579
site of potassium absorption, with approximately 90% of dietary potassium being
absorbed by passive diffusion (Demigné et al. 2004). Less information is available
on the health benifits and bioavailability of potassium from dietary sources
(Bechgaard and Shephard 1981; Betlach et al. 1987; Stone et al. 2016). The potassium in the ionic form is water soluble and is easily lost during cooking and processing of foods. Sodium is readily absorbed from the intestine of healthy adults, carried
to the kidneys, and subsequently returned to the blood to maintain appropriate levels
(Mahan and Raymond 2016). Salting foods and discarding the liquid from the food
materials induces sodium (Na
+
) for potassium (K
+
) exchange and reduces the
potassium content of foods (Stone et al. 2016). It has been observed that higher
consumption of cereal and processed foods, and lower consumption of fruits and
vegetables has led to a diet lower in potassium and higher in sodium (Macdonald–
Clarke et al. 2016).
Selenium compounds are efficiently absorbed by humans (Selenium–WHO
1987). For example, absorption of the selenite (inorganic form) is greater than 80%
whereas that of selenomethionine (organic form of selenium) or as selenate may be
greater than 90% (ReedáMangels 1992; Selenium–WHO 1987; Patterson et al.
1993). The overall availability of dietary selenium is not due to its absorption but its
conversion within tissues to its metabolically active forms (e.g. its incorporation
into GSHPx or 5′–deiodinase) (Contempre et al. 1996). The bioavailability of selenium in wheat, Brazil nuts, and beef kidney is 80–90%, but in tuna fish it is less
available (20–60%) from selenite than selenium from other seafoods (e.g. shrimp,
crab, and Baltic herring). The selenium in a variety of mushrooms has been reported
to be of less available to rats (Khokhar et al. 2012).
Trace minerals like chromium, copper, and manganese are probably as important
as iron, zinc and calcium. The bioavailability of these minerals from dietary sources
is not much examined and is influenced by the same dietary factors that influence
the bioavailability of iron, zinc and calcium (Campbell 2017; Gibney et al. 2009;
Platel and Srinivasan 2016). While amino, keto, ascorbic acid and chelating substances like oxalate form chromium complexes and enhance chromium bioavailability, inhibitors like phytates, zinc and iron reduce chromium bioavailability.
Copper (II) histidine chelate after complexation provides increased availability for
copper (Lönnerdal 1996). Excessive zinc has been reported to impair bioavailability
of copper at levels that exceed normal dietary intakes (Fairweather–Tait 1997; Platel
and Srinivasan 2016).
In the small intestine, the elements of sodium chloride split into sodium cations
and chloride anions. Chloride follows the sodium ion into intestinal cells passively,
making chloride absorption quite efficient. When chloride exists as a potassium salt,
it is also well absorbed. Other mineral salts, such as magnesium chloride, are not
that efficiently absorbed but bioavailability still remains high. Although very soluble potassium is highly bioavailable, it is easily lost during cooking and processing
of foods (Gibney et al. 2009; Titchenal et al. 2018). It has been reported that under
normal conditions, the absorption of dietary iodine is >90% (Jahreis et al. 2001;
Platel and Srinivasan 2016).
25 Bioavailability of Nutrients and Safety Measurements
site of potassium absorption, with approximately 90% of dietary potassium being
absorbed by passive diffusion (Demigné et al. 2004). Less information is available
on the health benifits and bioavailability of potassium from dietary sources
(Bechgaard and Shephard 1981; Betlach et al. 1987; Stone et al. 2016). The potassium in the ionic form is water soluble and is easily lost during cooking and processing of foods. Sodium is readily absorbed from the intestine of healthy adults, carried
to the kidneys, and subsequently returned to the blood to maintain appropriate levels
(Mahan and Raymond 2016). Salting foods and discarding the liquid from the food
materials induces sodium (Na
+
) for potassium (K
+
) exchange and reduces the
potassium content of foods (Stone et al. 2016). It has been observed that higher
consumption of cereal and processed foods, and lower consumption of fruits and
vegetables has led to a diet lower in potassium and higher in sodium (Macdonald–
Clarke et al. 2016).
Selenium compounds are efficiently absorbed by humans (Selenium–WHO
1987). For example, absorption of the selenite (inorganic form) is greater than 80%
whereas that of selenomethionine (organic form of selenium) or as selenate may be
greater than 90% (ReedáMangels 1992; Selenium–WHO 1987; Patterson et al.
1993). The overall availability of dietary selenium is not due to its absorption but its
conversion within tissues to its metabolically active forms (e.g. its incorporation
into GSHPx or 5′–deiodinase) (Contempre et al. 1996). The bioavailability of selenium in wheat, Brazil nuts, and beef kidney is 80–90%, but in tuna fish it is less
available (20–60%) from selenite than selenium from other seafoods (e.g. shrimp,
crab, and Baltic herring). The selenium in a variety of mushrooms has been reported
to be of less available to rats (Khokhar et al. 2012).
Trace minerals like chromium, copper, and manganese are probably as important
as iron, zinc and calcium. The bioavailability of these minerals from dietary sources
is not much examined and is influenced by the same dietary factors that influence
the bioavailability of iron, zinc and calcium (Campbell 2017; Gibney et al. 2009;
Platel and Srinivasan 2016). While amino, keto, ascorbic acid and chelating substances like oxalate form chromium complexes and enhance chromium bioavailability, inhibitors like phytates, zinc and iron reduce chromium bioavailability.
Copper (II) histidine chelate after complexation provides increased availability for
copper (Lönnerdal 1996). Excessive zinc has been reported to impair bioavailability
of copper at levels that exceed normal dietary intakes (Fairweather–Tait 1997; Platel
and Srinivasan 2016).
In the small intestine, the elements of sodium chloride split into sodium cations
and chloride anions. Chloride follows the sodium ion into intestinal cells passively,
making chloride absorption quite efficient. When chloride exists as a potassium salt,
it is also well absorbed. Other mineral salts, such as magnesium chloride, are not
that efficiently absorbed but bioavailability still remains high. Although very soluble potassium is highly bioavailable, it is easily lost during cooking and processing
of foods (Gibney et al. 2009; Titchenal et al. 2018). It has been reported that under
normal conditions, the absorption of dietary iodine is >90% (Jahreis et al. 2001;
Platel and Srinivasan 2016).
25 Bioavailability of Nutrients and Safety Measurements