Dr. Jim Stoppani On Why High-Intensity Interval Training (HIIT) Burns More Fat

Dr. Stoppani is in line with the science that says HIIT is better than steady-state cardio to effectively burn fat.

Episode five of Generation Iron and BarBend‘s interview series with exercise physiologist Dr. Jim Stoppani aired on March 18, 2022. So far, Stoppani’s conversation with Vlad Yudin has discussed contralateral and pre-exhaust training, the differences between whey and casein protein intermittent fasting, coffee and alcohol, and carb cycling vs. keto diets. In episode five, Yudin asked Stoppani a flurry of questions about cardio — When the best time for it is? Is it better to perform cardio fasted? Is cardio better in the morning or evening? Which is better: high intensity or steady-state cardio?

Dr. Stoppani acknowledges that the correct answer(s) is “pretty wide,” as it will vary depending on the person and their specific goals. Check out what Dr. Stoppani had to say about cardio in the video below, courtesy of Generation Iron‘s YouTube channel:

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What’s Cardio Again?

Cardio can fall into two categories — aerobic and anaerobic. According to The American College of Sports Medicine, aerobic exercise is classified as “any activity that uses large muscle groups, can be maintained continuously, and is rhythmic in nature.” Anaerobic is “intense physical activity of very short duration, fueled by the energy sources within the contracting muscles and independent of the use of inhaled oxygen as an energy source.” (1)(2)

Both aerobic and anaerobic exercise “help deter cardiovascular morbidity and mortality,” and it is likely never too late to reap those benefits from cardio. Per Frontiers in Cardiovascular Medicine, “to some extent, beginning exercise, even late in life, can be effective in reversing structural and functional changes in the cardiovascular system associated with aging and/or disease states such as heart failure.” (3)


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Fasted Cardio — Good or Bad?

Determining if cardio is good for someone with the goal of fat loss, Dr. Stoppani believes that “it’s about fat loss throughout the day,” meaning that it is not only what happens during the workout that matters. During steady-state cardio, more fat is likelier to be burned than carbs, but fewer calories overall. Whereas shorter bursts of intense cardio or high-intensity interval training (HIIT) will burn more carbs than fat during the workout, but the body will burn more fat throughout the day to recover.

Do you want to maximize fat-burning for two hours or for 22 hours of the day?

Dr. Stoppani states that to maximize fat-burning, one should train “as intensely as possible.”

You want to burn carbs. You want to [train] so intense to burn carbs because when the workout is over, your body won’t dare burn carbs.”

The body will burn fat rather than carbs to recover following HIIT training because it needs the carbs for the following workout — it conditions the metabolism to burn fat. Dr. Stoppani referred to studies that have found that 30-second sprints burn more fat than 30 minutes of running. While he didn’t state which studies those were, he’s right. Applied Physiology, Nutrition, and Metabolism determined sprint interval training is “a time-efficient strategy for decreasing body fat while increasing aerobic capacity.” The British Journal of Sports Medicine found that HIIT “provided 28.5% greater reductions in total absolute fat mass than moderate-intensity exercise.” (4)(5)

All this is to say that, unless you’re a professional bodybuilder trying to scrape off the last bit of fat from your physique during peek week, Dr. Stoppani would never recommend fasted cardio for fat loss.

You’re better off not being fasted so you can train harder.

If your goal is to burn fat, Dr. Stoppani and the science suggests that your target should not be burning calories during the workout but instead using the workout to fuel fat burning when you’re not training. Training with intensity is the way to do that, whether sprinting on a treadmill or lifting weights.


  1. Wahid, A., Manek, N., Nichols, M., Kelly, P., Foster, C., Webster, P., Kaur, A., Friedemann Smith, C., Wilkins, E., Rayner, M., Roberts, N., & Scarborough, P. (2016). Quantifying the Association Between Physical Activity and Cardiovascular Disease and Diabetes: A Systematic Review and Meta-Analysis. Journal of the American Heart Association5(9), e002495. https://doi.org/10.1161/JAHA.115.002495
  2. Patel, H., Alkhawam, H., Madanieh, R., Shah, N., Kosmas, C. E., & Vittorio, T. J. (2017). Aerobic vs anaerobic exercise training effects on the cardiovascular system. World journal of cardiology9(2), 134–138. https://doi.org/10.4330/wjc.v9.i2.134
  3. Nystoriak, M. A., & Bhatnagar, A. (2018). Cardiovascular Effects and Benefits of Exercise. Frontiers in cardiovascular medicine5, 135. https://doi.org/10.3389/fcvm.2018.00135
  4. Hazell, T. J., Hamilton, C. D., Olver, T. D., & Lemon, P. W. (2014). Running sprint interval training induces fat loss in women. Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme39(8), 944–950. https://doi.org/10.1139/apnm-2013-0503
  5. Viana, R. B., Naves, J., Coswig, V. S., de Lira, C., Steele, J., Fisher, J. P., & Gentil, P. (2019). Is interval training the magic bullet for fat loss? A systematic review and meta-analysis comparing moderate-intensity continuous training with high-intensity interval training (HIIT). British journal of sports medicine53(10), 655–664. https://doi.org/10.1136/bjsports-2018-099928

Featured image: @jimstoppani on Instagram