BACKGROUND: Physical activity (PA) has been consistently implicated in the etiology of obesity, whereas recent evidence on the importance of sedentary time remains inconsistent. Understanding of dose-response associations of PA and sedentary time with overweight and obesity in adults can be improved with large-scale studies using objective measures of PA and sedentary time. The purpose of this study was to examine the strength, direction and shape of dose-response associations of accelerometer-based PA and sedentary time with body mass index (BMI) and weight status in 10 countries, and the moderating effects of study site and gender. METHODS: Data from the International Physical activity and the Environment Network (IPEN) Adult study were used. IPEN Adult is an observational multi-country cross-sectional study, and 12 sites in 10 countries are included. Participants wore an accelerometer for seven consecutive days, completed a socio-demographic questionnaire and reported height and weight. In total, 5712 adults (18-65 years) were included in the analyses. Generalized additive mixed models, conducted in R, were used to estimate the strength and shape of the associations. RESULTS: A curvilinear relationship of accelerometer-based moderate-to-vigorous PA and total counts per minute with BMI and the probability of being overweight/obese was identified. The associations were negative, but weakened at higher levels of moderate-to-vigorous PA (>50 min per day) and higher counts per minute. No associations between sedentary time and weight outcomes were found. Complex site- and gender-specific findings were revealed for BMI, but not for weight status. CONCLUSIONS: On the basis of these results, the current Institute of Medicine recommendation of 60 min per day of moderate-to-vigorous PA to prevent weight gain in normal-weight adults was supported. No relationship between sedentary time and the weight outcomes was present, calling for further examination. If moderator findings are confirmed, the relationship between PA and BMI may be country- and gender-dependent, which could have important implications for country-specific health guidelines.

] Baker IDI Heart and Diabetes Institute Melbourne Victoria Australia [2] School of Population Health The University of Queensland Brisbane Queensland Australia [3] School of Population and Global Health Melbourne University Melbourne Victoria Australia [4] Department of Medicine Monash University Melbourne Victoria Australia

] Research Foundation Flanders Brussels Belgium [2] Department of Movement and Sport Sciences Faculty of Medicine and Health Sciences Ghent University Ghent Belgium

] Research Group of Physical Activity and Quality of Life School of Health and Biosciences Pontificia Universidade Catolica do Parana Curitiba Brazil [2] Department of Physical Education Universidade Federal do Parana Curitiba Brazil

Centre for Physical Activity and Nutrition Research School of Exercise and Nutrition Sciences Deakin University Burwood Victoria Australia

Centre for Research and Action in Public Health University of Canberra ACT Australia

Department of Family and Preventive Medicine University of California San Diego La Jolla CA USA

Department of Health Sciences Public University of Navarra Pamplona Spain

Department of Movement and Sport Sciences Faculty of Medicine and Health Sciences Ghent University Ghent Belgium

Department of Public Health School of Medicine Universidad de los Andes Carrera Bogotá Colombia

Faculty of Health and Environmental Sciences Auckland University of Technology Auckland New Zealand

Graduate Division of Biological and Biomedical Sciences Emory University Atlanta GA USA

Institute of Active Lifestyle Faculty of Physical Culture Palacký Universitsy Tř Míru 115 771 11 Olomouc Czech Republic

Institute of Human Performance Hong Kong University Hong Kong

Research Unit for Active Living Department of Sport Sciences and Clinical Biomechanics University of Southern Denmark Odense Denmark

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