Many people incorporate periods of fasting into their weekly routine to boost energy, lose weight, or improve metabolic health. But should a strength training session take place during that fasting window, or is it better to wait until after you’ve had a meal? Here’s what experts say.
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. Examples include:
“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, ABAAR, Vice President of Women’s Health, Hormone and Lifestyle Optimization at LifeMD, told Health.
Studies suggest that fasted strength training can be effective, and may be able to enhance fat loss by promoting the breakdown of stored fat.
However, 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.
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.
While some studies have found no difference in performance between fasted and non-fasted exercise, others have concluded that the practice could actually stifle your gym session.
Fasting can blunt performance, particularly during explosive or high-volume workouts, Lucas warned.
“Fasting is also an added stressor, which may or may not be beneficial depending on your current metabolic state and adrenal health,” he said.
Can Fasted Strength Training Be Dangerous?
Some people may 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.
Plus, the effects of strength training during a fast may not affect all people equally. For example, some women may thrive while strength training in a fasted state, while others may find it disrupts gains and performance while zapping their energy.
Increasing your activity levels in general is a healthy way to support weight loss. However, fasted workouts may or may not be helpful, depending on your health goals:
- 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.
