I know what you’re thinking – why am I writing about running fast when I’ve already confessed to my mid/back of the pack status? I’m not writing about that kind of fast. I’m writing about the other kind of fast – the food kind. In July, Runners World featured an article on fasted running – something that I had been doing thanks to a sensitive running stomach, but didn’t know was cool. Apparently I might be not only avoiding GI disaster, but might actually be doing something right by running some runs in a fasted state.
I decided to read up on the matter. The consensus suggests that running in a fasted state – as in first thing in the morning, prior to eating, not fasting as in not eating for a day or more before running – might be worthwhile. Here’s why: Fasting increases the concentration of free fatty acids in the blood, which have a glycogen-sparing effect during exercise. This suggests that performance could be improved during fasting because the existing glycogen could be using sparingly (c.f. Dohm et al., 1986), saving precious glycogen for later on. When in a reduced glycogen state, the body is better able to utilize fat for fuel. And, fasting before running might not cause lasting harm. Research suggests that during recovery, and after eating, the insulin secreted by the body facilitates glycogen resynthesis (c.f. De Bock et al., 2005 doi:10.1113/jphysiol.2005.083170) and glycogen synthase (Tuominem et al., 1996), building glycogen stores up to their pre-exercise levels and maintaining physical performance. So that bagel I eat post-run is heading straight to glycogen storage land, not to my thighs.
Interesting stuff. It seems like there is at least some evidence that short bouts of fasting before running could help the body learn to use fuel more effectively. And it doesn’t hurt that fasted running avoids GI troubles. That’s always a plus.
Want to read more? Check out one of the following resources. There’s a great collection of research on the subject by Running on the White Line. Fasted running is a hot topic on the Runners World discussion forums (go the their main site, click on “communities”).
So, what do you think, runners? Fasting – does it work for you?