The “Fat Burning Zone” Myth Explained

energy storage fat burning zone Jun 03, 2022

It doesn’t matter how much fat you burn during your workout here’s why:


Your body has short-term and long-term energy storage.

Short term storage is muscle/ liver glycogen (you can think of it as carbs stored in your muscles) and is around ~1,200-2,000 calories.

Long term storage is fat and is around ~150,000+ calories. 


Low intensity activity 

Sleeping, walking, the Macarena, etc. burns a greater % of calories from fat.

· For example:

1 hour of walking = 350 calories X 65% fat = 

~230 calories burned from fat

~120 calories from muscle glycogen


High intensity activity 

HIIT, CrossFit, etc. burns through mostly muscle glycogen.

· For example:

1 hour of CrossFit = 800 calories X 20% fat=

~160 calories from fat

~640 calories from muscle glycogen

So, here’s the thing… yes, walking burned more calories from fat, but as soon as you eat your next meal, you’ll replenish muscle glycogen quickly and the extra blood glucose will turn into fat. 

By contrast, after high intensity training, your next meal will mostly go toward replenishing muscle glycogen. 

The net effect is more overall fat loss. Trying to burn more fat during your workout usually makes as much sense as racking up credit card debt to pay off a mortgage.


Real life application:

During Ironman training, I purposefully ate about 5 pints of Ben and Jerry’s per week because ice cream replenishes depleted glycogen stores very quickly. 

This kept me “topped off” at the ~1,500 calorie of muscle glycogen and able to train hard for 1-3hrs without hitting a wall (aka depleting glycogen). 

I was still able to lose ~18 pounds of fat during training (DEXA scan confirmed) because #science.

Some bodybuilders may benefit from low intensity training for fat burning during a low calorie cutting phase

They aren’t eating enough to replenish glycogen fully, still want to train hard, probably have high carnitine palmityl transferase enzyme levels to allow for higher fat burning, etc. This is not the case for 99% of people. 


Bottom line: 

Most people don’t need to worry about the “fat burning zone”.




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