Most commercially available nutraceuticals contain a mixture of compounds since they are usually prepared from raw extracts from different food products. Often, the non-declared compounds are present in the supplement even at higher quantities than the actual declared bioactive polyphenol. Health claims are based on reported/known bioactivities of individual components and (or) of whole extracts, but the possible synergistic or inhibitory effects in complex mixtures have not been investigated. Also, interferences between compounds during uptake (bioavailability) are not known. Nutraceuticals may have captured the full health beneficial potency of a plant extract (multiple components, synergistic effects) but it is not known yet. If we believe all the rumours flying around the Web, the cure for many diseases would be at hand… For most phytochemicals and nutraceuticals preparations, there is some truth in all and also a lot of nonsense.
The nutraceuticals field offers a good opportunity to phytochemical research. Many of the research needs pointed out above will benefit of phytochemists helping in the following topics: a full and detailed characterization of the content of the extracts and nutraceutical products as well as their stability; the application of phytochemical analysis to the bioavailability, metabolism and tissue distribution of the metabolites; evaluation of the protein/, lipid/ and DNA/phytochemical interactions; a collaboration with microbiologists to evaluate the transformation of phytochemicals by the colon microflora is also needed; the synthesis of microbial metabolites from phytochemicals and the conjugates with glucuronic acid and (or) sulphate will allow the quantification of the metabolites in biological fluids, and the determination of the biological activity of the metabolites bioavailable in vivo.
The search for specific health-effects associated with diets rich in foods of plant origin is a difficult task. It appears that these effects are manifested through multiple mechanisms mediated by a wide range of substances and their metabolic transformation products, and that these benefits are only recognisable after long-term exposure to the diets. This scenario would imply particular difficulties for investigators seeking answers to rather intractable questions (Clifford and Brown, 2005).
To conclude it can be stated that, there is already some scientific basis to support biological activity of phytochemicals but the task is far from completed and further research is needed. More and better designed clinical trials should be carried out in order to prove the benefits of phytochemicals consumption in humans. Importantly, the bioavailability and metabolism of phytochemicals need to be clarified to understand the actual health benefits of food phytochemicals and their use in the nutraceutical market. As a final remark, the public should avoid to follow the advice of doubtfully qualified ‘doctors’ that proliferate on the Web (the so-called ‘Web-doctors’). It is not easy, however, to precisely identify who should be consulted for advice on this matter for various reasons. The current knowledge on this topic is: (i) scarce and inconclusive regarding the effects in humans and, (ii) fragmented amongst the scientific community working in the field. At present, there are already some health care professionals, such as physicians, nutritionists and pharmacists who prescribe and/or give advice on the consumption of some nutraceuticals (e.g. isoflavone-containing nutraceuticals), but most of them may not have the necessary knowledge on these compounds to give a convenient advice to both consumers and producers. Therefore, there is a gap between the scientific community who has the most updated knowledge on nutraceuticals and the health care professionals. So, the question is open for debate: do we need to define a new professional qualification to cover this gap? Or, should we ask the health care professionals to keep themselves updated on the continuously developing knowledge on phytochemicals and health provided by the scientists?