Brief report
Literacy, Numeracy, and Portion-Size Estimation Skills

https://doi.org/10.1016/j.amepre.2008.11.012Get rights and content

Background

Portion-size estimation is an important component of weight management. Literacy and numeracy skills may be important for accurate portion-size estimation. It was hypothesized that low literacy and numeracy would be associated with decreased accuracy in portion estimation.

Methods

A cross-sectional study of primary care patients was performed from July 2006 to August 2007; analyses were performed from January 2008 to October 2008. Literacy and numeracy were assessed with validated measures (the Rapid Estimate of Adult Literacy in Medicine and the Wide Range Achievement Test, third edition). For three solid-food items and one liquid item, participants were asked to serve both a single serving and a specified weight or volume amount representing a single serving. Portion-size estimation was considered accurate if it fell within ±25% of a single standard serving.

Results

Of 164 participants, 71% were women, 64% were white, and mean (SD) BMI was 30.6 (8.3) kg/m2. While 91% reported completing high school, 24% had <9th-grade literacy skills and 67% had <9th-grade numeracy skills. When all items were combined, 65% of participants were accurate when asked to serve a single serving, and 62% were accurate when asked to serve a specified amount. In unadjusted analyses, both literacy and numeracy were associated with inaccurate estimation. In multivariate analyses, only lower literacy was associated with inaccuracy in serving a single serving (OR=2.54; 95% CI=1.11, 5.81).

Conclusions

In this study, many participants had poor portion-size estimation skills. Lower literacy skills were associated with less accuracy when participants were asked to serve a single serving. Opportunities may exist to improve portion-size estimation by addressing literacy.

Introduction

Following dietary recommendations is an effective component of prevention and treatment for many common diseases.1 The current super-sizing of many foods may lead Americans to overestimate what a normal portion should be,2, 3, 4 and the overestimation of portion size may lead to overeating and contribute to obesity.5, 6, 7, 8 Patients with diabetes or other chronic illnesses often require accurate portion-size estimation to assess carbohydrate or other nutrient intake.9 In addition, dietitians and other healthcare providers often rely on portion size to communicate with patients.9

In the U.S., it is estimated that more than 90 million people have low literacy skills, and 110 million have low numeracy skills.10 Patients with low literacy skills can have difficulty following medical instructions, understanding health information, and performing self-management tasks, leading to decreased disease knowledge and poorer clinical outcomes.11, 12, 13, 14 Numeracy is an important component of literacy, and recent studies have suggested that lower literacy or numeracy skills are associated with a poorer understanding of food labels, poorer performance of diabetes-related self-management tasks, and increased BMI.15, 16, 17 Numeracy skills are important for estimation, measurement, and understanding spatial relationships.18 Literacy and numeracy skills are crucial for interpreting nutrition information, but have not been well-studied in that context.14, 15 This study sought to determine individuals' ability to estimate portion size and to evaluate the relationship between portion-size estimation skills and literacy and numeracy skills.

Section snippets

Methods

Patients aged >18 years who presented for routine visits at an academic primary care clinic were referred by clinic staff for possible participation in this study. Exclusion criteria included dementia, the inability to speak English, and corrected visual acuity ≥20/50 as measured by a Rosenbaum pocket vision screener. Participants were enrolled between July 2006 and August 2007. Participants gave verbal consent and received $20 after study completion, which took approximately 45 minutes. This

Results

From July 2006 to August 2007, a total of 248 patients were referred for possible study participation. Of these, 77 declined to participate because of time constraints or lack of interest; two patients were ineligible because of the inability to speak English or poor vision. Of the 169 who consented to participate, 164 (97%) completed the study.

Participant characteristics are presented in Table 1. The mean age (SD) was 46 (16) years; 71% were women, 64% were white, and 24% reported yearly

Discussion

Portion-size estimation is an important component of weight management and the management of other chronic illnesses. In this study, it was found that many participants had poor portion-size estimation skills. In unadjusted analyses, both literacy and numeracy were associated with overestimation when participants were asked to serve a single serving; however, in multivariate analyses, only literacy remained significantly associated. Inaccuracy in portion-size estimation was not associated with

References (23)

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      Health literacy describes an individual's capacity to obtain, process, and understand health information and services for appropriate health decision making; numeracy describes facility with basic probability and numerical concepts.7,8 Low health literacy and numeracy skills are linked to poor understanding of food labels, inaccurate portion-size estimation,5,9 and unhealthy dietary behaviors, such as increased consumption of energy-dense items: fried foods,10 higher-fat snacks,11 and sugar-sweetened beverages.12 The potential influence of health literacy and numeracy on diet and weight has implications for health promotion among populations with varying health literacy and numeracy skills.

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    The full text of this article is available via AJPM Online at www.ajpm-online.net.

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