The questions asked and discussed by the Energy Balance subcommittee deal with important issues related to the high prevalence of obesity in the US. For the first time, the Committee is examining how the food environment is associated with dietary intake and body weight. Additionally, behaviors associated with dietary intake and body weight are considered. The committee addressed the following behaviors and their relationship with body weight: Eating out, portion size, screen time, breakfast consumption, snacking, eating frequency and diet self-monitoring. The Committee also reviewed literature related to body weight during the life cycle, specifically the relationship between breastfeeding and maternal weight change. Because of the increase in childhood overweight and obesity, a series of questions addressing dietary intake and childhood adiposity was asked. The specific aspects of diet addressed in this set of questions include: Total energy intake, dietary fat, dietary energy density, dietary fiber, 100% fruit juice, fruits and vegetables, sugar-sweetened beverages and dairy/calcium. For adults, the Committee reviewed literature related to two areas of recent interest in published literature: The effects of dietary macronutrient proportion and energy density on body weight. For older adults, the relationships between weight loss and weight maintenance and mortality and disease risk were reviewed. Listed below are the formal research questions that were addressed by the Energy Balance subcommittee using Nutrition Evidence Library (NEL) systematic reviews.
FOOD ENVIRONMENT AND DIETARY BEHAVIORS
The methodology for discussing the questions listed above varied with the question. Aspects from Questions 4, 5 and a few dietary behaviors included in Question 1 were considered by the 2005 Dietary Guidelines Advisory Committee (DGAC). The remaining questions were not considered in previous iterations of the DGAC Report.
To answer the overall question of how the environment and dietary behaviors affect body weight, the Committee conducted a series of NEL evidence-based systematic reviews. For the environment question, only systematic reviews published since 2000 were considered because the Committee felt that several recent reviews had been published that address the broad range of components that make up the food environment. Energy intake, body weight and vegetable and fruit intake were selected as outcomes because they are frequent outcomes considered in this research.
The methodology addressing dietary behaviors varied, but in general, the studies considered for these questions included children and adults, were published between January 2000 and December 2009 and were not cross-sectional in design. Questions 4 and 5 were considered by the 2005 DGAC. The conclusions expressed in the 2005 DGAC report were based on evidence gathered prior to that date. The present conclusions for the 2010 Report are based on a NEL review of publications after June 2004.
For macronutrient proportions, the literature search included studies done in children and adults; however, after the search revealed few studies with children, it was decided that the review would be limited to studies done in adults older than age 19 years. Because Questions 2 and 6 were new questions considered by a DGAC, the searches for these questions were extended back to 2000 and 1995, respectively. The Committee focused their review of breastfeeding and maternal postpartum weight change to recent systematic reviews and excluded primary research citations.
Question 3 was answered using the NEL evidence-based systematic review. Eight research questions related to dietary intake in children were chosen. Several of the questions had previously been reviewed by the American Dietetic Association (ADA) Evidence Analysis Library (EAL), available at www.adaevidencelibrary.com, so that the NEL review process updated these reviews to incorporate the most recent five to six years, not been covered in the ADA reviews. Two new questions, however, were added to the NEL review (energy density and dietary fiber), and for these new reviews, literature searches extended back to 1980. Cross-sectional studies were excluded from the reviews on childhood adiposity.
Complementary topics were addressed by other subcommittees. The Nutrient Adequacy Subcommittee addressed questions regarding the effects of breakfast intake, snacking and eating frequency on nutrient intake. In addition, questions regarding the relationship between fruits and vegetables, sugar-sweetened beverages and dairy/calcium and health outcomes in adults were addressed by the Carbohydrate Subcommittee.
Needs for Future Research:
1. Conduct well-controlled and powered prospective studies to characterize the associations between specific dietary factors and childhood adiposity.
2. Conduct well-controlled and powered research studies testing interventions that are likely to improve energy balance in children at increased risk of childhood obesity, including dietary approaches that reduce energy density, total energy, dietary fat and calorically-sweetened beverages, and promote greater consumption of fruits and vegetables.
3. Conduct research to clarify both the positive and negative environmental influences that affect body weight.
4. Conduct research on the effect of local and national food systems on dietary intake.
5. Conduct considerable new research on other behaviors that might influence eating practices.
6. Conduct research on the influence of snacking behavior and meal frequency on body weight and obesity. Develop better definitions for snacking as the research moves forward.
7. Invest in well-designed randomized controlled trials with long-term follow-up periods to assess the influence of different dietary intake and physical activity patterns, and their combinations, on gestational weight gain patterns.
8. Conduct studies to refine gestational weight gain recommendations among obese women according to their level of pre-pregnancy obesity.
9. Substantially improve pre-pregnancy BMI and gestational weight gain monitoring and surveillance in the US.
10. Conduct longitudinal studies with adequate designs to further examine the association between breastfeeding and maternal postpartum weight changes, as well as impact on offspring.
11. Determine whether and how isocaloric solid foods and liquids differ in their influence on satiety (de Graaf, 2006; Rolls, 2009).
NEL Project Managers:
NEL Support Staff:
Dietary Guidelines Management Staff: