Carotenoids in food bioavailability and functional benefits

The types and quantities of phytochemicals present in foods may have very little bearing on the nutritional quality of these foods and their contribution to human health. This is because  

to explore the mechanisms of action of phytochemicals and their role in health promotion, an understanding of the factors that constrain their release from the foods in which they are contained, their extent of absorption and their fate in genetically diverse individuals is crucial. 

The term bioavailability has various definitions. Previously, the authors of this chapter have defined bioavailability as the proportion of a nutrient (or other food component) that is digested, absorbed and utilised in normal metabolism - with the practical measurement of bioavailability usually relying upon estimates of amounts absorbed (Southon and Faulks, 2001). Biological activity, or bioactivity , has been viewed and described as a separate stage which follows on from bioavailability in the journey of a compound from food to function. However, here we present a new definition of bioavailability that recognises the functional consequences of absorption. 

Any compound that enters the system alters the concentration within the pool . 

Such a change in concentration of one pool will have an impact on the concentration in other pools and can therefore be considered bioactive in that it will have an impact on metabolism. 

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All the actual or putative functional benefits of carotenoids are dependent on their bioavailability amounts consumed, amounts released from the food structure during digestion and extent of absorption and tissue distribution. The following three sections deal with each of these issues in turn. 

With investigations of phytochemicals and functional foods, the outcome measure is generally going to be a biomarker of disease, such as serum cholesterol level as a marker of heart disease risk, or indicators of bone turnover as markers of osteoporosis risk. Alternatively, markers of exposure may also indicate the benefit from a functional food by demonstrating bioavailability, such as increased serum levels of vitamins or carotenoids. Some components will be measurable in both ways. For instance, effects of a folic acid-fortified food could be measured via decrease in plasma homocysteine levels, or increase in red blood cell folate. 

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