A new systematic review and network meta-analysis of 99 randomized clinical trials suggests that alternate-day fasting may offer a modest short-term benefit for weight loss compared with other intermittent fasting strategies and traditional calorie-restricted diets.

Modest but Statistically Significant Weight Loss With ADF

Across 6,582 adults—most of whom were overweight or had conditions such as type 2 diabetes, metabolic syndrome, or fatty liver disease—alternate-day fasting (ADF) was associated with the greatest weight loss among the dietary strategies studied. Compared with typical eating patterns, participants on ADF lost an average of 3.4 kg. ADF also showed small, statistically significant weight differences compared with:

• Continuous energy restriction (CER): −1.29 kg

• Time-restricted eating (TRE): −1.69 kg

• Whole-day fasting (WDF): −1.05 kg

While these differences reached statistical significance, the study noted they were below the threshold typically considered clinically meaningful (2.0 kg). Certainty of evidence was rated moderate for these comparisons.

Weight Loss Most Evident in Short-Term Studies

Benefits of ADF and other diet strategies were most apparent in trials lasting fewer than 24 weeks. In longer studies (≥24 weeks), all diets—including CER and intermittent fasting approaches—produced only modest weight reductions when compared with ad-libitum (unrestricted) eating, and no meaningful differences emerged between the diets themselves.

This pattern may reflect both the challenges of long-term adherence and the limited number of extended-duration trials included in the analysis.

Lipid Effects Favor ADF

Beyond weight loss, ADF was also associated with improved lipid profiles, including reductions in:

• Total cholesterol

• Non–high-density lipoprotein (HDL) cholesterol

• Triglycerides

These improvements were more pronounced compared with TRE and WDF, although differences across all groups were generally small and supported by low to moderate certainty of evidence.

Notably, no meaningful differences between diets were observed for HbA1c or HDL cholesterol levels.

Adherence and Side Effects

Overall, adherence rates were high in most studies but tended to decline in trials longer than 6 months, especially for WDF. Reported side effects across all diet strategies were typically mild, such as nausea, dizziness, and hunger. A single serious adverse event of hypoglycemia with a fall was reported during one ADF study.

Bottom Line

The authors concluded that all structured diet interventions, including intermittent fasting and continuous calorie restriction, offer benefits for weight loss over unrestricted eating. Among intermittent fasting strategies, alternate-day fasting may offer modest short-term advantages, but longer-term effectiveness and sustainability remain uncertain.

They called for additional high-quality randomized trials, especially those exceeding 52 weeks, to clarify the comparative benefits of these diet strategies on weight loss and broader cardiometabolic health outcomes.

Full disclosures can be found in the study.

Source: The BMJ