Bioactive compounds are found in fruits, vegetables and whole grains. They include an extremely heterogeneous class of compounds (polyphenolic compounds, carotenoids, tocopherols, phytosterols and organosulfur compounds) with different chemical structures (hydrophilic or lipophilic), distribution in nature (specific to vegetable species or ubiquitous), range of concentrations both in foods and in the human body, possible site of action, effectiveness against oxidative species, and specificity and biological action.
Several factors interfere with the bioavailability of antioxidants, such as food source and chemical interactions with other phytochemicals and biomolecules present in the food include some of the factors interfering with the bioavailability of bioactive compounds. For example, fruit antioxidants are commonly mixed with different macromolecules such as carbohydrates, lipids, and proteins to form the food matrix. In plant tissue, carbohydrates are the major compounds found, mainly in free and conjugated forms.
After consumption, the nutrients that are present in a food or drink are released, absorbed into the bloodstream and transported to their target tissues. Different nutrients differ in their bioavailability, which means that they are not utilized to the same extent. Release of the nutrient from the food matrix, effects of digestive enzymes in the intestine, binding and uptake by the intestinal mucosa, transfer across the gut wall to the blood or lymphatic circulation, systemic distribution and deposition, metabolic and functional use, excretion can affect nutrient bioavailability. It is mediated by external (e.g. characteristics of the food matrix, chemical form of the nutrient etc) and consumer internal (e.g. gender, age, nutrient status and life stage) factors. The bioavailability of macronutrients (carbohydrates, proteins and fats) is usually very high, e.g. more than 90% of the amount ingested.
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