What is the question?

• The question is: What is the relationship between dietary patterns consumed during pregnancy and gestational weight gain? 

What is the answer to the question?

• Limited evidence suggests that certain dietary patterns during pregnancy are associated with a lower risk of excessive gestational weight gain during pregnancy. These patterns are higher in vegetables, fruits, nuts, legumes, fish, and lower in added sugar, and red and processed meat.

Why was this question asked?

• This important public health question was identified by the U.S. Departments of Agriculture (USDA) and Health and Human Services (HHS) to be examined by the 2020 Dietary Guidelines Advisory Committee.

How was this question answered?

• The 2020 Dietary Guidelines Advisory Committee, Pregnancy and Lactation Subcommittee conducted a systematic review to answer this question with support from the Nutrition Evidence Systematic Review (NESR) team.
• Dietary patterns were defined as the quantities, proportions, variety, or combination of different foods, drinks, and nutrients (when available) in diets, and the frequency with which they are habitually consumed. 
• Diets based on macronutrient distribution were examined when at least one macronutrient proportion was outside of the acceptable macronutrient distribution range (AMDR) for carbohydrate, fat, and/or protein, whether or not the foods/food groups consumed were provided.

What is the population of interest? 

• The population of interest is generally healthy, pregnant women.

What evidence was found? 

• This review includes 26 articles published between 2009 and 2019. 
• Many studies showed that “beneficial” dietary patterns were related to less weight gain during pregnancy.
• Dietary patterns that were consistently related to less weight gain during pregnancy were:
  • higher in vegetables, fruits, nuts, legumes, fish, and
  • lower in added sugar, red and processed meat.
• The body of evidence is limited in several ways:
  • Studies were mostly observational and cause-effect relationships between diet and weight gain during pregnancy were therefore difficult to determine. 
  • There was little racial/ethnic, socioeconomic, and age diversity in these studies.
  • It was difficult to compare studies due to inconsistencies in how diets were measured.
  • There were concerns about potential bias of the studies.
  • Many studies were not designed to study the relationship between dietary patterns and weight gain during pregnancy.

How up-to-date is this systematic review?

• This review searched for studies from January 2000 to November 2019.

Background

• This important public health question was identified by the U.S. Departments of Agriculture (USDA) and Health and Human Services (HHS) to be examined by the 2020 Dietary Guidelines Advisory Committee.
• The 2020 Dietary Guidelines Advisory Committee, Pregnancy and Lactation Subcommittee conducted a systematic review to answer this question with support from the Nutrition Evidence Systematic Review (NESR) team.
• The goal of this systematic review was to examine the following question: What is the relationship between dietary patterns consumed during pregnancy and gestational weight gain? 

Conclusion statement and grade

• Limited evidence suggests that certain dietary patterns during pregnancy are associated with a lower risk of excessive gestational weight gain during pregnancy. These patterns are higher in vegetables, fruits, nuts, legumes, fish, and lower in added sugar, and red and processed meat. (Grade: Limited)

Methods

• A literature search was conducted using four databases (PubMed, Cochrane, Embase, and CINAHL) to identify articles that evaluated the intervention/exposure of dietary patterns during pregnancy and the outcome of gestational weight gain. A manual search was conducted to identify articles that may not have been included in the electronic databases searched. Articles were screened by two NESR analysts independently for inclusion based on pre-determined criteria.
• Data extraction and risk of bias assessment were conducted for each included study, and both were checked for accuracy. The Committee qualitatively synthesized the body of evidence to inform development of a conclusion statement(s), and graded the strength of evidence using pre-established criteria for risk of bias, consistency, directness, precision, and generalizability.

Summary of the evidence

• This systematic review includes 26 articles, including five from four randomized controlled trials (RCTs) and 21 from 19 prospective cohort studies published between 2009 and 2019.
• Articles included in this review assessed one of the following interventions/exposures during pregnancy:
  • Dietary patterns (DPs) (24 studies).
  • Diets based on macronutrient distributions outside of the acceptable macronutrient distribution range (AMDR) (2 studies).
• Eight of the 15 articles that assessed maternal DPs using an index/score method showed an association with gestational weight gain (GWG). 
  • Five of the eight articles showed that greater adherence to a DP (identified as beneficial by the study) was associated with lower GWG.
  • Three articles showed that greater adherence to a DP (identified as beneficial by the study) was associated with greater GWG in all participants or only women with obesity.
• Four of the five articles that assessed maternal DPs using a factor or cluster analysis showed one or more associations between adherence to DPs and GWG. 
  • One article showed that greater adherence to a DP (identified as beneficial by the study) was associated with lower GWG.
  • Four articles showed that greater adherence to a DP (identified as detrimental by the study) was associated with higher GWG. 
• One study that assessed maternal DPs using reduced rank regression showed that greater adherence to a DP was associated with higher GWG. 
• Two RCTs showed that participants randomized to a DP (identified as beneficial by the study) had lower GWG. 
• One RCT and one prospective cohort study showed no association between maternal consumption of a diet higher in fat (i.e. >35 percent of total energy from fat, which is greater than the AMDR) and GWG.
• Although the DPs examined were characterized by combinations of different foods and beverages, the patterns that were consistently shown to be associated with lower risk of excessive GWG were: higher in vegetables, fruits, nuts, legumes, and fish and lower in added sugar and red and processed meat. 
  • Not all foods were part of the same DP. The evidence did not show a consistent association between grains or dairy and GWG. 
• The ability to draw strong conclusions was limited by the following issues:
  • There were few RCTs and thus data were primarily observational in nature, limiting the ability to determine causal effects of DPs on GWG.
  • Key confounders were not consistently controlled for in most of the studies.
  • Studies had risk-of-bias issues, including exposure misclassification, self-reported outcomes, and selection bias.
  • Most of the studies were not designed to assess the association between DPs and GWG.
  • People with lower SES, adolescents, and racially and ethnically diverse populations were underrepresented in the body of evidence.