The purpose of this study was to test if moderate to vigorous physical activity (MVPA) in less than the recommended ≥10-minute bouts related to weight outcomes. Secondary data analysis. Random sample from the U.S. civilian noninstitutionalized population included in the National Health and Nutrition Examination Survey (NHANES). A total of 4511 adults aged 18 to 64 years from the 2003-2006 NHANES. Clinically measured body mass index (BMI) and overweight/obese status were regressed on accelerometer measures of minutes per day in higher-intensity long bouts (≥10 minutes, ≥2020 accelerometer counts per minute [cpm]), higher-intensity short bouts (<10 minutes, ≥2020 cpm), lower-intensity long bouts (≥10 minutes, 760-2019 cpm), and lower-intensity short bouts (<10 minutes, 760-2019 cpm). Socioeconomic and demographic characteristics were controlled. Both higher-intensity short bouts and long bouts of PA related to lower BMI and risk of overweight/obesity. Neither lower-intensity short bouts nor long bouts related to BMI or risk of overweight/obesity. The current ≥10-minute MVPA bouts guideline was based on health benefits other than weight outcomes. Our findings showed that for weight gain prevention, accumulated higher-intensity PA bouts of <10 minutes are highly beneficial, supporting the public health promotion message that "every minute counts."