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The Problem of Exercising on a Low Carb Diet or Empty Stomach

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A major problem for people who workout on a low carb diet or empty stomach is that they burn lean muscle instead of FAT!  The problem has to do with possible low blood sugar and the intensity of your workout.  Keep in mind, when you perform a moderate to high intensity workout, your metabolism will burn carbohydrates and lean muscle (proteins), not fats!

If you don’t have enough glucose (carbohydrates) in you before you start a moderate to intense workout, your metabolism will shift over to the next available source of fuel and burn lean muscle (proteins), not FATS!  So the last thing you want to do is work out and burn-up whatever available glucose you have in the first 15 minutes of your 45-minute workout and have to resort to burning lean muscle (proteins) to get you through the next 30 minutes of your workout.

Burning the Wrong Fuel is a Common Problem 

Your body generates energy by burning calories from the breakdown of fats, carbohydrates and/or lean muscle (proteins).  These are the only three sources of fuel your body has!  The wrong workout or wrong diet could have you burning the wrong fuel source, which is why you’ve hit a plateau and aren’t getting the firmness and tone you want.  Keep in mind, burning calories is NOT the same as burning calories from the breakdown of FATS!

People who like to work out first thing in the morning or who follow a low carb diet are more prone than others of working out with low blood sugar, which really isn’t too big of a problem if it is a true low intensity, easy aerobic workout.

The typical person who works out first thing in the morning wakes up with low blood sugar, due to the fact they probably haven’t eaten anything in about 10 hours.  They aren’t suffering from any type of medical low blood sugar problem, but their blood sugar, even for a healthy person is on the low side.  So, when that person goes out and performs a somewhat intense workout – they could easily deplete all the glucose they have in their body and begin to burn calories from the breakdown of proteins (lean muscle). 

The same is true for anyone on a low carb diet, which I am somewhat of a fan of, but if they haven’t given their body enough carbs to get them through their moderate to intense workout – they too will be burning up lean muscle, instead of fats. 

Eat Right – Train Smart

I believe people exercise to add lean muscle – not burn it off!  So, if you’re about to start a moderate to intense workout and you just woke up or are following a low carb diet, swallow a couple of spoonful’s of raw honey, some grapes, strawberries or something to help get your blood sugar back up, so you get through your workout, and NOT burn lean muscle.  The reason I like these choices or similar is that they digest quickly and you can start your workout in 20-30 minutes. 

On the other hand, if your workout is a true low-intensity, easy, possibly long, boring Aerobic workout?  Your metabolism should be able to tap into that stored fat you are looking to burn away.  Keep in mind, the biggest mistake I see all too often are people doing their aerobic workout too fast for their current level of aerobic conditioning.

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About The Author


Dr. Len Lopez is a nutrition and fitness coach who takes a more natural, holistic approach Eating Right and Training Smart. He is an author and inventor who occasionally takes the time to run a race or two with his wife and kids in the greater Dallas area.