New Zealand Total Diet Study (NZTDS)
Approximately every 5 years, MPI undertakes the New Zealand Total Diet Study (NZTDS). The NZTDS is a nation-wide survey of foods available for sale and provides MPI with information on what is in the foods that New Zealanders eat.
The NZTDS surveys a range of common foods consumed in a typical diet to assess New Zealanders’ exposure to certain chemicals such as agricultural compounds, contaminants and nutrients. It is used to identify any potential food safety risks to New Zealanders, as well as monitoring changes to what we eat over time.
The next NZTDS will take place during 2016. In the lead up to this, we are seeking feedback on our proposed TDS, including the foods and chemicals to be included in the study. Following consultation on a draft proposal, MPI released a response to submissions.
The draft proposal includes discussion on the objectives of the study, the priority chemicals to be surveyed, key foods to be sampled, the simulated diet approach, as well as proposed timeframes.
MPI aims to implement a best practice NZTDS, which is consistent with previous NZTDSs and supports domestic and global confidence in the safety of the New Zealand food supply and its monitoring systems.
The last NZTDS was completed in 2009. The final report can be found here: http://www.foodsafety.govt.nz/elibrary/industry/total-diet-study.pdf
Purpose and aims
The NZTDS aims to assess New Zealanders’ exposure to certain agricultural compounds, contaminant elements and nutrients from a range of foods consumed in a typical diet.
Globally, a Total Diet Study (TDS) is considered a critical tool to identify any food safety risks that might exist. The NZTDS is part of MPI’s monitoring and testing regime which is focused on providing all consumers with the highest levels of assurance and confidence on the integrity and safety of New Zealand food.
Information obtained from the NZTDS can inform the development and review of New Zealand food standards to ensure that food eaten by the average New Zealander continues to be safe.
Choosing foods to test
Usually only the most commonly consumed foods (for instance foods that represent 90% of a population’s intake) are included in a TDS. This means about 120 foods (known as key foods) are purchased and tested, rather than the thousands of foods that other national nutrition surveys may identify.
Foods for the NZTDS are selected based on information from the most up to date New Zealand National Nutrition Surveys, which are undertaken by the Ministry of Health. The most recent National Children’s Nutrition Survey was completed in 2002 and the National Adult’s Nutrition Survey in 2008/09. Also included in the NZTDS are a small number of foods that are known to be high sources of contaminants.
For the 2016 NZTDS, the proposed key foods to be tested have been updated to include the most commonly eaten foods found in the 2008/09 National Adult’s Nutrition Survey. For packaged foods, recent sales data has been used to identify the most popular brands to include in the sampling plan.
Foods are also categorised as either:
- a national food, meaning that it can be bought anywhere in New Zealand
- a regional food, meaning the composition of the food varies around the country.
To ensure variety, foods tested in the NZTDS are purchased from retail outlets such as the supermarket, greengrocer, butcher, fish shop, takeaway or café. National foods are purchased in one city, while regional foods are purchased from 4 cities/towns.
How food is tested
Food samples are purchased over a calendar year from a number of regions, and prepared as they would be consumed (for example peeled bananas or cooked meat) before being tested. Each food is sampled twice over a calendar year to allow for seasonal variations. The sampling and analysis is managed in 4 testing periods, each lasting about 6 weeks.
The proposed priority chemicals to be analysed in the 2016 NZTDS are:
Many of the priority chemicals proposed were included in the 2009 NZTDS, enabling monitoring of trends overtime. Additional priority chemicals have been included based on international scientific evidence. The full list of chemicals for the 2016 NZTDS will be determined once the consultation phase is completed.
Estimating our exposure
Data on levels of certain agricultural compounds, contaminants and nutrients are combined with information on what people eat for different age-sex groups to give an estimate of dietary exposure to these chemicals. In particular, vulnerable groups (for example infants, children and adolescents) and groups likely to consume the most food (for example young adult males) are considered a priority.
Using the key foods, 14-day simulated diets are developed for each of these groups in order to estimate dietary exposure to certain chemicals.
Simulated diets for the following population groups were analysed in both the 2003/04 and 2009 NZTDSs:
- Adult males over 25 years
- Adult females over 25 years
- 19–24-year-old males
- 11–14-year-old boys
- 11–14-year-old girls
- 5–6 year-old-children
- 1–3-year-old infants
- 6–12-month-old infants.
The population groups for the 2016 NZTDS will be determined once the consultation phase is completed.
Once the level of exposure to chemicals for each of the age-sex groups has been estimated, these are compared with national/international health-based guidance and standards, such as the Acceptable Daily Intake. This information is used to identify the potential for adverse health effects associated with certain foods.
Reporting the results
Food sampling and testing for NZTDS is undertaken over a calendar year. Throughout that period, results of each sampling quarter will be made public when available. MPI will respond to any unusual or unexpected results as appropriate. A final comprehensive report which includes the dietary exposure estimates for specified population groups will be prepared and published once all the data has been consolidated.