What is the question?

• The question is: What is the relationship between portion size and energy intake? The populations of interest for this question include young children, children, adolescents, adults, older adults, 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?

• Serving larger portions of energy dense foods increases energy intake in children. This conclusion statement is based on evidence graded as strong. 
• Serving larger portions of vegetables and fruits increases intake of those foods without increasing energy intake in children. This conclusion statement is based on evidence graded as moderate.
• A conclusion statement cannot be drawn about the relationship between portion size and energy intake in young children and adolescents because there is no evidence available. 
• A conclusion statement cannot be drawn about the relationship between pre-portioned foods by young children, children, and adolescents and energy intake because there is not enough evidence available. 
• Serving larger portions of foods increases food and energy intake in adults and older adults. This conclusion statement is based on evidence graded as strong. 
• Portion size and energy density are independent and additive in their effects on energy intake in adults and older adults. This conclusion statement is based on evidence graded as moderate. 
• Serving foods as smaller pre-portioned amounts decreases energy intake in adults and older adults. This conclusion statement is based on evidence graded as moderate. 
• A conclusion statement cannot be drawn about the relationship between portion size and energy intake during pregnancy because there is no evidence available.
• A conclusion statement cannot be drawn about the relationship between pre-portioned foods and energy intake during pregnancy because there is no evidence available.
• A conclusion statement cannot be drawn about the relationship between portion size and energy intake during postpartum because there is no evidence available.
• A conclusion statement cannot be drawn about the relationship between pre-portioned foods and energy intake during postpartum 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 energy intake?

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 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 in young children, children, adolescents, adults, older adults, pregnancy, and postpartum. The comparator was a different portion size served or consumed. The outcome was energy intake. 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, and studies that examine portion size using liquid meal replacements. 
• 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

• Serving larger portions of energy dense foods increases energy intake in children. This conclusion statement is based on evidence graded as strong. (Grade: Strong)

Summary of the evidence

• Twenty-seven articles comprising 28 interventions met the inclusion criteria for this review. Twenty-five were crossover randomized controlled trials, 2 were parallel randomized controlled trials, and 1 was a non-randomized controlled trial. 
• The direction of results and size of effects were similar across studies.
• The size of study groups was large across studies. Most studies examined enough cases of energy intake. Variation around the effect estimates were narrow across studies. 
• Most studies were designed and conducted well.
• The populations, interventions/exposures, comparators, and outcomes that were examined directly represent those of interest in this review.
• The evidence applies to the U.S. population.

Conclusion statement and grade

• Serving larger portions of vegetables and fruits increases intake of those foods without increasing energy intake in children. This conclusion statement is based on evidence graded as moderate. (Grade: Moderate)

Summary of the evidence

• Six articles met the inclusion criteria for this review. Six were crossover randomized controlled trials.
• The direction of results and size of effects were similar across studies.
• The size of study groups was small in some studies. Some studies examined few cases of vegetable and fruit portion sizes and energy intake. 
• Most studies were designed and conducted well.
• The populations, interventions/exposures, comparators, and outcomes that were examined directly represent those of interest in this review.
• The evidence applies to the U.S. population, but may not apply to all race and ethnicities and socioeconomic positions.

Conclusion statement and grade

• A conclusion statement cannot be drawn about the relationship between portion size and energy intake in young children and adolescents because there is no evidence available. (Grade: Grade Not Assignable)

Summary of the evidence

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

Conclusion statement and grade

• A conclusion statement cannot be drawn about the relationship between pre-portioned foods by young children, children, and adolescents and energy intake 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.

Adults and Older Adults

Conclusion statement and grade

• Serving larger portions of foods increases food and energy intake in adults and older adults. This conclusion statement is based on evidence graded as strong. (Grade: Strong)

Summary of the evidence

• Forty-four articles comprising 51 interventions met the inclusion criteria for this review. Thirty-nine were crossover randomized controlled trials, 9 were parallel randomized controlled trials, and 3 were non-randomized controlled trials. 
• The direction of results and size of effects were similar across studies.
• The size of study groups was large across studies. Most studies examined enough cases of energy intake. Variation around the effect estimates were narrow across studies. 
• Most studies were designed and conducted well.
• The populations, interventions/exposures, comparators, and outcomes that were examined directly represent those of interest in this review.
• The evidence applies to the U.S. population.

Conclusion statement and grade

• Portion size and energy density are independent and additive in their effects on energy intake in adults and older adults. This conclusion statement is based on evidence graded as moderate. (Grade: Moderate)

Summary of the evidence

• Five articles comprising 6 interventions met the inclusion criteria for this review. Six were crossover randomized controlled trials.
• The direction of results and size of effects were similar across studies.
• The size of study groups was small in some studies. Some studies examined few cases of portion size, energy density, and energy intake. 
• Most studies were designed and conducted well.
• The populations, interventions/exposures, and comparators that were examined directly represent those of interest in this review.
• The evidence applies to the U.S. population, but may not apply to all race and ethnicities and socioeconomic positions.

Conclusion statement and grade

• Serving foods as smaller pre-portioned amounts decreases energy intake in adults and older adults. This conclusion statement is based on evidence graded as moderate. (Grade: Moderate)

Summary of the evidence

• Eight articles met the inclusion criteria for this review. Six were parallel randomized controlled trials and 2 were crossover randomized controlled trials.
• The direction of results was similar across studies, but effect size differed.
• The size of study groups was small in some studies. Some studies examined few cases of pre-portioned amounts of foods and energy intake. 
• Most studies were designed and conducted well.
• The populations, interventions/exposures, and comparators that were examined directly represent those of interest in this review.
• The evidence applies to the U.S. population, but may not apply to all race and ethnicities and socioeconomic positions.

Pregnancy

Conclusion statement and grade

• A conclusion statement cannot be drawn about the relationship between portion size and energy intake during pregnancy because there is no evidence available. (Grade: Grade Not Assignable)

Summary of the evidence

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

Conclusion statement and grade

• A conclusion statement cannot be drawn about the relationship between pre-portioned foods and energy intake during pregnancy because there is no 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 size and energy intake during postpartum because there is no evidence available. (Grade: Grade Not Assignable)

Summary of the evidence

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

Conclusion statement and grade

• A conclusion statement cannot be drawn about the relationship between pre-portioned foods and energy intake during postpartum 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: Andres A, Fisher JO, Anderson CAM, Gardner CD, Giovannucci E, Hoelscher DM, Jernigan VBB, Odoms-Young A, Palacios C, Raynor HA, Stanford FC, Fultz AK, Obbagy J, Butera G, Higgins M, Terry N. Portion Size and Energy Intake: 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.SR28.