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Will I Burn More Fat if I Workout on an Empty Stomach


Hey all you early morning exercisers! Have you heard about the research that states that you’ll burn MORE fat if you exercise or workout on an empty stomach? Is there any truth to it?

Actually there is. BUT, don’t get excited. Because do you know what else you’re losing? BTW It’s not good. Let me explain what happens when you workout on an empty stomach (you can read this...or go to the bottom and view the 4-minute white board animated video).

The Rest of the Story

To understand the rest of the story, you need to understand THREE facts about how the human body works.

  1. Most of the calories we burn is NOT from exercise. We burn calories 24/7 – even when we’re sleeping. In fact, about ¾ of all the calories we burn is just to keep us alive.  And, maintaining or increasing muscle mass is important. The more muscles we have, the higher our metabolism…the more calories we burn.
  2. Humans need fuel to survive. Just like cars need fuel to run, so do we. While cars mostly run on one fuel – gasoline…humans require a blend of fat and a carbohydrate called glucose – about a 50/50 mix.
  3. We need a mix of fuels. While most of the body is flexible – meaning it can adapt to burning fat or glucose as a fuel - the brain, nervous system, red blood cells (the cells that carry oxygen throughout our body) MUST have glucose. And a lot. These organs alone require about 800 calories of glucose every day. And, that’s our minimum glucose need. Exercising muscles also burn mostly glucose. So, we have a high glucose need.

I bet you’re thinking…can’t I turn my stored body fat into glucose when I workout on an empty stomach? Don’t we wish! If we could we’d all be lean. On average the body is burning about 50% of its fuel needs from fat…and another 50% from glucose. That does fluctuate up and down a little but we never run on anything close to 100% fat.

So, again, even if you’re body burns a bit more fat because you exercised on an empty stomach, it just means it’s burning a bit less glucose. It’s not like you’re burning any more CALORIES! The act of a workout on an empty stomach just changed WHERE the calories came from. Sorry…you’re not going to lose weight any quicker.

Where is That Glucose Coming From If We Skip Breakfast?

Here’s where it gets really interesting… Again about 50% of our fuel needs comes from fat – both from our meals and stored body fat.

The carbohydrates in your last meal of the day will provide no more than 2 hours of glucose - even if you ate a LARGE amount of carbs. If your blood glucose level stays higher than normal for more than 2 hours after a meal, you meet the criteria for diabetes.

Around 2 hours after that meal (even sooner if you didn’t eat any carbs), your body starts converting stored lived glycogen into glucose. Liver glycogen is what sustains our brain in between meals and while we’re sleeping.

BUT, since our liver only holds 300-400 calories worth…we’ll quickly run out. So, to conserve this glycogen, the body starts breaking down our muscles – and turning some of those proteins into glucose. Uh oh!

By the time you wake up and start thinking about your morning workout, you’re running out of liver glucose and most of your body’s glucose needs are coming from muscle.

The longer you go without eating, the more muscle mass is broken down. That’s not a good thing especially since you’re working out to build up stronger muscles.

Some of you athletes might be remembering that you have perhaps 2000 calories worth of glycogen in our muscles. Unfortunately, muscle glycogen is only available for fueling the muscle – to help your muscles workout longer and harder. Only liver glycogen can fuel your brain.

The solution for maintaining muscle mass and keeping your metabolic rate high? Don't workout on an empty stomach. Eat a small (100 calorie) higher carb snack before your morning workout.

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