Obesity Epidemiology

418 EPIDEMIOLOGIC STUDIES OF DETERMINANTS OF OBESITYDiet and Weight GainGenetic differences may predispose certain individuals more than others to excessiveweight gain; however, weight gain is also a function of energy intake exceeding energyexpenditure. The role of fat, protein, carbohydrate, certain food groups, and specific foodsin the development of obesity is not well understood. Many obesity-prevention interventionshave focused on increasing fruit and vegetable servings per day, 16,17 decreasing consumptionof fat, 18-20 and limiting soda intake, 21,22 but whether these changes effectivelyprevent weight gain remains unclear.Dietary Factors that Protect Against Weight GainAmong adults high fiber diets are associated with a decreased risk of many chronicdiseases; 23,24 however, the association of fiber, fruit, and vegetable intake to weight gainis not well understood among children and adolescents. Despite a lack of data, severalobesity-prevention interventions have included efforts to increase the consumption offruits and vegetables. 18-20 It is thought that the consumption of fruits and vegetablesmight lead to greater satiety due to their high dietary fiber and hence decrease totalcaloric intake. It is also thought they might be consumed as an alternative to moreenergy-dense food items, such as soda and snack foods, which are popular among childrenand adolescents, and thus lead to a decrease in total daily caloric intake. Althoughdietary fiber has been associated with less weight gain among adults, 25,26 the findingsamong children are conflicting. Among 6,149 girls and 4,620 boys, aged 9 to 15 years,in the Growing Up Today Study (GUTS), no association was observed between fiberintake and weight gain. 27 In contrast, fiber intake was inversely related to weight gainamong the African American and white young-adults and adults, aged 18 and older, inthe Coronary Artery Risk in Young Adults (CARDIA) study. 28 It is possible that thediscrepancy in results reflects the differences in ages between the study populations orit may be that the BMI gains in CARDIA were much larger than those seen in GUTS,thus making it easier to detect predictors of weight gain. One can assume that for thegreat majority of adults, weight gain is unhealthy, whereas, at younger ages weight gainis healthy and expected for most, therefore making it difficult to differentiate betweenpredictors of normal and healthy weight gain from predictors of excessive weight gain.Further research is necessary to establish whether increasing fiber intake will protectagainst excessive weight gain.Although fruit juice is included as a fruit serving in many campaigns to increase fruitand vegetable intake, there has been some concern that fruit juice intake might lead toweight gain among children. 29,30 Among children, fruit juice may account for considerableproportion of total fruit intake, thus it is possible that interventions aimed at increasingfruit intake could promote weight gain since it has been observed that total caloric intakeis positively related to intake of 100% fruit juice and fruit drinks, as well as soda. 31 Incontrast to fruit juice, fruit (other than juice) and vegetable intake is believed to protectagainst the development of overweight; however, the results have been inconsistent. In a3-year follow-up among 8,203 girls and 6,715 boys in GUTS, only a weak inverse associationbetween vegetable intake and BMI z-score change among the boys and no associationamong the girls were observed. 32 One explanation for the lack of effect could be thatfruit and vegetable consumption among children and adolescents were in addition to highcalorie-dense foods, rather than being a replacement for unhealthy food choices.Several intervention trials have incorporated components that focus on increasing fruitand vegetable intake; however, distinguishing the effect of increased fruit and vegetable