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What Is Best for Weight Loss According to Science: Intermittent Fasting vs. Calorie Counting

Dr Rohit Bhaskar
Dr Rohit Bhaskar
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A study by the University of Illinois Chicago found that time-restricted eating (intermittent fasting) led to similar weight loss and improved insulin sensitivity as traditional calorie restriction among adults with obesity. Participants in the time-restricted eating group ate fewer calories and lost more weight over a year compared to those who made no changes to their eating habits. Further research is needed to understand individual responses to each dietary intervention.

A small randomized controlled trial found that time-restricted eating, also known as intermittent fasting, produced similar weight loss results to traditional calorie counting in a racially diverse population of adults with obesity. The study also showed that participants who engaged in 8-hour time-restricted eating had improved insulin sensitivity compared to those in the control group who ate their calories any time over 10 or more hours a day. The study is published in the Annals of Internal Medicine.

Obesity is a major health issue. Many traditional weight loss diets involve counting calories, which can be cumbersome and difficult to do well. Time-restricted eating, without calorie counting, has become a popular weight loss strategy because it is simple to do. Whether it’s effective in producing weight loss, especially beyond the short term, is unclear.

Researchers from the University of Illinois Chicago studied 90 adults with obesity from the Greater Chicago area to determine whether intermittent fasting or calorie-restricted eating would be more effective for weight control and cardiometabolic risk reduction.

Participants were randomly assigned to 1 of 3 groups: 8-hour time-restricted eating (eating from noon to 8:00 p.m. only, without calorie counting); calorie restriction (reduce 25% of their calories daily), or no change in calorie consumption, with eating taking place over 10 hours or more throughout the day. Both the time-restricted eating and calorie-restriction groups met regularly with a dietician. Participants were not blinded.

The authors found that participants who engaged in time-restricted eating ate 425 fewer calories per day than the control group and lost about 10 more pounds than the control group after one year. The calorie-restricted group ate 405 fewer calories per day and lost about 12 more pounds after one year. Participants showed high adherence to both interventions.

The authors of an accompanying editorial from the Anschutz Health and Wellness Center and Division of General Internal Medicine, University of Colorado School of Medicine say that access to dieticians likely helped participants in the restricted eating group make healthier food choices.

They believe the results of this study can help guide clinical decision-making partially by taking individual preferences into consideration, rather than just choosing a diet that may be more effective. They emphasize that the results of this study highlight the substantial individual variability in weight loss using these interventions, and that further research is needed to determine who would most benefit from each of these interventions.


“Summary for Patients: Time-Restricted Eating Without Calorie Counting for Weight Loss” 27 June 2023, Annals of Internal Medicine.
DOI: 10.7326/P23-0003

“Time-Restricted Eating Without Calorie Counting for Weight Loss in a Racially Diverse Population: A Randomized Controlled Trial” by Shuhao Lin, MS, RD, Sofia Cienfuegos, PhD, Mark Ezpeleta, PhD, Kelsey Gabel, PhD, RD, Vasiliki Pavlou, MS, RD, Andrea Mulas, MS, RD, Kaitie Chakos, MS, RD, Mara McStay, MS, RD, Jackie Wu, MS, RD, Lisa Tussing-Humphreys, PhD, RD, Shaina J. Alexandria, PhD, Julienne Sanchez, MD, Terry Unterman, MD and Krista A. Varady, PhD, 27 June 2023, Annals of Internal Medicine.
DOI: 10.7326/M23-0052

“Time-Restricted Eating for Treatment of Obesity? The Devil Is in the (Counseling) Details” by Adam H. Gilden, MD, MSCE and Victoria A. Catenacci, MD, 27 June 2023, Annals of Internal Medicine.
DOI: 10.7326/M23-1396

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