Intakes and main food sources of protein for vegetarian and non-vegetarian adolescent females in New Zealand

Abstract

Background: Dietary protein is a macronutrient needed for enzyme and hormone synthesis, and creating, maintaining and repairing body tissue. Adolescent females have increased protein requirements to support optimal growth and development, sexual maturity and immunity. The vegetarian diet appears to be gaining traction in this age group. Vegetarians are at risk of having low protein intakes, however, data on current protein intakes of New Zealand adolescent females are limited, particularly for vegetarian adolescent females. The aim of this thesis, therefore, is to investigate the dietary protein intake and food sources of New Zealand vegetarian and non-vegetarian adolescent females.

Objective: To investigate the dietary protein intake and food sources of vegetarian and non-vegetarian New Zealand adolescent females aged 15 to 18 years.

Design: A cross-sectional study included 280 adolescent females aged 15 to 18 years from 8 locations across New Zealand. The study was carried out in two phases (February – April and July – September 2019) via school-based and targeted vegetarian recruitments. Participants were asked to complete three online self-administered questionnaires (enrolment; attitudes and motivations for food choice; dietary habits). Dietary intake was assessed using two 24-hour dietary recalls and the dietary assessment programme FoodWorks, which calculates nutrient intakes using the New Zealand Food Composition Tables. Usual protein intakes were estimated using the multiple source method and calculated per kilogram of body weight. Prevalence of inadequate intakes was calculated using the EAR cut off method. Height and weight were measured to allow calculation of body mass index (BMI) z-scores.

Results: Mean usual dietary intake of protein was 1.14 (95% CI: 1.10, 1.19) g/kg/day, which was above the estimated average requirements (EAR) for protein (0.62 g/kg/day) in this demographic group. There was a low prevalence of inadequate protein intakes in the overall population (7%), with the greatest prevalence being in participants of Māori ethnicity, living in high deprivation areas and who were obese (21%, 14% and 31% respectively). The vegetarian participants had a lower mean usual dietary protein intake (0.96 (95% CI: 0.87, 1.06) g/kg/day) compared to the non-vegetarian participants. The mean difference between both groups was 0.21 (95% CI: 0.10, 0.31) g/kg/day, although it should be noted that the mean of both groups exceeded the EAR. The mean contribution of protein to total energy intake for all adolescent females was 15.2 (95% CI: 14.8, 15.5) %, which falls at the lower end of the acceptable macronutrient distribution range (AMDR) of 15 – 25% of total energy. The AMDR was not achieved by all vegetarian participants across all demographic characteristics (age, ethnicity, deprivation category, weight status). Major sources of protein for non-vegetarian participants were poultry, bread (including rolls and specialty breads), and grains and pasta; whereas in the case of vegetarian participants, they were vegetables, grains and pasta, and bread (including rolls and specialty breads).

Conclusion: Usual dietary protein intake of vegetarian adolescent females was lower compared to their non-vegetarian peers, although both groups achieved the EAR for protein. There was a slight increase in the prevalence of inadequate protein intakes compared to the ANS08/09. Vegetarian participants did not meet the lower limit of the AMDR. Further investigation of all sources of energy for this group is warranted to determine the suitability of the current AMDR for ensuring adequate intakes of micronutrients.