Second international workshop on total diet studies, Brisbane, Australia, 4 - 15 February 2002
Research over the past number of years shows that toxic and nutritionally important chemicals exert a far greater influence over human health than previously thought. Toxic chemicals may affect all major organs of the body, causing serious health outcomes like cancer, birth defects, and brain damage. The relationship between nutrients, especially micronutrients, and health is well established.
Despite this, little attention has been given to assessing the actual dietary intake of these chemicals by humans. One reason is that most of the potential effects of these chemicals are chronic in nature, appearing often years after exposure, and thus cannot be traced to individual foods or food companies. In many cases, some of these effects are caused by exposure to groups of different chemicals. In such situations, the concentrations of each individual chemical in the group may be quite low and within current safety limits. However, when the group as a whole is assessed, exposure may be significant. Thus, it is becoming increasingly important to assess human exposure to background concentrations of a large number of chemicals. The responsibility and obligation to make these assessments usually rests with national health authorities.
For national authorities to ensure that toxic chemicals, such as pesticides, heavy metals, environmental contaminants and naturally occurring toxins, are not present in foods at levels that adversely affect the health of consumers, two complementary approaches are used. The first is to monitor individual foods for compliance with national and international regulatory standards. However, monitoring data of this type are focused on individual chemicals in raw commodities, and may not provide a direct link to the health assessment of the population.
The second approach is to measure the actual dietary consumption of these chemicals by the population, and compare these intakes with toxicological reference points, such as the Acceptable Daily Intake (ADI) or Provisional Tolerable Weekly Intake (PTWI). These comparisons provide a direct link to the health of the population, and total diet studies are the most reliable way to estimate the dietary intake of toxicants by large population groups. Therefore, total diet studies are essential to answer the fundamental question of whether or not the national diet is safe.
A total diet study consists of purchasing foods commonly consumed, processing them as for consumption, combining the foods into food composites or aggregates, homogenizing them, and analyzing them for toxic chemicals. The analytical results are then combined with food intake information for different population groups, and the dietary intakes of the chemicals by the groups are estimated.
Thus, the accuracy of total diet studies depends on two fundamental data components: the quantity of each prepared food consumed by individuals, usually collected in national surveys, and the background concentration of toxic chemicals in the foods as ready for consumption. In order to not overestimate the dietary intakes, the analytical methods used to measure toxicant levels should have appropriately low detection limits. Often, such methods are complex and require advanced instrumentation. Thus, total diet studies are expensive, particularly for developing countries. However, the cost of total diet studies and the laboratory infrastructure built around them is minuscule compared with their value in supporting good health and active trade. For example, dioxin contamination of food in Belgium is estimated to have cost over US$2 billion.
The Agreement on the Application of Sanitary and Phytosanitary Measures (SPS Agreement) of the World Trade Organization (WTO) requires that health and safety requirements related to food be based on scientific risk assessments. Risk assessments are based on both toxicological information and estimates of exposure of the population to the chemical. As mentioned above, the latter is most accurately obtained for large population groups using total diet studies. The SPS Agreement has referenced the standards, guidelines and other recommendations of the FAO/WHO Codex Alimentarius Commission as representing the international benchmark for health and safety requirements. However, countries may implement stricter standards if the need for such standards can be demonstrated based on sound scientific risk assessment. Thus, at a minimum, total diet studies in developing and industrialized countries are necessary to perform risk assessments and ensure that their food safety systems are effective in protecting the public health.
Internationally, the importance of conducting total diet studies is gradually being recognized, and more and more countries are initiating and expanding their total diet studies. However, the organization of these studies is complex and many different areas of expertise are required. Consequently, there is a need for a periodic forum to exchange information and experiences in conducting total diet studies.