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8 min read<\/p>\n8 min read<\/p>\n
Picture this: You wake up at the crack of dawn with just enough time to make that 6 a.m. workout class, if you leave home\u2026now. So, you speed to the studio without having breakfast, and feel fine during the workout. Since you didn’t notice any issues, does that mean it’s totally okay to do fasted workouts moving forward?<\/p>\n
First, a reminder: \u201cFasting is defined as a period of time when you have not eaten for 8 and 12 hours,\u201d or longer, says Nadia Agha, PhD, Assistant Teaching Professor of Kinesiology at Rice University. Fasted workouts are quite controversial: The science<\/a> used to suggest that they\u2019re more effective than fed training when it comes to growing muscle<\/a>, muscular oxidative capacity<\/a> (which you need for high bursts of energy in a workout), and weight loss<\/a>. Some endurance athletes<\/a> even swear by fasted workouts.<\/p>\n Meet the experts:<\/strong> Nadia Agha<\/a>, PhD, is an Assistant Teaching Professor of Kinesiology at Rice University. Grace Horan<\/a>, ACSM-EP, RRCA Coach, is an exercise physiologist at the Hospital for Special Surgery in New York City. Michael Fredericson<\/a>, MD, is the Director and Professor of Physical Medicine and Rehabilitation at Stanford University, and team physician for Stanford Track & Field and Swimming.<\/p>\n However, more recent research<\/a> shows that skipping a meal before a sweat sesh may not be as beneficial as previously thought. Ahead, learn what the new science says about fasted workouts, and whether or not they\u2019re good for anyone, according to experts.<\/p>\n Your Body on a Fasted Workout<\/strong><\/p>\n Let\u2019s go back to high school science class for a sec: There are three energy pathways<\/a>\u2014fueled by carbohydrates, fats, and proteins\u2014that your body taps into when you exercise (or do anything else), according to the Cleveland Clinic<\/a>. While all three work together to sustain your workout, one pathway will provide the most effective source of energy, depending on the kind of exercise you\u2019re doing.<\/p>\n For instance, anaerobic exercise (like HIIT<\/a>, heavy resistance circuits, or sprint intervals<\/a>) uses carbs to produce spikes of effort. Whereas aerobic exercise, like running or biking, relies on both carbs (primarily stored as glycogen) and fats (fatty acids) to keep you going. And exercises involving explosive power<\/a>, like box jumps or power cleans, rely on molecules called creatine<\/a> phosphate that the body stores in limited amounts, but naturally replenishes with rest (and can be nourished<\/a> with lean proteins) says Grace Horan, ACSM-EP, RRCA Coach, an exercise physiologist at Hospital for Special Surgery in New York City.<\/p>\n When you\u2019re doing a fasted workout, your body doesn\u2019t have its usual energy sources to pull from\u2014namely, glycogen. Instead, it resorts to alternative sources like stored fat \u201cto meet energy demands of daily functional and sport-specific activity,\u201d says Horan. While this might seem positive for anyone with weight loss goals, there are a number of other factors to consider before skipping a pre-workout meal. (More on that below!)<\/p>\n What the Evidence Actually Shows About Fasted Workouts<\/strong><\/p>\n According to a substantial amount of research<\/a>, when muscle glycogen (energy) is limited, \u201cathletes may see decreases in how much work they can do during a session, or [experience] earlier fatigue,\u201d says Horan. \u201cIt may reduce training quality for some individuals and it delays the availability of amino acids<\/a> needed to support muscle protein synthesis,\u201d or how muscles break down protein for energy and repair. Since fasting can cause you to generate less energy needed for a workout, it may take longer for you to build muscle<\/a> than it would with consistent fueled workouts, she adds.<\/p>\n However, some research tells a different story: A small 2023 study in Nutrients<\/a> tracked 11 female CrossFitters\u2019 progress through a range of exercises (like the standing long jump and a handgrip strength test) to gauge how being fasted for 24 hours impacted their power, overall strength, and speed. After completing the tests in both fasted and fed states, the researchers found little difference between the participants\u2019 performances, and suggested that fasting doesn\u2019t impair workout performance.<\/p>\n Another small 2025 study in Nature Communications<\/a> had 13 participants (seven men and six women) fast for seven days as they exercised and worked their jobs. During this time, they underwent testing for their resting metabolic rates, completed muscle biopsies and DXA scans, and completed strength and endurance testing. The participants maintained muscle strength, but their high-endurance capacity decreased.<\/p>\n While the data from these smaller studies is compelling, most experts believe you\u2019re better off strength training in a fed state. \u201cConsuming protein and carbohydrates before exercise can help support training performance, allowing an individual to potentially lift heavier loads, which is an important driver of muscle growth,\u201d Horan adds.<\/p>\n Data is murky on how fasting impacts other anaerobic workouts.<\/strong><\/p>\n One small 2025 study in the Journal of Bodywork and Movement Therapies<\/a> had 14 trained men perform various workouts (an anaerobic sprint test and leg and bench press repetitions to failure) in fed and 14-hour fasted states. Their anaerobic performance increased by 10 percent during the fasted state, and they were able to complete more leg presses to exhaustion.<\/p>\n However, more research is needed to assess how this approach may affect women. Horan says that because anaerobic workouts require \u201creadily available carbohydrates<\/a>,\u201d athletes are better off fueling ahead of their workout.<\/p>\n Fasting may be harmful for long endurance workouts.<\/strong><\/p>\n \u201cFasting during [endurance] exercise lasting longer than two hours can negatively impact your perceived exertion<\/a> and overall performance,\u201d says Agha. When you lose touch with your rate of perceived exertion (how much effort you think you\u2019re putting in), you may push harder than intended. Research backs up this notion: The above study in Nature Communications found that participants\u2019 VO2 max<\/a> (how much oxygen your body can transform into energy while working out) suffered during a high-intensity exercise test after fasting for six days.<\/p>\n Additionally, \u201cconsistently underfueling can contribute to Relative Energy Deficiency in Sport (RED-S), which can disrupt menstrual function and impact bone health<\/a>, recovery, and performance,\u201d Horan adds. If left untreated, athletes may experience heightened risk of menstrual irregularities<\/a>, impaired cardiovascular health<\/a>, and premature labor and pre-term delivery<\/a> (for those diagnosed prior to conception). RED-S can also impact how well you recover and build muscle<\/a>.<\/p>\n So, it\u2019s imperative to fuel before long endurance sessions, like training for a marathon<\/a> or triathlon. A 2024 study in Frontiers in Physiology<\/a> looked at marathon performance research over the past 15 years and highlighted how important carbs, protein, and electrolytes are for maintaining energy, skeletal muscle mass, and hydration, respectively, when training for a marathon.<\/p>\n That said, fasting <\/strong>may<\/strong> support shorter, low-intensity aerobic workouts. <\/strong><\/p>\n Fasting before a brief recovery run or chill walk or bike ride may help some athletes. \u201cDuring these sessions, exercising in a fasted state may increase the proportion of fat being used as fuel during the workout itself and may stimulate some metabolic adaptations related to fat oxidation,\u201d says Horan. (Meaning, when implemented strategically as part of a cohesive training program, your body can become more efficient at switching from using glycogen to fat for fuel.)<\/p>\n However, she notes that those metabolic changes don’t necessarily lead to meaningful results over time: \u201cLong-term outcomes related to fitness, body composition<\/a>, and endurance performance are often better when the nutrition intake matches the training load.\u201d<\/p>\n Build muscle and lose fat with our exclusive body recomp guide<\/a><\/p>\n Fasted workouts might accelerate weight loss.<\/strong><\/p>\n Since your body uses fat for energy when it doesn\u2019t have glucose, \u201cfasted workouts could be an advantage if you’re trying to lose weight,\u201d says Michael Fredericson, MD, Director and Professor of Physical Medicine and Rehabilitation at Stanford University, and team physician for Stanford Track & Field and Swimming.<\/p>\n Some studies have looked at intermittent fasting<\/a>\u2014or only eating during certain hours of the day\u2014in the context of fasted workouts. A 2025 study in Nutrition<\/a> had participants diagnosed as overweight or obese participate in moderate exercise and either follow an intermittent fasting plan or a calorie-restricted diet. (It\u2019s unclear how the study defines \u201cmoderate exercise,\u201d but according to the CDC<\/a>, it\u2019s any movement that raises your heart rate and causes you to breathe harder than normal and break a sweat.)<\/p>\n After four weeks, participants in the intermittent fasting group exhibited a \u201cstatistically significant\u201d amount of weight loss compared to the other group. During the four-week maintenance period, both groups experienced weight loss and improvements in body composition. At the six- and 12-week check-ins, the same group showed \u201csuperior\u201d weight maintenance and less weight regain. However, research on how non-overweight populations might react to this approach is still lacking.<\/p>\n Additionally, a 2021 meta-analysis of studies in Physiology and Behavior<\/a> looked at the impact of intermittent fasting (such as time-restricted feeding, alternate day fasting<\/a>, and periodic fasting) and resistance training on the body. It concluded that pairing the two methods could result in lower body mass, body mass index (BMI)<\/a>, and body fat percentage without losing muscle. Still, the research wasn\u2019t clear on what type of intermittent fasting provided the highest results in the long term.<\/p>\n Who, if Anyone, Can Benefit From Training Fasted<\/strong><\/p>\n It may be easier to lose weight<\/a> with fasted workouts than fed ones, at least in the short term. The key to losing weight is to remain in a calorie deficit<\/a> (or consuming less calories than you burn), so it can be helpful to pair intermittent fasting with moderate exercise, including resistance training<\/a>, says Agha.<\/p>\n However, fasted workouts may not be a long-term solution for those with weight loss goals \u201csince body composition changes are driven more by total energy balance, daily nutrition, and consistency over time,\u201d Horan says.<\/p>\n Overall, your fitness performance or gains likely won\u2019t improve in the long term with fasted workouts. For folks with other fitness goals, like \u201chigh-intensity sessions, long endurance efforts, or strength training<\/a>, where fueling plays a critical role in performance and adaptation,\u201d fasted workouts are not the move, says Horan.<\/p>\n You should always make sure your body has enough energy for workouts and to just get through the day, adds Fredericson.<\/p>\n If you want to try a fasted workout, connect with your healthcare provider to see what they think in the context of your overall wellness and fitness status. If you get the go-ahead, be sure to monitor how you feel during the workouts. Say you\u2019re dizzy, lightheaded, or not performing as you should\u2014in that case, \u201cfasted workouts may not be ideal for you,\u201d says Agha.<\/p>\n![\"Essential](\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2026\/07\/5eaaf924-057a-4656-98ea-ff565f1aef3b.jpeg\" "\\"Essential")
<\/a>New Balance Essential Run BraCredit: Courtesy![\"Ebb](\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2026\/07\/1752607719-LW1AX1S_052402_1.jpg\" "\\"Ebb")
<\/a>lululemon Ebb to Street Tank TopCredit: Courtesy![\"Airlift](\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2026\/07\/1771516115-screenshot-2026-02-19-at-10-47-41-am-699730a133328.png\" "\\"Airlift")
<\/a>Alo Airlift High-Waist Suit Up LeggingCredit: Courtesy<\/p>\n
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