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Energy Systems 2: Sugar vs. Fat and How to Know Which You’re Using

In Energy System Basics, we discussed the four (4) different ways (we know of) that the human body provides energy to working muscles.  Briefly, the Aerobic system burns either fat or sugar, the glycolytic energy system burns sugar and reprocesses the byproducts of doing that, and the phosphagenic system is there with ATP for use, and creatine phosphate to replenish it quickly.  Ok, neat, you say, but my goal is to burn off this spare tire, so…how do I know if I’m doing that?  That’s what we’re talking about here.

Related: Breathing: So Simple Anyone Can Do It

There are two things to look at to know which energy source you’re using: your level of exertion, and the hunger that drives your eating habits.

Your level of exertion is relatively simple.  Fat is a major source of fuel only at lower levels of physical activity.  So if you can’t speak a complete sentence while being active (whether it’s “exercise” or not), you’re burning at least some sugar, rather than fat.  This is why “fat burning” settings on exercise machines, or our Burn45 class, feel “easy” – the effort level is low to moderate to ensure your body uses fat, rather than sugar.  You should be at a 1, 2, or 3 of the rate of perceived exertion scale.

If you’re unable to speak complete sentences, or the effort is starting to feel “real” you’re beginning to burn more sugar than fat. Whether or not this is a problem depends of the goal of your workout.  If you’re intending to burn fat during the workout, you’re going too hard.  If you’re intending to get the most out of your workout, work hard, and achieve maximum improvement from that day’s effort, then you should go ahead an burn sugar.

If you’re unable to speak complete sentences, or the effort is starting to feel “real” you’re beginning to burn more sugar than fat.

The hunger that drives your eating habits is a less obvious clue, but once you start looking for the signs, it should be fairly clear whether you burn primarily sugar or fat throughout the day.  Do you get hungry every few hours?  Do you ‘graze’ or eat lots of small meals?  Do you frequently crave certain foods, especially those high in sugar?  If the answer to any of these is “yes” then you probably don’t burn much fat during the day.

Related: The Importance of Recovery

Not to worry though!  You can change this pattern by re-balancing your diet away from a constant stream of sugar towards a more balanced intake of fat, protein, and healthy carbohydrates.  Start by eating more healthy fat and protein at breakfast, eliminating sugary drinks, and avoiding snacking.  When you find yourself no longer having cravings, avoiding the post-lunch slump, and feeling great after light activity, you’ll know you’re on the path to burning fat.  And that’s what we are supposed to do!

If you have questions, or would like to know how you can use our workouts to enhance your fat-burning, contact me at john@crossfitslipstream.com or 612-644-9781.

–John Bryant

Founder & Head Trainer

john@crossfitslipstream.com