Whether cardio on an empty stomach can speed up fat loss is a commonly debated fitness topic. Some believe fasted cardio is more effective at burning fat while others believe it can decrease performance and limit fat loss.

Who is right? The following will inform you of what research has to say about the topic and offer compelling reasons why fueled exercise leads to greater overall fat burn.

Cardio on an Empty Stomach Burns More Fat DURING Exercise

Two fuel sources—carbs & fats—are used to generate energy for muscle contraction during exercise. For endurance exercise performed at a moderate intensity, you obtain 50–60% of energy needed from glycogen (which is stored energy from carbs) and the rest from fats.

When you deplete glycogen stores by fasting overnight, or going several hours without refueling, fatty acids break down in the mitochondria to be used as a secondary energy source. As workout intensity increases, your reliance on carbohydrates increases as well.

In one study that tested the fat burning effect cardio on an empty stomach, six healthy men cycled for 60 minutes at a low to moderate intensity:1

Group 1– Fasted overnight before the bike ride.

Group 2– Performed the bike ride after ingesting 0.8g/kg of glucose or fructose to replenish glycogen levels 1 hour prior to the workout.

Results: After 20-30 minutes of exercise, the rate of fat burn was higher in the fasted group than in the glucose or fructose group. This trend continued throughout 50-60 minutes of exercise. There was also a higher quantity of FFAs (Free flowing fatty acids) available in the blood in a fasted state throughout the exercise.

The Take Away: This particular study suggests that more fat was burned by the group that performed MODERATE activity on an empty stomach… DURING THE EXERCISE ITSELF.

But Empty Stomach Cardio Does Not Burn More TOTAL Fat

Not so fast. Notice how “moderate” exercise is emphasized in the example above? Research shows that people who burn fat during their workouts actually burn less fat the rest of the day. Overtime, fat burning is not an immediate process, rather, it occurs over the course of, not a few hours, but a few days.

As you burn more carbohydrates during your workout, the body will burn more fat post exercise. This “afterburn effect” where your metabolism is elevated for several hours or days following your workout is critical when debating the benefits of fasted cardio.

While you may burn more fat during your workout on an empty stomach, your overall workout intensity may decline.2 Your body’s ability to burn fat post-exercise is compromised. Consider the whole 24 hour period and cardio on an empty stomach is less effective.3

Evidence supporting fueled exercise

Researchers from Italy investigated the contrasting reports on whether training in a fasting condition enhances weight loss. There were 8 healthy young men who performed early morning slow cardio under 2 conditions:Adaptations to skeletal muscle with endurance exercise training in the acutely fed versus overnight-fasted state.

1. Empty stomach

2. After eating

Eating increased both oxygen consumption (VO2) and respiratory exchange ratio (RER) significantly, 12 hours after the cardio, VO2 was still higher for the group who had eaten, although RER was significantly lower in the FED test, indicating greater fat burn.

The group that ate before the cardio session continued to burn significantly more calories up to 24 hours after the exercise bout. The authors concluded that “when moderate endurance exercise is done to lose body fat, fasting before exercise does not enhance lipid utilization (fat loss); rather, physical activity after a light meal is advisable.” 4 Check out this article for more on pre-workout meal ideas.

High Intensity Cardio on an Empty Stomach Can Burn You Out

During intense exercise that approaches your maximum effort, most of your energy comes from glycogen. If you deplete your glycogen stores, you compromise your energy output. As glycogen stores in the muscles and liver are depleted, and the blood glucose level begins to fall, fatigue, lack of coordination, light-headedness and lack of concentration can occur. Commonly known as “hitting the wall” or “bonking,” fat simply can’t be metabolized fast enough to support the higher pace, so you slow down or even stop.

While research and studies are still ongoing, there are a few certainties. Steady state fasted cardio might burn more fat during your workout, but your post-workout fat burn is compromised. When performing high intensity cardio and exercises, glycogen levels need to be restored to achieve optimal performance and results. Doing cardio on an empty stomach if you aren’t able to sustain adequate energy levels, your workout will suffer.

Always choose energy and sustainability over anything else! Even early in the morning, grab a protein shake, piece of fruit, or handful of trail mix, to help your body to use efficient energy sources to power your workout.

Show 4 References

  1. Zoladz JA, Konturek SJ, Duda K, Majerczak J, Sliwowski Z, Grandys M, Bielanski W. Effect of moderate incremental exercise, performed in fed and fasted state on cardio-respiratory variables and leptin and ghrelin concentrations in young healthy men . J Physiol Pharmacol. 2005 Mar;56(1):63-85.
  2. The TRUTH About Fasted Cardio . MensHealth. 2011.
  3. Onunkwo, D. Fasted Cardio For Fast Loss…Does It Work? . Health & Fitness. 2011.
  4. Paoli A, Marcolin G, Zonin F, Neri M, Sivieri A, Pacelli QF. Exercising fasting or fed to enhance fat loss? Influence of food intake on respiratory ratio and excess postexercise oxygen consumption after a bout of endurance training. . Exp Biol Med (Maywood). Int J Sport Nutr Exerc Metab. 2011;21(1):48-54


  1. profile avatar
    Marc Perry, CSCS, CPT May 29, 2012 - 09:39 #

    Very good article, Kevin. I think the statement in the last paragraph “Always choose energy and sustainability over anything else” is GREAT advice.

  2. profile avatar
    P.M. May 29, 2012 - 10:52 #

    Hello Marc. Thanks for sharing that article. I like the part about “Always choose energy and sustainability over anything else” too.

  3. profile avatar
    Ray May 29, 2012 - 15:40 #

    Thank you for the great article! I always hear people doing cardio on an empty stomach and how great it is, but I could never do it. I always felt like I didn’t have the energy or drive that I typically do when I have a preworkout meal and it would bother me. I’m glad to hear I’m not missing out on much! I was wondering, since you mention it in your article, how significant is the calorie burn following cardio? Is it even worth looking into it? Once again, thanks!

    1. profile avatar
      Marc Perry, CSCS, CPT May 29, 2012 - 18:30 #

      @Ray – Kevin can chime in as well, but I actually did a 45 minute interview on the afterburn effect topic with one of the top exercise researchers who literally spends his entire day learning about the afterburn effect. Just about everything you would ever need to know is in that post. Here’s the link – Afterburn Effect 101.

  4. profile avatar
    Oscar May 30, 2012 - 16:15 #

    Hi Marc, I used to do it on an empty stomach and it is a lot different than when you have something on your stomach, you feel that you have more power, so my question is if I am going to workout first thing in the am, considering there is not much time to get ready for work and take daughter to school, how long before the workout should one get the protein juice or the fruit? 5 or 10 mins? Hopefully you say YES!!!
    Thank you.

    1. profile avatar
      Marc Perry, CSCS, CPT Jun 03, 2012 - 16:30 #

      @Oscar – Kevin who wrote this article can chime in, but 5-10 minutes can be fine before a workout. Even consider like a banana right before, which should not upset your stomach. Ultimately, you need to test the foods out to see what works best for you. For more info, check out this article – Pre-Workout Meal: What To Eat Before A Workout?

  5. profile avatar
    Scott Bradley Jun 01, 2012 - 13:34 #

    Marc – What about doing High Intensity Interval Training on an empty stomach in a fasted state in the morning?

    Is there any research on this?

    It seems that this is the only combination that wasn’t tested.


    1. profile avatar
      Marc Perry, CSCS, CPT Jun 03, 2012 - 17:22 #

      @Scott – Kevin can chime in who wrote the article, but the theme of the article is that fueled exercise helps create the most energetic workout possible. I have heard of people having intense workouts using BCAA supplements during a intermittent fasting program, but generally speaking, more energy for workouts will equate to higher fat burn over the entire day. So if your workout is 25% more intense after fueling vs. no eating, then I would have to imagine the fat burn would be considerably greater with the more energetic workout. Agreed that some more research would be helpful.

  6. profile avatar
    Anthony Jun 01, 2012 - 14:07 #

    Hi Marc, I have the same question as Oscar. I have limited time in the morning and that’s the time when I can workout. I also don’t want to feel bloated or like I’m going to throw up during the workout. Thanks and keep up the great work!

    1. profile avatar
      Marc Perry, CSCS, CPT Jun 03, 2012 - 17:24 #

      @Anthony – Eating 10-15 minutes before a workout can definitely work. In fact, athletes like cyclists eat during a workout. Something soft on your stomach like a banana can do the trick before an early morning workout. But it gets back to energy. If you feel a lot of energy without eating food, than fasted should be ok.

  7. profile avatar
    Hank Jun 01, 2012 - 14:08 #

    The problem with eating before an early workout is not just fat burn but amount. Breakfast is the most important meal of the day and just having a light snack before working out may be beneficial for the workout but not nutritionally.

    1. profile avatar
      Marc Perry, CSCS, CPT Jun 03, 2012 - 17:25 #

      @Hank – I think you make a great point. Ideally, a small snack before a workout would be followed by a breakfast that is more nutritionally dense after the early morning workout.

  8. profile avatar
    Priscilla L. Martin Jun 02, 2012 - 10:55 #

    Hello Marc. Burning fat and cardio activity is a good way to look at weight loss, in my opinion. In my personal interest concerning weight loss, I look at the whole picture. I think people who are below their normal body weight are closer to an empty stomach than others. When we do cardio, we should first consider some things: Do I need vitamins and minerals; do I need such as gatorade; do I need a sugar drink–really Marc, I would probably need a soda pop; or, do I need to eat something light to heavy to be successful. I also think something spicy is good in cardio burn. The intake of such as oil and other fats and water is important here too. Thank you for sharing.

  9. profile avatar
    Kevin Deeth Jun 04, 2012 - 20:14 #

    @Ray. I definitely agree with Marc and encourage you and everyone to read for your own knowledge base on the “Afterburn Effect”. It seems like new studies come out every day that encourage people to perform high intensity intervals due to the post-exercise calorie burn.

  10. profile avatar
    Kevin Deeth Jun 04, 2012 - 20:22 #

    @Oscar a simple carb such as a banana with 10-15 grams of whey protein and BCAA’s will ensure that you have energy during your workout and help to restore glycogen levels. Your pre-workout meal is largely dependent on your fitness goals. If you are trying to cut body fat and maintain lean body mass a simple carb with some protein should due the trick. We generally recommend that people give themselves time to fully digest their food before a workout but realize this is not realistic for everyone’s schedule

  11. profile avatar
    Kevin Deeth Jun 04, 2012 - 20:27 #

    @Scott, I generally do not recommend high intensity intervals in a fasted state for the sole fact that this usually compromises your work output and energy levels to perform at your peak. If you are the type of person that feels like a pre-workout meal has no substantial influence on your energy or work output than high intensity intervals might be permissible for you. Just remember, your body will also burn through muscle as well as fat if glycogen stores are depleted.

  12. profile avatar
    Kevin Deeth Jun 04, 2012 - 20:30 #

    @Anthony, I would like to echo what Marc said but also like to add sometimes water based fruits or fruits with less sugar are easier on people’s stomachs early in the morning. If you have a sensitive stomach try a less ripe banana as they have less sugar or half of a grapefruit.

  13. profile avatar
    Lauren Jun 08, 2012 - 22:15 #

    I’ve found a bunch of articles on this topic, but this is the best, most comprehensive one I’ve ever read! Thank you – I feel like this question has finally been answered!

    1. profile avatar
      Marc Perry, CSCS, CPT Jun 11, 2012 - 22:09 #

      That’s great to hear, Lauren. Thanks for sharing! Kevin did A LOT of research for this article.

  14. profile avatar
    Wajisa Jun 11, 2012 - 22:58 #

    Is it okay if I do HIIT in the morning after taking a protein shake??

    1. profile avatar
      Marc Perry, CSCS, CPT Jun 14, 2012 - 18:29 #

      Hi Wajia – As long as you don’t have a very light stomach, give yourself 30 minutes, and drink a light protein shake that you make yourself with whey protein (i.e. banana, crushed ice/water, chocolate whey protein) the short answer is you should be ok. I suggest trying different combinations and foods to see what works for you.

  15. profile avatar
    Paden Jun 15, 2012 - 16:53 #

    I have found that not eating before any type of exercise or activity directly affects the performance of that task in a negative way. At a minimum, it takes me 15 to 30 minutes longer to warm up physically (this probably also accounts for the mental fatigue as well).

    My question is this: What is the best preworkout meal? Is a protein shake the best thing to have, or is something like 2 or 3 eggs better to eat? Additionally, how many carbs are you looking to have in that meal?

    1. profile avatar
      Marc Perry, CSCS, CPT Jun 18, 2012 - 18:03 #

      @Paden – I strongly suggest you check out this article, which should answer your question – Pre-Workout Meal: What To Eat Before A Workout?

  16. profile avatar
    Eve Jul 12, 2012 - 10:44 #

    Okay sorry if I’ve missed something here….it seems these studies are conflicting?

    I have recently been told to do cardio (low intensity for one hour) each morn on an empty stomach and trying to decide whether it’s worth the extra effort I need to put in to do that.

    I eat 6 meals a day, a meal every 3 hours. The last two meals have carbs only in nuts and my breakfast has carbs in the form of oats and lts of protein.

    Would it be beneficial for me, in terms of fat burn, to go ahead and eat my carb / protein breakfast after a fasted cardio session and then go onto weights once I’ve eaten and sufficiently digested?

    1. profile avatar
      Marc Perry, CSCS, CPT Jul 12, 2012 - 16:50 #

      @Eve – Kevin can chime in, but it sounds like you are getting hung up on the minutiae while losing sight of the big picture. If you want to maximize fat burn, doing some form of interval training is vastly superior to hanging out on a piece of cardio equipment for an hour. Doing a full body strength training workout for 20-30 minutes followed by some interval training would be a very effective workout, and it’s along the lines of how I’ve structured the BuiltLean Program. I highly recommend checking out my free Get Lean Guide to learn the basics. Whether or not you should eat before hand has more to do with your energy levels. That’s really the entire conclusion of the article; it’s not about fat loss, it’s about energy levels.

  17. profile avatar
    Kush Aug 12, 2012 - 04:43 #

    This is a brilliant article! My question is …i do high intensity jogging for 45 to 55 minutes during late evenings rather than mornings…is it ok? Or should i switch to early mornings?…i just want to know..what’s the PERFECT time for high intensity cardio?? Ur help would be appericiated!!

    1. profile avatar
      Marc Perry, CSCS, CPT Aug 16, 2012 - 07:35 #

      @Kush – Whatever you can sustain and whatever time works best for your schedule is the best time to workout.

  18. profile avatar
    kael tan Sep 06, 2012 - 01:20 #

    may i ask?i am 26age 177cm weight 70kg and now my body fat% is 16% so i plan to loss my fat % i wish to to 10%….so i just do a cardio exercise to loss fat without doin muscle building exercise. So do i still need to consume protein source such as eggs,milk,etc….???? actually i want my abs to get ripped….Hope to get some advice from you.thank you. =]

    1. profile avatar
      Marc Perry, CSCS, CPT Sep 12, 2012 - 12:00 #

      @Kael – please check out my Get Lean Guide to learn the basics. It’s a good starting point for you.

  19. profile avatar
    Deepak Hari Sep 23, 2012 - 11:56 #

    HI, I would like to know if drinking coffee like 4 times a day interrupts my weight loss program? Thanks in advance. Extra info: i drink 1/2 a litre of coffee each day.

    Thanks in advance.

    1. profile avatar
      Marc Perry, CSCS, CPT Sep 29, 2012 - 17:02 #

      @Deepak Hari – drinking coffee should not interrupt your weight loss program, as long as you it’s not affecting your sleep. Generally speaking, drinking coffee much after 2-3pm may affect your sleep because caffeine can linger in your system for several hours. A quality sleep is very important because it helps you control your calorie intake.

  20. profile avatar
    Jeremy Monaco Sep 27, 2012 - 09:25 #

    Also to comment on the last 2 posters, coffee wont hurt you at all as long as your drinking it as is. Coffee actually has natural caffine in it, so it will actually probably help you lose weight slightly. Now if your adding creamer and sugar etc, its really bad for you, about as bad as drinking the same ammount of soda.

    With regards to protein intake, yes!!!! Protein is the most important building block your body needs to repair itself, and grow. You should aim for a high protein diet, but you also want to get a good macro setup with fats and carbs. this isnt ideal for everyone, but I do 40% protein 40% carbs 20% fat.

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