Testing the safety of phytochemicals

It is estimated that there are in excess of 20 000 unique chemicals present as plant primary and secondary metabolites (Ohlrogge, 1994). The levels present in foods can vary quite considerably depending on the variety and on agronomic and environmental factors. To attribute benefits to any one chemical or group of chemicals seems a daunting task. Thus, in spite of intensive work in the last decade or so, there is still insufficient evidence with which to support the antioxidant hypothesis , or any other hypothesis, and to attribute 

In all cases the process of risk assessment of food chemicals has up to now ignored the effect of the other constituents present in that food. The scientific approach to risk (or benefit) assessment has so far demanded a 

Because of the requirement by public health authorities that any chemical used in the production of food should pose no risk to the consumer, the safety of food chemicals has mostly been approached from the perspective of whether or not the chemical poses a toxicological hazard. If it does so then it is argued that it is likely to present some degree of risk to the consumer even if humans are exposed to very low levels of that chemical in their diets. However, if exposure is minimal, depending on the nature of the toxicity, it is likely that the risk is acceptable because it is so low. What is not considered, or even tested in the experimental systems designed to study the toxicological effects of chemicals, is whether there are levels of exposure where there might be potential health benefits. The assumption is made that any nonnatural, adventitious substance that can be shown to be toxic is unlikely to have health benefits. 

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One of the few phytochemicals that has been subjected to the rigorous testing procedures required by food safety authorities is P-carotene, a naturally-occurring carotenoid that is also a pre-cursor of vitamin A in humans. It is increasingly used as a food colour since the food product can be claimed to contain all natural ingredients. For this reason, detailed toxicological studies were undertaken that enabled the Joint FAO/WHO Expert Committee for Food Additives (JECFA) to set an ADI of 0-5 mg/kg/bw/day based on a NOAEL of 50 mg/day and the application of an uncertainty factor of 10 (JECFA, 1974). This low factor was used because it was argued that the compound occurred naturally in food, that its use as a food additive would not lead to a substantial increase in the total amount normally consumed, and that there had been no reports of adverse effects in humans. The ADI would correspond to an acceptable intake in humans of up to 350 mg/day. 

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