A comprehensive new review published in The BMJ reveals that intermittent fasting is as effective as traditional calorie-restricted diets for weight loss, with some fasting methods potentially offering modest additional benefits.
Researchers highlighted alternate-day fasting as showing slightly greater weight reduction, but emphasized that longer-term studies are necessary to confirm these findings.
The study’s results arrive amid a growing global obesity crisis. According to the World Health Organization, by 2022 approximately 2.5 billion adults worldwide were overweight, with nearly 900 million classified as obese. Obesity significantly increases the risk of chronic diseases such as type 2 diabetes, cardiovascular disease, and hypertension.
Intermittent fasting—characterized by cycles of fasting and eating—has gained popularity as an alternative to conventional calorie-counting diets. However, uncertainty remained about its long-term effectiveness compared to continuous calorie restriction.
To clarify this, researchers analyzed data from 99 randomized clinical trials involving over 6,500 adults, most with pre-existing health conditions and an average BMI of 31. The trials, lasting from three to 52 weeks, examined various intermittent fasting regimens including:
- Time-restricted eating (e.g., 16:8 method)
- Alternate-day fasting (24-hour fast every other day)
- Whole-day fasting (e.g., the 5:2 diet)
All fasting types and continuous calorie restriction led to modest weight loss compared to unrestricted diets. Among these, alternate-day fasting showed the greatest, though still modest, weight loss advantage—averaging 1.29 kg more than continuous calorie restriction. It also exceeded the weight loss seen with time-restricted eating and whole-day fasting by 1.69 kg and 1.05 kg respectively, though these differences fell short of the 2 kg clinical significance threshold defined by the study.
In cardiometabolic outcomes, alternate-day fasting more effectively reduced total and LDL (“bad”) cholesterol compared to time-restricted eating. Conversely, time-restricted eating was linked to a slight cholesterol increase relative to whole-day fasting. No significant changes were observed in blood sugar or HDL (“good”) cholesterol across fasting methods.
Weight loss benefits were primarily observed in trials shorter than 24 weeks. In longer studies, advantages were apparent only when comparing structured dietary approaches with unrestricted eating.
The authors noted several limitations, including heterogeneity in fasting protocols, small sample sizes, and generally low to moderate confidence in the evidence. Nonetheless, this review stands out as one of the first to rigorously compare all major dieting strategies.
“The current evidence indicates that intermittent fasting offers similar benefits to continuous energy restriction for weight loss and cardiometabolic risk factors,” the researchers concluded, underscoring the necessity for extended research.
An accompanying editorial from nutrition experts in Colombia emphasized that the success of any diet likely depends on structure and professional guidance rather than the specific method alone. They cautioned that alternate-day fasting should be considered a complementary, rather than replacement, strategy within personalized nutritional care.
“Sustainable lifestyle changes are paramount,” the editorial stated, adding, “Intermittent fasting can be an effective component of a holistic, patient-centered nutritional approach.”
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