Is One Fasting Method Better Than Another?

TOPLINE:

Various intermittent fasting strategies and calorie restriction diets similarly improved body weight compared with ad libitum diets; only alternate-day fasting delivered small-to-moderate additional benefits in weight loss, body composition, lipid levels, and systolic blood pressure — benefits not observed with other intermittent fasting approaches.

METHODOLOGY:

• Weight loss reduces cardiometabolic risks and the burden of chronic disease. Intermittent fasting — alternating periods of eating and fasting — may be a more sustainable alternative to daily calorie restriction, but its benefits compared with those of continuous calorie restriction or ad libitum diets remain unclear.
• Researchers conducted a systematic review and network meta‐analysis of 99 randomized clinical trials to compare intermittent fasting regimens with continuous calorie restriction and ad libitum diets.
• Intermittent fasting regimens were time-restricted eating (16-hour fasting period followed by an 8-hour eating window), alternate-day fasting (24-hour fast on alternate days), and whole-day fasting (5 days of unrestricted eating and 2 days of fasting).
• The included trials, which ranged from 3 to 52 weeks, involved 6582 adults (median age, 45 years; median BMI, 31.3; 66% women), of whom 5862 had existing health conditions such as diabetes, metabolic syndrome, or metabolic dysfunction-associated fatty liver disease.
• The primary outcome was body weight, and secondary outcomes encompassed anthropometric measures, glucose metabolism markers, blood pressure, lipid profiles, liver function, and C-reactive protein levels.

TAKEAWAY:

• A total of 54 studies evaluated ad libitum diets, 53 assessed continuous calorie restriction, 25 examined alternate-day fasting, 40 investigated time-restricted eating, and 38 focused on whole-day fasting.
• All intermittent fasting and continuous calorie restriction strategies reduced body weight compared with ad libitum diets, with alternate-day fasting showing additional benefit over continuous calorie restriction (mean difference, -1.29 kg; 95% CI, -1.99 to -0.59).
• Alternate-day fasting led to greater weight reduction than time-restricted eating (mean difference, -1.69 kg; 95% CI, -2.49 to -0.88) and whole-day fasting (mean difference, -1.05 kg; 95% CI, -1.90 to -0.19).
• The slightly greater weight loss benefits with alternate-day fasting were observed only in the 76 trials with less than 24 weeks of follow-up; however, the 17 moderate-to-long-term trials (≥ 24 weeks) demonstrated greater weight loss for all diet strategies, with no differences between intermittent fasting strategies.
• Alternate-day fasting was associated with greater reductions in BMI, non-high-density lipoprotein cholesterol levels, and triglyceride levels compared with time-restricted or whole-day fasting.

IN PRACTICE:

“The value of this study is not in establishing a universally superior strategy but in positioning alternate-day fasting as an additional option within the therapeutic repertoire,” experts wrote in an accompanying editorial. “Intermittent fasting does not aim to replace other dietary strategies but to integrate and complement them within a comprehensive, patient-centered nutritional care model,” they added.

SOURCE:

The study was led by Zhila Semnani-Azad, Department of Nutrition, Harvard T.H. Chan School of Public Health in Boston. It was published online on June 18, 2025, in BMJ.

LIMITATIONS:

While diet quality on nonfasting days may influence fasting outcomes on alternate days, this relationship has not yet been systematically evaluated in clinical trials. Considerable heterogeneity and incoherence in body weight outcomes across the diet strategy comparisons led to a downgrade in the certainty of the evidence.

DISCLOSURES:

This study was supported by the Diabetes and Nutrition Study Group of the European Association for the Study of Diabetes, the Canadian Institutes of Health Research, and other sources. Some authors received research support, honoraria, grants, speaker fees, served on advisory boards, and had several other ties with certain pharmaceutical companies and institutions.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.