Let me start by saying "No, I didn't run with a needle". But the thought crossed my mind, maybe next time. I'm not diabetic, so blood glucose testing is foreign to me. The idea to test blood glucose in response to certain stimuli came from guys like Jimmy Moore and Kent Altena. But rather than test my body's response to food, I was curious to see how it responded to exercise. I've posted before about keto-adaption and exercise. I thought I'd do my own experiment.
I've been following a low carb diet since March, defined by keeping my average carb intake under 100 grams. In the last month I started running again after a four month lay-off from an ab muscle pull in January. During those runs I have not experienced dizziness or excessive fatigue. I haven't drank Gatorade or ate Gu or Clif bars. Oh crap, so much for getting those companies to sponsor my blog. Anyway, it makes me wonder how far I can go on minimal outside fuel. Said another way, how far can I go on my internal body fat and glycogen fuel?
Last Saturday I ran my longest run since my last marathon in November 2010. I ran an approximate 1.5 mile loop around my neighborhood 8 times. I added a little extra on the end to make it a half marathon run, 13.1 miles. I chose a short loop in part because it gave me the opportunity to run by my house several times. I stopped at roughly 3.1 mile intervals to measure my blood glucose. Inspired by Moore and Altena, I was curious what the glucose fuel gauge needle looks like on a long run.
The chart below shows my nutrition leading up to the five days before a longish run, 13.1 miles.
I definitely followed a low carb diet in the previous week to the run, averaging less than 10% carb calories and over 60% fat calories. My diet for the last 5 months was similar, just not tracked consistently to show the stats. So I'd say I was keto-adapted as Dr. Stephen Phinney has described.
The run is charted below based on data collected on my Garmin 305. Total running time was just under 2.5 hours for an average pace of about 11 minutes/mile. It was a pedestrian pace, but hey, look at those hills in my neighborhood. My average heart rate was 136 bpm, or 70% maximum heart rate, so it was a decent effort for me.
So what about blood glucose you might ask? Well, here's the chart. The initial reading before the run was taken at 7 AM after an overnight fast. During the run, I only drank water, about 1.5 liters total. I suppose I expected ignorantly that sugar levels would drop throughout the run, but they didn't. They jumped up, rather consistently. About an hour after the run, my blood glucose returned to more normal levels, 91 mg/dL. A quick Google search suggests that these results could be explained by gluconeogenesis. I welcome comments from those folks that would like to explain what happened.
For those that are curious here's how I measured my blood sugar: