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Astringent foods

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What are

What does astringent foods mean?

Astringent foods are, as the term itself suggests, foods with astringent properties.

In chemistry, the term “astringent” indicates the ability to precipitate colloidal proteins in a solute. On the other hand, the same term is used in the nutritional field to indicate the property of foods and drinks to swell in the mouth and/or to increase the consistency of stool.

In practice, astringent foods are the most effective non-drug remedy for diarrhea.

See also: Diet and Diarrhea ed
Example Diet against Diarrhea

Astringent capacity due to precipitation of colloidal proteins

The astringent effect is exerted above all thanks to the combination of high and low molecular weight phenols, and tannins in the presence of proanthocyanidins (other polyphenols characterized by the oligometric repetition of flavonoids). This is a fairly complex topic, full of technicalities, which however can be summarized and interpreted by the reader as follows:

“the plant compounds that exert the astringent function are those that linger in the mouth (as happens with unripe persimmon), which color foods (for example the red of grapes and wine) and which, in general, are considered beneficial for health (antioxidants, hypocholesterolemics, etc.)”.

Astringent capacity for absorption of water in the feces

Secondly, thanks to their absorbent capacity, starchy foods poor in water and with very low fiber residue also exert an intestinal astringent action; some examples are boiled potatoes, refined cereals (such as polished rice), isolated starches (such as rice starch, cornstarch, wheat flour, tapioca) etc.

Astringent foods

What are astringent foods?

As anticipated, astringent foods are of plant origin. In addition to lapping (sensation felt mainly in the center and back of the tongue), these often have a sweet and/or sour taste.

There are therefore various vegetables, tubers, fruits, aromatic herbs, cereals, legumes (or parts of them) and herbal medicines (barks, roots, etc.) with astringent capacity. Examples of astringent foods are shown in the table below.

Astringent foods

Astringent fruits

Astringent Vegetables and Tubers

Astringent Seeds

Astringent spices
(if they do not irritate the intestinal mucosa)

Unripe bananas, unripe persimmons, avocado, cranberries, pomegranate (with seeds), prickly pears (with seeds), some varieties of apple, lemon

Alfalfa (alfalfa sprouts), raw carrots (with peel), boiled potato or yam, cassava and various powdered starches

Polished rice, popcorn, poppy seeds

Basil, bay leaves, cumin, coriander, dill, fennel, marjoram, nutmeg, oregano, parsley, rosemary, saffron, turmeric, vanilla

Controversies over astringent foods

An aspect overlooked by many is that many of these foods, in addition to containing astringent nutritional factors, are often also rich in fiber and water (two factors that soften the stool, preventing constipation).

To give an example, unripe bananas and persimmons (with the exception of the cacomela variety) are highly astringent fruits; this function is lost with maturation, during which certain enzymes convert tannins into fructose. However, bananas but especially persimmons are also rich in fiber and water; this means that, while unripe bananas and persimmons are mainly astringent, very ripe ones (or the cacomela variety) can instead prove anti-constipating. A persimmon or a medium-ripe banana could therefore prove to have a neutral action or emphasize the subjective tendency to constipation or too liquid stools.

Drinks

Astringent drinks: the ultimate solution

The most effective astringent drinks are those obtained from squeezing vegetables with the aforementioned properties, or composed of aqueous solutions of phytotherapeutic active ingredients (or drugs).
A classic example of an extracted and astringent drink is pomegranate or prickly pear juice.

Phytotherapeutic remedies rich in astringent polyphenols, however, mainly contain fruits, seeds, leaves, roots and bark (depending on the case): bearberry, camellia, eucalyptus, hawthorn, witch hazel, horse chestnut, ratania, guarana, oak, cinnamon, fern, late cherry, eugenia etc.

Action

Mechanism of astringent foods

Astringent mechanism of polyphenols

Polyphenols are therefore responsible for the precipitation of food proteins and the inactivation of digestive enzymes. This precipitation separates the solid part from the liquid part, causing it to sink in the form of a precipitate based on phenols and proteins. The reaction begins in the bolus, in the mouth, and continues in the intestine (first in the chyme and then in the feces) where it hinders protein absorption, also affecting digestive enzymes.
To demonstrate the astringent action of polyphenols we can note:

  1. In the mouth: the lumpy, dry, frictional and doughy sensation that requires increased salivation to facilitate swallowing.
  2. In the large intestine: more compact and less hydrated stools, often accompanied by an increase in smelly flatulence.

Astringent mechanism of refined starchy foods

As a consequence of the absorbent action of starches, however, we only notice a late effect caused by the reduction of intestinal peristalsis (due to lack of fibre) and an increase in fecal consistency.

However, it must be remembered that this last astringent mechanism has very subjective effects; in fact, the digestive system reacts spontaneously to the dryness of foods by releasing water into the digestive juices in adequate quantities. Reducing fiber (low residue diet) and increasing refined starches is not to be considered an immediate remedy, but rather a basic rule of diets against diarrhea.

Benefits

What are astringent foods used for?

Astringent foods fight enteritis, the symptom of diarrhea, the inflammatory states of chronic pathologies (Crohn's disease, ulcerative colitis), ulcers and metal intoxication; the mechanisms of action that regulate these effects are:

  • They reduce water in the stool
  • They decrease intestinal peristalsis (due to reduction of nervous sensitivity)
  • They are anti-inflammatory (as well as for the intestine, but also mildly for the esophagus and stomach)
  • They precipitate the protein molecules of the bacteria and complex the irritating ones
  • Mucous secretions decrease (see Mucus in the Stool)
  • By binding, they protect the surfaces of ulcerative lesions and promote hemostasis by optimizing coagulation
  • Chelating on metals such as aluminium, iron, copper, manganese and vanadium (normally the chelating action on dietary iron is considered anti-nutritional but in the pathology of haemochromatosis it is instead therapeutic).

Side effects

Are too many astringent foods bad for you?

  • In case of excessive intake of polyphenols and/or reduction of fiber and/or dietary water, the astringent action may be excessive, predisposing to constipation.
  • Furthermore, the lack of absorption of proteins in the small intestine (caused by the binding of polyphenols with food peptides and digestive enzymes on the mucosa) tends to increase their concentration up to the colon, where the bacteria process them with consequent onset of meteorism, tension abdominal and flatulence.
  • The chelating action of phenols on minerals reduces their absorption, especially favoring iron deficiency. Furthermore, inhibition of digestive enzymes (proteases) decreases the nutritional absorption of peptide amino acids.
  • An excess of tannins can be counterproductive in cases of serious inflammatory and ulcerative lesions of the digestive tract; furthermore, some statistical data indicate a correlation (unclear but present) between excess tannins and gastrointestinal tumors.
  • Polyphenol molecules also precipitate alkaloids and decrease the action of drugs containing them.
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