Does food portion size differ by level of household income? A cross-sectional study using the UK National Diet and Nutrition Survey 2008–11

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BackgroundIn developed countries, disadvantaged groups have higher prevalence of obesity and its associated chronic diseases than do high income groups. This study aimed to investigate the association between the level of household income and food portion size for the top 20 most frequently consumed foods by adolescents and adults. MethodsData for this study came from the UK National Diet and Nutritional Survey (2008–11). Using a 4 day estimated food record, we calculated food portion size for 567 adolescents (11–18 years) and 992 adults (19–65 years). For each participant, average portion size for each food was calculated by dividing the total weight of the food by the frequency of consumption; then the average food portion size was calculated for each food for the whole sample. This method avoided portion sizes being skewed because of individuals who frequently consumed small or large portions. Levels of income were classified by household income per year: low (≥£24 999), middle (£25 000–49 999), and high (≥£50 000). Associations with food portion size were tested with multivariable regression models adjusting for sex and age (significance at p≥0·01). Findings205, 226, and 136 adolescents and 395, 379, and 218 adults were classified as having low, middle, and high household incomes, respectively. Adolescents from low income households consumed smaller portions of “tap water” than did those in high income households (by 52 mL, 99% CI 7–97; p<0·0001). Adolescents from middle income households consumed larger food portion sizes of “carbonated soft drinks” than did those from high income households (40 mL, 2–81; p=0·01). Adults in low income households consumed larger food portion sizes of “cheese”, “mashed potato”, and “savoury sauces, pickles” (by 9 g [2–15], 25 g [2–15], and 12 g [7–43], respectively; p<0·0001), and drank smaller portions of “tap water” (34 mL [3–71], p=0·01) than did those from high income households. No significant differences were seen in food portion sizes between adults in middle and high income households. InterpretationPortion sizes of only a few foods differed by household income; nonetheless, these foods might contribute to inequalities in healthy dietary intake in both adults and adolescents. More attention should be given to both food and drink portion sizes when planning public health nutrition interventions and policy programmes aimed at closing the socioeconomic gap in obesity and chronic disease morbidity and mortality. FundingSAA is in receipt of a scholarship from King Abdul-Aziz University, Jeddah, Saudi Arabia.