A new year-long study comparing intermittent fasting and daily calorie restriction has found that the former may lead to “modestly” greater weight loss in overweight or obese adults
The findings challenge long-standing assumptions about the best path to losing weight and feeling healthier.
The randomized clinical trial found that participants who followed a 4:3 intermittent fasting regimen lost more weight than those who followed a daily caloric restriction plan—despite both groups receiving identical behavioral support and exercise guidance.
The results suggest that intermittent fasting, long pitted against calorie restriction diets, may be easier to maintain and more effective in the long term.
The trial, conducted by researchers at the University of Colorado, enrolled 165 local adults aged 18 to 60, with a body mass index (BMI) of 27 to 46.
Participants were randomly assigned to one of two groups. The intermittent fasting group practiced a 4:3 method—eating normally four days a week and reducing intake by 80 percent on three nonconsecutive days.
Meanwhile, the calorie restriction group was given a daily calorie goal equivalent to a 34.3 percent weekly energy deficit.
All participants had access to gym memberships, were encouraged to exercise for at least 300 minutes per week, and received support in calorie counting, nutrition and dietary guidelines.
After 12 months, participants in the 4:3 intermittent fasting group experienced an average weight loss of 7.6 percent of their body weight, compared to 5 percent in the calorie restriction group. Notably, 58 percent of those in the fasting group lost at least 5 percent of their body weight at 12 months, versus just 47 percent in the daily calorie restriction group.
Researchers noted that participants in the fasting group also achieved more positive cardiometabolic changes including systolic blood pressure, total and low-density lipoprotein cholesterol levels and fasting glucose level.
The team think that intermittent fasting may have been the more effective mode of losing weight and getting healthier because it does not require a focus on counting calories and restricting food intake every day
The later, they argue, creates a diet that can be both triggering and hard to follow.
“The results indicate that the 3:4 intermittent fasting group achieved significantly greater weight loss after 12 months, most likely due to a greater reduction in calorie intake during the 12-month intervention,” said human nutrition researcher professor Maria Chondronikola of the University of Cambridge, England—who was not involved in the study.
“It remains unclear whether the superior improvements in marker of insulin sensitivity observed in the 3:4 intermittent fasting group were due to greater weight loss or if they resulted from a direct effect of intermittent fasting.”
Although the researchers emphasized that intermittent fasting could be more effective for both general health and weight loss, Chondronikola had a different take on the results.
The academic cautioned that some cardiometabolic benefits may have been overstated and could be misinterpreted.
“There were no statistically significant differences between the two groups in terms of blood pressure, total and low-density lipoprotein cholesterol levels or fasting glucose levels,” she said.
“This is not surprising, as the study was not specifically designed to assess the effects of 3:4 intermittent fasting on cardiometabolic health.”
Importantly, 125 of the original 165 participants completed the 12-month program.
According to the study, intermittent fasting led to an average 2.89-kilogram greater weight loss than calorie restriction—a statistically significant difference, though researchers noted the limited generalizability of their findings due to the single-site study design and demographic makeup of participants, 73.9 percent of whom were women.
“Nonetheless, it is possible that 3:4 IMF, when combined with an intensive behavioral support program led by a dietitian, may lead to superior weight loss outcomes compared to standard caloric restriction,” Chondronikola said.
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Reference
Catenacci, V. A., Ostendorf, D. M., Pan, Z., Kaizer, L. K., Creasy, S. A., Zaman, Adnin., Caldwell, A. E., Dahle, J., Swanson, B., Breit, M. J., Bing, Kristen., Wayland, L, T., Panter, S. L., Scorsone, J. J.,Bessesen, D. H., MacLean, P., Melanson, E. L. (2025). The Effect of 4:3 Intermittent Fasting on Weight Loss at 12 Months. Annals of Internal Medicine. https://www.acpjournals.org/doi/10.7326/ANNALS-24-01631.
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