Joaquin Phoenix reacted with surprise after hearing a podcast host describe working out during extended fasts.
The Joker actor has followed a vegan lifestyle since he was three and a half, and over the years he has become well known for dramatically changing his diet when preparing for certain roles.
While getting ready to play Arthur Fleck, Phoenix previously revealed that he shed more than 50 pounds. At the time, he said his meals were made up mostly of steamed vegetables and lettuce.
“I’m now 49, I probably shouldn’t do this again. This is probably it for me,” he said during a press tour for the movie at the time.
More recently, Phoenix appeared on the This Past Weekend w/ Theo Von podcast, where the conversation turned to fasting and exercise.
Von explained that he had been doing frequent fasts lately, drinking only water.
“And a little bit of salt, but you even look foward to the salt,” the host laughed, before telling the Hollywood legend he even went to the gym during his fasts, which typically last a day to 36 hours. However, the host confirmed that the longest he had fasted for was 73 hours – but most recently, has been fasting for 24 hours once a week.
“Yeah that’s great, it’s good for you,” the actor responded. “But are you sure you should work out while your doing it?” he asked the host, who said he ‘wasn’t sure’.
“Maybe look into that,” Phoenix added. “I don’t know, but I remember doing that and I didn’t feel good. Maybe it was that.”
Medical experts say fasting and exercise can be combined in some cases, but the timing, the type of fast and a person’s overall health matter a lot. Shorter fasts are generally easier to manage than longer ones, and anyone who is pregnant, breastfeeding, underweight, has diabetes, kidney disease, a history of eating disorders or takes medication that affects blood sugar should be especially cautious.
Athletic trainer Jennifer Dix told Cleveland Clinic that there are ‘safe ways to work out while fasting’.
“When you’re physically active while fasting, you have a much higher risk of dehydration and heat illness,” she said. “It’s something to be very cautious about.”
She also noted that the best time to train is when the body is most hydrated, meaning workouts are often safer either before a fast begins or after it ends.
Because research in this area remains limited, Dix advises people to think carefully about timing, eat well beforehand, adjust workout expectations, and pay close attention to how they feel.
If water is allowed during a fast, staying hydrated before and after exercise becomes especially important.
For situations where even water is restricted, such as some religious fasts, Dix offered a stronger warning.
“There are risks to exercising when you can’t hydrate and don’t have any fuel in your system.”
“You’ve got to be cautious and monitor yourself for dehydration issues,” she added, which include dizziness, headaches and inability to focus.
Dr Donald Grant, GP and Senior Clinical Advisor at The Independent Pharmacy, also said longer fasts can place a heavy strain on the body.
“Prolonged fasting can have a significant impact on our bodies. After 36 hours, the body may have used much of its available glucose, meaning it will then rely on stored fat for energy,” Dr Donald Grant, GP and Senior Clinical Advisor at The Independent Pharmacy, says.
He explained that blood sugar levels may fall during that period, which can bring on headaches, weakness, fatigue, irritability and trouble concentrating.
“Extended fasting places stress on the body, so anyone with a long-term health condition, those taking regular medication, or women who are pregnant or breastfeeding should always seek medical advice before attempting this type of fast,” he warns.
While intermittent fasting has become increasingly popular, health experts say the evidence for its long-term benefits is still mixed, and it is not the right approach for everyone. For people who do choose to fast, hydration, moderation and medical guidance are key, especially if exercise is part of the routine.