A new global analysis published in The BMJ finds that intermittent fasting may be just as effective as traditional calorie-restricted diets when it comes to losing weight and improving markers of heart and metabolic health.
The comprehensive study-spanning 99 randomized clinical trials and more than 6,500 adults – compared the health impacts of intermittent fasting (IF) methods like alternate day fasting (ADF), time-restricted eating (TRE), and whole day fasting (WDF) against calorie restriction (CER) and unrestricted, or “ad libitum,” diets.
What Did the Study Find?
Researchers found all forms of intermittent fasting and calorie restriction were significantly more effective than unrestricted eating in promoting weight loss. Notably, alternate day fasting emerged as slightly more effective than traditional calorie restriction—helping participants lose, on average, 1.3 kilograms (about 2.9 pounds) more than those simply cutting calories. However, experts emphasize that the difference is statistically modest and may not have a major clinical impact on its own.
“Minor differences were noted between some intermittent fasting diets and continuous energy restriction,” the authors noted. “The current evidence suggests both strategies offer comparable benefits for weight loss and cardiometabolic risk factors.”
Which Intermittent Fasting Strategy Works Best?
Of the three intermittent fasting strategies:
- Alternate Day Fasting (ADF): Produced the greatest weight loss and modest improvements in cholesterol and triglyceride levels.
- Whole Day Fasting (WDF) and Time-Restricted Eating (TRE): Also led to weight loss, but benefits over calorie restriction were minimal.
No significant differences were observed between fasting and calorie restriction for blood sugar control (HbA1c), high-density lipoprotein (HDL), or insulin sensitivity across most trials.
A Closer Look at Adherence
While the initial weight loss findings are promising, the study also revealed a common challenge: sticking to the diet. Trials shorter than 24 weeks saw adherence rates above 80%, but long-term studies (52 weeks or more) often dropped below 25% adherence, especially with whole-day fasting.
What Does This Mean for You?
For people looking to manage their weight or reduce cardiometabolic risk, this study confirms what many health professionals have been saying: the best diet is the one you can stick to.
“The slight edge seen with alternate day fasting shouldn’t overshadow the larger message,” said the researchers. “Intermittent fasting offers flexibility. That means more people might find it easier to follow over time compared to counting calories every day.”
However, not everyone should try fasting. Older adults, people who are pregnant or nursing, and individuals with a history of disordered eating or low blood pressure should consult a healthcare provider first.
Not a Magic Bullet
Intermittent fasting isn’t a magic bullet—but it is a valid and flexible option in the fight against obesity and heart disease. Whether you choose to fast, restrict calories, or combine both approaches, consistency and sustainability are still the keys to long-term success.
Source: Semnani-Azad et al. Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomized clinical trials. The BMJ, June 2025.
View the full study on BMJ.com
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