Changes in Portion Size of Selected Foods from 1997 to 2008/09 in New Zealand

Background: The cause for increasing obesity rates in New Zealand is thought to be multifaceted. One factor shown to be associated with rising obesity rates is an increase in food portion size. Obesity rates have increased dramatically in New Zealand in recent years, yet to our knowledge no studies have investigated changes in portion size in New Zealand. Objectives: To compare data from the National Nutrition Survey 1997(1) with data from the Adult Nutrition Survey 2008/2009(ANS08/09) to investigate whether any changes in portion size occurred for selected foods in New Zealand between 1997 and 2008/09. To compare the mean portion sizes of selected foods from the ANS08/09 with the values listed in the Common Standard Measures used in Food Files. Design: Both the NNS97 (n=4636) and ANS08/09 (n=4721) collected dietary information from representative samples of New Zealand adults (15+ years) using the twenty-four hour recall method. The two surveys used similar standardized interview procedures and food group classifications. Food groups selected for analysis in this study were: energy and sports drinks, soft drinks, biscuits, cakes, crackers, doughnuts, muffins, pancakes, pastries, scones, slices, puddings, chocolate, lollies, breakfast cereals, hash browns, hot chips, ice-blocks, ice-cream, yoghurt, muesli bars and snack foods. Food groups were collapsed and expanded to create suitable sized samples and ensure consistency between surveys. All foods included in the surveys were linked to nutrient profiles to compare the mean grams, fat, carbohydrate and energy per portion for consumers between surveys. All data was weighted to reflect the adult New Zealand population (15years+) at the time each survey was conducted. Where possible results were stratified by sex and linear regression was used to compare means between surveys. Results: In general portion sizes remained constant between the two surveys. Significant increases were shown however, in the portion size of lollies (9.0g, p=0.039), breakfast cereals (4.7g, p=0.042) and ice-cream (12.8g, p=0.047). A significant decrease was also found in the portion size of muffins (23.8g, p=0.010). Several changes in fat, carbohydrate and energy per portion were observed indicating either true changes to the food composition of these foods, or significant changes to the New Zealand food composition database from which these values were attained. ANS08/09 mean portion sizes for selected foods were generally larger than those listed in Common Standard Measures. Conclusion: Few differences were observed between the NNS97 and the ANS08/09 in the portion sizes of selected foods. This indicates that other factors may have been more important influences on obesity in New Zealand during this time period