What is the question?

• The question is: What is the relationship between portion size and growth, body composition, and risk of obesity? The populations of interest for this question include young children, children, adolescents, adults, older adults, and pregnancy and postpartum.

Why was this question asked?

• This systematic review was conducted by the 2025 Dietary Guidelines Advisory Committee as part of the process to develop the Dietary Guidelines for Americans, 2025-2030.

How was this question answered?

• The Committee conducted a systematic review to answer this question with support from the USDA Nutrition Evidence Systematic Review team.

What is the answer to the question?

• A conclusion statement cannot be drawn about the relationship between portion sizes consumed by young children, children, and adolescents and growth, body composition, and risk of obesity because there is not enough evidence available.
• A conclusion statement cannot be drawn about the relationship between portion sizes consumed by adults and older adults and body composition or risk of obesity because of inconsistency in the interventions, comparators, and outcomes in the body of evidence.
• A conclusion statement cannot be drawn about the relationship between portion sizes consumed during pregnancy and gestational weight gain because there is not enough evidence available.
• A conclusion statement cannot be drawn about the relationship between portion sizes consumed during postpartum and postpartum weight change because there is no evidence available

How up-to-date is this systematic review?

• Conclusion statements from this review are based on articles published between January 2000 and January 2024. 

Background

• This systematic review was conducted by the 2025 Dietary Guidelines Advisory Committee as part of the process to develop the Dietary Guidelines for Americans, 2025-2030. The U.S. Departments of Health and Human Services (HHS) and Agriculture (USDA) appointed the 2025 Dietary Guidelines Advisory Committee (Committee) in January 2023 to review evidence on high priority scientific questions related to diet and health. Their review forms the basis of their independent, science-based advice and recommendations to HHS and USDA, which is considered as the Departments develop the next edition of the Dietary Guidelines. As part of that process, the Committee conducted a systematic review with support from USDA’s Nutrition Evidence Systematic Review (NESR) team to answer the following question: What is the relationship between portion size and growth, body composition, and risk of obesity?

Methods

• The Committee conducted a systematic review using the methodology of the USDA NESR team. The Committee first developed a protocol. The intervention/exposure was a food-based strategy targeting food and/or beverage portion size and pre-portioned foods that considers energy density, nutrient density and/or the quality or type of food served or consumed by young children, children, adolescents, adults, older adults, pregnancy, and postpartum, the comparator was a different portion size served or consumed, and the outcomes were measures of growth (in young children, children, and adolescents) including: height, length/stature-for-age, weight, weight-for-age, stunting, failure to thrive, wasting, BMI-for-age, weight-for-length/stature, body circumferences (arm, neck, thigh), head circumference; body composition (in young children, children, adolescents, adults, and older adults) including: skinfold thickness, fat mass, ectopic fat, fat-free mass or lean mass, waist circumference, waist-to-hip-ratio; risk of obesity (in children, adolescents, adults, and older adults) including: BMI, underweight, normal weight, overweight and/or obesity, weight loss and maintenance (in adults and older adults); Pregnancy and postpartum-related weight change including: gestational weight gain and postpartum weight change. Additional inclusion criteria were established for the following study characteristics: a) use randomized or non-randomized controlled trial, prospective or retrospective cohort, or nested case-control study designs, b) be published in English in peer-reviewed journals, c) be from countries classified as high or very high on the Human Development Index, and d) enroll participants with a range of health statuses. The review excluded studies with infants (birth up to 12 months), studies that exclusively enrolled participants diagnosed with a disease, studies that examined portion size using liquid meal replacements, and studies with an intervention length less than 12 weeks.
• NESR librarians conducted a literature search in PubMed, Embase, CINAHL, and Cochrane to identify articles published between January 2000 and January 2024. Two NESR analysts independently screened all electronic results and the reference lists of included articles based on the pre-determined criteria.
• NESR analysts extracted data, from each included article, with a second analyst verifying accuracy of the extraction. Two NESR analysts independently conducted a formal risk of bias assessment, by study design, for each included article, then reconciled any differences in the assessment. The Committee qualitatively synthesized the evidence according to the synthesis plan, with attention given to the overarching themes or key concepts from the findings, similarities and differences between studies, and factors that may have affected the results. The Committee developed conclusion statements and graded the strength of evidence based on its consistency, precision, risk of bias, directness and generalizability.

Results

Young children, Children, and Adolescents

Conclusion statement and grade

• A conclusion statement cannot be drawn about the relationship between portion sizes consumed by young children, children, and adolescents and growth, body composition, and risk of obesity because there is not enough evidence available. (Grade: Grade Not Assignable)

Summary of the evidence

• There was not enough evidence available to answer this question. The one study that was included had numerous risks of bias concerns.

Adults and Older Adults

Conclusion statement and grade

• A conclusion statement cannot be drawn about the relationship between portion sizes consumed by adults and older adults and body composition or risk of obesity because of inconsistency in the interventions, comparators, and outcomes in the body of evidence. (Grade: Grade Not Assignable)

Summary of the evidence

• The body of evidence was inconsistent in the interventions, comparators, and outcomes examined. All included articles were part of weight loss trials.

Pregnancy

Conclusion statement and grade

• A conclusion statement cannot be drawn about the relationship between portion sizes consumed during pregnancy and gestational weight gain because there is not enough evidence available. (Grade: Grade Not Assignable)

Summary of the evidence

• There was not enough evidence available to answer this question.

Postpartum

Conclusion statement and grade

• A conclusion statement cannot be drawn about the relationship between portion sizes consumed during postpartum and postpartum weight change because there is no evidence available. (Grade: Grade Not Assignable)

Summary of the evidence

• There was not enough evidence available to answer this question.

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Suggested citation: Raynor HA, Gardner CD, Anderson CAM, Andres A, Fisher JO, Giovannucci E, Hoelscher DM, Jernigan VBB, Odoms-Young A, Palacios C, Stanford FC, Fultz AK, Obbagy J, Butera G, Higgins M, Terry N. Portion Size and Growth, Body Composition, and Risk of Obesity: A Systematic Review. November 2024. U.S. Department of Agriculture, Food and Nutrition Service, Center for Nutrition Policy and Promotion, Nutrition Evidence Systematic Review. Available at: https://doi.org/10.52570/NESR.DGAC2025.SR17