The prevalence of obesity is increasing in most parts of the world and becoming one of the major global public health problems. Although the components of energy balance have not been adequately estimated over time, available evidence suggests that the increase in obesity is the result of reduced physical activity. Increases in physical activity have been shown to be strongly associated with improving physical fitness and body composition, with probably a positive effect on resting metabolic rate. The Surgeon General's Report on Physical Activity and Health advocates that 30 min of regular, moderate-intensity physical activity is associated with decreases in the risk of chronic diseases and may contribute to quality of life. However, the small changes that contribute 10 min for 3 times a day for aerobic training, or one set instead of three sets of repetitions on resistance training will provide individuals with health benefits. Indeed, nutrition and physical activity should be considered an integral part of fitness and good health, and should be encouraged in all age groups, particularly early in life. The question is no longer centered around the health benefit of increasing physical activity, but rather creating self awareness and behavior changes in individuals. Hence, effective intervention programs are needed that foster long term changes in physical activity. Among various interventions, the Nutrifit program was recently conducted in Thailand and found to improve health related fitness in children. The development of more effective interventions and approaches is a major challenge in this field today.