Fasted Cardio: Did We All Get It Wrong?

You need carbs before cardio to really perform says one side. No, you don’t, says the other. Digging deep into research shows that both may have been wrong. And right.

Fasted Or Not Fasted Was The Wrong Question

There are those arguing you need energy to fuel you on a run. This includes me, who wrote about it more than once.

Then there are the many for whom fasted training prove to be an effective technique.

For a long time it seemed that these two sides were irreconcilable, but it could be that both got it wrong. Because they saw it as a black and white issue: you either always go fasted or never.

Research looking at it treated it in much the same fashion: feeding one test group, keeping the other fasted and then compare how they did. That often led to conflicting results.

It Could Take The Right Amount Of Fasted Cardio

I wondered what would happen if you instead restrict the number of fasted workout sessions per week. Say, doing one or two fasted, the other three fed. Would the body adapt by storing more carbohydrates in the form of glycogen? After all, similar effects were observed for whey protein timing after resistance training and in the carb-loading technique some endurance athletes use.

It took time hunting for research that looked at this, but at least some was done:

• In a 2005 Danish study, the researchers found that low muscle glycogen due to fasted training led to the body storing more of it once carbohydrates were available again.
• A 2008 Dutch study examined short-term effects of fasted vs. fed training, and found that in the short term, both states yielded the same training results.
• In a 2010 Australian study, the researchers came to the conclusion that when selective endurance training sessions were done in fasted state, the training effect was higher than when all sessions were done in fed state (PDF).
• Another 2010 study, this time from New Zealand, observed a similar effect, with one interesting difference: men responded better than women to fasted training. The latter, the study’s authors advise, are better off during endurance exercise with carbohydrates in their system.

Most of these were small studies, but the hint at least is there: do the right amount of fasted cardio and your performance can improve. But how would you do that?

Using Fasted Cardio The Right Way

Too much fasted cardio and the body may get used to basing its endurance energy household on fat. Too little and the fasted state training effect won’t happen.

Extrapolating from the above research, I suggest the following:

• Try 1/3 of your training sessions in fasted state
• Have these sessions in the morning, when glucose / glycogen are lowest
• Choose shorter sessions at moderate intensity, not exceeding 1h
• Base the following breakfast around carbs
• Get enough protein from your general nutrition, to prevent muscle protein breakdown
• Do not attempt this before “live” events where performance counts

When you try this also keep in mind that your performance will very likely be worse. This technique isn’t meant to break new personal records, but to budge the body into higher glycogen retention later on.

Last but not least I also suggest to give this at least three months and to keep track how your personal performance changes. Doing it for shorter amounts of time may not be enough to fully accustom the body to it.

Share Your Experiences

If you try it, let me know how it goes for you. If you already do this, please share your experiences. Maybe we’ll see a small paradigm change here.

Picture courtesy of Ed Yourdon.