This once-a-week workout may help cut belly fat, study shows

The findings support once weekly brisk interval walking as a practical therapeutic option for adults with central obesity, especially those who have difficulty fitting several workouts into their schedules. The study was published in Nature Communications.

A More Practical Approach to Reducing Body Fat

Obesity is a chronic health condition involving an unhealthy buildup of body fat. Fat that accumulates around the abdomen is especially concerning because it is associated with cardiovascular disease, metabolic disorders, and a higher risk of premature death.

Exercise plays an important role in managing obesity and offers a wide range of health benefits. Even so, many people, particularly those living with obesity, struggle to maintain regular physical activity over time.

Interval training alternates between more vigorous periods of exercise and lower-intensity periods of active recovery. Research has shown that it can be a time-efficient way to reduce overall body fat and visceral fat compared with continuous exercise performed at a moderate intensity.

Most exercise recommendations call for interval training three days each week. That schedule may be difficult for people with demanding jobs, family responsibilities, limited time, or restricted access to exercise facilities.

Previous research has suggested that a "weekend warrior" pattern, in which most weekly exercise is completed over one or two days, can still produce health benefits. However, there has been relatively little evidence showing whether interval training remains effective when concentrated into a single weekly session.

Professor Parco Siu Ming-fai, Professor and Head of Division of Kinesiology at the School of Public Health, HKUMed, said it was important to determine whether once weekly interval training could match the results of a traditional three-session schedule and provide a more accessible alternative.

One Session Versus Three

From September 2021 to September 2024, the HKUMed team carried out a randomized trial in Hong Kong involving 315 Chinese adults aged 18 or older. All participants were overweight and had central obesity.

Participants were assigned to one of three groups. One group completed interval training once each week, another completed interval training three times each week, and the third served as a control group.

The control group took part in a 2.5-hour health education session every two weeks for four months. Both exercise groups completed a total of 75 minutes of interval training each week. One group performed the full amount in a single session, while the other divided it across three sessions.

Researchers measured body fat using dual-energy X-ray absorptiometry at three stages: before the program began (baseline), after 16 weeks (post-intervention), and at 32 weeks (four-month post-intervention follow-up).

Similar Fat Loss and Fitness Benefits

At the 16-week assessment, both interval training groups showed similar improvements. Participants who exercised once per week and those who exercised three times per week reduced total body fat mass, body fat percentage, and waist circumference. Both groups also improved their cardiorespiratory fitness compared with the control group.

"While thrice-weekly interval training remains a commonly recommended approach for the therapeutic management of excess adiposity, our findings show that once-weekly interval training offers similar benefits and represents a practical exercise strategy," said Professor Siu. "For many adults with central obesity who struggle to balance work, study, family and other commitments, time constraints are a primary barrier to exercising multiple days per week."

"Instead of relying solely on high-frequency exercise prescriptions, once-weekly interval training can be considered a feasible and effective alternative," added Professor Siu.

The study was led by Professor Parco Siu Ming-fai, Professor and Head of Division of Kinesiology at the School of Public Health, HKUMed. The co-first authors were Dr. Leung Chit-kay and Mr. Joshua Bernal, both from the same School.

The research was supported by the General Research Fund of the Research Grants Council, the University Grants Committee of Hong Kong, China, and the Seed Fund for Basic Research, HKU.