Int. J. Environ. Res. Public Health 2012, 9 1369 Keywords: pediatric weight management; childhood obesity; fruits and vegetables; snack foods 1. Introduction Early childhood is a critical period for obesity treatment interventions because children are developing behaviors to be carried into adulthood [1]. Ideally, these learned healthy behaviors during childhood will be implemented over the lifecourse to prevent future obesity. In children, increasing fruit and vegetable (FV) consumption is one recommended dietary strategy for treating obesity [2]. To impact energy balance and help with improving weight status, increasing FVs must reduce energy intake. Solely increasing FVs in the diet with no other dietary changes will only increase energy intake [3]. Thus, for FVs to be an effective dietary strategy for pediatric weight management, increasing FVs must decrease (i.e., displace) the consumption of other more energy-dense foods, thereby reducing energy intake [4]. Behavioral economics is a framework that provides a foundation to understand that eating behaviors can be complementary to or substitutes for each other [5,6]. Complementary eating behaviors change in the same direction (e.g., as one behavior increases, the other behavior also increases), while substitute behaviors change in opposite directions (e.g., as one behavior increases the other behavior decreases) [7]. Understanding if eating FVs substitute for eating low-nutrient-dense, high-energy-dense snack foods (SFs) (e.g., eating an apple instead of potato chips) is important in understanding the role of FVs in pediatric weight management. Limited research has investigated the relationship between FVs and SFs, with most research in this area conducted in adults. Of the studies conducted mixed results have been found. Several studies were unable to find a significant relationship between consumption of FVs and SFs [3,8,9] while other studies do demonstrate a relationship between intake of FVs and SFs [10,11]. For those studies suggesting that an increase in FVs is related to a decrease in energy-dense foods, analyses have examined changes in dietary intake across time. However, none of these investigations has examined the direct relationship between changes in FVs and energy-dense foods, such as SFs, to understand if they are natural substitutes. Additionally, few of the investigations have examined if an increase in FVs is also related to reductions in energy intake. Thus, the purpose of this secondary data analysis was to examine the relationship between changes in FVs and SFs when these food groups are individually targeted for change without an energy intake goal in children aged 4 to 9 years, who are enrolled in a 6-month, family-based behavioral pediatric weight management program. Additionally, the relationship between change in servings/day of FVs and SFs and change in energy intake from 0 and 6 months was examined. The source of this secondary data analyses is the trial conducted by Raynor and colleagues [12]. The main trial was a 6-month, family-based pediatric intervention, with 12-month follow-up, with overweight (≥85th to <95th percentile for body mass index [BMI]) and obese (≥95th percentile for BMI) children (4–9 years) randomized to one of three treatment conditions: (1) increased growth monitoring with feedback provided to families [GROWTH]; (2) decrease SFs and sugar sweetened beverages [DECREASE]; or