Introduction to total diet studies
A total diet study involves collecting samples of foodstuffs regularly consumed by the population from various points of sale, preparing them as they are consumed, and mixing them into "composite" samples to obtain a limited number of test mixtures. These mixtures are then examined to detect a certain number of toxic substances and nutrients: residues of plant health products, environmental contaminants, newly-formed compounds, natural toxins, additives, substances migrating from food contact materials, trace elements or minerals, for example. The purpose of these studies is to measure the quantity of chemical substances ingested by the general population and by various specific population groups (by region, age, etc.). These data are needed to assess the health risks for the consumer associated with chemical substances.
Since foodstuffs are analysed after being prepared as in real-life conditions, i.e. washed, peeled and cooked as appropriate, this method has the advantage of providing “background noise” exposure data that are more realistic than approaches based on food standards or on the results of monitoring and control programmes. Relying on a standardised method that has been recommended for several years by the World Health Organization (WHO), and more recently by the European Food Safety Authority (EFSA), this type of study also facilitates international comparisons of consumer exposure.
These studies constitute an important scientific tool for decision-making at the EU and international levels concerning regulation of chemical substances, food safety, and consumer protection. TDS surveys are therefore implemented by numerous countries in order to assess nutritional and health risks.
TDSs in France
The first total diet study in France (TDS1) was carried out between 2000 and 2004 by the French National Institute for Agricultural Research (INRA), in collaboration with the Agency. It provided an overview of exposure of the population, both adults and children, to inorganic and mineral contaminants, and to mycotoxins.
In 2006, the Agency issued an internal request to carry out a second study (TDS2), including 445 substances compared to 30 analysed in the first study. This TDS was financed by public funding from the Ministries of Agriculture, Health and Consumer Affairs, with a contribution from the French Observatory for Pesticide Residues, and results were published in June 2011.
In total, the TDS2 study involved collecting 20,000 food products covering 212 food types, for which 445 substances of interest were analysed.
In 2011, ANSES launched a new TDS targeting the population of infants and young children (0-3 years of age): the infant Total Diet Study (iTDS). The results of this study, published in 2016, enabled an assessment of the risks associated with the dietary exposure of children to 670 substances.
Lastly, from 2012 to 2015, ANSES coordinated the TDS-Exposure European research project to harmonise and distribute the TDS methodology in Europe.
The substances tested in TDSs
All of the substances analysed in TDS1 were also screened for in TDS2 and the iTDS in order to monitor dietary exposure levels of the general and infant populations over time. Many other substances were added to this list in order to strengthen knowledge on this exposure.
ANSES identified the substances to be analysed based on the following criteria: existing needs in terms of risk assessment, the need to obtain data on changes in exposure and to better describe exposure for certain contaminants, identification in the literature of emerging substances for which a risk assessment may be necessary, recommendations on monitoring included in Agency opinions, analytical capacities, the particular susceptibility of population sub-groups of interest (women of childbearing age, young children, etc.). A total of 445 substances were screened for in TDS2, and 670 in the iTDS:
- Inorganic contaminants or trace elements
- Dioxins and furans
- Polychlorinated biphenyls (PCBs)
- Perfluorinated compounds
- Brominated flame retardants
- Phyto-oestrogens and sex steroids of animal origin (only in the iTDS)
- Active plant protection substances
- Newly-formed compounds
- Substances migrating from food contact materials (only in the iTDS)
In general, both the iTDS and TDS2 confirmed the high level of risk management in France concerning the potential presence of chemical contaminants in food, on the basis of the regulatory thresholds and toxicity reference values available.
However, these studies also demonstrated that in certain population groups there is a risk of toxicological thresholds being exceeded for some substances, such as lead, cadmium, inorganic arsenic and acrylamide, requiring efforts to reduce exposure. Since these risks are often associated with high levels of consumption of a particular foodstuff or group of foodstuffs, ANSES highlights the importance of a diversified, balanced diet in which the types of food and their quantities are varied.
Finally, the TDSs have shown that there is a need to develop scientific knowledge concerning both toxicology and analytical techniques for a number of regulated or non-regulated substances, for which the risk assessment is currently not conclusive.