As with protein, the contents of other nutrients in foods determined by chemical or physical analysis may be quite misleading in terms of the nutrient status of a food. Apart from amount, what is important is whether the nutrient is in a form that can Be utilized in metabolism; that is, whether the nutrient is bioavailable. For example, adding small iron pellets to cereals would increase their iron content, but the iron would not be very available to people eating the cereal and, therefore, be of little value. Many factors influence a nutrient’s bioavailability, including the food’s digestibility and the nutrient’s absorbability from the intestinal tract, which are affected by nutrient binding to indigestible constituents and nutrient—nutrient interactions in food raw materials. Processing and cooking procedures also can influence nutrient bioavailability. Apart from the food itself, different animal species exhibit variations in bioavailability of specific nutrients from a particular food. The age, sex, physiological health, consumption of drugs, general nutritional status, combinations of foods eaten together, and other factors all influence the ability of an individual to make use of a particular
Nutrients:
Bioavailability of carbohydrates, proteins, fats, vitamins, and minerals may be in. creased or decreased since all nutrients are reactive and generally present in varying amounts in food systems. There are many examples of how food composition, processing, and storage affect nutrient bioavailability. One example is the essential mineral iron. Under practical conditions its bioavailability from foods may be only 1—10% of its total level determined by chemical analysis. The recommended dietary allowances for nutrients in the United States and other countries attempt to take bioavailability into account, However, the many factors influencing nutrient bioavailability and the difficulties inherent in meaningful evaluation procedures leave much research in this
area still to be done.
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