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Children's food portion sizes: Estimation of typical portion sizes for children of different ages

Project Code: N08018

16/09/2002

School of Pharmacy and Life Sciences, Robert Gordon University, St Andrew Street, Aberdeen, AB25 1HG
Wrieden, W ;
Centre for Public Health Nutrition Research, Division of Clinical & Population Sciences & Education, University of Dundee, Ninewells Hospital and Medical School, Dundee DD1 9SY
Lonngbottom, P; Barton, K

1.1 Aims and Objectives

The overall aim of the project was to produce and test a set of typical food portion weights for children of ages 1-3, 4-6, 7-10, 11-14 and 15-18 years.
The individual objectives were:
• To extract food portion information from recent dietary surveys of children (NDNS of children aged 1½-4½ years and of young people aged 4-18 years).
• To collate current information on portion sizes of packaged and fast foods (commonly eaten by children) and of school meals.
• To produce a list of typical food portion sizes for each age range.
• To trial the use of typical food portion weights in dietary surveys.
• To recommend and justify the list of portion sizes for foods eaten by children.

1.2 Approach
1.2.1 Calculated Portion Weights

Food intake data of 3374 children aged 1½ to 4½ and 4 to 18 years, reported in the National Diet and Nutrition Surveys (NDNS) was standardised, merged and grouped in Microsoft Access by an age group allocated to each child to match the corresponding age ranges used for Dietary Reference Values. Food portion data were examined and foods eaten by ≥ 1% of all children were established. These foods were grouped by similar type and composition, and a list was compiled of grouped foods eaten by ≥ 2% of all children, and then reported by age group. It was decided to record portion size for all foods consumed by 10% or more of all children and that portion size for foods consumed by 2-9.5% of all children would be recorded as estimates. Food groupings were allocated a new code and food name in order to ease future calculations. Foods that were likely to have a different serving size depending on the mode of use (e.g. milk on cereal and as a drink) were allocated separate codes. The mean portion weight for each subject’s consumption of each of the grouped foods was calculated and the data were transferred to SPSS for further analysis. The data were split by age group and thereafter statistical tests and calculations were carried out to obtain the mean, standard deviation, median, 25th and 75th percentiles, minimum and maximum, and predicted values calculated by linear, quadratic and exponential regression. The predicted values enabled portion weights to be estimated for age groups where <2% of children consumed the food.
A database was constructed in Microsoft Access to compare the use of the calculated portion sizes against actual weights recorded in food diaries collected for previous studies at the Universities of Edinburgh and Dundee. Food weights from 50 diaries in each of the age groups 1-3, 4-6 and 11-14 years were available and were entered into the database entry form and checked by a second researcher (no such data was available for the other age groups). The resulting tables were then linked to tables containing data on the calculated portion sizes and nutrient data (derived from the NDNS nutrient data bank), for the most commonly eaten food in each of the food groupings. This enabled the creation of a file containing the average daily nutrient consumption for each of the diaries using the calculated portion weights and the actual weights. Mean daily energy (kJ) and nutrient intakes for each subject’s diary in the form of protein, fat, carbohydrate, total sugars, NSP, iron, calcium, folate, and vitamin C were exported to SPSS and paired t-tests carried out for each nutrient (derived from actual and calculated portion weights). If no statistical difference was apparent then Bland Altman plots were carried out to assess agreement.

1.2.2 Manufactured and catered portion weights

A range of companies including food manufacturers, supermarkets, restaurant chains and school meals’ contractors were contacted and information on portion sizes used for children obtained. The final lists of manufactured and catered portion sizes (as weights served) were selected following the examination of the NDNS databases of foods eaten by children and as advised by the Food Standards Agency. Supermarkets were visited and an extensive search of websites made to obtain further information.

1.3 Key Findings

The number of children in each of the age groups 1-3, 4-6, 7-10, 11-14 and 15-18 years was 1457, 574, 481, 475 and 387 respectively. Overall 119 foods were consumed by 10% or more of children and 134 (for which portion sizes were stated as estimates) by 2-9.5%. The foods reported in the final list covered all food groups, including pasta, rice, pizza, bread, breakfast cereals, biscuits, cakes, puddings, milk, cheese, yogurt, eggs, meat, meat dishes, fish, vegetables, fruit, crisps and savoury snacks, confectionery and beverages.
Mean daily energy and nutrient values were calculated from the food diaries using the mean, median, and age adjusted portion weights. Each set of values was significantly correlated with their counterparts, calculated using the actual weights (e.g. energy using actual portion weight versus energy using each type of calculated portion weight). Paired t-tests showed that the energy and nutrient data from the following portion weights gave no significant differences from those calculated using actual weights:
• Age group 1(1-3y) median
• Age group 2(4-6y) median and age adjusted (linear regression)
• Age group 4(11-14y) mean and age adjusted (linear regression)
For the manufactured foods, package sizes were collected for an extensive range of foods that may be eaten by children. This included pasta dishes, pot snacks, pizza, individual packets of breakfast cereals, cereal and breakfast bars, biscuits (especially those marketed for children), desserts, milk drinks, cheese, fromage frais, yogurts, coated chicken and turkey, burgers, sausages, meat pies, potato products, fruit snacks, ice cream, savoury snacks and confectionery. Children’s complete ready meals (a relatively recent introduction to supermarkets) were also included but most breads were excluded, as this information is included in the adult food portion book.

1.4 Technical Evaluation and Interpretation

As the calculated portion sizes could only be tested in three age groups it was necessary to use the data from the two younger age groups and the 11-14 year olds to deduce the most appropriate data for the 7-10 and 15-18 year olds. The age adjusted (linear regression) portion weights gave no significant differences in energy and nutrient values from those calculated using the actual weights for both the 4-6 and 11-14 year olds. It was also assumed that they provided more robust figures than the median or mean for some foods that were eaten by small numbers of children in some age groups. However the median values were the only ones that gave non-significant differences for the youngest age group and showed a better profile of non-significant p-values for the 4-6 year olds. Thus the final list of typical children’s portion sizes was based on the following.
• Age Group 1 (1-3 year olds) - median
• Age Group 2 (4-6 year olds) - median
• Age Group 3 (7-10 year olds) - age adjusted (linear regression)
• Age Group 4 (11-14 year olds) - age adjusted (linear regression)
• Age Group 5 (15-18 year olds) - age adjusted (linear regression)
These, together with the extensive list of manufactured and catered portion sizes will be useful in assessing the diets of groups of children. In addition the typical weights can be used as a guide for researchers devising dietary assessment tools for children.

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