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Intermittent fasting may not be more effective for weight loss in overweight or obese adults compared to traditional dietary advice, according to a recent review.
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Obesity is a major public health issue and a leading cause of mortality in high-income countries. According to the World Health Organization (WHO), global adult obesity has more than tripled since 1975.
In 2022, approximately 2.5 billion adults were categorized as overweight, with 890 million suffering from obesity.
The popularity of intermittent fasting, which involves extended periods without food, has surged in recent years, largely driven by social media and influencer endorsements claiming rapid weight loss.
One widely-used method includes fasting for 16 hours and eating within an 8-hour window, while others practice 24-hour fasts twice a week.
However, current findings indicate that the advantages of these techniques may be limited.
How was the study conducted?
The researchers analyzed data from 22 randomized clinical trials involving 1,995 adults from diverse regions, including North America, Europe, China, Australia, and South America.
The studies explored various forms of intermittent fasting, including alternate-day fasting, periodic fasting, and time-restricted feeding, with most tracking participants for up to 12 months.
Published in the Cochrane Library, the review compared intermittent fasting to standard dietary guidance (such as the Mediterranean diet) and no intervention. The results showed that intermittent fasting had no clinically significant impact on weight loss compared to conventional dietary advice or no intervention at all.
Participants following intermittent fasting lost, on average, about 3 percent of their body weight—below the 5 percent benchmark that healthcare professionals often regard as clinically significant for improving health outcomes.
Reporting of side effects varied across trials, complicating the ability to draw definitive conclusions. The quality of evidence remains limited due to the small number of trials and inconsistent reporting.
“Intermittent fasting doesn’t seem to be effective for overweight or obese adults looking to lose weight,” remarked Luis Garegnani, the lead author of the study from Universidad Hospital Italiano de Buenos Aires Cochrane Associate Centre.
He also noted the need for caution regarding the enthusiasm surrounding fasting on social media, stating, “While intermittent fasting may be a viable option for some, the existing evidence does not support the excitement that is often showcased online.”
The need for broader research
Few studies have explored the long-term effects of intermittent fasting, which poses a challenge since obesity is a chronic condition. “Short-term studies make it hard to provide guidance for long-term strategies for patients and healthcare providers,” Garegnani added.
Many of the studies focused on predominantly white populations in high-income countries. As obesity continues to escalate in low and middle-income regions, further investigation is necessary in these communities.
The authors emphasized that while the findings provide insights, they cannot be generalized to the entire population due to variations based on gender, age, ethnicity, health status, or pre-existing eating disorders.
“With the current data, it’s challenging to make universal recommendations,” explained Eva Madrid, a senior author from Cochrane Evidence Synthesis Unit Iberoamerica. “Healthcare providers must adopt a personalized approach when advising overweight adults on weight loss strategies.”
