Bioavailability is defined as the fraction of a nutrient that the body is able to absorb and use for its own physiological functions.
Bioavailability can vary in relation to numerous factors, depending in part on the nature of the food and in part on the characteristics of the organism that takes it. As such, these factors are divided into:
intrinsic, ie linked to the individual: age, sex, physiological, nutritional and health status, intestinal microflora, genotype, any intolerances, etc.
and extrinsic, that is, linked to the nutritional source: chemical form of the mineral, interaction with other nutrients, cooking, pH, technological treatments, presence of anti-nutritional factors that limit its absorption or, vice versa, of others that enhance it.
The data reported in the common nutritional tables tell us how many nutrients are contained in a particular food, but they do not provide us with any information on the bioavailability of these substances. Thus, for example, 100 grams of spinach contain approximately twice as much iron as those present in a "similar amount of beef. Bioavailability, however, is considerably higher for iron of animal origin (20-25%). compared to that obtained from plant sources (3-5%).
In order for a food or a set of foods to be able to cover the need for a nutrient, this must be present in correct quantities and in a sufficiently bioavailable form, also in relation to the intrinsic factors of the subject.
In general, while the bioavailability of macronutrients and vitamins tends to be very good, the same cannot be said for most minerals.
In relation to the numerous factors that can influence it, the bioavailability of a nutrient is very difficult to assess. As far as the state of health of the organism is concerned, there are disorders and pathologies that decrease it and others that increase it. The first group includes: diarrhea, celiac disease, food intolerances, intestinal resections, bariatric surgery, short bowel syndrome, chronic inflammatory bowel diseases (Crohn's disease, ulcerative colitis), chronic alcoholism, constipation treated with laxatives, contamination syndrome small intestine bacterial, intestinal parasitosis, hypochlorhydria, achlorhydria, atrophic gastritis, liver and pancreatic insufficiency, intra and extrahepatic cholestasis, tropical sprue. Diseases that increase nutrient absorption include - for example - familial sitosterolemia (enhanced absorption of cholesterol and plant sterols) and genetic or hereditary hemochromatosis (enhanced iron absorption). Even different drugs and supplements can modulate the bioavailability of the various micronutrients.
Lipids
Carbohydrates
Peptides and amino acids
Iron
Folic acid
Football
Waterfall
Electrolytes
Carbohydrates
Peptides and amino acids
Football
Waterfall
Electrolytes
Bile salts
Vitamin B12
Waterfall
Electrolytes
Waterfall
Electrolytes
Some products of
fermentation of
local microbial flora
As for cooking, this has a generally positive action on the bioavailability of macronutrients, as it increases the digestibility of starches and proteins. Fats, on the other hand, especially when exposed to high temperatures undergo a degradation process that limits their bioavailability For vitamins and other micronutrients, there are generally considerable losses in the cooking water and degradations related to heat. Minerals, unlike vitamins, are not altered by cooking or light, but are easily eliminated with urine, sweat and feces. Bioavailability undergoes the greatest fluctuations for divalent cations and for trivalent cations, such as Ca2 +, Zn2 +, Mg2 + and Fe3 +.
The refining of the flour deprives the derived foods of a good part of the vitamin and mineral content. Another typical problem with minerals is that some share the same absorption mechanisms, so a high intake of one reduces the bioavailability of others. A high intake of zinc, for example, can reduce the absorption of copper and so on; the excess of iron, on the other hand, can limit the absorption of zinc. This evidence contributes to making the spontaneous use of megadoses of a single micronutrient.
The link between bioavailability and food associations is particularly complicated and full of examples. Let's see some of them. The presence of fiber in a meal tends to decrease the bioavailability of the various nutrients, both for the stimulation of peristalsis and for the ability to form a soft mush in which numerous substances are retained. Vitamin C and citric acid increase intestinal absorption of iron, while oxalic acid (contained mainly in spinach, cocoa, beets and cabbage), phytic acid (whole grains, legumes, dried fruit) and tannins (tea) reduce it. The lactose present in milk favors the absorption of calcium, while phytic acid, oxalates and tannins reduce it. Vitamin D enhances the absorption of calcium, phosphorus and magnesium.
