August 31, 2005
Rationale and Objectives for the Working Group
A low cardiovascular disease (CVD) risk status in middle age has been linked to lower CVD morbidity and mortality, lower lifetime health care costs, increased life expectancy, and higher quality of later life (1-7). The prevalence of CVD risk factors is generally low among young adults in their twenties but increases by middle age. Cohort studies have suggested an etiologic role for weight gain in CVD risk factor progression. Moreover, observational data suggest that if weight gain is avoided, risk factor progression by middle age may be reduced. Yet, young adults are at high risk for weight gain. In US adults ages 25-74, major weight gain over 10 years, defined as increased BMI = 5 kg/m2, was highest at ages 25-34 (8). In the Coronary Artery Risk Development in Young Adults (CARDIA) Study, even though secular trends were constant across 10 years of follow-up, aging-related weight gain was larger in the early- to mid-20s than for older ages (9). Average 15-year weight gain was 16 kg in African-American women, 14 kg in African-American men, 10 kg in white women, and 11 kg in white men, with a =15 kg gain in 48%, 41%, 26%, and 29%, respectively.
Waiting until middle age to treat CVD risk factors may not be an optimal public health approach. Drug therapy, while effective, frequently fails to meet guideline goals, may produce side effects, and adherence is often inadequate. Irreversible damage from above-optimal levels may occur prior to treatment, and having one or more risk factors may lower quality of life. Modest weight loss can reduce CVD risk factor levels and, in high-risk individuals, prevent the development of diabetes and hypertension (10-14). But despite ample evidence that short-term weight loss is achievable, if and how weight loss can be maintained long-term is less certain (15). Thus, avoiding excess weight gain during early adult years may be pivotal in preventing adverse changes in risk factors and subsequent CVD, and in reducing, delaying, or obviating the need for drug therapy later in life. In addition, interventions may establish an early foundation for maintaining lifelong healthy habits in adulthood, and as parents, young adults will serve as lifestyle role models for their children.
The objectives of the Working Group meeting were to assess the state of knowledge about preventing weight gain in young adults, identify the most relevant and compelling research questions, and discuss barriers/opportunities and design issues related to intervention research in young adult populations. This report provides a summary of findings and recommendations from the working group.
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Summary of Findings
Data from CARDIA provide the impetus and possible directions for developing interventions to prevent CVD in young adults. CARDIA is one of the largest prospective, observational studies in young adults; its primary purpose is to study the evolution and determinants of CVD risk factors and subclinical CVD in adults initially aged 18-30 at baseline in 1985. Average weight gain in the bi-ethnic cohort was 1 kg per year over 15 years, with the highest mean gains (1.2-1.4 kg/y) at ages younger than 30. Maintaining a stable weight and a healthy lifestyle during young adult years was associated with less progression of CVD risk factors and decreased risk of developing metabolic syndrome and subclinical atherosclerosis early in middle age. Although overweight and obese young adults had better risk factor profiles if they were active and fit vs. inactive and unfit, they had worse profiles than those who were normal weight, active, and fit. Predictors of weight gain or overweight/obesity identified in CARDIA provide clues about subgroups to target and potential factors on which to intervene, including younger age, overweight at baseline, declining physical activity and fitness levels, higher dietary fat and lower dietary fiber and dairy intake, more frequent fast food consumption and TV watching, quitting cigarette smoking, more frequent attempts to lose weight, first pregnancy, and becoming a parent (16-25).
Although young adults are at high risk for weight gain, very few randomized trials have focused on this age group, and most studies have been small. Two studies tested correspondence- and clinic-based approaches to increase exercise and improve dietary habits. While a 4-month pilot in young men showed promise using either approach (26), the correspondence-based approach was not successful in a recent, longer, larger study in normal and overweight women. The overriding lesson from these studies is that most young adults are not interested in solely preventing weight gain; many are already overweight or obese and are trying to lose weight. For this reason, these studies had difficulty recruiting and retaining young adults to remain weight stable. The largest trial, the Pound of Prevention Study, evaluated the effectiveness of a low-cost educational approach, primarily through monthly newsletters, in reducing weight gain in adults ages 20-45 (27). Although frequency of weighing and healthy weight loss practices were associated with lower rates of weight gain, the rate of weight change in the treatment groups did not differ significantly from controls.
A few studies have focused on subgroups of young adults during periods identified as critical for developing overweight and/or obesity, that is, the period surrounding pregnancy and freshman year of college. In a small, randomized trial, behavioral interventions were effective at reducing excessive weight gain during pregnancy among normal weight women but not in those who were overweight (28). In another trial, correspondence-based approaches were effective at reducing weight retention postpartum, although the attrition rate was high (29). Whether the first year of college is a critical period for developing obesity remains unclear; some long-term observational studies suggest that without intervention, weight returns to normal (30). Intervention studies in freshman have been limited by high loss to follow-up that is differential by treatment arm and thus it is difficult to draw conclusions about efficacy of interventions from these studies.
Improved cardio-respiratory fitness has been associated with less weight gain over time in adults. A 16-month trial of supervised exercise in young adults suggested that increased exercise may reduce weight or prevent weight gain (31), but only 55% of participants completed the study. Preliminary data indicate that there is no difference between moderate (150 minutes/week) vs. high (300 minutes per week) amounts of exercise for preventing weight gain, although fitness and health-related outcomes may improve more in the latter group. In the latter study, recruitment within a tight BMI eligibility range (25-29.9 kg/m2) has been difficult, and many participants desired weight loss rather than weight gain prevention.
Cultural tailoring of behavioral interventions takes into account not only ethnic influences but also income-related factors, literacy, language preference, degree of acculturation, age, gender, geography, and access to care. Although strategies for cultural tailoring have rarely been evaluated in controlled studies, there is consensus that advice to change weight-related behaviors, such as diet and physical activity, needs to be adapted so that they are culturally appropriate and acceptable. For example, an important challenge for weight control studies among Latinos is to identify physical activities that will be acceptable for women in this cultural setting. Due to the high prevalence of overweight and obesity in many minority populations, it is likely that programs to prevent weight gain will not be perceived by minority participants as acceptable unless they include weight loss as an outcome. Tailoring for both African Americans and Latinos must be based on a deeper understanding of cultural beliefs about body image so as not to introduce harmful psychosocial effects in efforts to encourage weight control. In addition, barriers to engaging younger African-American adults in weight control trials need to be better understood, as engagement of young adults has been limited thus far.
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The magnitude of weight gain in young adults and associated behavioral and environmental factors, along with adverse health consequences, have been well documented, and these findings warrant translation to intervention studies. This is an understudied population at high risk for weight gain, and thus, preventing weight gain in young adults is a priority research area. However, concerns about recruitment, retention, and lack of efficacy of the few prior intervention trials in young adults limit enthusiasm for a large multi-center trial at this time.
Several medium-sized randomized controlled trials are recommended, with weight change as the primary outcome. In addition to identifying innovative approaches to weight control in young adults, they can build the foundation for a longer, multi-center randomized controlled trial, if needed.
Specific Research Needed in Young Adults
- Determine whether proven weight loss approaches are also effective for weight gain prevention, and are acceptable and adaptable to young adult populations.
- Determine strategies to improve recruitment, retention, and adherence among young adults in weight control trials, particularly given the challenges posed during this transitional life stage.
- Identify strategies to improve engagement of largely asymptomatic young adults in adopting and maintaining adequate levels of physical activity and of healthy eating behaviors.
- Refine strategies to reduce weight gain in specific subgroups, including gender-tailored interventions and culturally-appropriate and contextually-relevant prevention approaches for ethnic minorities, immigrants, low-income populations.
- Identify approaches for weight control at high risk times when weight gain is largest, e.g., the period surrounding pregnancy, parenthood, and smoking cessation attempts.
- Determine approaches to overcoming barriers posed by research challenges in this age group, including high mobility of the population and low statistical power to detect small weight differences from controls.
- Weight gain prevention studies in young adults should target groups with the following characteristics, although each study could justify selecting a subset of this age range depending upon the research question.
- Ages 18-35
- Normal, overweight, and obese young adults with no upper limit for BMI
- Socio-economically- and ethnically-diverse
- Since weight gain in young adults averages about 1 kg/year, studies will need sufficiently large sample sizes or long duration to detect significant differences between treatment groups and controls. Alternatively, targeting of young adults at highest risk of weight gain (e.g., those already overweight) or at times of greatest weight change (e.g. pregnancy or parenting) should be considered.
Nature and Content of Intervention
- The definition of weight gain prevention should be broadened to include periods of modest weight loss (e.g., 5-15 lb) to improve the acceptability of the intervention.
- Approaches should include behavioral lifestyle interventions, environmental interventions, or both. Behavioral approaches should focus on increasing physical activity and improving dietary behaviors. Environmental approaches should intervene on smaller organizational units than a community.
- Interventions with potential for sustainability and broad-scale dissemination should be encouraged; when possible, studies should deliver cost-effective interventions within existing infrastructure (e.g., community agencies, universities, community colleges, and trade schools).
- Studies should address strategies for retaining persons in the control group, e.g., by providing an alternative, non-weight intervention.
- The group recommended a research program consisting of several studies, each of which has two phases.
- The first phase (1-2 years) would be used if needed to refine the proposed intervention or recruitment and retention strategies, through qualitative and quantitative techniques such as further analysis of existing data, focus groups, small-scale surveys, and small-scale pilot testing.
- In the second phase, a medium-sized randomized controlled trial of 1-2 years duration would be implemented to test effects of the intervention.
- An external peer review (e.g., DSMB) could assess progress before allowing each study to continue to the second phase.
- Either individual- or cluster-randomized designs would be acceptable, although they must have sufficient power to detect small differences in weight change. If cluster-randomized, the trial should include at least 2 sites per condition.
- Future studies in this age group should consider sites for recruitment and intervention that young adults frequent on an ongoing basis, e.g. pediatric or obstetrics practices, well-baby clinics, parenting classes, universities, community colleges, and trade schools. WIC programs are a good source for recruiting low-income women. Worksites are being studied in other NHLBI initiatives, and churches probably will not work well as intervention sites but might be good sources for recruitment.
- Future studies will need to demonstrate the ability to recruit and retain young adult participants before beginning, possibly refining strategies during the developmental phase.
- The primary outcome for each trial should be weight change.
- Change in key weight-related behaviors should be required measures (e.g., diet, physical activity), and collection of psychosocial measures and environmental influences encouraged.
- If possible, a meeting of investigators should be held during the first phase to standardize collection of key measures across single-center trials.
- Investigators should justify measurement of CVD risk factors, body composition and distribution (e.g., DEXA, CT, MRI, bioelectrical impedance), resting metabolic rate, and fitness, as costs are high and likely will reduce sample size.
- Collection and storage of DNA is optional, but would be of interest.
- Study investigators should address possible adverse effects of the intervention. For example, methods to detect prevalent and incident disordered eating and depression should be included.
- Investigators should demonstrate sensitivity to cultural beliefs about body image, and address how weight gain prevention or weight loss will be approached within these cultural contexts to avoid harm to their study population.
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