**4. Conclusions**

To explore and understand the mechanism of action of olive oil polyphenols and their role in disease prevention and human health improvement, extensive studies of absorption, metabolism, excretion, toxicity, and efficacy are needed. Although *in vitro* studies can be

Metabolism and Bioavailability of Olive Oil Polyphenols 351

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very useful and provide valuable information, they have to be completed with extensive *in vivo* research. The first requirement for a beneficiary dietary compound is that it enters into the blood circulation; therefore to demonstrate *in vivo* effects of olive oil phenolics it is necessary to assess first their *bioavailability*.

Analysis of plasma and urine provide valuable information on the identity and pharmacokinetics of circulating metabolites after ingestion. Since the metabolites sequestered in body tissues are not usually taken into account, results from urine samples could be an underestimation. There have been several studies which have determined the metabolites of the various olive oil polyphenols (mainly Hyty, Ty, and Ol) in human plasma and urine after oral intake, although the information is still scarce. The conjugation mechanisms that occur in the small intestine and later in the liver are highly efficient. The resulting metabolites are mainly glucuronate and sulfate conjugates with or without methylation across the catechol group (many are multiply conjugated).

Bioavailability studies are gaining increasing interest as food industries are continually involved in developing new products, defined as ''functional'' by virtue of the presence of specific antioxidants or phytochemicals. The difference between functional foods and medicines calls for moderation when the "medicinal" properties of individual food items, be it olive oil, are indicated. The correct message should be to select foods whose components have proven, albeit limited in magnitude, biological activities and build a balanced diet round them, to reduce several chronic diseases.
