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The role of dietary fibre and plant-based foods in the diets of teenagers (13-18y) in Ireland
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Date
2024
Authors
McGowan, Clíodhna
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Publisher
University College Cork
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Abstract
Background: Adequate nutrition during the teenage years is essential to support optimal growth and lay the foundations for long term health. This life stage is also characterised by social development, increasing autonomy and independence and is a critical stage for the optimisation of health and health-related behaviours as habits developed during this time often continue into adulthood.
Dietary fibre is a nutrient of interest in public health due to its essential role in normal laxation and association with reduced incidence of non-communicable diseases. Plant-based foods such as ‘fruit & vegetables’ and ‘cereals, grains & potatoes’ are key sources of dietary fibre in the diet, and feature prominently in all food based dietary guidelines (FBDG) due to their nutrient density and association with a number of health benefits.
Data from the National Teens’ Food Survey (NTFS) (2005-06) (a nationally representative survey of teenagers in Ireland) reported an intake of dietary fibre below recommendations, and a poor compliance with the Irish FBDG for ‘fruit & vegetables’ and ‘cereals, grains & potatoes’.
There have been many changes in the environmental, social and cultural contexts which influence teenagers lifestyles including dietary choices since the NTFS, along with updated international recommendations for dietary fibre intake for teenagers and updated Irish FBDG. New detailed dietary data for teenagers has become available from the nationally representative National Teens’ Food Survey II (NTFS II) (2019-20).
Aim: The overall aim of this PhD thesis was to use data from the NTFS II (2019-20) to examine intakes of dietary fibre and the role of plant-based foods such as ‘fruit & vegetables’ and ‘cereals, grains & potatoes’ in the diets of teenagers (13-18y) in Ireland. An additional aim of this thesis was to examine changes over time compared to the previous NTFS (2005-06).
Methods: The analyses for this thesis were based on data from the NTFS II (13-18 years, n 428) and the NTFS (13-17 years, n 441). Dietary intake data was collected at brand level using a 4-day weighed food record (NTFS II) and a 7-day semi-weighed food record (NTFS). Energy and nutrient intakes were estimated using Nutritics© (NTFS II) and WISP© (NTFS) based on food composition data from McCance & Widdowson’s ‘The Composition of Foods’ 5th, 6th and 7th editions (plus all nine supplemental volumes). During both surveys, modifications were made to the food composition database to include recipes of composite dishes, fortified foods, generic Irish foods and new foods on the market.
Usual intakes of energy and dietary fibre were estimated using the National Cancer Institute (NCI) method using SAS Enterprise Guide©. Dietary fibre intakes were compared to the adequate intake (AI) for normal laxation, proposed by EFSA for this age group (13-14y: 19g/d, 15-17y: 21g/d, 18y: 25g/d). All further analyses were conducted using SPSS© Version 29.0. The percent contribution of food groups to the mean daily intake (MDI) of dietary fibre were calculated by the mean proportion method. Differences in the intake of dietary fibre between sexes (boy, girl), age groups (13-14y, 15-18y) and surveys (NTFS II, NTFS) were calculated using independent sample t-tests.
Dietary determinants of dietary fibre intake were investigated by splitting the population into low, medium and high dietary fibre intake groups and examining the key food groups which contributed to the difference in dietary fibre intake between the high and low intake groups and associated patterns of consumption of these food groups. Differences in the MDI of dietary fibre between the low, medium and high intake groups were assessed using ANOVA and Tuckey’s post-hoc analysis. The difference in the percentage of consumers of each food group identified as determinants of dietary fibre intake between dietary fibre intake groups (low, high) were assessed using the Chi-Square test for independence. The differences in consumption patterns between the low and high dietary fibre intake groups were assessed in consumers only using the Mann Whitney U test.
To examine the role of ‘fruit & vegetables’ and ‘cereals, grains & potatoes’ in the diets of teenagers in Ireland, the MDI of each food group and subgroup was estimated by summing the weight of each food group consumed for each participant and dividing the total by the number of recording days (NTFS II: 4, NTFS: 7). The percent contribution of ‘fruit & vegetables’ and ‘cereals, grains & potatoes’ to energy, macro- and micro-nutrient intakes were calculated by the mean proportion method. Differences in the intake of ‘fruit & vegetables’ and ‘cereals, grains & potatoes’ between sexes (boy, girl), age groups (13-14y, 15-18y) and surveys (NTFS II, NTFS) were calculated using independent sample t-tests. Analyses to estimate intakes of fruit & vegetables included intake of fruit and/or vegetables from composite dishes and the calculation of inedible or unconsumed portions. To assess compliance with Irish FBDG, intakes of ‘fruit & vegetables’ and ‘cereals, grains & potatoes’ were converted to servings using the Irish FBDG recommendations and standard food portion sizes.
Results: Teenagers in Ireland had a usual intake of dietary fibre of 16.9g/d, which was below the AI proposed by EFSA across all age groups examined (13-14y, 15-17y, 18y). Teenage boys had higher usual intakes of dietary fibre compared to girls, however, girls had higher energy adjusted intakes, indicating girls consume a more fibre dense diet. Older teenagers (18y) had higher absolute and energy adjusted intakes of dietary fibre than younger teenagers (13-14y, 15-17y), indicating that older teenagers consumed a more fibre dense diet. The key sources of dietary fibre were identified as ‘bread & rolls’ (19%) (‘white bread & rolls’, 10%), ‘grains, rice, pasta & savouries’ (14%), ‘potato & potato products’ (13%) (‘chipped, fried & roasted potatoes’, 8%), ‘breakfast cereals’ (12%) (RTEBC, 11%), ‘meat & meat products including dishes’ (9%), ‘vegetables & vegetable dishes’ (9%) and ‘fruit & fruit juices’ (7%). Intakes of dietary fibre have increased in teenagers in Ireland since the NTFS (2005-06) (16.9g/d vs 15.5g/d), albeit remain below the EFSA AI for all age groups examined. The increased intakes are due to a higher intake of dietary fibre from ‘grains, rice, pasta & savouries’ and ‘breakfast cereals’ in teenagers in the NTFS II compared to the NTFS.
To identify the dietary determinants of dietary fibre intake, teenagers were split into low, medium and high dietary fibre intake groups based on their MDI of dietary fibre. Those in the high intake group had over double the intake of dietary fibre compared to those in the low intake group (24g/d vs 11g/d). The main food groups that contributed to the difference in dietary fibre intake between the high and the low intake groups were ‘high fibre RTEBC’ (17%), ‘wholemeal & brown bread & rolls’ (11%), ‘vegetables & vegetable dishes’ (14%), ‘grains, rice, pasta & savouries’ (10%) and ‘fruit’ (10%). For ‘high fibre RTEBC’ there were more consumers in the high intake group compared to the low intake group (53% vs 33%) and those in the high intake group consumed it more often over the 4 days (2.8 vs 2.0 times) and consumed more at each eating occasion (72g vs 47g). For ‘wholemeal & brown bread & rolls’ there were more consumers in the high intake group compared to the low intake group (63% vs 24%). For ‘grains, rice, pasta & savouries’ there was no difference in the number of consumers between the groups but those in the high intake group consumed it more often over the 4 days (3.2 vs 2.4 times). For ‘vegetables & vegetable dishes’ and ‘fruit’, both food groups were more likely to be consumed by teenagers in the high intake group compared to the low intake group (vegetables & vegetable dishes: 90% vs 75%, fruit: 89% vs 57%) and be consumed more frequently during the recording period (vegetables & vegetable dishes: 6.9 vs 3.4 times, fruit: 5.5 vs 2.4 times).
‘Fruit & vegetables’ were consumed by all teenagers in the NTFS II with an MDI of 218g/d (‘fruit & fruit juices’: 122g/d and ‘vegetables’: 96g/d). Teenagers in the NTFS II had lower intakes of fruit & vegetables compared to teenagers in the NTFS (NTFS II: 218g/d, NTFS: 240g/d). The MDI of 218g/d equated to approx. 2.7 servings of ‘fruit & vegetables’ per day. This is below the Irish FBDG recommendation of 5-7 servings/day, with the majority of teenagers (92%) not meeting the recommended 5-7 servings per day and 22% of teenagers consuming less than one serving (80g) of ‘fruit & vegetables’ per day. For ‘vegetables’, 50% of intakes were from ‘vegetables in composite dishes’, which highlights the important contribution of composite dishes to vegetable intakes in teenagers, and the importance of including fruit and vegetables in composite dishes in estimates of fruit and vegetable intake (particularly for vegetables).
‘Fruit & vegetables’ contributed a small proportion of energy (5%) in the diets of teenagers in Ireland and made important contributions to the intake of dietary fibre (16%) and several micronutrients which have been identified as low in this population, including vitamin C (42%), vitamin A (24%), potassium (14%), folate (DFE) (14%) and vitamin B6 (11%). ‘Fruit & vegetables’ also contributed to the intake of total sugars (20%), due to the natural sugars present in ‘fruit & fruit juices’ and a negligible amount to free sugars (2%) due to ‘fruit juices & smoothies’.
‘Cereals, grains & potatoes’ were consumed by all teenagers in the NTFS II with an MDI of 345g/d (‘grains, rice, pasta & savouries’:128g/d, ‘total bread’: 85g/d, ‘potato & potato products’:84g/d and ‘breakfast cereals’: 48g/d). The overall food group contributed 4.8 servings for boys and 3.8 servings for girls with 1.6 and 1.1 servings, respectively, from ‘wholemeal & brown breads, cereals, pasta and rice and unprocessed potatoes’. This is well below the recommended intake of 4-7 and 3-4 servings per day for boys and girls respectively of ‘wholemeal & brown breads, cereals, pasta and rice and unprocessed potatoes’ in the Irish FBDG.
‘Cereals, grains & potatoes’ contributed significantly to intakes of energy (39%), carbohydrate (55%), protein (30%) and dietary fibre (60%) and made important contributions to a number of micronutrients including B vitamins (15-50%), vitamin D (25%), vitamin C (21%), vitamin E (22%), calcium (35%), potassium (33%) and iron (22%) in the diets of teenagers in Ireland. ‘Cereals, grains & potatoes’ also contributed to intakes of saturated fat, sodium and free sugars, primarily due to specific subgroups including ‘pizza’, ‘savoury dishes & products’ and ‘chipped, fried & roasted potatoes’, ‘bread’ and ‘breakfast cereals’.
Teenagers in the NTFS II had lower overall intakes of ‘cereals, grains & potatoes’ compared to teenagers in the previous NTFS (NTFS II: 345g/d, NTFS: 364g/d) with lower intakes of ‘potatoes & potato products’ and ‘low fibre RTEBC’ and higher intakes of ‘grains, rice, pasta & savouries’.
Conclusion: In conclusion, the findings from this thesis indicate that overall, teenagers in Ireland are not meeting dietary guidelines for dietary fibre, fruit & vegetables and cereals, grains & potatoes. However, a positive finding was that there is a proportion of the teenage population that had intakes of dietary fibre that reached the AI proposed by EFSA based on existing dietary patterns, providing an evidence base to develop dietary strategies to improve dietary fibre intake in this population group. Based on this evidence, these strategies should focus on increasing intake of ‘fruit & vegetables’ and promoting a swap from refined grains to wholemeal & brown breads, cereals, pasta and rice and unprocessed potatoes which would improve intakes of dietary fibre in teenagers in Ireland and also support FBDG for ‘fruit & vegetables’ and ‘cereals, grains & potatoes’, which have a much wider nutritional role in the diet as evidenced in this thesis.
Findings from this thesis may provide evidence to public health campaigns to improve dietary fibre intakes and promote the consumption of plant-based foods to increase compliance with the Irish FBDG in teenagers in Ireland. The findings from this thesis may also provide information to policy makers across various sectors of Irish society including education and health to gain a more comprehensive understanding of the plant-based foods influencing intakes of dietary fibre in teenagers in Ireland.
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Keywords
Dietary fibre , Plant based foods , Teenagers , Dietary determinants, dietary patterns , Food-based dietary guidelines , Cross-sectional surveys , Public health campaigns , Adolescents
Citation
McGowan, C. 2024. The role of dietary fibre and plant-based foods in the diets of teenagers (13-18y) in Ireland. PhD Thesis, University College Cork.