Mark Sisson posted a great article on July 4th, What Does It Mean to Be Fat-Adapted? The article explains what fat-adapted means – your body burns fat as your primary source of fuel and the opposite of fat-adapted – your body burns sugar as it’s primary source of fuel.

A fat-burning beast can effectively burn stored fat for energy throughout the day. If you can handle missing meals and are able to go hours without getting ravenous and cranky (or craving carbs), you’re likely fat-adapted.

I really liked that he gave specific criteria that helps determine if all the hard work and dedication transitioning from a Standard American Diet (SAD) to a whole foods, primal/paleo/ancestral type diet has really worked. By “really worked” I mean creating a healthy metabolic state that allows our bodies to use the food we eat effectively and efficiently.

The article spends a lot of time explaining what life is like as a “sugar-burner”. Most Americans are “sugar-burners”, they can not access dietary fat as energy. Here is a list of criteria to help you determine if you are still a sugar-burner:

  • Can’t effectively access stored fat for energy so you get ravenously hungry after several hours without food (don’t even think about skipping a whole meal).
  • Can’t effectively access dietary fat for energy – more dietary fat is stored than burned, your body fat continues to increase even though you exercise.
  • Depend on a perpetually-fleeting source of energy – glucose. Probably snack on sweets (candy perhaps???).
  • Will burn through glycogen fairly quickly during exercise.

Here are some more helpful examples of being fat-adapted:

  • You will store less dietary fat (become leaner)
  • You can handle exercising without having to carb-load
  • You can workout effectively in a fasted state
  • Steady, even energy throughout the day
  • Naps are a choice not a need

If you have time you should follow the link above and read the whole article. He goes into a lot more detail and it’s pretty interesting. Here’s a final quote from the article:

a fat-burning beast will be able to burn glucose when necessary and/or available, whereas the opposite cannot be said for a sugar-burner. Ultimately, fat-adaption means metabolic flexibility. It means that a fat-burning beast will be able to handle some carbs along with some fat. A fat-burning beast will be able to empty glycogen stores through intense exercise, refill those stores, burn whatever dietary fat isn’t stored, and then easily access and oxidize the fat that is stored when it’s needed. It’s not that the fat-burning beast can’t burn glucose – because glucose is toxic in the blood, we’ll always preferentially burn it, store it, or otherwise “handle” it – it’s that he doesn’t depend on it. I’d even suggest that true fat-adaptation will allow someone to eat a higher carb meal or day without derailing the train.

Eat Well, Feel Good, Have Fun!


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