Findings from the current study raise concerns about the high prevalence of dieting and unhealthy weight control behaviors in adolescents, particularly females, and the implications of these behaviors for weight gain over time. Persistent use of dieting and unhealthy weight control behaviors longitudinally predicted greater increases in BMI from adolescence to young adulthood in both overweight and non-overweight respondents. Of concern, was the large magnitude of the BMI increases associated with the use of these behaviors. Specific weight control behaviors used during adolescence that predicted large increases in BMI at ten-year follow-up included skipping meals and reporting eating very little (females and males), use of food substitutes (males), and diet pill use (females). It is crucial to find ways to steer young people away from these ineffective and potentially harmful weight control behaviors, and provide support for the adoption of healthful eating and physical activity behaviors that can be implemented on a long-term basis.
An important question raised in the literature is why we see associations between dieting and weight gain [19
]. “Dieting” or “going on a diet” are somewhat ambiguous terms, and lend themselves to different interpretations by adolescents and researchers. In a qualitative study involving 25 focus groups, adolescents were asked: “What does the term diet mean to you? What do you and your friends do when you diet?” Responses indicated a variety of interpretations; dieting was described in terms of healthy behaviors (e.g., eating more fruit) and unhealthy behaviors (e.g., starvation, not eating), but also in non-behavioral terms (e.g., interested in losing weight, planning for behavioral change) [34
]. Along these same lines, Larsen and colleagues have reported that it may be important to distinguish between intentions to restrict food intake and actual restrictive behaviors [35
], both of which may get reported by adolescents as “dieting”. It may be that the vast majority of youth who indicate that they have dieted, have engaged in “unsuccessful” dieting or failed attempts at restricting their dietary intakes over extended periods of time. Finally, researchers have proposed that dieting may be a proxy or marker for a tendency towards overeating and/or weight gain and that if dieters stopped their behaviors, they would gain more weight over time [23
]. We were able to partially address this question in that we examined and compared weight gain trajectories among young people who reported that they stopped dieting halfway throughout the study and those who reported that they persisted in their dieting behaviors. In no cases did we find that “stopping dieting” was associated with greater weight gains over time than persistent efforts to diet. In fact, males who dieted at Time 1 but not at Time 2 (i.e., stoppers) had much lower weight gains than the persistent dieters and similar weight gains to the non-dieters. Thus, our findings do not lend support to the idea that dieting is a proxy for a tendency to overeat and that if one stops trying to diet, one will overeat and gain weight.
Previous research has suggested that dietary restraint may lead to increased disinhibition and overeating in the presence of large portion sizes [37
], which may, in turn, lead to weight gain over time. In working toward reducing obesity within a society in which a certain amount of dietary restraint is needed, given the ready accessibility to foods high in calories, the question then becomes how can we encourage restraint that will be helpful rather than harmful. Findings from the current study indicate that skipping meals, trying to eat very little, using food substitutes, and diet pills and are not helpful and should be discouraged. In a previous analysis using our five-year follow-up data from Project EAT-II, we distinguished between adolescents reporting dieting without the use of specific unhealthy weight control behaviors (i.e., healthy dieting) and those using unhealthy weight control behaviors [18
]. Among adolescent girls both healthy dieting and unhealthy weight control behaviors increased risk for weight gain over time, whereas in boys the picture was less clear-cut. Given that dieting or attempts to “undereat” are not sustainable over the long-term for most individuals, Herman and colleagues have suggested a shift toward decreasing overeating tendencies, as an alternative to dietary restraint [39
]. For example, clinicians can focus on identifying individuals at risk for external or emotional overeating and intervening to help reduce these overeating tendencies through some type of behavioral therapy. In a four-year longitudinal study, Field and colleagues [40
] found that limiting portion sizes, in conjunction with frequent physical activity, was the most successful strategy for weight gain prevention. Additional strategies that may be effective include the consumption of foods that have higher nutrient density and foods that lead to a greater feeling of satiety, but have lower caloric values. Efforts to encourage the consumption of appropriate portion sizes and healthier food options through educational efforts with youth and changes in the food and restaurant industries may be effective vehicles for reducing the need for unhealthy restraint, and for promoting healthy weight management.
Strengths of the current study, study limitations, and strategies for addressing these limitations, should be taken into account in interpreting the findings. Important study strengths include the ten-year follow-up period that captured a critical transitional period between adolescence and young adulthood, a diverse study population, and the assessment of different types of weight control behaviors. Although respondents reporting dieting and unhealthy weight control behaviors at both Time 1 and Time 2 are called persistent dieters or users, we only have data at five-year intervals, thus we cannot be sure about the persistency of the use of these behaviors between assessments. For example, individuals may have stopped and started weight control behaviors in between the assessments, and these patterns may not have been detected. However, had we been able to better measure persistency of behaviors, with more data points and more questions on frequency and duration of use of behaviors, we would expect to have seen less diluted, and thus stronger associations. The use of self-reported height and weight data at follow-up is a study limitation and it would have been preferable to have measured heights and weights. However, as previously described, our substudy at Time 3 showed high correlations between measured and self-reported BMI (r=.95–.98). Finally, although the population-based nature of the sample allows for more generalization than is possible from clinical samples, the population was drawn from one urban area and there was attrition from the sample over time. The sample was weighted to allow for generalization back to the original sample and no differences were found between the full original sample and the final weighted sample of responders in terms of mean baseline BMI (p-values =.63 and .81 for females and males, respectively); percentage of unhealthy weight control behaviors at baseline (p-values=.97 and .61 for females and males, respectively) and baseline dieting (p-values=.87 and .60 for females and males, respectively). Thus, our weighting procedures were successful, minimizing concerns about any impact of attrition on the results of this analysis.
Implications for research and practice
Study findings strongly suggest the futility and counter-productivity of dieting attempts and unhealthy weight control practices for long-term weight management for the majority of adolescents. Research is needed to further explore why for some adolescents dieting and unhealthy weight control behaviors lead to excessive weight loss and eating disorders, while for most adolescents these behaviors lead to weight gain over time. Intervention research is needed to assess whether helping adolescents substitute dieting and unhealthy weight control behaviors with healthier behavioral patterns results in long-term improvements in weight status. Research should also explore what young people mean when they say that they are dieting, and whether this has changed since the aforementioned study [34
], given that over the past decade there has been greater discussion about weight-related topics. Likewise, within practice settings, health care providers working with adolescents who report that they are dieting should try to determine what exactly is meant by this behavior, and intervene accordingly. We suspect that many reports of dieting are actually unsuccessful and short-term efforts at food restrictions. Given the high prevalence of unhealthy weight control behaviors (e.g., skipping meals), and the associations between these practices and long-term weight gain, it is important to discourage these practices. Health care practitioners can play an important role in directing adolescents away from these ineffective, and potentially harmful, weight control practices.