Zinc intakes and food sources in vegetarian compared to non-vegetarian adolescent females in New Zealand

Background: The number of individuals choosing to follow a vegetarian, or reduced meat, diet is thought to be increasing in high income countries such as New Zealand. Consuming a vegetarian diet with adequate macro- and micro-nutrients is achievable, however a vegetarian diet needs to be appropriately planned. The adequacy of zinc intake, in particular, has been reported to be lower in those following a vegetarian diet. This is due to both the exclusion of flesh foods, a rich source of bioavailable zinc, and due to higher intakes of food components that have an inhibitory effect on zinc absorption in vegetarian diets. This is of concern due to the plethora of roles zinc plays in the body, including in the immune system and numerous metabolic pathways. It also plays an important role in growth and development as individuals progress from childhood to young adulthood. However, data comparing the zinc intakes of vegetarian and non-vegetarian adolescent females do not exist in New Zealand. Objective: To compare the zinc intakes, adequacy of zinc intake, and food sources of zinc in healthy adolescent female vegetarians and non-vegetarians in New Zealand. Design: The SuNDiAL (Survey of Nutrition, Dietary Assessment, and Lifestyle) project was a cross-sectional, observational study. Participants were recruited throughout New Zealand through high schools, or recruitment targeted at vegetarians. Participants were females 15 to 18 years of age who were asked to self-identify as either vegetarian or non-vegetarian. Methods: Online questionnaires were completed to gather demographic and lifestyle information. Two 24-hour diet recalls were used to collect dietary data: one face-to-face, with a second non-consecutive one collected via telephone. The second diet recall was to allow usual intake to be calculated using the Multiple Source Method (MSM). The diet recalls were entered into, and analysed, in FoodWorks, a dietary assessment software programme which uses NZ food composition tables to calculate nutrient intakes. The prevalence of inadequate intake was determined using the estimated average requirement (EAR) cut-point method. Results: The Candidate’s analysis comprised 250 participants: 31 vegetarians and 219 non-vegetarians. Zinc intake on average was 7.5mg and 9.5mg per day for vegetarians and non-vegetarians, respectively. This difference of -2.0mg/day was statistically significant. Using the EAR cut-point method with an EAR at 6mg per day, 16.1% of the vegetarians were observed to be at risk of inadequate intake compared to 6.4% in the non-vegetarian group. However, when the EAR was increased to 9mg per day based on recommendations for strict vegetarians, 80.6% of the vegetarians had an inadequate intake. The ‘grains and pasta’ food group provided the highest proportion of zinc in the diets of both groups. The vegetarians were consuming more zinc (15.2%) from ‘vegetables’ than the non-vegetarians (6.6%). Conclusion: When using an EAR recommended for those following a vegetarian diet, a large proportion of the vegetarian group had inadequate intake which warrants further investigation. This indicates vegetarians may be at a higher risk of having inadequate zinc status. Further research into the biochemical zinc status of vegetarians will give more insight into the risk of deficiency