Intermittent Fasting: New Study Questions Weight Loss Hype

With intermittent fasting, individuals extend periods without food as part of their daily routine. The appeal? Simplified weight management. However, a comprehensive review is now questioning the widespread enthusiasm surrounding this dietary approach when compared to more traditional methods.

Intermittent fasting is the subject of a new review paper that suggests its effectiveness may be less substantial than many believe. For adults struggling with overweight or obesity, the weight loss achieved through intermittent fasting is likely no greater than that seen with other dietary strategies, according to the British organization Cochrane, which regularly publishes high-quality reviews of health-related topics. It’s important to note, however, that the results are subject to considerable uncertainty.

“So far, these are only indications, not proof – meaning we cannot yet assess the effectiveness of intermittent fasting with sufficient certainty,” explained Jörg Meerpohl from the University Hospital of Freiburg, director of Cochrane Germany, who was not directly involved in the research.

The analysis, led by Luis Garegnani from the Universidad Hospital Italiano in Buenos Aires, Argentina, encompassed 22 studies involving nearly 2,000 participants from North America, Europe, China, Australia and South America. The researchers aimed to determine whether intermittent fasting is more effective for weight loss than conventional dietary advice for adults with overweight or obesity, and how it impacts quality of life.

The review found that intermittent fasting demonstrated no better, or only a slightly better, effect on weight loss compared to other methods. The report, published in the “Cochrane Database of Systematic Reviews”, also revealed no evidence of a noticeable improvement in quality of life. “Intermittent fasting may be a reasonable option for some people, but current research does not justify the enthusiasm we are seeing on social media,” Garegnani stated.

According to data from the World Health Organization (WHO), approximately 2.5 billion people worldwide were overweight in 2022, representing 43 percent of adults aged 18 and over. Of these, 890 million – 16 percent of all adults – were classified as obese.

“Weight loss remains the most important strategy for reducing the health risks and social consequences of overweight and obesity,” the Cochrane analysis emphasizes. However, due to the current state of research, making a general recommendation for a specific approach is challenging, according to co-author Eva Madrid from the Universidad de Valparaíso in Chile.

Previous meta-analyses have consistently shown no particular advantage of intermittent fasting over comparable diet interventions, explained Stefan Kabisch from the Charité in Berlin, who was not involved in the Cochrane study. Noticeable weight loss typically occurred only when compared to making no changes to one’s diet at all.

the evidence remains uncertain – largely because of the wide variety of intermittent fasting methods. Examples include the 16:8 method (eating for eight hours and fasting for 16), the 5:2 method (eating normally five days a week and restricting calories on two days), and Alternate Day Fasting (ADF), which involves fasting every other day.

“The entire study includes dozens of types of intermittent fasting that shouldn’t be lumped together,” says Kabisch. “Long-term data, such as studies lasting more than two years, are practically non-existent.” Small participant numbers and missing data are common in analyses in this field – even the studies selected for the Cochrane review had methodological weaknesses, as noted by the researchers.

However, Kabisch clarifies that the hype surrounding intermittent fasting was never supported by convincing human studies, and was premature and even unjustified.

Annette Schürmann from the German Center for Diabetes Research (DZD) also points out that the selected studies were extremely heterogeneous, varying in terms of participants and fasting types. It’s not possible to draw a definitive conclusion that intermittent fasting generally has no better effect on weight loss. This proves also known from animal studies that intermittent fasting can have a positive effect on blood sugar levels.

the new data suggests that if someone wants to lose weight and improve their health, they can choose the method that best suits them – ideally with medical advice and support, and one that they can maintain long-term. The key takeaway is that intermittent fasting isn’t a guaranteed shortcut, and its effectiveness appears to be comparable to other well-established dietary approaches.