Food Safety Focus (227th Issue, June 2025) – Article 2
Understanding Total Diet Studies: an Important Tool for Dietary Exposure Estimation
Reported by Ms. Joey KWOK and Ms. Waiky WONG, Scientific Officers,
Risk Assessment Section, Centre for Food Safety
Total Diet Studies (TDS) are internationally recognised as an effective approach for estimating population dietary exposure to a broad spectrum of chemicals across the entire diet within one study. For decades, the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) have been actively promoting the global adoption of this comprehensive approach. This article elaborates on the details of the implementation of TDS in Hong Kong and their value in dietary exposure assessment.
TDS in Hong Kong
The Centre for Food Safety (CFS) conducted the First Hong Kong Total Diet Study (1st HKTDS) during 2010-2014, and is currently conducting the Second Hong Kong Total Diet Study (2nd HKTDS). The results of HKTDS provide a scientific basis for food safety risk assessment in Hong Kong. In the international context, HKTDS also provide valuable data on chemical levels in foods and the associated population dietary exposure in this region. Being a WHO Collaborating Centre for Risk Analysis of Chemicals in Food since 2010, the CFS will continue to contribute the relevant analytical data arising from HKTDS to WHO GEMS/Food.
Building on the foundation of the 1st HKTDS and global methodological advancements in TDS, the 2nd HKTDS utilises these improved techniques to ensure a more comprehensive and reliable assessment of dietary exposure of the population in Hong Kong. Notably, with the availability of a set of food consumption data acquired for the younger population (aged 6-17) in 2023, dietary exposure assessment in the 2nd HKTDS can be extended to cover both the adult and younger populations.
Essential Principles of the 2nd HKTDS
The 2nd HKTDS is a large and complex project that systematically evaluate population-level dietary exposure to chemical substances. It employs a rigorous methodological framework comprising: (i) selection of representative foods, designated as 187 TDS food items, based on local food consumption data that reflect typical dietary patterns; (ii) procurement of 2 244 individual food samples throughout one year from the retail market across different districts and online sales platforms in Hong Kong; (iii) preparation of foods using habitual methods (e.g. washing, peeling, cooking) to simulate actual consumption; (iv) laboratory analysis of over 130 selected chemical substances of interest; (v) estimation of dietary exposure for the local population by integrating laboratory analytical results with the latest food consumption data; and (vi) comparison of the dietary exposure estimates against appropriate health-based guidance values to assess public health risks.
Unlike the routine food surveillance programme (FSP), HKTDS examine the entire diet and differ from FSP in the following areas (i) food samples representing the entire diet are included for sampling and testing; (ii) food samples are prepared as for consumption to take into account the effects of kitchen processing steps which may decrease or increase the levels of chemical substances present in foods; and (iii) individual food samples are pooled into composite samples for conducting laboratory analysis to reduce analytical costs. These distinctive features enable HKTDS to generate more realistic dietary exposure estimates of the local population.
Brief results of the 2nd HKTDS
The reports of the 2nd HKTDS are being prepared and published in phases. As of June 2025, the reports on the results of comprehensive dietary exposure assessment of sulphites and nitrate/nitrite have been released.
Sulphites
Sulphites have a long history of use in food production for their multifunctional properties, particularly as preservatives and antioxidants. The 2nd HKTDS results revealed that the estimated dietary exposure to sulphites of the local adult and younger populations were well below the Acceptable Daily Intake (ADI) allocated to sulphites by the Joint FAO/WHO Expert Committee on Food Additives (JECFA), indicating low health concern.
Nitrate and nitrite
Nitrate and nitrite are part of the nitrogen cycle, and are ubiquitous in the environment including soil, water, and air. The 2nd HKTDS results revealed that the estimated dietary exposure to nitrate of the average and high consumers of the overall local adult and younger populations fell within the range of ADI values estimated for nitrate by the European Food Safety Authority (EFSA), and the estimated dietary exposure to nitrite also fell below the ADI established by JECFA and EFSA for nitrite, indicating the general population is unlikely to experience any immediate health risks. Further reports from the 2nd HKTDS will be released in 2025 and 2026 through the designated webpage.
Figure 2. Components of TDS