Since 1960s, various countries, such as the United Kingdom, the United States of America, Canada, Australia, New Zealand and Mainland China, have been conducting their own TDS. The frequency for conducting TDS varies from country to country. For instance, TDS in the USA has been an ongoing programme since 1960s, whereas Mainland China has started to conduct TDS since 1990.
The approaches and methodologies may vary from country to country. For example, in the UK and Mainland China, a relatively small number of samples are required to be analysed for applying a "food group composite approach", in which samples from the same food group are prepared and then combined in the proportion of amount consumed among the population to form a single food group sample for laboratory analysis, but it provides less flexibility in dietary exposure estimation. In contrast, in the USA, Australia and New Zealand, an "individual food approach", in which samples are analysed separately, is applied, leading to a larger number of samples are required to be analysed, but it provides greater flexibility in calculating dietary exposures for various segments of the population.
Besides, substances to be studied in the TDS also vary from country to country, and basically, include various types of contaminants such as pesticide residues and heavy metals, and to a lesser extent, nutrients and food additives.