In today's environment, where large portions are often the norm, strategies that aid in portion control are increasingly relevant. Portion control tools, including utensils and tableware, have been developed to guide portion size intake, but their effectiveness remains a subject of debate. This article examines the breadth and effectiveness of existing portion control tools, focusing on their impact on awareness of appropriate portion sizes, portion size choice, and portion size consumption. Additionally, it explores the effects on energy intake and weight loss.
The Problem of Large Portion Sizes
Large portion sizes contribute to increased consumption, making the practice of eating smaller portions a recommended strategy for weight control. However, many individuals find it challenging to implement this advice. While broader changes in the food environment are necessary to impact portion control at the population level, individual-level strategies, such as portion-controlled meals, reduced pack sizes, modified tableware, attentive eating, and portion control strategies within weight management programs, have shown promise.
Evolution of Portion Control Tools
Traditionally, educational aids, often image or text-based, have been used to guide portion sizes within weight management programs. However, the effectiveness of these aids has been limited, partly due to inconsistent portion size standards. In recent years, three-dimensional portion control tools have been commercialized. These tools aim to control portion sizes by physically delineating volume (e.g., portion pots, guided tableware) or by providing visual prompts for appropriate amounts, such as calibration marks on tableware and serving utensils. These practical instruments have the potential to be a useful strategy in an environment where large portions are common.
Factors such as impulsivity and perceptions of appropriate eating amounts can influence an individual's intention to consume larger or smaller portions. Portion control tools may help modulate these factors by promoting meal planning and correcting misperceptions of inappropriate portion sizes at the time of serving.
Comprehensive Review and Meta-Analysis
To comprehensively assess the impact of portion control tools, a systematic review of the literature was conducted. This review aimed to:
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- Describe the range and effectiveness of existing portion control tools for foods and drinks.
- Quantify the effects of these tools on learning/awareness of appropriate portion sizes, portion size choice, and portion size consumption in adults and children, using a meta-analytic approach.
This systematic review and meta-analysis followed the Cochrane Guidelines for Systematic Reviews and PRISMA reporting recommendations.
Search Strategy
Searches were conducted on PubMed and Web of Science (WoS) in July 2018, February 2019, and July 2020. These searches were supplemented with an internal database of publications (1989-2020) and Google for non-validated tools and grey literature. Restrictions included publication dates between January 2006 and July 2020, studies on humans, and publications in English or Spanish. Articles were identified using combinations of keywords such as tableware, dishware, portion control, portion size, and calibrated.
Inclusion Criteria
Records were included if they reported the use of a tool or instrument (validated or not) to control food and drink portion sizes, including portion size estimation aids that referenced recommended portion sizes. The tools had to provide immediate feedback to the user, enabling appropriate use with minimal professional input. Instruments for controlling portion sizes of coffee, tea, diet drinks, and decaffeinated drinks were included. Discontinued tools and packaging-based portion control strategies were excluded.
Study Selection
Two authors performed the searches and conducted title and abstract screening. A total of 1486 titles were identified, with 1241 records retained after removing duplicates. Of these, 101 abstracts were assessed for eligibility, and 51 full-text articles were retrieved, resulting in a final sample of 36 eligible publications for narrative synthesis.
Data Extraction
Data were extracted by two investigators using a standardized form to collect methodological and outcome variables from each source. These variables included authors, publication year, country, number of studies, exposures to stimuli, serving condition, type of manipulation, study design, study duration, nature and number of tools used, main outcome measures, sample size, sex, age, and BMI. Main outcome measures included portion size awareness, choice, and intake for the whole meal and/or meal components. Other data included tool-related perceptions/experiences, biochemical and anthropometric markers, portion-size perceptions, and eating context.
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Risk of Bias Assessment
Risk of bias (ROB) was explored using an adaptation of the Cochrane ROB guidelines, suitable for behavioral studies. Items assessed included the use of blinded participants, potential confounding variables, and methodological limitations. ROB evaluation was carried out in duplicate by three independent authors. Publication bias and other sources of heterogeneity were explored via funnel plot asymmetry when sufficient studies were available.
Meta-Analysis
For the meta-analysis, continuous outcomes were summarized by effect size, calculated as the standardized mean difference (SMD) or Cohen's d. A negative value for the SMD/Cohen’s d reflects a desired impact of the intervention tool (i.e., smaller portion size chosen or consumed), with a larger mean difference reflecting a larger effect. For portion size awareness, a negative value for SMD/Cohen´s d reflects no impact of the tool on portion size learning or awareness. A database was generated from the articles that reported the necessary quantitative data for calculating the effect size.
Findings and Analysis
The analysis of 36 publications revealed that 55% of studies reported a significant impact of using a portion control tool, typically smaller bowls, forks, or glasses, or calibrated plates.
Impact on Food Intake
A meta-analysis of 28 articles confirmed an overall effect of portion control tools on food intake. The analysis showed that combinations of reduced-size bowls and spoons decreased serving sizes and consumed amounts/energy. However, reduced-size plates did not show a significant impact on food intake.
Impact on Weight Loss
Portion control tools marginally induced weight loss, especially when calibrated tableware was used.
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Impact on Portion Size Awareness
No significant impact was detected on portion size awareness; however, few studies quantified this outcome.
Types of Portion Control Tools
The review considered a range of portion control tools, including:
- Non-tableware tools: Cooking utensils, educational aids, and computerized applications.
- Tableware: Mostly reduced-size and portion control/calibrated crockery/cutlery.
Practical Strategies for Portion Control
For individuals aiming to manage their food intake and lose weight, several practical strategies can be employed:
- Use measuring cups and spoons: To ensure accurate portion sizes.
- Relate food portions to everyday objects: For example, a medium pepper is about the size of a baseball and equals one vegetable serving.
- Be mindful of serving sizes: A serving is an exact amount of food, while a portion is the amount of food you put on your plate.
Examples of Serving Sizes
- Fruits: One fruit serving is about the size of a tennis ball. For example, a small apple equals one serving, or about 60 calories.
- Vegetables: One vegetable serving is about the size of a baseball. Half a cup of cooked carrots equals one serving, or about 25 calories.
- Carbohydrates: One carbohydrate serving is about the size of a deck of cards. Half a cup of whole-grain cooked pasta equals one serving, or about 70 calories.
- Protein: One protein serving is no bigger than a deck of cards. A piece of cooked skinless chicken (2 to 2 1/2 ounces) equals one serving, or about 110 calories.
- Fats: One fat serving is about the size of a pair of dice. For example, 2 teaspoons of regular mayonnaise equal one fat serving, or about 45 calories.
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