This study aimed to determine the motivation of overweight/obese persons to participate in and withdraw from a health promotion program, and to determine the program’s effectiveness. 91 women and 89 men enrolled in the program. Their motivation was described with modified EMI-2. The reasons for withdrawal were given by the participants. Body composition was determined with Tanita BC 418 MA. Improved appearance, weight loss and health were the main reasons why overweight/obese persons decided to become physically active. Approximately 56% women and 60% men quit the program because they were unable to cope with the fitness regime, lost interest or could not find the time. The participants who completed the program (> 600 MET) significantly (p < 0.01) reduced their BM (1.84 kg and 2.37 kg), BMI (0.70 kg/m2 and 0.74 kg/m2), fat percentage (1.58% and 1.81%) and fat mass (1.70 kg and 2.20 kg). Significant loss of the adipose tissue and an increase in muscle mass were observed in various parts of the body. The 7-month health program involving physical activities with MET > 600 led to a significant decrease in fat mass and fat percentage and a significant increase in muscle mass.