Background

An under-explored strategy for increasing physical activity is the dietary treatment of obesity, but empirical evidence is lacking.

Objectives

To compare the effects of weight loss via severe versus moderate energy restriction on physical activity over 36 months.

Methods

101 postmenopausal female adults (45–65 years, 30–40 kg/m², <180 minutes per week of structured exercise) were randomized to either 12 months of moderate energy restriction (25–35% of energy requirement) with a food-based diet, or a severe intervention involving 4 months of severe energy restriction (65–75% of energy requirement) with a total meal replacement diet, followed by 8 months of moderate energy restriction. Physical activity was encouraged, but no tailored or supervised exercise prescription was provided. Physical activity was assessed with an accelerometer worn for 7 days prior to baseline (0 months) and 0.25, 1, 4, 6, 12, 24 and 36 months after intervention commencement.

Results

Compared to the moderate group, the severe group exhibited greater mean levels of: total volume of physical activity; duration of moderate-to-vigorous-intensity physical activity (MVPA); duration of light-intensity physical activity; and step counts, as well as lower mean duration of sedentary time. All these differences (except step counts) were apparent at 6 months (e.g., 1006 [95% confidence interval 564, 1449] MET-minutes per week for total volume of physical activity), and some were also apparent at 4 and/or 12 months. There were no differences between groups in the two other outcomes investigated (self-efficacy to regulate exercise; and proportion of participants meeting the World Health Organization's 2020 Physical Activity Guidelines for MVPA). When the analyses were adjusted for weight at each time point, the differences between groups were either attenuated or abolished.

Conclusions

Among female adults with obesity, including a dietary component to reduce excess body weight—notably one involving severe energy restriction—could potentially enhance the effectiveness of physical activity interventions.