Fasting has become increasingly popular, with many people finding that it boosts energy, supports weight loss, and improves metabolic health.
If you’re engaging in fasting, you may wonder if lifting weights is safe, or even beneficial, while fasting. Should strength training take place during your fasting window, or is it better to wait until after you’ve had a meal?
Keep reading to dive into the research and decide whether combining fasting and resistance training can help you reach your fitness goals.
Fasting involves restricting calorie intake for any period of time. Intermittent fasting (IF), which is one of the most popular and well-researched forms of fasting, involves alternating periods of fasting and normal calorie intake, on a recurring basis. The 16:8 method and alternate-day fasting (ADF) are examples of IF.
“The benefits of fasting for metabolic health are well-documented, including improved insulin sensitivity, reduced inflammation, and, in some cases, fat loss,” Doug Lucas, DO, FAAMM, AOBOS, ABAARM, Vice President of Women’s Health, Hormone and Lifestyle Optimization at LifeMD, told Health.
Overall, there’s no strong evidence suggesting that strength-training in a fasted state is superior to training in a fed state for muscle growth or performance.
Studies suggest that fasted strength training can be safe and effective. However, a recent study found that young adults who performed resistance training twice weekly for 12 weeks after an overnight fast experienced similar improvements in muscle thickness, strength, and power compared to those who trained in a fed state after eating a carbohydrate-rich meal.
Although fasted training might enhance fat loss through promoting the breakdown of stored fat, he warned that fasting can blunt performance, particularly during explosive or high-volume workouts. “Fasting is also an added stressor, which may or may not be beneficial depending on your current metabolic state and adrenal health,” he said.
Studies investigating the effects of fasting on exercise have had mixed results, with some finding no difference in performance while others have found that fasting decreases performance. In fact, combining fasting periods of over 24 hours with prolonged exercise and very high-intensity exercise is more likely to have a negative impact on exercise performance.
Are Men and Women Affected Differently?
Some women may thrive while strength training in a fasted state, while others may find it disrupts gains and performance while zapping their energy.
Some people may also feel dizzy or faint when working out in a fasted state, which can be dangerous if lifting heavy weights. Dehydration can increase the risk of experiencing negative side effects, so if you’re working out fasted, it’s important to make sure you’re properly hydrated.
Increasing your activity levels in general is a healthy way to support weight loss. However, you may wonder if workout timing is important when you’re fasting.
- If fat loss is your goal: Try working out in the morning. “Try extending your overnight fast and train before your first meal,” Lucas suggested.
- If improving exercise performance or strength is your goal: Lucas doesn’t recommend working out in a fasted state. “A fed state supports better performance, strength, and recovery,” he explained.
Ro Huntriss, RD, Chief Nutrition Officer at Simple, agrees. “Training in a fed state, ideally one to two hours after a balanced meal, is more supportive of strength, energy, and recovery,” Huntriss told Health.
“For those following a time-restricted eating pattern, like 16:8, exercising during the eating window or shortly after breaking the fast allows for pre- and post-workout nutrition, which is key for muscle protein synthesis,” she explained.
Different fasting protocols, such as intermittent fasting and prolonged fasting, can influence how you time your workouts.
Here’s a breakdown of how each protocol impacts workout timing and energy availability:
- 16:8: This fasting method involves eating within an 8-hour window. “A 16-hour fast with an 8-hour eating window may be the most flexible for strength training,” Morgan Walker, MS, RDN, told Health. “Training in the middle of the eating window (for example, 1–2 hours after your first meal) will allow for pre and post-training nutrition to support muscle retention and performance,” she said.
- One Meal a Day (OMAD): “If you’re only eating dinner, working out in the morning without replenishing afterward could hurt recovery and energy levels,” Lucas warned. If you’re following OMAD, Lucas suggested training before your meal if your schedule allows.
- Alternate-day fasting (ADF): This method may be trickier to balance in terms of workout timing. “Recovery windows become compressed, so training days need to be more strategic,” explained Lucas. Lucas recommended training on feasting days and resting or working on recovery exercise, like stretching, on fasting days, depending on how you feel.
Though fasted strength training has its place, the most important aspect of strength training is consistency.
“Until you have a consistent solid base, adding fancy tools like fasted training can derail success,” said Lucas. He recommended holding off on adding in tools like fasting until you’ve trained consistently and have added on intensity.
“Then when you are looking for ways to progressively overload and help with specific goals like fat loss, consider adding in fasted training to see how you feel and perform,” he said.
“When eating before a workout, include a mix of carbohydrates and protein, for example, Greek yogurt with fruit or a protein smoothie with oats,” recommended Huntriss.
After training, Lucas and Huntriss recommend consuming a protein-rich meal, ideally containing between 20–30 grams of high-quality protein, to support muscle repair, along with carbohydrates to replenish glycogen stores. This could be as simple as a chicken or tuna salad sandwich, or a smoothie made with plant-based protein, a frozen banana, and berries.
If you’re interested in strength training while fasted, you may wonder whether or not it’s safe and effective.
While fasted strength training may benefit fat loss, overall, there’s no evidence that this method is superior to fed training in terms of exercise performance, recovery, or muscle building. Also, pairing fasting with strength training may harm performance, especially when engaging in prolonged fasting and intense workouts.
If you choose to work out while fasted, it’s best to plan your workouts around your eating schedule to ensure your body has the proper fuel to get you through your training session.
