Acute effects of high-sugar/low-fiber meals vs low-sugar/high-fiber meals on hormones and behavior were studied in 10 overweight Latina females, age 11 to 12 years, using a crossover design. In this exploratory pilot study, participants arrived fasted at an observation laboratory on two occasions and randomly received either a high-sugar/low-fiber meal or a low-sugar/high-fiber meal at each visit. Glucose, insulin, and leptin were assayed from serum drawn at 0, 15, 30, 60, 90, and 120 minutes. Ad libitum snacks were provided at 120 minutes. Physical activity was measured using an observational system that provides data on time spent lying down, sitting, standing, walking, and in vigorous activity. Data were collected between March 2005 and July 2006. In the high-sugar/low-fiber condition, glucose and leptin levels decreased more slowly, glucose levels were higher at 60 minutes (111.2 mg/dL vs 95.4 mg/dL, P=0.03), and leptin levels were higher at 90 minutes (49.3 ng/mL vs 46.7 ng/mL, P=0.017) than in the low-sugar/high-fiber condition. Meals did not affect insulin or ad libitum dietary intake. Sitting, standing, lying down, and vigorous activity differed by condition, but not walking. Participants were significantly more active in the first 30 to 60 minutes after the high-sugar/low-fiber meal, but after 60 minutes there was a trend for activity to be lower after the high-sugar/low-fiber meal vs the low-sugar/high-fiber meal. High-sugar meals sustain glucose and leptin levels longer, which may play an important role in modulating levels of physical activity in this group at high risk for obesity-related disease.