A YouTube video walks through every hour of a 36-hour fast, but the experts quoted alongside it say the science doesn’t quite hold up

A YouTube video simulating what happens inside the human body during a 36-hour fast has racked up millions of views since it was posted. The video, from the channel Wellness Wise, uses detailed visuals of internal structures to walk viewers through a series of metabolic claims, hour by hour, across a 56-minute runtime. The channel has 198,000 subscribers.

The simulation maps out a timeline of alleged physiological changes. It claims digestion slows and insulin drops within four hours of eating, glycogen stores are tapped by the eight-hour mark, and the body enters ketosis by hour 12. The video goes further after the 16-hour point, suggesting a cellular cleanup process called autophagy begins, before asserting that insulin sensitivity improves at 24 hours, growth hormone rises at 30, and autophagy peaks at 36 hours, supporting what the video calls a “metabolic reset.”

The story was highlighted by Bored Panda, which noted the sharp divide between the video’s confident health claims and the far more cautious views of researchers. Autophagy is a real biological process in which cells break down and recycle damaged components, as the Cleveland Clinic explains, but experts say presenting it as something that can be reliably triggered or timed through fasting oversimplifies what the science actually supports.

The viral fasting video is getting attention its expert voices probably didn’t intend

James Betts, a professor of metabolic physiology at the University of Bath, pushed back on the premise directly. “There are a lot of proposed benefits to running on fats,” he said, adding that the research “hasn’t really been borne out in human beings” and that dramatic short-term benefits are not what studies have shown. The bulk of existing autophagy research has been conducted on animals, and scientists have not yet established reliable timelines for triggering the process in humans, or confirmed that the benefits observed in animal models translate cleanly to people.

Beyond the scientific gaps, health professionals have raised concerns about physical side effects. Organizations like The Emily Program have noted that extended fasting can produce dizziness, headaches, fatigue, sleep disturbances, and digestive problems, as well as longer-term risks including nutrient deficiencies and reproductive health impacts. Amid broader scrutiny of food-related content on social media, a TikToker’s viral food safety warning about a restaurant meal drew similar waves of public concern earlier this year.

A December 2022 study by Kyle T. Ganson, an assistant professor at the University of Toronto, examined the habits of 2,762 Canadian adolescents and young adults and found a link between intermittent fasting and disordered eating patterns, with the correlation particularly pronounced among women. Adam Collins, an associate professor of nutrition at the University of Surrey, offered a partial defense of the practice, suggesting extended fasts can help with “metabolic flexibility,” though he represents a minority view in the academic literature.

Former UK Prime Minister Rishi Sunak has been publicly associated with 36-hour fasting, though health experts note that prominent practitioners do not make the practice appropriate or safe for everyone. Amid ongoing questions about food labeling and consumer health claims, a TikToker’s investigation into Walmart’s meat weights also recently went viral, highlighting how quickly food-related content can reach millions without independent verification.

Anyone considering major dietary changes, including prolonged fasting, is advised to consult a healthcare provider first, particularly those with underlying conditions such as diabetes, or those who are pregnant or breastfeeding.