Whey Protein Before Cardio: Debunking the Fat Metabolism Myth Summary

  • The study investigates the influence of fasted state cardio or whey protein before exercise (i.e., 20 or 40 grams of whey protein hydrolysate) and fat metabolism.
  • Fat oxidation rates during exercise did not significantly differ between fasted cardio and whey protein before exercise.
  • Protein doses up to 40 g do not seem to impair fat oxidation rates during exercise compared to fasted exercise. This could be a nutritional strategy for those who find it challenging to include fasted exercise in their training.

Does Fasted Cardio Burn More Fat

The myth that fasted cardio (i.e., training on an empty stomach) is better for burning stored fat still exists in the fitness world. As discussed in a previous article on Evidence-Based Muscle, a recent study found that most bodybuilders still do fasted aerobic exercise first thing in the morning to lose fat before a competition.

Is Fasted Cardio Every Morning Better for Fat Loss?

Losing muscle mass is widely noted in many studies while in a calorie deficit and trying to lose body fat, but a recent study suggests a strategy to prevent this is consuming whey protein before a cardio session. However, whey protein is known to spike insulin, which could suppress fat metabolism during exercise. To minimize the risk of muscle loss, it’s important to incorporate strength training into your exercise routine and to make sure you’re getting enough protein in your diet. So, does fasted cardio burn more fat when compared to consuming whey protein and incorporating strength training? Let’s delve into the science to find out.

Background on Fat Metabolism and Fasted Cardio

fasted cardio in the morning fasted cardio whey protein before weight training fasted cardio fasted cardio every morning whey protein before a workout does fasted cardio burn more fat whey protein before exerciseFat metabolism is the intricate process where our bodies convert fats into energy. This process is influenced by various factors, including our diet, hormones, exercise routines, and even genetics. During exercise, the body primarily relies on carbohydrates as the primary fuel source. However, as the intensity and duration of exercise increase, the body gradually shifts to using a higher proportion of fat for energy. (Mortensen et al., 2009) This shift is influenced by factors such as the availability of fatty acids, the rate of lipolysis (breakdown of fat), and the rate of fat oxidation (conversion of fat into energy).

Protein, although not a direct source of energy during exercise, plays a crucial role in supporting fat metabolism. It provides the building blocks (amino acids) necessary for synthesizing enzymes and hormones involved in fat breakdown and metabolism. Additionally, protein helps preserve lean muscle mass during weight loss, which is important for maintaining a healthy metabolic rate and optimizing fat metabolism. Amidst this, the role of protein, especially whey protein, has been a topic of much debate.

The theory of fasted cardio is often linked to endurance exercise to increase fat metabolism during exercise is the “train-low compete high” approach, which involves training in a “low” carbohydrate-restricted state to enhance fat oxidative capacity. (Vieira et al., 2016; Yeo et al., 2008) This practice involves training with low glycogen stores for your cardio workout. The complete “high” eludes to the carbohydrate loading phase before the race to maximize energy levels and carbohydrate metabolism.

Despite the unclear evidence on its impact on performance, around 63% of athletes incorporate fasted training into their regimen. (Rothschild et al., 2020) An alternative to this approach is to use whey protein before exercise, as whey protein has been shown not to affect fat metabolism during exercise training.

Whey Protein and Its Properties

Whey protein, a by-product of cheese production, is renowned for its rich amino acid profile. It’s categorized into isolates, concentrates, and hydrolysates.

  • Whey protein isolate is the most refined form, with higher protein content and lower levels of lactose and fat.
  • Whey protein concentrate contains a slightly lower protein content but retains more of the natural components found in milk, such as lactose and minerals.
  • Whey protein hydrolysate is a pre-digested form of whey protein rapidly absorbed by the body. (Whetstine et al., 2005)

The rapid absorption and high bioavailability of whey protein make it an ideal choice for high intensity resistance training training.

The Theory Behind Whey Protein Before Exercise Boosting Fat Metabolism

fasted cardio in the morning fasted cardio whey protein before weight training fasted cardio fasted cardio every morning whey protein before a workout does fasted cardio burn more fat whey protein before exerciseA prevalent hypothesis suggests that whey protein can amplify thermogenesis and fat oxidation, especially when combined with weight training. Thermogenesis refers to the production of heat in the body, which is associated with an increase in metabolic rate and energy expenditure. The amino acids in whey, particularly leucine, are believed to drive these effects. Leucine has an effect on increasing insulin, which suppresses fat metabolism. (Camillo et al., 2014) However, despite being an insulinotropic macronutrient, recent studies have shown that pre-exercise protein consumption doesn’t significantly alter fat oxidation rates (i.e., fat burning), even with a temporary spike in insulin post-consumption.(Impey et al., 2015; Power et al., 2009; Taylor et al., 2013)

Research Studies and Findings on Fasted Cardio vs Whey Protein Before Exercise

Studies that support the theory have shown that whey protein supplementation, when combined with exercise, can improve body composition, including increased fat loss and preservation of lean muscle mass. (Naclerio & Larumbe-Zabala, 2015) These studies suggest that whey protein may positively impact fat metabolism during exercise. Recent research has delved into the effects of whey protein before exercise on fat metabolism. The study investigates the influence of pre-exercise protein consumption on fat metabolism during exercise compared to fasted exercise and if the protein dose impacts this effect.

Study Protocol

a woman is running on a treadmill15 healthy, active males and females underwent cycling exercise at 60% peak power output (i.e., if you’re exercising at 60% of your VO2 max, you’re working at a moderate intensity, not too easy, but not going all out either) for 30 minutes. The subjects consumed either after no protein, 20 or 40 g of whey protein before exercise. The researchers took blood samples and measured fat metabolism during exercise.

Results of the Fasted Cardio vs Whey Protein Before Exercise Study

Fat oxidation/fat burning significantly increased over time during exercise in all groups, while carbohydrate oxidation decreased. The study found that fat oxidation rates (i.e., fat burning) during exercise remained consistent, regardless of whether participants consumed protein or not. There were no significant differences between the fasted cardio and whey protein groups.

Protein dose significantly affected insulin concentrations; specifically, those who consumed more protein (i.e., 40 grams) had higher insulin levels at the beginning of their exercise than those who consumed less or no protein. Interestingly, Resting energy expenditure (i.e., calories you burn at rest) increased post-exercise in all exercise groups, but protein did not affect this.(Peeters et al., 2023)

In sum, there were no differences between the fasted and whey protein groups. This finding aligns with previous studies that showed similar fat oxidation rates between fasted exercise and those who consumed protein. (Gieske et al., 2018; Ratliff et al., 2023)

The Counter-Argument: Whey Protein Before Exercise Does Not Affect Fat Metabolism

Contrary to popular fitness advice, scientific evidence suggests that pre-exercise whey protein consumption doesn’t significantly alter fat metabolism. Consuming whey protein before exercise may be valuable for preserving lean muscle mass while dieting.

Practical Implications for Fasted Cardio

For fitness enthusiasts, the takeaway is clear: fasted workout with cardio and consuming whey protein before exercise yield similar fat metabolism rates, but there may be drawbacks in terms of protein loss when exercising in a fasted state. There don’t seem to be any benefits of fasted cardio compared to fed state aerobic workout with a dose of whey protein before exercise. This debunks the myth that fasted cardio is the ultimate solution for fat loss. Whether you choose to do fasted cardio every morning or consume whey protein before a workout, the potential benefits in terms of fat metabolism seem to be comparable.


Camillo, B. D., Eduati, F., Nair, S., Avogaro, A., & Toffolo, G. (2014). Leucine Modulates Dynamic Phosphorylation Events in Insulin Signaling Pathway and Enhances Insulin-Dependent Glycogen Synthesis in Human Skeletal Muscle Cells. BMC Cell Biology. https://doi.org/10.1186/1471-2121-15-9

Gieske, B. T., Stecker, R. A., Smith, C. R., Witherbee, K. E., Harty, P. S., Wildman, R., & Kerksick, C. M. (2018). 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, 15(1), 56. https://doi.org/10.1186/s12970-018-0263-6

Impey, S. G., Smith, D., Robinson, A. L., Owens, D. J., Bartlett, J. D., Smith, K., Limb, M., Tang, J., Fraser, W. D., Close, G. L., & Morton, J. P. (2015). Leucine-enriched protein feeding does not impair exercise-induced free fatty acid availability and lipid oxidation: beneficial implications for training in carbohydrate-restricted states. Amino Acids, 47(2), 407-416. https://doi.org/10.1007/s00726-014-1876-y

Mortensen, L., Hartvigsen, M. L., Brader, L., Astrup, A., Schrezenmeir, J., Holst, J. J., Thomsen, C., & Hermansen, K. (2009). Differential Effects of Protein Quality on Postprandial Lipemia in Response to a Fat-Rich Meal in Type 2 Diabetes: Comparison of Whey, Casein, Gluten, and Cod Protein. American Journal of Clinical Nutrition. https://doi.org/10.3945/ajcn.2008.27281


Naclerio, F., & Larumbe-Zabala, E. (2015). Effects of Whey Protein Alone or as Part of a Multi-Ingredient Formulation on Strength, Fat-Free Mass, or Lean Body Mass in Resistance-Trained Individuals: A Meta-Analysis. Sports Medicine. https://doi.org/10.1007/s40279-015-0403-y

Peeters, W. M., Cook, L. E., & Page, O. (2023). The effect of pre-exercise protein intake on substrate metabolism, energy expenditure, and energy intake: a dose–response study. Journal of the International Society of Sports Nutrition, 20(1), 2275006. https://doi.org/10.1080/15502783.2023.2275006

Power, O., Hallihan, A., & Jakeman, P. (2009). Human insulinotropic response to oral ingestion of native and hydrolysed whey protein. Amino Acids, 37(2), 333-339. https://doi.org/10.1007/s00726-008-0156-0

Ratliff, K. M., Kerksick, C. M., Moon, J. M., Hagele, A. M., Boring, J. L., Walden, K., Gaige, C. J., Stecker, R. A., Sunderland, K. L., & Mumford, P. W. (2023). Metabolic impact of feeding prior to a 60-min bout of moderate-intensity exercise in females in a fasted state [Brief Research Report]. Frontiers in Sports and Active Living, 4. https://doi.org/10.3389/fspor.2022.1070477


Rothschild, J. A., Kilding, A. E., & Plews, D. J. (2020). Prevalence and Determinants of Fasted Training in Endurance Athletes: A Survey Analysis. International Journal of Sport Nutrition and Exercise Metabolism, 30(5), 345-356. https://doi.org/10.1123/ijsnem.2020-0109

Taylor, C., Bartlett, J. D., van de Graaf, C. S., Louhelainen, J., Coyne, V., Iqbal, Z., MacLaren, D. P. M., Gregson, W., Close, G. L., & Morton, J. P. (2013). Protein ingestion does not impair exercise-induced AMPK signalling when in a glycogen-depleted state: implications for train-low compete-high. European Journal of Applied Physiology, 113(6), 1457-1468. https://doi.org/10.1007/s00421-012-2574-7

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

Whetstine, M. E. C., Croissant, A. E., & Drake, M. A. (2005). Characterization of Dried Whey Protein Concentrate and Isolate Flavor. Journal of Dairy Science. https://doi.org/10.3168/jds.s0022-0302(05)73068-x

Yeo, W. K., Paton, C. D., Garnham, A. P., Burke, L. M., Carey, A. L., & Hawley, J. A. (2008). Skeletal muscle adaptation and performance responses to once a day versus twice every second day endurance training regimens. J Appl Physiol (1985), 105(5), 1462-1470. https://doi.org/10.1152/japplphysiol.90882.2008

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