Application of Adult-Based Dietary Guidelines to Children: Evidence, Knowledge Gaps and Policy Implications
Prepared by: Ronette R. Briefel, Allison Hedley Dodd, Charlotte Cabili and Carol West Suitor
Recommendations to promote healthy living, such as the Dietary Guidelines for Americans, are intended to translate scientific knowledge into everyday practice. The science base to support the dietary guidance for children ages 2 to 18 years is known to be limited, and the extent to which it has grown over the past five years has not been documented. To address the science base supporting dietary guidance for children, Mathematica Policy Research, Inc. conducted a study for the Department of Health and Human Services’ Office of the Assistant Secretary for Planning and Evaluation. The study had four primary objectives:
- To examine the literature supporting major dietary guidance statements that target children, using the 2005 Dietary Guidelines for Americans as a foundation but also including other contemporary guidance statements, and to determine whether the guidance draws from research done with children or is adapted from research done with adults.
- To identify and describe new evidence in support of child-focused dietary guidance.
- To identify knowledge gaps in the science base related to dietary guidance for children.
- To assess the implications of the science base in supporting dietary guidance for children that will promote health in childhood and beyond.
The study involved a systematic approach to assess the evidence base for child-focused dietary guidance. First, we examined the literature cited in the 2000 and 2005 Dietary Guidelines and in 11 other contemporary guidance statements by authoritative organizations. Then, we identified and reviewed evidence published in the peer-reviewed literature between 2004 (the year that the Dietary Guidelines Advisory Committee completed its work) and February 2008 by searching electronic databases, bibliographies of contemporary guidance statements and scientific nutrition reviews, and tables of contents of relevant nutrition and health journals not covered in the electronic databases. We reviewed nearly 6,000 abstracts and determined whether studies met specific criteria for further review (that is, relevant to one of the dietary guidelines topics, conducted with children ages 2 to 18 years, published in English, applicable to populations living in developed countries, and involving study outcomes that were direct measures of health or nutrition status, biologic outcomes, or dietary-related behaviors).
For the 104 “primary research” articles that met the criteria, we reviewed the full articles and classified studies by the following Dietary Guideline topic areas: adequate nutrients within calorie needs; weight management; fats; fruits and vegetables; whole grains; dairy and calcium; carbohydrates; sodium and potassium; and tracking (that is, studies that measured behaviors and/or biologic or health outcomes at more than one time from early to later childhood or from childhood to adulthood). Within each topic area, we cataloged the research studies by type (tracking studies, systematic reviews or meta-analyses, controlled trials, or observational studies), summarized the design and characteristics of each study, grouped the article summaries by outcome(s) measured, and summarized the evidence. A stand-alone companion report (Dodd et al. 2008), provides a synopsis. We also identified 142 articles that contain useful data on children’s dietary intake or behavior, risk factors, and related health outcomes; discuss methods pertinent to diet; or address other dietary guidance topics that were not the main focus of this review.
Next, we reviewed and summarized the science base for children’s dietary guidance, taking into consideration our review of the historical evidence and the 2004-2008 literature. We identified new evidence as well as topics where there are knowledge gaps for developing future guidance.
Since the completion of work on 2005 Dietary Guidelines (in 2004), the science base has grown in the areas of added sugars and weight, dairy foods/calcium and bone health and weight, and to some extent for diet and weight as well as for sodium and blood pressure. Studies published in 2004-February 2008 that contributed most to the child-focused science base, based on their being systematic reviews or meta analyses often containing randomized controlled trials (RCTs), include:
- One systematic review including 13 RCTs (Lanou et al. 2005) and one other RCT on calcium, dairy food consumption, and bone health (Cheng et al. 2005)
- One systematic review of RCTs to prevent childhood obesity (Connelly et al. 2007) and one meta-analysis on weight and asthma among children (Flaherman and Rutherford 2006)
- Two systematic reviews of the consumption of sugar-sweetened beverages on weight (Malik et al. 2006; Vartanian et al. 2007); and one systematic review of their consumption on dental heath including eight case control studies (Harris et al. 2004)
- One meta-analysis on salt intake and blood pressure (He and MacGregor 2006)
- Forty-five studies that provided some type of tracking data; nearly half on dietary patterns and weight, but also six studies each on bone health and cardiovascular health.
Organizing our findings by dietary guidance topic, the numbers and results of recent child-focused studies are summarized briefly below.
- Adequate nutrients within calorie needs. Twenty studies evaluated aspects of adequate nutrients (especially calcium) within calorie needs; intakes of the nutrients or foods studied tended to be weakly associated with the outcomes investigated.
- Weight management. Eight studies examined dietary correlates of weight status; higher body mass index or overweight was associated with greater fast food consumption, higher protein intake, and less vigorous physical activity. Three studies of effects of weight management interventions on weight status found only modest and inconsistent success rates. One systematic review found that the primary factor distinguishing successful interventions was inclusion of a compulsory physical activity component.
- Fats. The 17 studies on dietary fat targeted many different outcomes including serum cholesterol and fatty acids, weight, asthma, cancer, insulin sensitivity, and others; results were mixed.
- Food Groups to Encourage:
- Fruits and Vegetables. The 14 studies of fruit and/or vegetable intake showed little or no favorable association with risk factors or health outcomes.
- Whole Grains. Two observational studies reported beneficial health effects of the consumption of whole grains on serum homocysteine and on folate and other B vitamins.
- Dairy Foods. Of the 21 studies related to consumption of dairy and calcium, seven focused on bone health and eight focused on weight. Most of the bone health studies showed a small benefit to bone health from a higher intake of milk products and/or calcium, but findings were mixed. Six studies investigated the intake of milk in relation to body mass index; three showed an inverse relationship, two showed no effect, and one showed a positive relationship.
- Carbohydrates. The body of evidence from 29 cross-sectional and longitudinal studies indicates that sugar-sweetened beverages and other items with added sugars (such as candy) are associated with increased body mass index and increased dental caries among children and adolescents. A meta-analysis of 88 studies of the effects of soft drinks concluded that consumption was linked to increased calorie intake and weight in children.
- Sodium and potassium. Three studies, including one meta-analysis study of 13 controlled trials, demonstrated that modest decreases in salt intake reduced blood pressure and pulse pressure in children and adolescents. No studies were found on children’s intake of potassium and health outcomes.
- Knowledge gaps. Among studies that focused on a specific dietary area, there is little information on variety of intake within that food group, or on variety of intake in general. Only one study reported on children’s dietary quality and adherence to the Dietary Guidelines and their body mass index. Other knowledge gaps include the behavioral determinants of eating patterns among children and the extent to which dietary behaviors track through childhood and into adulthood. Evidence is lacking in many areas, especially the health effects of children’s consumption of whole grains, potassium, and specific fats.
- Data limitations. Our review of the evidence is limited to the information contained in published articles and the quality and characteristics of the research itself. The most serious limitation is the paucity of information across several of the dietary guidance topics of interest. Individual studies with children, especially those with clinical measures, were often limited by small sample sizes (restricting the power to detect associations), or they pertained only to a high-risk group (for example, children with asthma or diabetes); their findings may not be relevant to the general child population or to both sexes. Further, longer-term follow-up data were not available for many topics. In some areas, a lack of a valid biomarker for nutrient intake makes it difficult to draw conclusions based on self-reported dietary data.
The body of evidence provided by the 2005 Dietary Guidelines Advisory Committee and by the expert groups that authored other contemporary guidance statements provides very limited direct support for dietary guidance for children. Relatively little growth of the science base has occurred since 2004, except on a few topics (added sugars and weight, dairy foods/calcium and bone health, and sodium and blood pressure). Because few 2004-2008 studies reported the dietary measure in a comparable way to the actual dietary recommendation, drawing evidence-based conclusions about children’s short- or long-term health effects of following the Dietary Guidelines remains a challenge.