For years, the fitness community has been preaching about fasted cardio benefits fat loss. Fasted cardio and intermittent fasting have long been popular ways to increase fat loss. Many bodybuilders and fitness enthusiasts swear by it, claiming that performing cardio on an empty stomach is the secret to optimal fat loss. But is this practice backed by science? This article aims to provide evidence-based insights into whether fasted cardio is good for weight loss and its impact on fat loss.
Bodybuilders and Fasted Cardio Benefits Fat Loss Summary
- A recent study investigated nutrition, training, supplement, and performance-enhancement drug practices of male and female physique competitors 30 days before a competition.
- Most bodybuilding competitors reported performing cardio in a fasted state despite a lack of objective evidentiary support for the practice.
What is Fasted Cardio?
Fasted cardio involves performing cardiovascular exercise in a state of fasting, typically in the morning before consuming any food. It aims to deplete glycogen stores and rely on stored fat for fuel. Most people do fasted cardio first thing in the morning, which can lead to higher fat oxidation. Many forms of cardio include low-intensity steady-state activities like walking or cycling and high-intensity interval training (HIIT).
The idea is that when you exercise without eating, your body will burn more fat for fuel. But does the science support this claim? While some studies suggest an early morning fast workout may lead to greater fat loss (Kim et al., 2015; Trabelsi et al., 2012); however, other studies have found no benefit of a fasted cardio workout. (Liu et al., 2023; Schoenfeld et al., 2014) So, should I do fasted cardio?
The inconsistent findings in some studies may be due to differences in study duration, sample size, lack of calorie control (i.e., different energy balance between subjects), and subject demographics. Factors such as exercise intensity, duration, and frequency may also play a role in the observed benefits of a fasted workout or lack thereof. However, fasted cardio can lead to low blood sugar and cause dizziness, nausea, or even vomiting. Muscle breakdown is another concern.
The Appeal of Fasted Cardio
Fasted cardio has gained popularity among fitness enthusiasts for several reasons. One of its main appeals is the potential for increased fat oxidation, leading to greater calorie and fat burning during exercise. While fasted cardio may increase fat oxidation during exercise (Vieira et al., 2016), this does not necessarily translate to greater fat loss over time. For more insights, read the article on Evidence Based Muscle, “Fat Burning Does Not Always Mean Fat Loss.” Therefore, it may not be the best option if your primary goal is weight loss. The research suggests otherwise.
Studies Comparing Benefits Fasted Cardio to Fed Cardio
Study 1: A study involving thirty overweight and obese young adult males randomly divided into a fasted cardio group, a fed aerobic exercise group, and a control group. Both exercise groups underwent a six-week indoor treadmill intervention, combined with diet control, five days a week. The results showed no difference between the fasted and fed cardio groups for fat loss, suggesting that the timing of meals relative to exercise did not significantly affect the outcomes. (Liu et al., 2023)
Study 2: Studies have shown that HIIT and low-intensity exercise results in similar fat loss when calories are identical. (D’Amuri et al., 2021) Although low-intensity exercise acutely increases fat mobilization/burning, this is not a sustained effect over 24 hours. (Harris & Kuo, 2021) High-intensity exercise results in fat loss despite not being in the fat-burning zone.
Newest Study on Bodybuilding Competition Practices Regarding Fasted Cardio
The newest study by Professor Escalante out of California State University-San Bernardino sheds some light on how many bodybuilders believe fasted cardio benefits fat loss. Researchers conducted interviews with 29 competitors 30 days leading into a bodybuilding competition to gather information on their nutrition, training, supplementation, and use of performance-enhancing drugs (PEDs).
- Every competitor engaged in cardio workouts, varying in frequency, intensity, and duration from 1 to 14 sessions per week, each lasting between 15 to over 60 minutes and ranging from low to high intensity. Of the 29 competitors, 24 regularly or occasionally participated in fasted cardio. This is quite shocking given that most bodybuilders still believe fasted cardio benefits fat loss as most of the competitors performed fasted cardio (i.e., 24/29 performed fasted cardio).
- Other interesting findings from the study are most bodybuilders consumed 95% of male competitors reported using at least three different supplements concurrently, while 75% of female competitors used at least one. Caffeine, supported by substantial research, was consumed by 75% of females and 42.8% of males.
- Conversely, branched-chain amino acids and fat burners, which lack strong evidentiary backing, were used by 71.4% of males, 62.5% of females, 53.8% of males, and 62.5% of females, respectively.
- Interestingly, only one male competitor reported using creatine despite being one of the most research-supported supplements for bodybuilding. These statistics reflect supplement usage in the 30 days leading up to the competition.
The Physiology Behind Fasted Cardio
Understanding the physiological mechanisms behind fasted cardio is essential to grasp why it doesn’t offer a fat-loss advantage. When you exercise in a fasted state, your body does indeed rely more on fat oxidation for energy. However, this doesn’t necessarily mean you’re losing more fat. Fat oxidation is just one part of a complex metabolic process, and burning more fat during exercise doesn’t automatically translate to losing more fat overall.
It is important to consider the role of energy balance in fat loss. To lose weight, individuals must create a calorie deficit by consuming fewer calories than they expend. While fasted cardio may increase fat oxidation during exercise, the overall impact on fat loss may be minimal if the individual consumes excess calories throughout the day. Therefore, the timing of cardio exercise, whether fasted or fed, should be considered in the context of overall energy balance.
So, Should I Do Fasted Cardio?
Despite hearing that fasted cardio benefits fat loss, no research supports this concept. Whether you do cardio on an empty stomach or not is a personal preference. Go for it if you perform better or feel more comfortable doing cardio on an empty stomach. However, don’t expect it to be a magic bullet for fat loss.
Is Fasted Cardio Better Than Regular Cardio?
Based on the current scientific evidence, the notion that fasted cardio benefits fat loss is not true. Both forms of exercise can effectively burn calories and improve cardiovascular health, but neither has a significant advantage in fat loss.
Is Fasted Cardio Good for Weight Loss?
While fasted cardio may increase fat oxidation during exercise, this does not necessarily translate to greater fat loss over time. Therefore, it may not be the best option if your primary goal is weight loss. Whether performed in a fasted state or not, exercise can reduce fat loss by creating a calorie deficit and improving cardiovascular fitness. Both fed and fasted cardio benefits fat loss for those following a calorie-restricted diet.
When incorporating fasted cardio into your routine, starting with low-intensity activities is important if you’re new to this type of training. Additionally, staying hydrated before and during your fasted cardio sessions is key to preventing dehydration and maintaining optimal performance. If you experience lightheadedness or low energy levels, consider consuming a small snack to stabilize your blood sugar levels.
Remember to experiment with different types of fasted cardio, such as aerobic exercises on the treadmill or even CrossFit workouts, to find what works best for you. Lastly, always monitor your body’s response and make adjustments accordingly to ensure a safe and effective workout.
Multiple scientific studies have debunked the myth that fasted cardio benefits fat loss. While it may increase fat oxidation during exercise, this does not translate to greater fat loss in the long term. So you’ll know better the next time someone tells you that fasted cardio is good for weight loss.
D’Amuri, A., Sanz, J. M., Capatti, E., Di Vece, F., Vaccari, F., Lazzer, S., Zuliani, G., Dalla Nora, E., & Passaro, A. (2021). Effectiveness of high-intensity interval training for weight loss in adults with obesity: a randomised controlled non-inferiority trial. BMJ Open Sport & Exercise Medicine, 7(3), e001021. https://doi.org/10.1136/bmjsem-2020-001021
Escalante, G., Barakat, C., Tinsley, G. M., & Schoenfeld, B. J. (2023). Nutrition, Training, Supplementation, and Performance-Enhancing Drug Practices of Male and Female Physique Athletes Peaking for Competition. Journal of strength and conditioning research, 37(8), e444–e454. https://doi.org/10.1519/JSC.0000000000004462
Harris, M. B., & Kuo, C.-H. (2021). Scientific Challenges on Theory of Fat Burning by Exercise. Frontiers in Physiology, 12, 685166-685166. https://doi.org/10.3389/fphys.2021.685166
Kim, T. W., Lee, S. H., Choi, K. H., Kim, D. H., & Han, T. K. (2015). Comparison of the effects of acute exercise after overnight fasting and breakfast on energy substrate and hormone levels in obese men. Journal of Physical Therapy Science, 27(6), 1929-1932. https://doi.org/10.1589/jpts.27.1929
Liu, X., He, M., Gan, X., Yang, Y., Hou, Q., & Hu, R. (2023). The Effects of Six Weeks of Fasted Aerobic Exercise on Body Shape and Blood Biochemical Index in Overweight and Obese Young Adult Males. J Exerc Sci Fit, 21(1), 95-103. https://doi.org/10.1016/j.jesf.2022.11.003
Schoenfeld, B. J., Aragon, A. A., Wilborn, C. D., Krieger, J. W., & Sonmez, G. T. (2014). Body composition changes associated with fasted versus non-fasted aerobic exercise. Journal of the International Society of Sports Nutrition, 11(1). https://doi.org/10.1186/s12970-014-0054-7
Trabelsi, K., Stannard, S. R., Maughan, R. J., Jammoussi, K., Zeghal, K., & Hakim, A. (2012). Effect of resistance training during Ramadan on body composition and markers of renal function, metabolism, inflammation, and immunity in recreational bodybuilders. Int J Sport Nutr Exerc Metab, 22(4), 267-275. https://doi.org/10.1123/ijsnem.22.4.267
Vieira, A. F., Costa, R. R., Macedo, R. C., Coconcelli, L., & Kruel, L. F. (2016). Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: a systematic review and meta-analysis. Br J Nutr, 116(7), 1153-1164. https://doi.org/10.1017/s0007114516003160