Word on the town is that fasted cardio is the thing to do if you’re looking for fat loss… and realistically, nothing feels better than getting out of bed in the morning, hitting the treadmill or bike, and getting your cardio out of the way first thing.
But if you’re looking for muscle growth or strength gains, should you be hitting the weights first thing in the morning without food in your belly?
Research is mixed, so keep reading to find out for yourself.
By the end of this article, you should have a solid understanding of what happens in your body in both the fed and fasted state, and whether lifting fed or fasted is more beneficial for your long-term goals and overall health.
What’s Happening: The Fed State And The Fasted State
The fed state, also referred to as the absorptive state, is the 4-to-6-hour period (on average) after a meal is consumed whereby food is broken down, assimilated, and shuttled through the body for use. If not used, these compounds (glucose, amino acids, lipids) are stored.
When it comes to your training, the absorptive, or anabolic state is especially important because it’s when peripheral tissues, primarily skeletal muscles, buffer ingested glucose and store it in muscle tissue and the liver in the form of glycogen, which can be easily accessed when needed.
Insulin secretion also occurs in the fed state in response to glucose, which stimulates the storage of fuels and the synthesis of proteins, among other physiological activities 1.
The fasting state, also called the post-absorptive state, is the period whereby food has been completely digested, absorbed, and/or stored.
During the fasted state, the body initially relies on glycogen stores to support energy needs. As blood glucose drops, however, insulin levels follow suit, and glycogen and triglyceride storage come to a halt.
But for organs to function, blood glucose levels must be maintained within a specific range.
Glucagon is released from the pancreas and acts upon the liver to stimulate glycogen breakdown into glucose via the gluconeogenic pathway, as well as the release of fatty acids via hydrolysis of triacylglycerols.
Peripheral tissues and the brain then use this glucose to supply energy. Once glycogen stores have been depleted, gluconeogenesis begins in the liver; gluconeogenesis is the process of creating glucose from non-carbohydrate substrates (triglycerides and amino acids).
In the absence of sufficient glucose, the liver and muscle use fatty acids to meet their own energy needs so that glucose is conserved for use by the brain 1.
Many of the benefits that occur during the fasted state are thought to be mediated through changes in metabolic pathways and cellular processes including stress resistance, lipolysis, and autophagy (cellular clean up) 2.
Benefits Of Fasted Weight Training
There are tons of available studies on the benefits of fasting for chronic diseases and weight management, but when it comes to athletes and performance, the research is sparse.
Study # 1
One of the best studies to date on intermittent fasting and strength training was published in the Journal of Translational Medicine in 2016 and dug deep into the impact of time-restricted feeding (the 16/8 method of IF) on basal metabolic rate, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males 2.
Researchers found interesting results. Their data showed that time-restricted feeding used in conjunction with a resistance training program is capable of maintaining muscle mass, reducing body fat, and reducing inflammation markers.
However, it also appeared to reduce anabolic hormones such as testosterone and IGF-1, both of which are critical to muscle protein synthesis. Researchers noted that changes in anabolic hormone levels did not contribute to comprised muscular strength, though.
One mechanism behind the results seen are increases in levels of adiponectin, which acts in the brain to increase energy expenditure and stimulate weight loss 3.
Another proposed mechanism was enhanced thermogenic response to epinephrine, a stress hormone.
It’s important to keep in mind that the results of this study—muscle maintenance, fat loss, and decreased inflammation—were achieved by keeping caloric intake stable, despite reducing the frequency of meals 2.
Study # 2
Another study published in 2017 sought a similar course of action to look at how eight weeks of resistance training (RT) with and without time-restricted feeding (TRF) affected nutrient intake, and changes in body composition and muscular strength in active young males 4.
The time-restricted feeding protocol consisted of consuming all calories within a four-hour window for four days per week, but did not specify the type or quantity of food consumed. Resistance training was performed three days per week and consisted of both upper and lower body workouts.
Unlike the previous study, caloric intake was reduced by approximately 650 kcal per day during time-restricted feeding days, but did not appear to have any effect on total body composition.
Contrary to the other study, results showed that time-restricted feeding decreased energy intake without altering body composition 4.
However, TRF did not appear to compromise any improvements in muscular strength and did not lead to a decrease in lean soft tissue.
Researchers concluded TRF might be beneficial for reducing caloric intake and maintaining lean mass, but it may hinder hypertrophic adaptations to resistance training.
Based on the results of these two studies, a modified intermittent fasting protocol in the form of time-restricted feeding (not reducing caloric intake) could be a feasible option for strength athletes looking to lose fat and enhance performance, without compromising strength and muscle mass.
Benefits Of Fed Weight Training
We’re probably all familiar with weight lifting in the fed state; among anyone looking to maximize performance and boost muscle growth, it’s the only way to train.
We’ve been conditioned to believe that consuming the right pre-workout nutrition can boost our athletic performance while also boosting post-workout muscle repair.
And there are studies to back it up.
However, training in the fed state mostly depends on the type of training you’re doing. Powerlifters and endurance athletes, for example, find loads of benefits from consuming pre-workout meals.
Interestingly, though, studies support the fact that whether resistance training is done in a fed or fasted state, there are no significant changes in body mass or body composition experienced in either state 5—they’re pretty much on a level playing field.
Also, markers of immune function and inflammation remained unchanged when performed in a fed compared to a fasted state.
This lack of change between the fed and fasted state may be partly attributed to nutrient timing.
Consuming a meal 60 minutes before training appears to elicit minimal benefit, but when consumed 3-4 hours prior to exercise, performance may be categorically improved 6, 7.
However, there have been several studies that support pre-exercise feeding, especially carbohydrates, for boosting continuous aerobic exercise performance 8.
All in all, whether you train fasted or fed comes down to how you train and what you’re looking to achieve.
If you’re trying to pull your max on a deadlift, the chances are that won’t happen on an empty stomach because you don’t have the ATP supply to support it.
But if you’re doing a relatively light lift that won’t require loads of immediate ATP availability or a 30-minute run, you’ll probably be fine.
- JM Berg, JL Tymoczko, L Stryer. Biochemistry. 5th edition. New York: W H Freeman; 2002. Summary.
- T Moro, G Tinsley, A Bianco, et al. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. J Transl Med. 2016; 14(1): 290.
- NE Gulcelik, M Halil, S Ariogul, A Usman. Adipocytokines and aging: adiponectin and leptin. Minerva Endocrinol. 2013; 38(2): 203-210.
- GM Tinsley, JS Forsse, NK Butler, et al. Time-restricted feeding in young men performing resistance training: A randomized controlled trial. Eur J Sport Sci. 2017; 17(2): 200-207.
- K Trabelsi, SR Stannard, Z Ghlissi, et al. Effect of fed- versus fasted state resistance training during Ramadan on body composition and selected metabolic parameters in bodybuilders. J Int Soc Sports Nutr. 2013; 10(1): 23.
- PD Neufer, DL Costill, MG Flynn, JP Kirwan, JB Mitchell, J Houmard. Improvements in exercise performance: effects of carbohydrate feedings and diet. J Appl Physiol. 1987 Mar; 62(3): 983 -8.
- WM Sherman, G Brodowicz, DA Wright, WK Allen, J Simonsen, A Dernbach. Effects of 4 h preexercise carbohydrate feedings on cycling performance. Med Sci Sports Exerc. 1989 Oct; 21(5): 598 -604
- MJ Ormsbee, CW Bach, DA Baur. Pre-exercise nutrition: the role of macronutrients, modified starches and supplements on metabolism and endurance performance. Nutrients. 2014 Apr; 6(5): 1782 -808