Intakes and food sources of dietary protein among New Zealand adolescents

Abstract

Background: Adolescence is a nutritionally vulnerable period, characterised by rapid growth and development as an individual transitions from childhood to adulthood. Protein is necessary to support these rapid changes and is paramount to supporting immunity, bone health and hormone production. There is limited up-to-date data on the protein intakes among New Zealand (NZ) adolescents, as the last assessment was conducted over a decade ago. Objective: To assess the protein intakes and main food sources of protein among New Zealand adolescents aged 15-18 years. Furthermore, the present study aimed to compare intakes, sources and the prevalence of inadequacy between males and females. Design: The present thesis is part of a wider population-based cross-sectional study, the Survey of Nutrition, Dietary Assessment and Lifestyle, which was conducted over an 18-month period in NZ adolescents, aged 15-18 years. A convenience sample of adolescents, clustered by high schools were the study participants. Measurements were taken over three phases from February 2019 to April 2020. Two 24-hour diet recalls, taken on non-consecutive days, were undertaken to assess the protein intakes of adolescents using the ‘multiple pass method’. Participants also completed online questionnaires on demographics and dietary habits. Usual average protein intake was estimated using the multiple source method in absolute terms, as a percentage of total energy and per gram per kilogram of bodyweight. The Estimated Average Requirement (EAR) cut off method was used to determine the prevalence of inadequacy among adolescents. Body mass index (BMI) z-scores were calculated using standardised height and weight measurements. Results: The population comprised 66% females (n=266) and 34% males (n=135). Mean usual dietary protein intakes were significantly higher among males compared with females (109.5 g/day (95% CI: 104.1, 114.9) and 1.63 g/kg (95% CI: 1.54, 1.73) vs 73.0 g/day (95% CI: 70.6, 75.3) and 1.14 g/kg (95% CI: 1.09, 1.18)). The prevalence of inadequacy among females was low (0.3%) in absolute terms (g/day), although increased to 6.3% when body weight is accounted for (g/kg). Females who were Māori, resided in areas of high deprivation or were obese had the highest rates of inadequacy, while no male had inadequate mean protein intake. Contribution of protein to total energy was statistically 18% higher among males compared with females (18.6% total energy (TE) (95% CI: 18.1, 19.2) vs 15.4% TE (95% CI: 15.1, 15.7). Notably, mean contributions to total energy sit towards the lower end of the Acceptable Macronutrient Distribution Range (AMDR). A concerning 47.7% of females had intakes below the AMDR (15- 25% TE) while only 13.7% of males were below this limit. Main food sources for adolescents were similar between sexes, with poultry (12.8%), grains and pasta (10.0%), and bread (9.4%) contributing the main sources of protein. Conclusion: Protein intakes among the adolescent population in New Zealand are mostly sufficient to meet their physiological needs, and the prevalence of inadequacy appears to be low. Males consistently consume more dietary protein than females. In turn, females living in highly deprived areas or of Māori ethnicity are at higher risk of protein inadequacy. Increasing intakes to sit within the AMDR is an avenue in which adolescent health can be optimised on a population level by ensuring a balanced diet. Protein quality and the amino acid composition of foods should be assessed in future analyses to determine the contribution of protein-rich foods to overall diet quality. Larger, nationally representative studies are required to support the present findings