New findings on intermittent fasting: Does it promote more weight loss than other diets?

A comprehensive analysis of clinical trials by renowned researchers published this week in The BMJ suggests that intermittent fasting diets, including strategies such as alternate-day fasting, may have similar benefits to traditional calorie-restricted diets for weight loss and improving cardiometabolic risk factors. However, the researchers caution that the observed effects are relatively modest, and that more long-term studies are needed to confirm these results.

In this meta-analysis, which included 99 clinical trials involving a total of 6,582 adults (66% women, with a mean age of 45 years), different intermittent fasting approaches were compared with continuous calorie restriction diets and unrestricted diets. Intermittent fasting methods analyzed included time-restricted fasting, such as the 16:8 diet (16 hours of fasting followed by an 8-hour eating window); alternate-day fasting, where participants fast for 24 hours every other day; and full-day fasting, such as the 5:2 diet, where participants are allowed to eat freely for 5 days a week and fast for the other 2 days.

The results of the meta-analysis were clear: both intermittent fasting and continuous calorie restriction diets led to modest weight reductions compared to unrestricted diets. However, alternate-day fasting showed the greatest benefits . This approach demonstrated a slight weight reduction compared to continuous calorie restriction and other intermittent fasting modalities, with an average weight loss of 1.29 kg compared to continuous calorie restriction diets. It also showed a slight improvement in total cholesterol and "bad" cholesterol levels compared to time-restricted fasting.

Despite these benefits, the researchers emphasize that the results obtained did not reach the minimum clinical weight loss threshold of 2 kg, which is considered relevant for people with obesity. This indicates that, although intermittent fasting has positive effects on body weight reduction, these effects may not be sufficient to produce significant changes in patients' long-term health.

Another important aspect highlighted by the researchers is the short duration of the trials included in the meta-analysis, which ranged from 3 to 52 weeks, with an average of only 12 weeks. This has raised concerns about the sustainability of the effects obtained, as the impact of long-term intermittent fasting on weight maintenance and risk reduction for chronic diseases such as type 2 diabetes and cardiovascular disease could not be assessed. Furthermore, the researchers noted that the heterogeneity among the analyzed studies—due to variations in fasting strategies and variable trial quality—limits the certainty of the conclusions.

Despite the study's limitations, the researchers concluded that current evidence suggests intermittent fasting diets could be as effective as traditional calorie-restricted diets in terms of weight loss and improving certain cardiometabolic risk factors. However, they emphasize the need for larger, more closely controlled trials to confirm these benefits and determine whether these dietary strategies can be sustained over time without adverse effects.

In response to this study, Ismael San Mauro Martín , a researcher at the CINUSA Group , highlighted that the meta-analysis was conducted "with rigor and breadth" and presented a solid methodological analysis that allowed for accurate estimates. San Mauro also praised the clarity with which the study's authors outlined the limitations of the research, which lends transparency to the conclusions. Regarding the results, San Mauro indicated that, although the weight loss was "modest," alternate-day fasting is positioned as a "valid additional tool" within a personalized dietary approach, with no intention of replacing other more conventional strategies. He also noted that the clinical application of intermittent fasting should be tailored to the needs of each patient, considering their context and individual characteristics.

Maik Pietzner, a professor of health data modeling at Queen Mary University of London , agreed with the study's findings in a statement to the same agency, highlighting the balanced execution of the research. However, Pietzner noted that the weight loss observed across all diets, including those based on intermittent fasting, was relatively modest. He also cautioned about the lack of long-term studies assessing the impact of these diets on weight sustainability and the onset of chronic disease. Pietzner suggested that long-term adherence to these diets can be challenging, which is crucial for any dietary intervention to be truly effective.

Furthermore, Pietzner emphasized the need to investigate the effects of intermittent fasting diets on muscle mass , an aspect he believes has been overlooked in most obesity studies. The effects of these diets on preserving muscle mass are especially important in the context of pharmacological interventions for obesity, which have already begun to address this concern.

In summary, the study provides valuable information about intermittent fasting diets, but emphasizes that, while they can be helpful in weight loss , they should not be considered a one-size-fits-all solution. Dietary strategies should be personalized and tailored to each patient's needs, with a focus on long-term sustainability and improved overall health.