Fasted Cardio is Overrated and So is Fasted Strength Training

Fasted exercise is training while you haven’t had food for a while, like going for a jog after waking up. Many clueless Instagram influencers are big proponents of fasted exercise and love making extreme claims about it. Fortunately, you’ve stumbled onto this science-based article, where the truth will be revealed to you.

But enough small talk, let’s see what the research clearly says about all things fasted cardio and fasted strength training.

Fasted Cardio

Fasted cardio is more commonly performed than fasted strength training. It’s often done in an attempt to enhance fat loss. Fasted cardio bunnies often over-exaggerate claims about how fasted cardio burns more fat than fed cardio.

This is technically true, but not practically relevant. Fasted cardio can burn more fat than fed cardio, but burning more fat doesn’t mean you lose more fat off your body.

Here’s why.

  1. The additional fat burning comes at the expense of burning less carbohydrate during exercise. This means you’re not burning additional fuel (calories), you’re simply burning more of one fuel source at the expense of another (1).
  2. It’s also been shown that after both fasted or fed exercise, your body will burn more of the fuel source it didn’t burn during exercise, basically a compensation effect (2,6,24).
  3. Fed cardio actually causes a slight increase in energy expenditure compared to fasted cardio (6,7,8,29). This may come from an enhanced thermic effect of food along with the energy cost of food’s anabolic effect (9,10,11).
  4. Ultimately, net calories burned over the course of the day is similar whether fed or fasted when conditions are matched (2). In other words, fasted cardio doesn’t burn more calories, boost your metabolism, or enhance fat loss.

This is why looking at a short-term bout of fasted vs fed cardio is shortsighted. Your long-term energy balance (total calories in vs calories out) is what matters, not whether or not food is in your stomach when jog.

This has consistently played out in all research comparing fed vs fasted cardio while total daily calories are matched (3,4,5). The end result is always similar weight loss and body composition changes. Sorry fasted cardio bunnies, nothing magically superior about hungry running.

That being said, fasted cardio can have some merit in specific conditions:

  • If you don’t control for calories, doing fasted cardio will likely decrease your total energy intake (25). So if you tell someone to do fasted cardio, especially if they’re a big breakfast eater, they’ll go through almost half their day without food encouraging less total consumption. Fasted cardio can encourage you to unconsciously eat less similar to how intermittent fasting cuts down the hours you’re allowed food (26).
  • Fasted cardio can also decrease fat gain and improve insulin sensitivity better than fed cardio when eating a high fat, low protein calorie surplus without strength training (27). This becomes irrelevant the moment you do strength training because your metabolic markers will be maximally improved especially when done in a fed state (20). So I guess if you ever plan on intentionally getting fat from a suboptimal diet without lifting weights, fasted cardio can mitigate the damage a bit better.

Fasted Strength Training

I don’t really know many people who strength train fasted, but let’s go over it anyways. As you could probably predict by now, fasted strength training doesn’t have any body composition advantages either (3,4,18). Again, energy balance is king.

Furthermore, fed strength training has been shown to improve glucose control and metabolic markers better than fasted strength training in type 2 diabetic patients (20). This debunks the myth that fasted lifting improves nutrient partitioning better than fed strength training.

Fasted Exercise and Performance

So now that you understand fasted cardio and fasted strength training doesn’t boost your metabolism nor enhance body composition when all else is equal, a reasonable question is does fasted training impact exercise performance?

For cardio, fasted workouts seem to be fine if it’s low intensity and well under 1 hour, but longer bouts are compromised (19,29).

And the research for how it impacts strength training performance is quite mixed. Some studies show fasted strength training performance makes no difference (12,13,14) while others show lifting fed boosts performance (15,16,17).

A systematic review on ramadan fasting’s effect on exercise performance in sport’s athletes, found fasting didn’t impact endurance or strength performance, but did compromise power and sprint performance (28). Keep in mind, this is done in sports athletes, not advanced strength trainees, so it’s safe to say that advanced lifters will likely have their performance compromised.

Fasted Exercise and Muscle Loss

From the body of research I discussed above, fasted exercise doesn’t cause muscle loss when calories are matched. The body composition changes were generally the same in the short term assuming exercise is within an hour.

However, keep in mind, fasted training is likely suboptimal over the long term especially if taken to extremes. Fasting is never more anabolic than eating. Your body will produce additional growth hormone to compensate and minimize muscle breakdown, but compromise IGF-1 (a very anabolic hormone) production in the process (21).

Physiologically speaking, you can only fast for so long before losing muscle even if you increase anabolic signaling through strength training (30).

Eventually protein breakdown increases and anabolic signaling diminishes cause well, you got no food (22,23). This occurs as early as 15 hours, but isn’t too impactful. However, this will likely affect lean individuals more as they’re more prone to muscle loss especially those who lift weights

This is why long fasts (even with exercise) beyond about 16-20 hours are not advised for those looking to maximize muscle growth, especially in lean lifters (29).

So What’s The Verdict?

Fasted exercise doesn’t have any of the benefits often claimed. However, the potential drawbacks of fasted exercise like performance/muscle loss is largely overstated. Performance/muscle loss may only be relevant to lean advanced lifters.

If you prefer to workout fasted or if it helps you naturally eat less for fat loss, I can see some practical reasons why someone would want to do it, especially if it’s merely light cardio. That being said, I don’t recommend it for advanced lifters looking to maximize results because at the end of the day, while you have little to lose from fasted exercise, you have nothing to gain. It’s a low risk, no reward style of training.

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  1. Vieira, Alexandra Ferreira, et al. “Effects of Aerobic Exercise Performed in Fasted v. Fed State on Fat and Carbohydrate Metabolism in Adults: a Systematic Review and Meta-Analysis.” The British Journal of Nutrition, U.S. National Library of Medicine, Oct. 2016, www.ncbi.nlm.nih.gov/pubmed/27609363.
  2. Shimada, Kenshiro, et al. “Effects of Post-Absorptive and Postprandial Exercise on 24 h Fat Oxidation.” Metabolism: Clinical and Experimental, U.S. National Library of Medicine, June 2013, www.ncbi.nlm.nih.gov/pubmed/23313101.
  3. Schoenfeld, Brad Jon, et al. “Body Composition Changes Associated with Fasted versus Non-Fasted Aerobic Exercise.” Journal of the International Society of Sports Nutrition, BioMed Central, 18 Nov. 2014, www.ncbi.nlm.nih.gov/pmc/articles/PMC4242477/.
  4. Hackett, et al. “Effect of Overnight Fasted Exercise on Weight Loss and Body Composition: A Systematic Review and Meta-Analysis.” MDPI, Multidisciplinary Digital Publishing Institute, 25 Nov. 2017, www.mdpi.com/2411-5142/2/4/43/htm.
  5. Gillen, Jenna B, et al. “Interval Training in the Fed or Fasted State Improves Body Composition and Muscle Oxidative Capacity in Overweight Women.” Obesity (Silver Spring, Md.), U.S. National Library of Medicine, Nov. 2013, www.ncbi.nlm.nih.gov/pubmed/23723099.
  6. Wegman, et al. “Metabolic Impact of Protein Feeding Prior to Moderate-Intensity Treadmill Exercise in a Fasted State: a Pilot Study.” Journal of the International Society of Sports Nutrition, BioMed Central, 1 Jan. 1970, jissn.biomedcentral.com/articles/10.1186/s12970-018-0263-6.
  7. Hulmi, Juha J, et al. “Protein Ingestion Prior to Strength Exercise Affects Blood Hormones and Metabolism.” Medicine and Science in Sports and Exercise, U.S. National Library of Medicine, Nov. 2005, www.ncbi.nlm.nih.gov/pubmed/16286871.
  8. Hackney, Kyle J, et al. “Timing Protein Intake Increases Energy Expenditure 24 h after Resistance Training.” Medicine and Science in Sports and Exercise, U.S. National Library of Medicine, May 2010, www.ncbi.nlm.nih.gov/pubmed/19997003?dopt=Abstractplus.
  9. Goben, K W, et al. “Exercise Intensity and the Thermic Effect of Food.” International Journal of Sport Nutrition, U.S. National Library of Medicine, Mar. 1992, www.ncbi.nlm.nih.gov/pubmed/1299486.
  10. Lee, Y S, et al. “The Effects of Various Intensities and Durations of Exercise with and without Glucose in Milk Ingestion on Postexercise Oxygen Consumption.” The Journal of Sports Medicine and Physical Fitness, U.S. National Library of Medicine, Dec. 1999, www.ncbi.nlm.nih.gov/pubmed/10726436.
  11. Davis, J. Mark, et al. “Weight Control and Calorie Expenditure: Thermogenic Effects of Pre-Prandial and Post-Prandial Exercise.” Addictive Behaviors, Pergamon, 28 May 2002, www.sciencedirect.com/science/article/abs/pii/030646038990066X.
  12. Waterhouse, Jim, and Liverpool. “The Effects of Ramadan Intermittent Fasting on Athletic Performance: Recommendations for the Maintenance of Physical Fitness.” Taylor & Francis, www.tandfonline.com/doi/abs/10.1080/02640414.2012.698297.
  13. Dalton, R A, et al. “Acute Carbohydrate Consumption Does Not Influence Resistance Exercise Performance during Energy Restriction.” International Journal of Sport Nutrition, U.S. National Library of Medicine, Dec. 1999, www.ncbi.nlm.nih.gov/pubmed/10660864.
  14. Kulik, Justin R, et al. “Supplemental Carbohydrate Ingestion Does Not Improve Performance of High-Intensity Resistance Exercise.” Journal of Strength and Conditioning Research, U.S. National Library of Medicine, July 2008, www.ncbi.nlm.nih.gov/pubmed/18545201.
  15. 1National Center of Sport and Exercise Medicine. “Breakfast Omission Reduces Subsequent Resistance Exercise… : The Journal of Strength & Conditioning Research.” LWW, journals.lww.com/nsca-jscr/Citation/2019/07000/Breakfast_Omission_Reduces_Subsequent_Resistance.5.aspx.
  16. Haff, G G, et al. “The Effects of Supplemental Carbohydrate Ingestion on Intermittent Isokinetic Leg Exercise.” The Journal of Sports Medicine and Physical Fitness, U.S. National Library of Medicine, June 2001, www.ncbi.nlm.nih.gov/pubmed/11447365.
  17. Krings, Ben M, et al. “Effects of Acute Carbohydrate Ingestion on Anaerobic Exercise Performance.” Journal of the International Society of Sports Nutrition, BioMed Central, 10 Nov. 2016, www.ncbi.nlm.nih.gov/pmc/articles/PMC5105234/.
  18. Trabelsi, Khaled, et al. “Effect of Fed- versus Fasted State Resistance Training during Ramadan on Body Composition and Selected Metabolic Parameters in Bodybuilders.” Journal of the International Society of Sports Nutrition, BioMed Central, 25 Apr. 2013, www.ncbi.nlm.nih.gov/pubmed/23617897.
  19. Aird, T P, et al. “Effects of Fasted vs Fed-State Exercise on Performance and Post-Exercise Metabolism: A Systematic Review and Meta-Analysis.” Scandinavian Journal of Medicine & Science in Sports, U.S. National Library of Medicine, May 2018, www.ncbi.nlm.nih.gov/pubmed/29315892.
  20. Heden, Timothy D., et al. “Postdinner Resistance Exercise Improves Postprandial Risk Factors More Effectively than Predinner Resistance Exercise in Patients with Type 2 Diabetes.” Journal of Applied Physiology, 1 Mar. 2015, www.physiology.org/doi/full/10.1152/japplphysiol.00917.2014.
  21. Nørrelund, Helene. “The Metabolic Role of Growth Hormone in Humans with Particular Reference to Fasting.” Growth Hormone & IGF Research, Churchill Livingstone, 21 Mar. 2005, www.sciencedirect.com/science/article/abs/pii/S1096637405000201.
  22. Tsalikian, E, et al. “Increased Leucine Flux in Short-Term Fasted Human Subjects: Evidence for Increased Proteolysis.” The American Journal of Physiology, U.S. National Library of Medicine, Sept. 1984, www.ncbi.nlm.nih.gov/pubmed/6476111.
  23. R, Maarten, et al. “Intermittent Fasting Does Not Affect Whole-Body Glucose, Lipid, or Protein Metabolism.” OUP Academic, Oxford University Press, 23 Sept. 2009, academic.oup.com/ajcn/article/90/5/1244/4598111.
  24. Zouhal, Hassane, et al. “Exercise Training and Fasting: Current Insights: OAJSM.” Open Access Journal of Sports Medicine, Dove Press, 21 Jan. 2020, www.dovepress.com/exercise-training-and-fasting-current-insights-peer-reviewed-article-OAJSM.
  25. Edinburgh, Robert M, et al. “Skipping Breakfast Before Exercise Creates a More Negative 24-Hour Energy Balance: A Randomized Controlled Trial in Healthy Physically Active Young Men.” The Journal of Nutrition, Oxford University Press, 1 Aug. 2019, www.ncbi.nlm.nih.gov/pmc/articles/PMC6675614/.

  26. Sievert, Katherine, et al. “Effect of Breakfast on Weight and Energy Intake: Systematic Review and Meta-Analysis of Randomised Controlled Trials.” The BMJ, British Medical Journal Publishing Group, 30 Jan. 2019, www.bmj.com/content/364/bmj.l42.
  27. Van Proeyen, Karen, et al. “Training in the Fasted State Improves Glucose Tolerance during Fat-Rich Diet.” The Journal of Physiology, Blackwell Science Inc, 1 Nov. 2010, www.ncbi.nlm.nih.gov/pmc/articles/PMC3002457/.

  28. B. Sadeghirad, S. Motaghipisheh, et al. “Effects of Ramadan Fasting on Physical Performance: A Systematic Review with Meta-Analysis.” Sports Medicine, Springer International Publishing, 1 Jan. 1970, link.springer.com/article/10.1007%2Fs40279-020-01257-0.

  29. Bernardino, 1California State University San. “Fasted Versus Nonfasted Aerobic Exercise on Body… : Strength & Conditioning Journal.” LWW, journals.lww.com/nsca-scj/Abstract/9000/Fasted_Versus_Nonfasted_Aerobic_Exercise_on_Body.99259.aspx.

  30. Yasuda. “Breakfast before Resistance Exercise Lessens Urinary Markers of Muscle Protein Breakdown in Young Men: A Crossover Trial.” Nutrition (Burbank, Los Angeles County, Calif.), U.S. National Library of Medicine, pubmed.ncbi.nlm.nih.gov/33418493/.

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