level would both indicate a higher degree of fat metabolism AND allow for more wiggle room for carb screw-ups.

In the prior two weeks I didn’t notice any consistent effect of exercise on my blood ketones the following morning.  Every morning it seemed like the blood ketone meter would spit out a random number.  My diet however was certainly widely varied so I couldn’t be sure whether it was the diet or the exercise that was predominantly influencing my measurements.

To better understand how my blood ketones are influenced, I devised this 3 day experiment to isolate the effects of one variable on my blood ketones: exercise.

For 3 consecutive days (12/27, 12/28, and 12/29) I ate the same exact meals and did the same exact things with the exception of my exercise regimen, which I did in a fasting state an hour or so after my AM ketone measurements.   I ensured that my daily activities were as identical as possible by performing this experiment during my workweek where not much changes between each workday.  With the help of the awesome folks at the Low Carb Friends forums, I calculated the macronutrient profile of my total meals, which came out to:

Fat: 167 gm (77%)
Protein: 97 gm (20%)
Carbs: 33.25 gm (7%)
Calories: 1962.5
(You can see exactly what I ate in the picture above)

I wanted to see how exercise effected my blood ketones the following morning and here are the results of what happened:

12/27/2012 – AM Ketones 0.6, No exercise
12/28/2012 – AM Ketones: 1.0, BJJ
12/29/2012 – AM Ketones: 1.2, Crossfit
12/30/2012 – AM Ketones: 2.0

It’s interesting to see that despite not doing anything, my ketones jumped from 0.6 to 1.0 mmol.  After doing BJJ, they went a little higher to 1.2 mmol and after doing Crossfit they went much higher to 2.0 mmol (my second highest measurement at the time).

Possible confounding factors that could explain the change in my blood ketones include:

• Maybe the fact that I started rigorously tracking my food intake and the macronutrient ratios were more ketogenic than what I was eating before.
• Dr. Phinney has explained that while it can take 2 weeks to become ketoadapted, your body will be constantly fine-tuning your system for an additional few weeks.  Perhaps the reason my ketones started climbing were because my body was finally near the end of the fine tuning phase.
• The times I ate the meals were not exactly identical.  Due to life circumstances, sometimes I would eat a few hours later or earlier as compared to the previous day.  If I ate dinner later than normal, the effects of the food I ate could potentially affect my AM ketone levels since it can take 4-6 hours to digest fats and proteins, if not longer (this is why I stopped measuring PM ketones).
• The amount of sleep I had wasn’t consistent on the last night.  On the first two nights I had a little over 6 hours of sleep, and on the last night I had almost 8 hours of sleep.  It might be that having more sleep caused the jump from 1.2 to 2.0 in my ketones.
• The exercise routines were different, so one may have had a greater effect than the other.
• I had come down with a bit of a cough and sinus infection during this time so maybe the stress of this affected my ketones.

Despite these confounding factors, I feel comfortable concluding, albeit tentatively, that exercise probably does in fact have a beneficial effect on my body’s ketone production.  This was the only time in which my AM ketones have consecutively risen from one day to the next.

Subjectively, after my exercise sessions I felt the typical “after-burn” effect manifested by increased body temperature and faster heart rate for the rest of the day.  I imagined my body doing a better job of burning fat in this state to meet its increased metabolic demands because my glycogen stores must’ve been pretty depleted from the minimal intake of carbohydrates.

If I had unlimited resources and unlimited time I would try to limit the confounding factors by recreating this experiment under the following conditions:

• Ensure ketoadaptation for at least 30 days to give enough time for “fine-tuning” phase of my body to stabilize.
• Eat the same thing at the same time every day and obtain blood ketone measurements once every hour while awake.  This would give us a good idea as to what effects each meal have on ketone levels, and how long those effects persist.
• Perform the same exact exercise routine in a fasting state, at the same exact time every third day, and continue to track hourly ketone measurements.  I say every third day in order to allow adequate time for recovery.
• Have the same quantity and quality of sleep.
• Make sure every other thing in my life is the same.  No external stressors, illnesses, etc…

Since my resources and time ARE limited and I actually have a life to live, I don’t think I’ll be able to flesh this out.  So in the end, from what I’ve seen in this short experiment, I’m convinced enough to say:

Exercise probably increases my body’s production of blood ketones.

Naturally, this actually leads to the next big question: Do higher ketone levels matter?

Or more specifically…

Do higher ketone levels correlate with increased fat loss or is the fat loss the same regardless of the level as long as it is within the nutritional ketosis range?