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True or False: Exercising on an empty stomach will burn more fat calories?

Posted on October 30, 2017


The idea that exercising on an empty stomach will burn more fat calories has been around for some time. You have maybe heard of the book Body for Life by Bill Phillips. It came out in the late 1990s, and in  it, Phillips suggests performing cardiovascular exercise in the morning prior to eating breakfast to allow your body to burn more fat calories.

The theory is that if you work out the first thing in the morning before breakfast—or even later in the day after having fasted for 6 or 8 hours—your body will have less glycogen (stored carbohydrates) to burn for fuel. As a result, your body will tap fat stores sooner during the exercise session to maintain energy levels. Theoretically, this would lead to burning more fat calories, and you potentially would lose more weight from your workouts.

It is true that during lower-intensity workouts—walking, for example— you burn from fat stores a higher proportion of the calories you require for fuel or energy, as compared with higher-intensity workouts such as running. However, the absolute or overall number of calories you burn during higher-intensity workouts is much greater than when you are doing lower-intensity workouts. That’s why even though the proportion of fat calories burned during high-intensity workouts is lower, you actually burn more fat calories overall during high-intensity workouts. I know this is confusing!
Look at it another way: If you work out prior to eating breakfast or after a 6–8 hour fast, it is likely your energy levels will be lower and you will not be able to exercise at higher intensities, if that is your goal. The result could be that you burn fewer calories (even fat calories) during your workout. Most fitness professionals recommend eating 100–200 calories prior to exercising to help you maintain your blood glucose level as well as your energy level during exercise.

Researchers have studied this topic, and a review article titled “Does cardio after an overnight fast maximize fat loss?” was published in the Strength and Conditioning Journal (Schoenfeld, 2011). The author states, “In conclusion, the literature does not support the efficacy of training early in the morning on an empty stomach as a tactic to reduce body fat. At best, the net effect on fat loss associated with such an approach will be no better than training after meal consumption, and quite possibly, it would produce inferior results. Moreover, given that training with depleted glycogen levels has been shown to increase proteolysis (muscle breakdown), the strategy has potential detrimental effects for those concerned about muscle strength and hypertrophy.”

Research has also clearly shown that if we wait for long periods of time to eat between meals, we often get ravenously hungry and overeat when we do sit down for a meal. Imagine not eating for 6 or 8 hours and then also performing a workout prior to eating something!

Safety should be considered as well. Many people get light-headed or dizzy if they try to perform physical activity on an empty stomach, which could lead to fainting and possible injury.

I certainly understand the desire to try to tweak our workout routines in an attempt to burn a few more calories or shed a few extra pounds. However, I urge you to always use the common sense test when you hear or read about new workout programs, techniques or suggestions—especially if someone is selling a new and exciting product. I know many people who tried the don’t- eat-before-working-out-in-the-morning routine. Almost all of them lost a few pounds, but the routine didn’t last. After a few weeks or a few months at most, they were back to their normal habits.


Schoenfeld, B. Does cardio after an overnight fast maximize fat loss? Strength and Conditioning Journal (2011), Vol 33, pp. 23-25.

True or False: You must burn approximately 3,500 calories to lose a pound?

Posted on October 10, 2017


YOU’VE JUST COMPLETED another 30-minute workout on the exercise bike. You worked up a good sweat, and you’re feeling great about yourself! As you climb off, you check the number of calories you burned during the workout. The digital display says 300 calories. You think to yourself, “Hey, that’s pretty good!”

Then you remember what your mother-in-law told you last week—that you have to burn 3,500 calories to lose a pound. Arrrgghh! After some quick calculations in your head (and praying she was wrong), you figure you need to climb on that bike about 11 more times to reach that number.

The calories that need to be burned to lose a pound can seem overwhelming to some, but don’t despair; it’s not as difficult as it might seem.

Your mother-in-law indeed was right: You need to burn around 3,500 calories if you want to see your scale register a pound less. An article on states, “Because 3,500 calories equals about 1 pound (0.45 kilograms) of fat, you need to burn 3,500 calories more than you take in to lose 1 pound. So if you cut 500 calories from your typical diet each day, you’d lose about 1 pound a week (500 calories x 7 days = 3,500 calories). It isn’t quite this simple, however, as you usually lose a combination of fat, lean tissue and water.”

As stated in the article, the concept of having to burn 3,500 calories to lose a pound might be a bit of an oversimplification. Consider that there are 454 grams in a pound and roughly 9 calories in a gram of fat. It would appear that you would really need to lose 4,086 calories (454 x 9) if you wanted to lose a pound—a pound of fat, that is.

But fat (adipose tissue) contains things other than pure fat—small amounts of protein, connective tissue and water, for example. When we work out, we generally don’t burn just fat, so that is where the 3,500 number comes from. Experts have worked on highly complex calculations that attempt to determine how many calories we would need to burn to lose weight if that weight loss comes from fat, lean tissue, a combination of the two, etc. This short chapter is not the venue to fully explore these calculations, as they truly are complex and can be confusing. Although 3,500 calories might not be the exact number of calories you need to burn to shed a pound, it certainly is in the ballpark. And it is a great benchmark or place to start if you want to begin monitoring your calories for weight-loss  purposes.

So what do you need to do to achieve a caloric deficit of approximately 500 calories a day (3,500 calories a week) and lose a pound? I would highly recommend using a combination of physical activity and a slight calorie reduction. If you can manage to burn 300 calories a day from physical activity and eat 200 fewer calories (there are about 200 calories in a bagel)—and do it consistently—you should be able to lose about a pound a week. That would be over 50 pounds in a year!

Most people don’t  gain weight that fast, but many get frustrated when it doesn’t come off as quickly as they would like. I believe small, sensible changes that you can tolerate and maintain are the key to weight-loss success.

Mayo Clinic Staff. Counting calories: Get back to weight-loss basics. health/calories/WT00011. Website accessed July 20, 2012.