Fibre intakes between vegetarian and non-vegetarian adolescent females in New Zealand

Abstract

Background: The mean fibre intakes for 15-18-year old females from the last national nutrition survey (2008/09 New Zealand Adult Nutrition Survey) was 16.0 grams/day, well below the adequate intake for this age group of 22.0 grams/day. However, no analysis into vegetarians was carried out in this survey. There are no data on the fibre intakes of vegetarian and non-vegetarian adolescent females in New Zealand, emphasising the need for further research in this area. Objective: To compare the dietary fibre intakes between vegetarian and non-vegetarian adolescent females in New Zealand and to identify the main food groups contributing to fibre intake with a secondary aim of gathering data on bowel habits using questions relating to the Bristol Stool Chart. Design: This thesis is part of a multi-centre, observational, cross-sectional study continuing for two years that began in 2019. Current data were collected between February and April 2019 and July and August 2019 from thirteen high schools across New Zealand as well as targeted recruitment of 15 to 18-year-old vegetarians in Dunedin. Recruitment was based on the location of the data collectors, thereby producing a convenience sample. Targeted recruitment of vegetarians caused a possible over-representation of this group. Food intakes were obtained through interviewer-led 24-hr recalls with a subset of participants agreeing to a second recall via phone or video call. Dietary data were analysed for nutrient content using FoodWorks 9 (Xyris Software, Australia) which used the full dataset of the New Zealand Food Composition Database, FOODfiles 2016 Version 01. Mean fibre intakes were estimated using repeat 24-hr recalls and were adjusted using the Multiple Source Method to estimate usual intakes of fibre, with adjusted estimates applied to the whole dataset. Vegetarian status and bowel habits were self-reported with an online enrolment questionnaire. Results: Of the sample, 251 participants completed one 24-hr recall with 213 of those completing a second recall. Of those who completed at least one 24-hr recall, 31 self-identified as vegetarian. Vegetarians has significantly higher mean fibre intakes than non-vegetarians (29.3 g/day and 24.0 g/day respectively) with a mean difference (95% CI) of 5.2 (1.8, 8.7) g/day. Overall, the mean fibre intakes of both vegetarians and non-vegetarians was higher than the recommended AI for this age group (22.0 g/day). Vegetarians had a significantly higher mean fibre density than non-vegetarians (3.9 g/MJ and 2.9 g/MJ respectively) with a mean difference of 0.9 (0.5, 1.1) g/MJ. Vegetables were the highest contribution to fibre intake in both vegetarians and non-vegetarians; however, vegetarians had a significantly higher vegetable contribution with a mean difference of 5.8% (0.5, 11.1). Fruits and breads were higher contributions to fibre intake for non-vegetarians. Mean bowel frequency was significantly higher in vegetarians than non-vegetarians with a mean difference of 1.6 (0.2, 3.1) times/week and vegetarians tended to have softer stool consistency than non-vegetarians. Conclusion: Vegetarians had significantly higher fibre intakes than non-vegetarians. Encouraging a more plant-based diet may help in achieving adequate fibre intake with beneficial health outcomes such as bowel regularity.