Current physical activity recommendations call for 30 minutes of moderate-intensity activity on most days of the week, or the equivalent of expending approximately 1000 kcal in activity per week. These recommendations were formulated based on reducing the risk for chronic disease, but they do not appear adequate for weight loss and maintenance. Data from epidemiologic studies and randomized trials indicate that closer to 60 to 90 minutes of moderate-intensity activity every day is required for maintaining a reduced body weight, equivalent to expending 2500 to 2800 kcal in activity per week. Relevant studies leading to this conclusion are reviewed in this manuscript. However, to make a dent in the prevalence of obesity by targeting physical activity and food intake, it is imperative to address the current "built" environment, which is conducive to a sedentary lifestyle and overconsumption of energy. Only then will rigorous activity recommendations be easier to implement.