Systematic review methods for the Pregnancy and Birth to 24 Months Project

USDA Nutrition Evidence Systematic Review's collaborative approach for conducting systematic reviews: Promoting diversity of expertise while managing potential conflicts of interest

U.S. Department of Agriculture's (USDA) Nutrition Evidence Systematic Review (NESR) Branch develops food-and nutrition-related systematic reviews and other evidence synthesis products. NESR has established itself as a key resource for the Federal government when making evidence-informed decisions related to public health nutrition, such as the development of the Dietary Guidelines for Americans. NESR's systematic review methodology is rigorous, protocol-driven, and highly collaborative. NESR's systematic reviews examine the complex interplay between diet and health with input and support from various collaborators, including Federal stakeholders, expert groups, and public stakeholders. Implementing NESR's rigorous methodology ensures that the appropriate steps are taken to minimize conflict of interest, producing systematic reviews that are high-quality, trustworthy, and useful to end users who make decisions based on their findings. This article describes how NESR's systematic review process leverages a diversity of expertise and experience, while managing potential conflicts of interest. It describes the groups who collaborate to conduct NESR systematic reviews, their expertise, and why their involvement is critical for ensuring the rigor and utility of NESR's work.

Breastfed and mixed fed infants who do not consume infant cereal are at risk for inadequate iron intake:data from the feeding infants and toddlers study 2016, a cross-sectional survey

BACKGROUND

According to the Feeding Infants and Toddlers Study (FITS), the percentage of older infants consuming infant cereal has declined from 72% of 6-11.9 month old infants in 2002 to 52% in 2016. This is especially concerning for breastfed and mixed fed infants because of their increased need for dietary sources of iron. This study explored the association between infant cereal consumption and nutrient intakes among breastfed and mixed fed infants.

METHODS

FITS 2016 is the largest cross-sectional survey of food and nutrient intakes among caregivers of children less than 4 years old in the United States. For this analysis, we evaluated 24 h dietary recalls for infants 6-11.9 months who were either breastfed (no infant formula provided, n = 296) or mixed fed (breastmilk and infant formula provided, n = 102). Infants were further categorized as infant cereal consumers or non-consumers. Nutrient intakes were compared with Adequate Intakes or Estimated Average Requirements when available. Differences between cereal consumers and non-consumers were calculated using unpaired T-tests.

RESULTS

Significantly fewer breastfed cereal consumers had intakes below the Estimated Average Requirement for iron (19% vs. 96%) and zinc (61% vs. 16%, p < 0.0001). Additionally, significantly more breastfed cereal consumers had intakes above the Adequate Intake level for 12 other nutrients compared to non-consumers. Among mixed fed infants, significantly fewer cereal consumers had intakes below the Estimated Average Requirement for iron compared to non-consumers (5% vs. 70%), but differences in other nutrients were not observed.

CONCLUSIONS

Almost all (96%) of the breastfed infants who did not consume infant cereal had inadequate iron intakes. Even among mixed fed infants, significantly fewer infant cereal consumers had inadequate iron intakes compared to non-cereal consumers. Infant cereal is an important source of iron and other key nutrients, especially for infants receiving breastmilk.

Perspective: USDA Nutrition Evidence Systematic Review Methodology: Grading the Strength of Evidence in Nutrition- and Public Health-Related Systematic Reviews

The USDA's Nutrition Evidence Systematic Review (NESR) team conducts food- and nutrition-related systematic reviews used to inform US Federal guidelines and programs, including the Dietary Guidelines for Americans. NESR's systematic review methodology includes a step to grade the strength of the evidence underlying conclusion statements, which is critical for ensuring that end users understand the level of certainty in conclusions when using them to make decisions. Over time, NESR has ensured its grading process not only remains state of the art but is also designed specifically for systematic reviews that inform Federal guidelines and programs on nutrition and public health. The NESR grading process used by the 2020 Dietary Guidelines Advisory Committee included 5 grading elements: risk of bias, consistency, directness, precision, and generalizability. Evidence was grouped by study design and assessed against these elements, and the grade assigned to the entire body of evidence took into consideration the strengths and limitations of each design. Based on this assessment, 1 of 4 grades was assigned: strong, moderate, limited, or grade not assignable. The grade was clearly communicated by integrating specific language into each conclusion statement (e.g., "strong evidence demonstrates" or "limited evidence suggests"), and supported by rationale documented in the review. NESR's grading process aligns with approaches used by other organizations that conduct systematic reviews, while retaining aspects unique to NESR's role in informing Federal nutrition and public health guidelines and programs. It provides a framework that promotes consistency in grading across food- and nutrition-related reviews, while offering flexibility that allows for thorough consideration of the body of evidence underlying an individual conclusion statement. NESR's rigorous and transparent methods for grading the strength of evidence in food- and nutrition-related systematic reviews ensure that decisions related to nutrition and public health are based on the strongest available evidence.

Omega-3 Fatty Acid Dietary Supplements Consumed During Pregnancy and Lactation and Child Neurodevelopment: A Systematic Review

BACKGROUND

Maternal nutrition during pregnancy and lactation has profound effects on the development and lifelong health of the child. Long-chain PUFAs are particularly important for myelination and the development of vision during the perinatal period.

OBJECTIVES

We conducted a systematic review to examine the relationship between supplementation with omega-3 fatty acids during pregnancy and/or lactation and neurodevelopment in children, to inform the Scientific Report of the 2020 Dietary Guidelines Advisory Committee.

METHODS

We identified articles on omega-3 fatty acid supplementation in pregnant and lactating women that included measures of neurodevelopment in their children (0-18 y) by searching PubMed, CENTRAL, Embase, and CINAHL Plus. After dual screening articles for inclusion, we qualitatively synthesized and graded the strength of evidence using pre-established criteria for assessing risk of bias, consistency, directness, precision, and generalizability.

RESULTS

We included 33 articles from 15 randomized controlled trials (RCTs) and 1 prospective cohort study. Of the 8 RCTs that delivered omega-3 fatty acid dietary supplements during pregnancy alone (200-2200 mg/d DHA and 0-1100 mg/d EPA for approximately 20 wk), 5 studies reported ≥1 finding that supplementation improved measures of cognitive development in the infant or child by 6%-11% (P < 0.05), but all 8 studies also reported ≥1 nonsignificant (P > 0.05) result. There was inconsistent or insufficient evidence for other outcomes (language, social-emotional, physical, motor, or visual development; academic performance; risks of attention deficit disorder, attention-deficit/hyperactivity disorder, autism spectrum disorder, anxiety, or depression) and for supplementation during lactation or both pregnancy and lactation. Populations with a lower socioeconomic status and adolescents were underrepresented and studies lacked racial and ethnic diversity.

CONCLUSIONS

Limited evidence suggests that omega-3 fatty acid supplementation during pregnancy may result in favorable cognitive development in the child. There was insufficient evidence to evaluate the effects of omega-3 fatty acid supplementation during pregnancy and/or lactation on other developmental outcomes.

Supporting strategies for enhancing vegetable liking in the early years of life: an umbrella review of systematic reviews

BACKGROUND

Many children worldwide do not eat recommended amounts of vegetables. Disliking vegetables is a key factor associated with low intake.

OBJECTIVE

This umbrella review synthesized systematic reviews to determine the effectiveness of sensory and behavioral strategies to facilitate liking of vegetables (primary outcome) in young children up to 5 y of age, as key predictors of vegetable intake (secondary outcome).

METHODS

Nine databases were searched up to May 2019 (updated in September 2020). Two reviewers independently conducted study screening and selection, data extraction, and assessment of methodological quality using AMSTAR 2 (A MeaSurement Tool to Assess systematic Reviews). Eleven reviews (n = 1 rated strong quality, n = 4 moderate quality, n = 6 low/critically low quality) examining 85 primary studies met the review criteria: systematic reviews and meta-analyses of primary studies (any quantitative design) that examined sensory or behavioral strategies on vegetable liking or intake (outcomes reported separately for children ≤5 y). Strategy effectiveness was synthesized into 3 categories based on evidence strength: 1) promising (large and consistent body of moderate quality evidence), 2) emerging (small to moderate body of mixed consistency and quality evidence), and 3) limited (small body of limited consistency and quality evidence).

RESULTS

Promising evidence was identified for repeated exposure to a single or a variety of vegetables. Emerging evidence was identified for several strategies that increase familiarity with vegetable flavors (e.g., via exposure in utero and through breast milk, and a "vegetable first" approach to complementary feeding) and/or willingness to try vegetables (e.g., via parental role modeling, nonfood rewards, and vegetable-based story books).

CONCLUSIONS

Current evidence supports incorporation of tailored advice into guideline documents for parents and carers to repeatedly expose their children to a variety of vegetables to increase vegetable intake. Ongoing robust research on strategies to facilitate children's liking of vegetables is warranted to strengthen the evidence base underpinning advice for parents and health professionals.

Perspective: Nutritional Status as a Biological Variable (NABV): Integrating Nutrition Science into Basic and Clinical Research and Care

The field of nutrition has evolved from one focused primarily on discovery of the identities, metabolic functions, and requirements for essential nutrients to one focused on the application of that knowledge to the development and implementation of dietary recommendations to promote health and prevent disease. This evolution has produced a deeper appreciation of not only the roles of nutrients, but also factors affecting their functions in increasingly complex global health contexts. The intersection of nutrition with an increasingly more complex global health context necessitates a view of nutritional status as a biological variable (NABV), the study of which includes an appreciation that nutritional status is: 1) not limited to dietary exposure; 2) intimately and inextricably involved in all aspects of human health promotion, disease prevention, and treatment; and 3) both an input and an outcome of health and disease. This expanded view of nutrition will inform future research by facilitating considerations of the contexts and variability associated with the many interacting factors affecting and affected by nutritional status. It will also demand new tools to study multifactorial relations to the end of increasing precision and the development of evidence-based, safe, and effective standards of health care, dietary interventions, and public health programs.

Relationships between seafood consumption during pregnancy and childhood and neurocognitive development: Two systematic reviews

Abundant data are now available to evaluate relationships between seafood consumption in pregnancy and childhood and neurocognitive development. We conducted two systematic reviews utilizing methodologies detailed by the Dietary Guidelines for Americans Scientific Advisory Committee 2020-2025. After reviewing 44 publications on 106,237 mother-offspring pairs and 25,960 children, our technical expert committee developed two conclusion statements that included the following: "Moderate and consistent evidence indicates that consumption of a wide range of amounts and types of commercially available seafood during pregnancy is associated with improved neurocognitive development of offspring as compared to eating no seafood. Overall, benefits to neurocognitive development began at the lowest amounts of seafood consumed (∼4 oz/wk) and continued through the highest amounts, above 12 oz/wk, some range up to >100 oz/wk.", "This evidence does not meet the criteria for "strong evidence" only due to a paucity of randomized controlled trials that may not be ethical or feasible to conduct for pregnancy" and "Moderate and consistent evidence indicates that consumption of >4 oz/wk and likely >12 oz/wk of seafood during childhood has beneficial associations with neurocognitive outcomes." No net adverse neurocognitive outcomes were reported among offspring at the highest ranges of seafood intakes despite associated increases in mercury exposures. Data are insufficient for conclusive statements regarding lactation, optimal amounts, categories or specific species characterized by mercury content and neurocognitive development; although there is some evidence that dark/oily seafood may be more beneficial. Research was conducted in healthy women and children and is generalizable to US populations. Assessment of seafood as a whole food integrates inherently integrates any adverse effects from neurotoxicants, if any, and benefits to neurocognition from omega-3 fats, as well as other nutrients critical to optimal neurological development. Understanding of the effects of seafood consumption on neurocognition can have significant public health implications.

Infant milk-feeding practices and childhood leukemia: a systematic review

BACKGROUND

During the Pregnancy and Birth to 24 Months Project, the US Departments of Agriculture and Health and Human Services initiated a review of evidence on diet and health in these populations.

OBJECTIVES

The aim of these systematic reviews was to examine the relation of 1) never versus ever feeding human milk, 2) shorter versus longer durations of any human milk feeding, 3) shorter versus longer durations of exclusive human milk feeding, and 4) feeding a lower versus higher intensity of human milk to mixed-fed infants with acute childhood leukemia, generally, and acute lymphoblastic leukemia, specifically.

METHODS

The Nutrition Evidence Systematic Review team conducted systematic reviews with external experts. We searched CINAHL, Cochrane, Embase, and PubMed for articles published January 1980 to March 2016, dual-screened the results using predetermined criteria, extracted data from and assessed risk of bias for each included study, qualitatively synthesized the evidence, developed conclusion statements, and graded the strength of the evidence.

RESULTS

We included 24 articles from case-control or retrospective studies. Limited evidence suggests that never feeding human milk versus 1) ever feeding human milk and 2) feeding human milk for durations ≥6 mo are associated with a slightly higher risk of acute childhood leukemia, whereas evidence comparing never feeding human milk with feeding human milk for durations <6 mo is mixed. Limited evidence suggests that, among infants fed human milk, a shorter versus longer duration of human milk feeding is associated with a slightly higher risk of acute childhood leukemia. None of the included articles examined exclusive human milk feeding or the intensity of human milk fed to mixed-fed infants.

CONCLUSIONS

Feeding human milk for short durations or not at all may be associated with slightly higher acute childhood leukemia risk. The evidence could be strengthened with access to broadly generalizable prospective samples; therefore, we recommend linking surveillance systems that collect infant feeding and childhood cancer data.

Caregiver feeding practices and child weight outcomes: a systematic review

BACKGROUND

As part of the USDA-Department of Health and Human Services Pregnancy and Birth to 24 Months Project, we conducted systematic reviews (SRs) on topics important for health and nutrition of young children.

OBJECTIVES

The purpose of the present SR was to examine the relation between caregiver feeding practices in children from birth to 24 mo and child weight gain, size, and body composition.

METHODS

A search of articles published from January 1980 to January 2017 in 4 databases identified 8739 references. Nutrition Evidence Systematic Review (NESR) analysts used the Nutrition Evidence Library Risk of Bias Assessment Tool to assess potential bias in the studies, and a Technical Expert Collaborative graded the body of evidence using the NESR grading rubric.

RESULTS

Twenty-seven articles were included in this review (8 controlled trials, 19 longitudinal cohort studies). Moderate evidence from randomized controlled trials suggests that providing responsive feeding guidance to teach mothers to recognize and respond appropriately to children's hunger and satiety cues can lead to "normal" weight gain and/or "normal" weight status in children aged ≤2 y compared with children whose mothers did not receive responsive feeding guidance. Moderate evidence from longitudinal cohort studies indicates an association between maternal feeding practices and the child's weight status and/or weight gain, but the direction of effect has not been adequately studied. Restrictive feeding practices are associated with increased weight gain and higher weight status, and pressuring feeding practices are associated with decreased weight gain and lower weight status. Evidence suggests that a mother's feeding practices are related to concerns about her child's body weight.

CONCLUSIONS

This review highlights the importance of the interaction between caregivers and infants and toddlers related to child feeding practices on children's weight outcomes. Research is needed on more diverse populations with consistent methodological app-roaches and objective measures.

Dietary patterns before and during pregnancy and maternal outcomes: a systematic review

BACKGROUND

Hypertensive disorders of pregnancy (HDP) and gestational diabetes mellitus (GDM) are common maternal complications during pregnancy, with short- and long-term sequelae for both mothers and children.

OBJECTIVE

Two systematic review questions were used to examine the relation between 1) dietary patterns before and during pregnancy, 2) HDP, and 3) GDM.

METHODS

A search was conducted from January 1980 to January 2017 in 9 databases including PubMed, Embase, and Cochrane. Two analysts independently screened articles using a priori inclusion and exclusion criteria; data were extracted from included articles, and risk of bias was assessed. After qualitative synthesis, a conclusion statement was drafted for each question and the evidence supporting the conclusion was graded.

RESULTS

Of the 9103 studies identified, 8 [representing 4 cohorts and 1 randomized controlled trial (RCT)] were included for HDP and 11 (representing 6 cohorts and 1 RCT) for GDM. Limited evidence in healthy Caucasian women with access to health care suggests dietary patterns before and during pregnancy that are higher in vegetables, fruits, whole grains, nuts, legumes, fish, and vegetable oils and lower in meat and refined grains are associated with reduced risk of HDP, including preeclampsia and gestational hypertension. Limited but consistent evidence suggests certain dietary patterns before pregnancy are associated with reduced risk of GDM. These protective dietary patterns are higher in vegetables, fruits, whole grains, nuts, legumes, and fish and lower in red and processed meats. Most of the research was conducted in healthy, Caucasian women with access to health care. Insufficient evidence exists on the associations between dietary patterns before and during pregnancy and risk of HDP in minority women and those of lower socioeconomic status, and dietary patterns during pregnancy and risk of GDM.

CONCLUSIONS

Although some conclusions were drawn from these systematic reviews, more research is needed to address gaps and limitations in the evidence.

Complementary feeding and micronutrient status: a systematic review

BACKGROUND

Proper nutrition during early life is critical for growth and development.

OBJECTIVES

The aim was to describe systematic reviews conducted by the Nutrition Evidence Systematic Review team for the USDA and the Department of Health and Human Services Pregnancy and Birth to 24 Months Project to answer the following: What is the relation between 1) timing of introduction of complementary foods and beverages (CFBs) or 2) types and/or amounts of CFBs consumed and micronutrient status (iron, zinc, vitamin D, vitamin B-12, folate, and fatty acid status)?

METHODS

A literature search identified articles from developed countries published from January 1980 to July 2016 that met the inclusion criteria. Data were extracted and risk of bias assessed. Evidence was qualitatively synthesized to develop a conclusion statement, and the strength of the evidence was graded.

RESULTS

Nine articles addressed the timing of CFB introduction and 31 addressed types or amounts or both of CFBs. Moderate evidence suggests that introducing CFBs at age 4 mo instead of 6 mo offers no advantages or disadvantages in iron status among healthy full-term infants. Evidence is insufficient on the timing of CFB introduction and other micronutrient status outcomes. Strong evidence suggests that CFBs containing iron (e.g., meat, fortified cereal) help maintain adequate iron status or prevent deficiency in the first year among infants at risk of insufficient iron stores or low intake. Benefits for infants with sufficient iron stores (e.g., infant formula consumers) are less clear. Moderate evidence suggests that CFBs containing zinc (e.g., meat, fortified cereal) support zinc status in the first year and CFB fatty acid composition influences fatty acid status. Evidence is insufficient with regard to types and amounts of CFBs and vitamin D, vitamin B-12, and folate status, or the relation between lower-iron-containing CFBs and micronutrient status.

CONCLUSIONS

Several conclusions on CFBs and micronutrient status were drawn from these systematic reviews, but more research that addresses specific gaps and limitations is needed.

Infant milk-feeding practices and diagnosed celiac disease and inflammatory bowel disease in offspring: a systematic review

BACKGROUND

During the Pregnancy and Birth to 24 Months Project, the USDA and US Department of Health and Human Services initiated an evidence review on diet and health in these populations.

OBJECTIVE

The aim of these systematic reviews was to examine the relationships of never versus ever feeding human milk, shorter versus longer durations of any and exclusive human milk feeding, and feeding a lower versus a higher intensity of human milk to mixed-fed infants with diagnosed celiac disease and inflammatory bowel disease (IBD).

METHODS

The Nutrition Evidence Systematic Review team (formerly called the Nutrition Evidence Library) conducted systematic reviews with external experts. We searched CINAHL, Cochrane, Embase, and PubMed for articles published January, 1980 to March, 2016, dual-screened the results using predetermined criteria, extracted data from and assessed risk of bias for each included study, qualitatively synthesized the evidence, developed conclusion statements, and graded the strength of the evidence.

RESULTS

We included 9 celiac disease and 17 IBD articles. Limited case-control evidence suggests never versus ever being fed human milk is associated with higher risk of celiac disease, but concerns about reverse causality precluded a conclusion about the relationship of shorter versus longer durations of any human milk feeding with celiac disease. Evidence examining never versus ever feeding human milk and IBD was inconclusive, and limited, but consistent, case-control evidence suggests that, among infants fed human milk, shorter versus longer durations of any human milk feeding are associated with higher risk of IBD. For both outcomes, evidence examining the duration of exclusive human milk feeding was scant and no articles examined the intensity of human milk fed to mixed-fed infants.

CONCLUSION

Limited case-control evidence suggests that feeding human milk for short durations or not at all associates with higher risk of diagnosed IBD and celiac disease, respectively. The small number of studies and concern about reverse causality and recall bias prevent stronger conclusions.

The Pregnancy and Birth to 24 Months Project: a series of systematic reviews on diet and health

Nutrition exposures during the earliest stages of life are integral to growth and development and may continue to affect health through adulthood. The purpose of the Pregnancy and Birth to 24 Months (P/B-24) Project was to conduct a series of systematic reviews on diet and health for women who are pregnant and for infants and toddlers from birth to 24 mo of age. The P/B-24 Project was a joint initiative led by the USDA and the US Department of Health and Human Services. The USDA's Nutrition Evidence Systematic Review team, previously known as the Nutrition Evidence Library, carried out the series of systematic reviews in collaboration with programmatic and scientific experts. Systematic review questions were prioritized based on federal policy, program, or guidance needs, potential to support the development of healthy dietary intake, and public health importance. Systematic reviews were conducted on specific topics related to dietary intake before and during pregnancy, infant milk feeding practices, complementary feeding, flavor exposures, and infant/toddler feeding practices. Across the reviews, relationships were observed between P/B-24 diet exposures and a variety of outcomes of public health importance. Evidence showed links between dietary intake before and during pregnancy, during the period of human milk or infant formula feeding, and through introduction of complementary foods and beverages and health outcomes. Additionally, the reviews on flavor exposure and infant/toddler feeding practices highlight the importance of maternal diet during pregnancy and lactation and caregiver feeding strategies and practices. Systematic reviews are an important tool to inform our understanding of the body of evidence related to diet and health, and scientists can use the P/B-24 Project reviews to continue to advance research in these areas.

Infant milk-feeding practices and diabetes outcomes in offspring: a systematic review

BACKGROUND

During the Pregnancy and Birth to 24 Months Project, the US Departments of Agriculture and Health and Human Services initiated a review of evidence on diet and health in these populations.

OBJECTIVES

The aim of these systematic reviews was to examine the relation of 1) never versus ever feeding human milk, 2) shorter versus longer durations of any human milk feeding, 3) shorter versus longer durations of exclusive human milk feeding, and 4) feeding a lower versus higher intensity of human milk to mixed-fed infants with type 1 and type 2 diabetes in offspring.

METHODS

The Nutrition Evidence Systematic Review team conducted systematic reviews with external experts. We searched CINAHL, Cochrane, Embase, and PubMed for articles published January 1980-March 2016, dual-screened the results according to predetermined criteria, extracted data from and assessed the risk of bias for each included study, qualitatively synthesized the evidence, developed conclusion statements, and graded the strength of the evidence.

RESULTS

The 4 systematic reviews included 21, 37, 18, and 1 articles, respectively. Observational evidence suggests that never versus ever feeding human milk (limited evidence) and shorter versus longer durations of any (moderate evidence) and exclusive (limited evidence) human milk feeding are associated with higher type 1 diabetes risk. Insufficient evidence examined type 2 diabetes. Limited evidence suggests that the durations of any and exclusive human milk feeding are not associated with intermediate outcomes (e.g., fasting glucose, insulin resistance) during childhood.

CONCLUSIONS

Limited to moderate evidence suggests that feeding less or no human milk is associated with higher risk of type 1 diabetes in offspring. Limited evidence suggests no associations between the durations of any and exclusive human milk feeding and intermediate diabetes outcomes in children. Additional research is needed on infant milk-feeding practices and type 2 diabetes and intermediate outcomes in US populations, which may have distinct metabolic risk.

Complementary feeding and developmental milestones: a systematic review

BACKGROUND

Systematic reviews were conducted as part of the USDA and the US Department of Health and Human Services Pregnancy and Birth to 24 Months Project to examine the relation between complementary feeding and developmental milestones.

OBJECTIVES

The aim of this study was to describe systematic reviews examining the relationship between timing of introduction of complementary foods and beverages (CFB), and the types and amounts of CFB consumed, and developmental milestones.

METHODS

The literature was searched using 4 databases (PubMed, Cochrane, Embase, and CINAHL) to identify articles that met predetermined criteria for inclusion. Data extraction and risk of bias assessment were conducted for each included study. The body of evidence for each systematic review was qualitatively synthesized to develop a conclusion statement, and the strength of evidence was graded.

RESULTS

Three included articles (1 randomized controlled trial; 2 observational studies) examined timing of introduction of CFB. Eight included articles (3 randomized controlled trials; 5 observational studies) examined types and amounts of CFB. There was insufficient evidence to draw conclusions about the relation between either timing of CFB introduction or types and amounts of CFB, and developmental milestones.

CONCLUSIONS

The ability to draw conclusions about the relationship between complementary feeding and developmental milestones was restricted by an inadequate amount of evidence with potential for issues with reverse causality and wide variation in design, type/age of outcome assessment, exposure assessment, and reported results. Additional research to address these gaps and limitations would be useful.

Infant milk-feeding practices and food allergies, allergic rhinitis, atopic dermatitis, and asthma throughout the life span: a systematic review

BACKGROUND

During the Pregnancy and Birth to 24 Months Project, the USDA and Department of Health and Human Services initiated a review of evidence on diet and health in these populations.

OBJECTIVES

The aim of these systematic reviews was to examine the relation of 1) never versus ever feeding human milk, 2) shorter versus longer durations of any human milk feeding, 3) shorter versus longer durations of exclusive human milk feeding prior to infant formula introduction, 4) feeding a lower versus higher intensity of human milk to mixed-fed infants, and 5) feeding a higher intensity of human milk by bottle versus breast with food allergies, allergic rhinitis, atopic dermatitis, and asthma.

METHODS

The Nutrition Evidence Systematic Review team conducted systematic reviews with external experts. We searched CINAHL, Cochrane, Embase, and PubMed for articles published between January 1980 and March 2016, dual-screened the results according to predetermined criteria, extracted data from and assessed the risk of bias for each included study, qualitatively synthesized the evidence, developed conclusion statements, and graded the strength of the evidence.

RESULTS

The systematic reviews numbered 1-5 above included 44, 35, 1, 0, and 0 articles, respectively. Moderate, mostly observational, evidence suggests that 1) never versus ever being fed human milk is associated with higher risk of childhood asthma, and 2) among children and adolescents who were fed human milk as infants, shorter versus longer durations of any human milk feeding are associated with higher risk of asthma. Limited evidence does not suggest associations between 1) never versus ever being fed human milk and atopic dermatitis in childhood or 2) the duration of any human milk feeding and allergic rhinitis and atopic dermatitis in childhood.

CONCLUSIONS

Moderate evidence suggests that feeding human milk for short durations or not at all is associated with higher childhood asthma risk. Evidence on food allergies, allergic rhinitis, and atopic dermatitis is limited.

Repeated exposure to food and food acceptability in infants and toddlers: a systematic review

BACKGROUND

Repeated exposure has been found to be an effective strategy to increase acceptability of foods in older children and adults, but little is known about its effectiveness in the birth to 24-mo population.

OBJECTIVES

This systematic review was conducted to examine the effects of repeated exposure to a single or multiple foods on acceptance of those or other foods among infants and toddlers.

METHODS

A search was conducted for peer-reviewed articles related to food acceptability, flavor, taste, and infants and toddlers in 12 databases (e.g., PubMed, Embase, Cochrane, and CINAHL) with a date range of January 1980 to July 2017. The Nutrition Evidence Library (NEL) Bias Assessment Tool was used to assess potential bias in the included studies, and the NESR grading rubric was used to grade evidence supporting the conclusion statement.

RESULTS

From the 10,844 references obtained, 21 studies (19 controlled trials and 2 longitudinal cohort studies) published from 1980 to 2015 were included in this review. Moderate evidence indicates that tasting a single vegetable or fruit or multiple vegetable(s) or fruit(s) 1 food per day for 8-10 or more days is likely to increase acceptability of an exposed food (indicated by an increase in intake or faster rate of feeding after comparison with before the exposure period) in infants and toddlers 4-24 mo old. The effect of repeated exposure on acceptability is likely to generalize to other foods within the same food category but not foods from a different food category. Findings are based on the effects of repeated exposure to mostly vegetables with some findings on repeated exposure to fruits.

CONCLUSION

This review advances the understanding of early food experiences and the development of food acceptability. Additional research is needed using diverse foods and textures with a focus on the transition to table foods.

Complementary feeding and bone health: a systematic review

BACKGROUND

Proper nutrition during infancy and toddlerhood is crucial for supporting healthy growth and development, including bone health. Complementary feeding is the process that starts when human milk or infant formula is complemented by other foods and beverages, beginning during late infancy and continuing to 24 mo of age.

OBJECTIVES

This article aims to describe systematic reviews (SRs) conducted by the Nutrition Evidence Systematic Review team for the USDA and the Department of Health and Human Services Pregnancy and Birth to 24 Months Project to answer these questions: what is the relationship between 1) timing of introduction of complementary foods and beverages (CFBs) or 2) types and/or amounts of CFBs consumed and bone health? Methods: The literature was searched with the use of 4 databases (CINAHL, Cochrane, Embase, and PubMed) to identify articles published from January 1980 to July 2016 that addressed these topics and met predetermined criteria for inclusion. For each study, data were extracted and risk of bias was assessed. The evidence was qualitatively synthesized to develop a conclusion statement, and the strength of the evidence was graded.

RESULTS

Three articles addressed the timing of introduction of CFBs and bone health during childhood (through 18 y of age), and 2 addressed the types and/or amounts of CFBs consumed relative to bone health.

CONCLUSIONS

Insufficient evidence was available to draw conclusions about the relationships between the timing of CFB introduction and types and/or amounts of CFBs consumed and bone health. Therefore, a grade was not assignable for these SRs. The ability to draw conclusions was limited by an overall lack of research, failure to adjust for several key confounding factors, and heterogeneity in studies with regard to methodology, subject populations, and results. Additional research is needed that addresses these gaps and limitations.

Types and amounts of complementary foods and beverages consumed and growth, size, and body composition: a systematic review

BACKGROUND

Systematic reviews (SRs) were conducted by the Nutrition Evidence Systematic Review (NESR) team for the USDA's and the Department of Health and Human Services' Pregnancy and Birth to 24 Months Project.

OBJECTIVES

The aim was to describe the SRs examining the relationship between types and amounts of complementary foods and beverages (CFBs) and growth, size, and body-composition outcomes.

METHODS

The NESR team collaborated with subject matter experts to conduct this SR. The literature was searched and screened using predetermined criteria. For each included study, data were extracted and risk of bias was assessed. The evidence was qualitatively synthesized to develop a conclusion statement, and the strength of evidence was graded.

RESULTS

This SR includes 49 articles that examined type, amount, or both of CFBs consumed and growth, size, and body-composition outcomes. Moderate evidence suggests that consuming either different amounts of meat, meat instead of iron-fortified cereal, or types of CFBs with different fats or fatty acids does not favorably or unfavorably influence growth, size, or body composition. In relation to overweight/obesity, insufficient evidence is available with regard to the intake of meat or CFBs with different fats or fatty acids. Limited evidence suggests that type and amount of fortified infant cereal does not favorably or unfavorably influence growth, size, body composition, or overweight/obesity. Limited evidence suggests that sugar-sweetened beverage consumption during the complementary feeding period is associated with increased obesity risk in childhood but is not associated with other measures of growth, size, or body composition. Limited evidence showed a positive association between juice intake and infant weight-for-length and child body mass index z scores. Insufficient evidence is available on other CFBs or dietary patterns in relation to outcomes.

CONCLUSIONS

Although several conclusions were drawn, additional research is needed that includes randomized controlled trials, examines a wider range of CFBs, considers issues of reverse causality, and adjusts for potential confounders to address gaps and limitations in the evidence.

Complementary feeding and food allergy, atopic dermatitis/eczema, asthma, and allergic rhinitis: a systematic review

BACKGROUND

Nutrition during infancy and toddlerhood may influence health and disease prevention across the life span. Complementary feeding (CF) starts when human milk or infant formula is complemented by other foods and beverages, beginning during infancy and continuing to age 24 mo.

OBJECTIVES

The aim of this study was to describe systematic reviews conducted for the USDA and the Department of Health and Human Services Pregnancy and Birth to 24 Months Project to answer the following question: What is the relationship between the timing of the introduction of complementary foods and beverages (CFBs), or types and amounts of CFBs consumed, and the development of food allergy, atopic dermatitis/eczema, asthma, and allergic rhinitis?

METHODS

The literature was searched using 4 databases (CINAHL, Cochrane, Embase, PubMed) to identify articles published from January 1980 to February 2017 that met predetermined inclusion criteria. For each study, data were extracted and risk of bias was assessed. The evidence was qualitatively synthesized to develop a conclusion statement, and the strength of the evidence was graded.

RESULTS

Thirty-one included articles addressed the timing of CFB introduction, and 47 articles addressed the types and amounts of CFBs consumed.

CONCLUSIONS

Moderate evidence suggests that there is no relationship between the age at which CF first begins and the risk of developing food allergy, atopic dermatitis/eczema, or childhood asthma. Limited to strong evidence, depending on the specific food, suggests that introducing allergenic foods in the first year of life (after 4 mo) does not increase the risk of food allergy and atopic dermatitis/eczema but may prevent peanut and egg allergy. There is not enough evidence to determine a relationship between diet diversity or dietary patterns and atopic disease. Research is needed to address gaps and limitations in the evidence on CF and atopic disease, including research that uses valid and reliable diagnostic measures and accounts for key confounders and potential reverse causality.

Dietary patterns before and during pregnancy and birth outcomes: a systematic review

BACKGROUND

Maternal diet before and during pregnancy could influence fetal growth and birth outcomes.

OBJECTIVE

Two systematic reviews aimed to assess the relationships between dietary patterns before and during pregnancy and 1) gestational age at birth and 2) gestational age- and sex-specific birth weight.

METHODS

Literature was searched from January, 1980 to January, 2017 in 9 databases including PubMed, Embase, and Cochrane. Two analysts independently screened articles using predetermined inclusion and exclusion criteria. Data were extracted from included articles and risk of bias was assessed. Data were synthesized qualitatively, a conclusion statement was drafted for each question, and evidence supporting each conclusion was graded.

RESULTS

Of the 9103 studies identified, 11 [representing 7 cohorts and 1 randomized controlled trial (RCT)] were included for gestational age and 21 (representing 19 cohorts and 2 RCTs) were included for birth weight. Limited but consistent evidence suggests that certain dietary patterns during pregnancy are associated with a lower risk of preterm birth and spontaneous preterm birth. These protective dietary patterns are higher in vegetables; fruits; whole grains; nuts, legumes, and seeds; and seafood (preterm birth, only), and lower in red and processed meats, and fried foods. Most of the research was conducted in healthy Caucasian women with access to health care. No conclusion can be drawn on the association between dietary patterns during pregnancy and birth weight outcomes. Although research is available, the ability to draw a conclusion is restricted by inconsistency in study findings, inadequate adjustment of birth weight for gestational age and sex, and variation in study design, dietary assessment methodology, and adjustment for key confounding factors. Insufficient evidence exists regarding dietary patterns before pregnancy for both outcomes.

CONCLUSIONS

Maternal dietary patterns may be associated with a lower preterm and spontaneous preterm birth risk. The association is unclear for birth weight outcomes.

Timing of introduction of complementary foods and beverages and growth, size, and body composition: a systematic review

BACKGROUND

The systematic review described in this article was conducted as part of the USDA and Department of Health and Human Services Pregnancy and Birth to 24 Months Project.

OBJECTIVES

The aim was to describe the relationship between timing of introduction of complementary foods and beverages (CFBs) and growth, size, and body-composition outcomes across the life span.

METHODS

The literature was searched and selected using predetermined criteria. Data were extracted and risk of bias assessed for each included study. Evidence was qualitatively synthesized, conclusion statements were developed, and the strength of the evidence was graded.

RESULTS

Eighty-one articles were included in this systematic review that addressed timing of CFB introduction relative to growth, size, and body-composition outcomes from infancy through adulthood. Moderate evidence suggests that introduction of CFBs between the ages of 4 and 5 mo compared with ∼6 mo is not associated with weight status, body composition, body circumferences, weight, or length among generally healthy, full-term infants. Limited evidence suggests that introduction of CFBs before age 4 mo may be associated with higher odds of overweight/obesity. Insufficient evidence exists regarding introduction at age ≥7 mo.

CONCLUSIONS

Although several conclusions were drawn in this systematic review, additional research is needed to address gaps and limitations in the evidence on timing of introduction of CFBs and growth, size, and body composition, such as randomized controlled trials that examine multiple outcomes and/or CFB introduction between the ages of 4 and 6 mo, and research that accounts for potential confounders such as feeding practices and baseline growth status and considers issues of reverse causality.

Infant milk-feeding practices and cardiovascular disease outcomes in offspring: a systematic review

BACKGROUND

During the Pregnancy and Birth to 24 Months Project, the US Departments of Agriculture and Health and Human Services initiated a review of evidence on diet and health in these populations.

OBJECTIVES

The aim of these systematic reviews was to examine the relation of 1) never versus ever feeding human milk, 2) shorter versus longer durations of any human milk feeding, 3) shorter versus longer durations of exclusive human milk feeding, and 4) lower versus higher intensities of human milk fed to mixed-fed infants with intermediate and endpoint cardiovascular disease (CVD) outcomes in offspring.

METHODS

The Nutrition Evidence Systematic Review team conducted systematic reviews with external experts. We searched CINAHL, Cochrane, Embase, and PubMed for articles published January 1980-March 2016, dual-screened the results using predetermined criteria, extracted data from and assessed the risk of bias for each included study, qualitatively synthesized the evidence, developed conclusion statements, and graded the strength of the evidence.

RESULTS

The 4 systematic reviews included 13, 24, 6, and 0 articles, respectively. The evidence was insufficient to draw conclusions about endpoint CVD outcomes across all 4 systematic reviews. Limited evidence suggests that never versus ever being fed human milk is associated with higher blood pressure within a normal range at 6-7 y of age. Moderate evidence suggests there is no association between the duration of any human milk feeding and childhood blood pressure. Limited evidence suggests there is no association between the duration of exclusive human milk feeding and blood pressure or metabolic syndrome in childhood. Additional evidence about intermediate outcomes for the 4 systematic reviews was scant or inconclusive.

CONCLUSIONS

There is insufficient evidence to draw conclusions about the relationships between infant milk-feeding practices and endpoint CVD outcomes; however, some evidence suggests that feeding less or no human milk is not associated with childhood hypertension.