The Half Marathon Experiment

Back in January, I did The Marathon Experiment, where I took both glucose and ketone measurements at every five kilometers. It went a bit off the rails toward the end, but you can read about that in the post.

Last weekend, I did a variation of this experiment while performing a half marathon. This time I took measurements every two miles instead.

Oh — and by the way, I was very undertrained for this race (as I was in the previous experiment). My longest training run was a paltry 4.5 miles the week before. The silver lining to this was my additional soreness would provide some relevant lipid response regarding muscle repair, but more on that later.

[Full disclosure: Keto Mojo provided me sample strips in support of my research, which I used for this experiment. But as always, I take no direct compensation from any business entity, nor have agreements of any kind.]


(Click to enlarge)


  • Each stop to take blood readings required several minutes. I had to find an appropriate place out of the way of the raceway, stage on surface(s), and I tried to wipe/disinfect the finger(s) used.
  • Unfortunately, I sustained a minor injury early on following the 5th mile. Another runner accidentally bumped me in such a way that I fell, but caught myself stretching my leg out awkwardly to catch my bodyweight. I pulled an inner thigh muscle which I carried with me moving forward.

Here’s the table in graph form:


My readings at 11:01 am following the race were four in total. I retested both the glucose and the ketones (BHB) due to the latter being the highest reading I’d ever had. Ironically, the first reading of 6.6 was then topped by the second reading of 6.9. (The reading of 6.75 above reflects the average between both)

As with the prior experiment, my ketones rose the highest following completion of the race, and started heading back downward following big meals. However, this downward trend was still much higher relative to previous experiment — staying as high as 3.5 until just before bedtime.

One other thing worth mentioning is that for an hour or so after we had been returning to the hotel I felt cold hypersensitivity coupled with nausea for around an hour and a half. This was somewhat relieved during a shower back at the hotel, but then returned right after. At first, I thought I might not be up for breakfast, but then it subsided and everything was fine. At the time, I attributed the nausea to my not getting enough sodium before and throughout the race given I normally bring pink salt to mix with water to drink during those periods. However, I had been popping Sports Salts instead (2 before, 2 during, 2 after the nausea spell), given it was the only thing I had on hand.

The next morning I had my blood taken and I’ll be interested in getting back the new lipid numbers, especially triglycerides.

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Elaine Funk
Elaine Funk
6 years ago

Dave, I appreciate your stick to itness and creativity in these studies. But I was wondering if it would be possible for you to also post results in SI units? If your computer brain could do these for the charts in particular. Thank you. My brain is sort of bilingual but not precisely.

6 years ago

Wouldn’t it just be blood sugar? Just divide by 18.

6 years ago

I’ve tested my glucose reading after my 21K (unfortunately no ketone test strips available here in my side of the world).

Right after half marathon: 57 mg/dl.
2 hours post half marathon: 74 mg/dl
2 hours post heavy protein intake: 82 mg/dl

Fasted Day after the marathon: 78 mg/dl

Dave S
Dave S
6 years ago

Dave, I came across your videos and blog a week ago. Fascinating! I’ve recently become more LCHF and I’m training for a marathon later this year. I have no idea if I’m a hyper-responder but previous bloodwork over the years maybe suggest I trend that way (low TGs, relatively high LDL and HDL, but these were taken when I wasn’t really LCHF). I will do bloodwork later this year that hopefully will be more revealing. Anyway, I was wondering if you could share what you ate before the half-marathon (and the marathon from your other post) and the approximate macronutrient composition? Thanks!

Dave S
Dave S
6 years ago
Reply to  Dave

Dave. thanks for the info. I was wondering more about what you ate the morning of the races, and did you eat anything during the races? I appreciate your time and help!

Dave S
Dave S
6 years ago
Reply to  Dave

Thanks. I just read your comment in the marathon experiment where you said you had water and pink salt before and during the race. I think you should include this fact in future presentations, as this is so contrary to the conventional carb-loading philosophy for endurance events. It’s also remarkable that you finished the races while fasted and without training adequately beforehand! I think this is a strong argument for endurance athletes to use a LCHF diet.

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